WO2013111252A1 - サンプリング回路、a/d変換器、d/a変換器、codec - Google Patents
サンプリング回路、a/d変換器、d/a変換器、codec Download PDFInfo
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- WO2013111252A1 WO2013111252A1 PCT/JP2012/008400 JP2012008400W WO2013111252A1 WO 2013111252 A1 WO2013111252 A1 WO 2013111252A1 JP 2012008400 W JP2012008400 W JP 2012008400W WO 2013111252 A1 WO2013111252 A1 WO 2013111252A1
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/12—Analogue/digital converters
- H03M1/124—Sampling or signal conditioning arrangements specially adapted for A/D converters
- H03M1/1245—Details of sampling arrangements or methods
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/06—Continuously compensating for, or preventing, undesired influence of physical parameters
- H03M1/0617—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence
- H03M1/0634—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale
- H03M1/0656—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale in the time domain, e.g. using intended jitter as a dither signal
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/12—Analogue/digital converters
- H03M1/124—Sampling or signal conditioning arrangements specially adapted for A/D converters
- H03M1/1245—Details of sampling arrangements or methods
- H03M1/1265—Non-uniform sampling
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/12—Analogue/digital converters
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/66—Digital/analogue converters
Definitions
- the present invention relates to a sampling circuit, an A / D converter including the sampling circuit, a D / A converter, and a CODEC.
- noise countermeasures there is an increasing demand for downsizing electronic devices, and electronic components mounted on electronic devices are downsized, and electronic components are arranged closer to each other.
- noise countermeasures When electronic components are arranged close to each other, noise generated in the electronic components may be transmitted to other electronic components directly or via a mounting substrate or wiring, and may interfere with normal operation of the other electronic components. For this reason, recent electronic devices are required to be reduced in size and to suppress the influence of noise (hereinafter also referred to as noise countermeasures).
- D / A converters or A / D converters as electronic components mounted on electronic devices.
- the D / A converter and the A / D converter are electronic components that are frequently used for audio functions of electronic devices, and are electronic components that particularly require noise countermeasures.
- Patent Document 1 As a conventional technique for noise countermeasures for D / A converters and A / D converters, for example, there is an invention described in Patent Document 1.
- jitter is added to a D / A converter or a synchronization signal (control clock signal) of an input signal of the A / D converter.
- conversion clock signal conversion clock signal
- a circuit for inputting jitter In order to reduce the influence of radiation noise generated by individual electronic components directly or indirectly on the D / A converter and A / D converter using conventional technology, A circuit for inputting jitter must be provided in a plurality of other components to be mounted. In such a configuration, it is necessary to provide a large number of circuits for inputting jitter, and it is considered that miniaturization of electronic devices is hindered.
- the present invention has been made in view of the above-described points, and does not hinder downsizing of electronic components and avoids the advancement of process technology, while reducing the noise received by electronic components mounted on electronic devices.
- an A / D converter including this circuit, a D / A converter, and a CODEC in which such an A / D converter and a D / A converter are mounted together With the goal.
- the digital unit includes a general digital circuit and transmits a quantized and sampled signal.
- the sample and hold unit includes a general switched capacitor circuit (SC circuit), and transmits a sampled signal without being quantized.
- the continuous unit includes a general continuous signal circuit (continuous circuit), and transmits a signal that is not quantized and not sampled.
- One embodiment of the present invention operates based on a continuous unit (for example, the continuous unit 130a illustrated in FIG. 18) that transmits a continuous signal and a first clock signal (for example, the clock signal ⁇ 2 ′ illustrated in FIG. 18).
- a sample-and-hold unit (for example, the sample-and-hold unit 130b shown in FIG. 18) connected to the continuous unit and transmitting a sampled and non-quantized signal;
- a digital unit for example, the digital unit 130c shown in FIG. 18) that transmits the quantized and quantized signal, and the first clock signal is a signal obtained by adding jitter to the base clock signal.
- the continuous unit may sample an input analog signal, and the sample and hold unit may hold a signal sampled by the continuous unit.
- the continuous section (for example, the continuous section 130a shown in FIG. 18) operates based on a second clock signal (for example, the clock signal ⁇ 1 shown in FIG. 18), and the second clock signal jitters to the base clock signal. Is the signal to which the signal is not added, that is, the base clock signal itself, and the first clock signal (for example, the clock signal ⁇ 2 ′ shown in FIG. 18) and the second clock signal are in reverse phase. And it may be in a non-overlapping relationship.
- the continuous section (for example, the continuous section 130a shown in FIG. 22) operates based on a second clock signal (for example, the clock signal ⁇ 1 ′′ shown in FIG. 22), and the second clock signal is the base clock signal.
- the clock signal (for example, clock signal ⁇ 2 ′ shown in FIG. 22) and the second clock signal may be in opposite phases and non-overlapping.
- the sample-and-hold unit samples a reference signal based on a digital signal from the digital unit (for example, the digital unit 150c shown in FIG. 24), and the continuous unit (for example, FIG. 24). 24 may transfer the signal sampled by the sample / hold unit as an analog signal.
- the continuous section (for example, the continuous section 150a shown in FIG. 24) operates based on a second clock signal (for example, the clock signal ⁇ 12 shown in FIG. 24), and the second clock signal is jittered to the base clock signal.
- a second clock signal for example, the clock signal ⁇ 12 shown in FIG. 24
- the first clock signal for example, clock signal ⁇ 11 ′ shown in FIG. 24
- the second clock signal are in reverse phase and non-over. May be in a rap relationship.
- the continuous section (for example, the continuous section 150a shown in FIG. 28) operates based on a second clock signal (for example, the clock signal ⁇ 12 ′′ shown in FIG. 28), and the second clock signal is the base clock signal.
- a second clock signal for example, the clock signal ⁇ 12 ′′ shown in FIG. 28
- jitter is not added to an edge that is a trigger for determining the operation start time
- jitter is added to an edge that is a trigger for determining the operation end time
- the signal for example, the clock signal ⁇ 11 ′ shown in FIG. 28
- the second clock signal may be in reverse phase and non-overlapping.
- a continuous unit for example, the continuous unit 130a shown in FIG. 18 that samples an input analog signal and a sample / hold unit (for example, FIG. 18) that holds a signal sampled by the continuous unit.
- a sampling circuit for example, sampling circuit 140 shown in FIG. 18
- a digital unit for example, 130c shown in FIG. 18
- a first clock signal for example, a control circuit 139 shown in FIG. 18 for supplying a first clock signal (for example, a clock signal ⁇ 2 ′ shown in FIG. 18) to the sample and hold unit,
- the signal must have jitter added to the underlying clock signal A / D converter, wherein a.
- the clock signal supply unit supplies a second clock signal (for example, the clock signal ⁇ 1 illustrated in FIG. 18) to the continuous unit (for example, the continuous unit 130a illustrated in FIG. 18), and the second clock signal is based on Is a signal in which jitter is not added to the clock signal, that is, the base clock signal itself, and the first clock signal (for example, clock signal ⁇ 2 ′ shown in FIG. 18) and the second clock signal are They may be in reverse phase and non-overlapping.
- a second clock signal for example, the clock signal ⁇ 1 illustrated in FIG. 18
- the continuous unit for example, the continuous unit 130a illustrated in FIG. 18
- the second clock signal is based on Is a signal in which jitter is not added to the clock signal, that is, the base clock signal itself
- the first clock signal for example, clock signal ⁇ 2 ′ shown in FIG. 18
- the second clock signal may be in reverse phase and non-overlapping.
- the sample-and-hold unit (for example, the sample-and-hold unit 130b illustrated in FIG. 17) includes a capacitive element (for example, the capacitor 132 illustrated in FIG. 17) that accumulates electric charges generated by the analog signal, and the electric charge accumulated in the capacitive element.
- a first switching element (for example, a switch 133 illustrated in FIG. 17) that holds and transfers to the digital unit (for example, the digital unit 130c illustrated in FIG. 18), and the first switching element includes the first switching element
- An on operation and an off operation may be performed in accordance with a clock signal (for example, clock signal ⁇ 2 ′ shown in FIG. 17).
- the clock signal supply unit (for example, the control circuit 139 shown in FIG. 22) supplies a second clock signal (for example, the clock signal ⁇ 1 ′′ shown in FIG. 22) to the continuous unit (for example, the continuous unit 130a shown in FIG. 22).
- a second clock signal for example, the clock signal ⁇ 1 ′′ shown in FIG. 22
- the continuous unit for example, the continuous unit 130a shown in FIG. 22.
- jitter is added to an edge which is a trigger for determining the operation start time of the base clock signal
- jitter is added to an edge which is a trigger for determining the operation end time.
- the signal may not be added.
- the sample-and-hold unit (for example, the sample-and-hold unit 130b illustrated in FIG. 21) includes a capacitive element (for example, the capacitor 132 illustrated in FIG. 21) that accumulates electric charges generated by the analog signal, and the electric charge accumulated in the capacitive element.
- a first switching element (for example, a switch 133 illustrated in FIG. 21) that holds and transfers to the digital unit (for example, the digital unit 130c illustrated in FIG. 22), and the first switching element includes the first switching element
- the continuous operation (for example, the continuous portion 130a shown in FIG. 21) is turned on and off by a clock signal (for example, the clock signal ⁇ 2 ′ shown in FIG. 21), and the second switching device (for example, the continuous portion 130a shown in FIG.
- the second switching element includes switches 131 and 135) shown in FIG.
- Serial second clock signal by (for example, a clock signal ⁇ 1 shown in Fig. 21 ") may be treated in an on-operation and off operation.
- the clock signal supply unit (for example, the control circuit 139 shown in FIG. 18) supplies the first clock signal (for example, the clock signal ⁇ 2 ′ shown in FIG. 18) to the digital unit (for example, the digital unit 130c shown in FIG. 18). It may be.
- Another aspect of the present invention is a digital unit that outputs a digital signal (for example, the digital unit 150c in FIG. 24) and a sample and hold unit that samples a reference signal based on the digital signal (for example, the sample and hold unit shown in FIG. 24).
- 150b) and a sampling unit for example, the sampling unit 160a shown in FIG. 24
- a continuous unit for example, the continuous unit 150a shown in FIG. 24
- a clock signal supply unit for example, a control circuit 159-1 illustrated in FIG. 24
- a first clock signal for example, the clock signal ⁇ 11 ′ illustrated in FIG. 24
- the first clock signal Is a signal with jitter added to the underlying clock signal D / A converter, wherein the door is.
- the clock signal supply unit (for example, the control circuit 159-1 shown in FIG. 24) supplies a second clock signal (for example, the clock signal ⁇ 12 shown in FIG. 24) to the continuous unit (for example, the continuous unit 150a shown in FIG. 24).
- the second clock signal is a signal in which jitter is not added to the base clock signal, that is, the base clock signal itself, and the first clock signal and the second clock signal May be in opposite phase and non-overlapping.
- the sample-and-hold unit (for example, the sample-and-hold unit 150b illustrated in FIG. 23) includes a capacitor element (for example, the capacitor 152 illustrated in FIG. 23) that accumulates charges generated by the reference signal, and a capacitor element that accumulates charges in the capacitor element.
- 1 switching element (for example, switches 151 and 153 shown in FIG. 23), and the first switching element is turned on according to the first clock signal (for example, clock signal ⁇ 11 ′ shown in FIG. 23). An off operation may be performed.
- the clock signal supply unit (for example, the control circuit 159-2 shown in FIG. 28) supplies the second clock signal (for example, the clock signal ⁇ 12 ′′ shown in FIG. 28) to the continuous unit (for example, the continuous unit 150a shown in FIG. 28).
- the second clock signal is an edge which is a trigger for determining the operation end time without adding jitter to the edge which is a trigger for determining the operation start time of the base clock signal. Is a signal to which jitter is added, and the first clock signal (for example, ⁇ 11 ′ in FIG. 28) and the second clock signal may be in opposite phase and non-overlapping.
- the sample-and-hold unit (for example, the sample-and-hold unit 150b illustrated in FIG. 27) includes a capacitor element (for example, the capacitor 152 illustrated in FIG. 27) that accumulates charges generated by the reference signal, and a first element that accumulates charges in the capacitor element.
- 1 switching element for example, switches 151 and 153 shown in FIG. 27
- the first switching element is turned on according to the first clock signal (for example, clock signal ⁇ 11 ′ shown in FIG. 27).
- the continuous section (for example, the continuous section 150a shown in FIG. 27) is turned off, and the second switching element (for example, shown in FIG. 27) transfers the charge accumulated in the capacitive element (for example, the capacitor 152 shown in FIG. 27).
- Switches 156, 157) and the second switching element includes the second clock signal.
- the signal may be turned on and off by a signal (for example, a clock signal ⁇ 12 ′′ shown in FIG. 27).
- the clock signal supply unit (for example, the control circuit 159-1 illustrated in FIG. 24) sends the first clock signal (for example, the clock signal ⁇ 11 ′ illustrated in FIG. 24) to the digital unit (for example, the digital unit 150c illustrated in FIG. 24). It may come to supply.
- an A / D converter according to any one of claims 8 to 13 for example, an A / D converter ADC shown in FIG. 31
- claims 14 to 19 A CODEC in which the D / A converter according to any one of the above (for example, the D / A converter DAC shown in FIG. 31) is mixedly mounted.
- the A / D converter and the D / A converter may operate asynchronously.
- a sampling circuit capable of reducing the influence of noise received by an electronic component mounted on an electronic device, an A / D converter including the circuit, a D / A converter, and the like A CODEC in which an A / D converter and a D / A converter are mixedly mounted can be provided.
- Such an effect can be obtained by operating the sample and hold unit based on the clock signal to which jitter has been added, so that downsizing of the electronic component is not hindered.
- the continuous unit based on the clock signal to which jitter has been added, the radiation noise caused by the inrush current of the analog unit can be diffused, so that the radiation noise can be effectively suppressed.
- FIG. 10 is a diagram for explaining signals when the sampling circuit performs the operation shown in FIG. 9. It is another figure for demonstrating operation
- FIG. 9 is a diagram for explaining periodic noise generated when the sampling circuit shown in FIG. 8 operates.
- a / D converter of the 2nd mode of the present invention it is a figure for explaining periodic noise at the time of adding jitter to a clock signal which operates a digital part. It is a figure for demonstrating the periodic noise at the time of adding a jitter to the clock signal which operates the digital part of the A / D converter of the 2nd aspect of this invention.
- 1 is a diagram illustrating a pipeline type A / D converter according to a first embodiment. It is a figure for demonstrating the calculation which calculates a digital output signal of a pipeline type A / D converter. 1 is a diagram for explaining a sampling circuit according to Embodiment 1-1.
- FIG. 1 is a functional block diagram for explaining an A / D converter including a sampling circuit and a control circuit according to Embodiment 1-1.
- FIG. FIG. 6 is a timing chart of clock signals ⁇ 1, ⁇ 1 ′, ⁇ 1 ′′, ⁇ 2, and ⁇ 2 ′. It is a figure for demonstrating the specific structure of a jitter selection part.
- FIG. 6 is a diagram for explaining a sampling circuit according to the embodiment 1-2.
- FIG. 3 is a functional block diagram for explaining an A / D converter including a sampling circuit and a control circuit according to Embodiment 1-2.
- FIG. 6 is a diagram for explaining a sampling circuit according to the embodiment 2-1.
- FIG. 3 is a functional block diagram for explaining a D / A converter including a sampling circuit and a control circuit according to the embodiment 2-1.
- FIG. 7 is a timing chart of clock signals ⁇ 11, ⁇ 11 ′, ⁇ 12, and ⁇ 12 ′. It is a figure for demonstrating the specific structure of a jitter selection part.
- FIG. 10 is a diagram for explaining a sampling circuit according to the embodiment 2-2.
- FIG. 10 is a functional block diagram for explaining a D / A converter including a sampling circuit and a control circuit according to the embodiment 2-2.
- FIG. 6 is a timing chart of clock signals ⁇ 11, ⁇ 11 ′, ⁇ 12, ⁇ 12 ′, and ⁇ 12 ′′.
- FIG. 10 is a diagram for explaining a CODEC according to a third embodiment. It is a figure for demonstrating the effect of Embodiment 3.
- FIG. 10 is a diagram for explaining another CODEC of the third embodiment.
- the digital unit includes a general digital circuit, and transmits a quantized and sampled signal.
- the sample and hold unit includes a general switched capacitor circuit (SC circuit), and transmits a sampled signal without being quantized.
- the continuous unit includes a general continuous signal circuit (continuous circuit), and transmits a signal that is not quantized and not sampled.
- the sampling circuit shown in FIG. 1 is a sampling circuit in a mode (hereinafter also referred to as “first mode”) that is a basis of the present embodiment, and is for explaining the sampling circuit in the D / A converter of the first mode.
- FIG. The sampling circuit shown in FIG. 1 has a sample and hold unit that samples and holds a signal, and a continuous unit that processes an analog signal, and includes capacitors 111-1, 112, and 113, and an operational amplifier 121-1. Contains. In FIG. 1, a digital unit that handles digital signals is not shown.
- the reference signal Vref sampled by the switches 101-1 and 102-1 (the sampled reference signal Vref is referred to as the input signal Vin) is added to the capacitor 111-1, and charges are accumulated.
- the electric charge accumulated in the capacitor 111-1 is input to the inverting input terminal of the operational amplifier 121-1 according to the switching of the switches 101-1, 102-1.
- the operational amplifier 121-1 receives the reference signal Vcom from the non-inverting input terminal and outputs an analog output signal Vout.
- FIG. 2A to 2D are diagrams for explaining the operation of the D / A converter shown in FIG. 1 when there is no periodic noise in the reference signal Vref.
- FIG. 2A shows the sampling timing of the reference signal Vref.
- FIG. 2B shows the timing at which the capacitor 111-1 holds and releases the charge accumulated by the input signal Vin
- FIG. 2C shows the reference signal Vref which is a DC voltage
- FIG. An output signal Vout which is an analog signal, is output from the operational amplifier 121-1.
- the signal indicated by the solid line is the input signal Vin generated by the charge transferred from the capacitor 111-1
- the output signal Vout indicated by the broken line is generated by feedback via the capacitor 112.
- FIG. 3 is a diagram for explaining how the input signal Vin appears in the output signal Vout.
- a graph (a) is a diagram for explaining a signal output from the capacitor 111-1 shown in FIG. 1, and shows a spectrum obtained by converting the input signal Vin into a frequency axis by Fourier transform.
- a graph (b) shows a spectrum obtained by converting the clock that regulates the timing at which the capacitor 111-1 holds and releases the charge accumulated by the input signal Vin into the frequency axis by Fourier transform.
- c) shows a spectrum obtained by converting the output signal Vout into the frequency axis by Fourier transform.
- the vertical axis indicates the intensity of the signal spectrum
- the horizontal axis indicates the frequency.
- the position of the vertical axis indicated by the arrow line in the graphs (a), (b), and (c) in FIG. 3 indicates the frequency reference (“0”).
- the signal (indicated by the spectrum p1 in the figure) output from the capacitor 111-1 has a constant frequency.
- the spectrum q shows the noise shaped floor noise in the input signal Vin.
- FIGS. 4A to 4D are diagrams for explaining the operation of the D / A converter when the reference signal Vref has periodic noise in the sampling circuit shown in FIG.
- FIG. 4A shows the sampling timing of the reference signal Vref.
- FIG. 4B shows the timing at which the capacitor 111-1 holds and releases the charge accumulated by the reference signal Vref.
- the switches to which the clock signals shown in FIGS. 4A and 4B are supplied are driven so as to be turned on when the clock signal is High and turned off when the clock signal is Low.
- FIG. 4C shows a reference signal Vref which is a DC voltage
- FIG. 4D shows an output signal Vout which is an analog signal output from the operational amplifier 121-1.
- the D / A converter has the periodic noise N2 corresponding to the periodic noise N1 in the output signal Vout shown in FIG. Will occur.
- FIG. 5 is a diagram for explaining how the input signal Vin and the periodic noise appear in the output signal Vout.
- a graph (a) is a diagram for explaining a signal output from the capacitor 111-1 shown in FIG. 1, and shows a spectrum obtained by converting the input signal Vin into a frequency axis by Fourier transform.
- the graph (b) shows a spectrum obtained by converting the clock that regulates the timing at which the capacitor 111-1 holds and discharges the charge accumulated by the input signal Vin into the frequency axis by Fourier transform.
- Graph (c) shows a spectrum obtained by converting the output signal Vout to the frequency axis by Fourier transform.
- the vertical axis indicates the intensity of the signal spectrum
- the horizontal axis indicates the frequency.
- the position of the vertical axis indicated by the arrow in each of the graphs (a), (b), and (c) indicates the frequency reference (“0”).
- jitter is added to a clock signal for operating a device such as a sampling circuit to diffuse periodic noise appearing in the in-band by a signal output from another device, and the signal quality of an output signal such as speech This is based on the technical idea of preventing the damage.
- the A / D converter and D / A converter are a digital unit that processes a digital signal that is a non-continuous signal, a sample / hold unit (S / H unit) that samples and holds a signal, and a continuous signal.
- a sampling circuit including a continuous unit (Continuous unit) for processing an analog signal is included.
- FIG. 6 is a diagram for explaining how the input signal Vin and the periodic noise appear in the output signal Vout when jitter is added to the clock signal for operating the digital unit in the D / A converter.
- graph (a) is a diagram for explaining a signal output from the capacitor 111-1 shown in FIG. 1, and shows a spectrum obtained by converting the input signal Vin into the frequency axis by Fourier transform.
- a graph (b) shows a spectrum obtained by converting the clock that regulates the timing at which the capacitor 111-1 holds and discharges the charge accumulated by the input signal Vin into the frequency axis by Fourier transform.
- a graph (c) shows a spectrum obtained by converting the output signal Vout to the frequency axis by Fourier transform.
- the vertical axis indicates the intensity of the signal spectrum
- the horizontal axis indicates the frequency.
- the position of the vertical axis indicated by an arrow in the graphs (a), (b), and (c) indicates the frequency reference (“0”).
- jitter is added to the clock signal of the digital part of the D / A converter.
- the energy of the periodic noise N3 is dispersed in a wider frequency region than before adding jitter.
- the peak of the spectrum of the periodic noise N3 is lower than the peak of the spectrum of the periodic noise N2 shown in FIG.
- the peak of the spectrum of the periodic noise N3 'generated in the in-band is also low as with the periodic noise N3. According to such a configuration, the noise generated by the D / A converter itself can be reduced, and the influence of noise on other devices can be reduced.
- An object of the present invention is to provide a sampling circuit capable of performing In the first aspect, in order to realize the above-described object, jitter is added to the clock signal of the sample and hold unit of the D / A converter.
- FIG. 7 shows how the input signal Vin and the periodic noise appear in the output signal Vout when jitter is added to the clock signal of the digital unit and the clock signal of the sample and hold unit in the D / A converter. It is a figure for demonstrating.
- a graph (a) in FIG. 7 is a diagram for explaining a signal output from the capacitor 111-1 shown in FIG. 1, and shows a spectrum obtained by converting the input signal Vin into a frequency axis by Fourier transform.
- a graph (b) in FIG. 7 shows a spectrum obtained by converting the clock that regulates the timing at which the capacitor 111-1 holds and releases the charge accumulated by the input signal Vin into the frequency axis by Fourier transformation.
- a graph (c) in FIG. 7 shows a spectrum obtained by converting the output signal Vout to the frequency axis by Fourier transform.
- the vertical axis indicates the intensity of the signal spectrum
- the horizontal axis indicates the frequency.
- the position of the vertical axis indicated by an arrow in the graphs (a), (b), and (c) indicates the frequency reference (“0”).
- the periodic noise due to the inrush current of the analog unit can be diffused. Can be made smaller than the spectrum peak of the periodic noise N3 shown in FIG. Further, since jitter is added to the operation clock, modulation is applied at the time of folding, and the spectrum peak of the periodic noise N4 'generated in the in-band is further smaller than the spectrum peak of the periodic noise N4. . From this, it is clear that the first aspect can reduce the periodic noise generated in the in-band as compared with the prior art.
- the periodic noise generated in the in-band in the D / A converter. can be reduced.
- This periodic noise is not limited to only the periodic noise generated by the D / A converter, and an example thereof is periodic noise from an A / D converter mounted on the same substrate.
- the periodic noise of this electronic component can be reduced by applying a 1st aspect to the electronic component in which a periodic noise influences operation
- Such a first aspect is advantageous in reducing the size and configuration of the electronic device.
- the sampling circuit shown in FIG. 8 is a sampling circuit of a mode (hereinafter also referred to as “second mode”) that is the basis of the present embodiment.
- This sampling circuit has a continuous part, a sample and hold part, and a digital part.
- the digital unit has a general digital circuit, and outputs a quantized and sampled signal.
- the sample and hold unit has a general switched capacitor circuit (SC circuit), and outputs a sampled signal without being quantized.
- the continuous unit has a general continuous signal circuit (Continuous circuit), and outputs a signal that is not quantized and not sampled.
- the continuous unit inputs the analog input signal Ain.
- the sample / hold unit intermittently samples the analog input signal Ain input by the continuous unit, and holds and transfers the sampled signal.
- a digital unit that handles digital signals is not shown.
- the sampling circuit shown in FIG. 8 includes a capacitor 111-2 and an operational amplifier 121-2.
- the capacitor 111-2 receives the analog input signal Ain sampled by the switches 101-2 and 102-2 (the analog input signal Ain after sampling is referred to as the input signal Vin), and charges are accumulated.
- the electric charge accumulated in the capacitor 111-2 is input to the inverting input terminal of the operational amplifier 121-2 in accordance with the switching of the switches 101-2, 102-2, and 103.
- the operational amplifier 121-2 receives the reference signal Vcom from the non-inverting input terminal and outputs the analog signal VAin.
- FIGS. 9A to 9F are diagrams for explaining the operation of the sampling circuit of the second mode when the reference signal Vcom has no periodic noise.
- FIG. 9A shows the sampling timing of the analog input signal Ain.
- FIG. 9B shows the timing at which the capacitor 111-2 holds and releases the charge accumulated by the analog input signal Ain.
- FIGS. 9A and 9B The switches to which the clock signals shown in FIGS. 9A and 9B are supplied are driven so as to be turned on when the clock signal is High and turned off when the clock signal is Low.
- 9C shows the analog input signal Ain
- FIG. 9D shows the reference signal Vcom that is a DC voltage
- FIG. 9E shows the analog signal Vin generated by the charge transferred from the capacitor 111-2. Is shown.
- FIG. 9F shows an output signal VAin that is an analog signal output from the operational amplifier 121-2.
- the signal indicated by the broken line is the analog input signal Ain.
- the input signal Vin is generated.
- the signal indicated by the broken line is an analog signal Vin generated by the charge transferred from the capacitor 111-2, and the output signal VAin indicated by the solid line is generated by feedback via the switch 103.
- a graph (a) in FIG. 10 is a diagram for explaining a signal output from the capacitor 111-2 shown in FIG. 8, and shows a spectrum obtained by converting the analog signal Vin into the frequency axis by Fourier transform.
- a graph (b) in FIG. 10 shows a spectrum obtained by converting VAin, which is an output signal of the operational amplifier 121-2, into a frequency axis by Fourier transform.
- the vertical axis indicates the intensity of the signal spectrum
- the horizontal axis indicates the frequency.
- the position of the vertical axis indicated by the arrow line in the graphs (a) and (b) in FIG. 10 indicates the frequency reference (“0”).
- the signal output from the capacitor 111-2 (indicated by the spectrum P2 in the figure) has a constant frequency.
- an output signal VAin (indicated by the spectrum p2 in the figure) shown in the graph (b) in FIG. 10 is generated. .
- FIGS. 11A to 11F are diagrams for explaining the operation of the sampling circuit shown in FIG. 8 when the reference signal Vcom has periodic noise.
- FIG. 11A shows the sampling timing of the analog input signal Ain.
- FIG. 11B shows the timing at which the capacitor 111-2 holds and releases the charge accumulated by the analog input signal Ain.
- FIG. 11C shows the analog input signal Ain
- FIG. 11D shows the reference signal Vcom that is a DC voltage
- FIG. 11E shows the analog signal Vin generated by the charge transferred from the capacitor 111-2. Is shown.
- FIG. 11F shows an output signal VAin that is an analog signal output from the operational amplifier 121-2.
- the periodic noise N11 shown in FIG. 11D is generated in the reference signal Vcom
- the sampling circuit superimposes the periodic noise N11 on the output signal Vin via the operational amplifier 121-2. Therefore, when the output signal Vin including periodic noise is sampled and held, the output signal VAin also generates periodic noise N12 corresponding to the periodic noise N11.
- the periodic noise shown in FIGS. 11D, 11E and 11F will be described with reference to graphs (a) and (b) shown in FIG.
- a graph (a) shown in FIG. 12 is a diagram for explaining a signal output from the capacitor 111-2 shown in FIG. 8, and shows a spectrum P2 obtained by converting the analog signal Vin into the frequency axis by Fourier transform.
- the graph shown in FIG. 12B shows a spectrum p2 obtained by converting VAin, which is an output signal of the operational amplifier 121-2, into a frequency axis by Fourier transform.
- the vertical axis indicates the intensity of the signal spectrum
- the horizontal axis indicates the frequency.
- the positions on the vertical axis indicated by the arrow lines in graphs (a) and (b) in FIG. 12 indicate the frequency reference (“0”).
- the periodic noise N12 is turned back, and FIG. As shown, periodic noise N12 'appears near DC.
- the periodic noise N12 ′ appears in the frequency domain used for output sound, that is, in-band.
- jitter is added to a clock signal for operating a device such as a sampling circuit, thereby spreading periodic noise appearing in the in-band by a signal output from another device, and signal quality of an output signal such as sound Is based on the technical idea of preventing the damage.
- the A / D converter includes a sampling circuit including a continuous part (continuous part), a sample and hold part (S / H part), and a digital part.
- the A / D converter includes the sampling circuit shown in FIG.
- graphs (a) and (b) are diagrams for explaining periodic noise when jitter is added to a clock signal for operating the digital unit in the A / D converter.
- a graph (a) shown in FIG. 13 is a diagram for explaining a signal output from the capacitor 111-2 shown in FIG. 8, and shows a spectrum P2 obtained by converting the analog signal Vin into the frequency axis by Fourier transform.
- a graph (b) shown in FIG. 13 shows a spectrum p2 obtained by converting VAin, which is an output signal of the operational amplifier 121-2, into a frequency axis by Fourier transform.
- VAin which is an output signal of the operational amplifier 121-2
- the vertical axis indicates the signal spectrum intensity
- the horizontal axis indicates the frequency.
- the positions of the vertical axis indicated by the arrow lines in the graphs (a) and (b) in FIG. 13 indicate the frequency reference (“0”).
- jitter is added to the clock signal of the digital part of the A / D converter.
- the energy of the periodic noise N13 is dispersed in a wider frequency region than before adding jitter.
- the spectrum peak of the periodic noise N13 is lower than the spectrum peak of the periodic noise N12 shown in FIG.
- the peak of the spectrum of the periodic noise N13 'generated in the in-band is also low as with the periodic noise N13.
- the noise generated by the A / D converter itself can be reduced, and the influence of noise on other devices can be reduced.
- the spectral peak of the periodic noise N13 ′ shown in FIG. 13 is further dispersed, and the influence of noise generated by other devices can be canceled by itself.
- An object of the present invention is to provide a sampling circuit or the like that can be used.
- jitter is added to the clock signal of the sample and hold unit of the A / D converter in order to realize the above-described object.
- FIG. 14 Graphs (a) and (b) shown in FIG. 14 are for explaining the periodic noise when jitter is added to the clock signal of the digital part and the clock signal of the sample and hold part in the A / D converter.
- FIG. A graph (a) in FIG. 14 is a diagram for explaining a signal output from the capacitor 111-2 shown in FIG. 8, and shows a spectrum P2 obtained by converting the analog signal Vin into the frequency axis by Fourier transform. .
- a graph (b) in FIG. 14 shows a spectrum p2 obtained by converting VAin, which is an output signal of the operational amplifier 121-2, into a frequency axis by Fourier transform.
- VAin which is an output signal of the operational amplifier 121-2
- the vertical axis indicates the intensity of the spectrum of the signal
- the horizontal axis indicates the frequency.
- the position of the vertical axis indicated by the arrow line in the graphs (a) and (b) shown in FIG. 14 indicates the frequency reference (“0”).
- the periodic noise generated in the in-band in the A / D converter. can be reduced.
- This periodic noise is not limited to only the periodic noise generated by the A / D converter.
- the second aspect is applied to an electronic component in which the periodic noise affects the operation, thereby reducing the periodic noise of the electronic component. be able to.
- Such a second aspect is advantageous in reducing the size and the configuration of the electronic device.
- FIG. 15 is a diagram illustrating the pipeline type A / D converter according to the first embodiment.
- the pipeline type A / D converter of Embodiment 1 is a converter that converts an analog input signal Ain into an N-bit digital output signal Dout. Therefore, a sampling circuit 801 for sampling and holding the analog input signal Ain (denoted as S / H in the drawing) 801 and k stages connected in cascade for determining each bit (denoted as S in the drawing) S1, S2... Sk, a memory 803 for storing n-digit digital output signal dj (j is 1 to k) determined in each stage, and an analog input signal based on the digital output signal dj stored in memory 803 And an arithmetic circuit 804 for calculating a digital output signal Dout which is an A / D conversion value of Ain.
- a sampling circuit 801 for sampling and holding the analog input signal Ain (denoted as S / H in the drawing) 801 and k stages connected in cascade for determining each bit (denoted as S in the drawing) S1, S2... Sk
- a memory 803
- the A / D converter includes a control circuit 139 that controls a plurality of stages.
- the control circuit 139 is a clock signal ⁇ 1 that does not include jitter indicating an operation clock signal at each stage, and a non-overlapping clock of opposite phase that does not become high simultaneously with the clock signal ⁇ 1, and includes a clock signal ⁇ 2 that does not include jitter, a clock signal At least one of clock signals ⁇ 1 ′ and ⁇ 1 ′′ obtained by adding jitter to ⁇ 1 and clock signal ⁇ 2 ′ obtained by adding jitter to clock signal ⁇ 2 is output.
- the sampling circuit 801 is a circuit that samples the analog input signal Ain and sends the held value as the analog input signal VAin to the first stage S1.
- a non-feedback sampling circuit including an analog switch and a capacitor is applied.
- the stages S1 to Sk are connected in series and send an n-digit digital output signal dj to the memory 803 based on each input signal VAin.
- the input signal VAin is input from the previous stage, and the analog output signal VAout generated by the digital output signal dj and the input signal VAin is output to the next stage.
- an input signal VAin and an output signal VAout with the stage S1 as a reference are shown.
- the memory 803 receives and stores an n-digit digital output signal dj from each of the k stages S1 to Sk. For this reason, the memory 803 is a semiconductor memory that can store at least k n-bit addresses.
- the arithmetic circuit 804 performs an operation based on the digital output signal dj stored in the memory 803 and outputs an N-digit digital output signal Dout. The calculation for calculating the digital output signal Dout is performed as follows.
- the arithmetic circuit 804 adds the most significant digit of the digital output dk of the stage Sk and the least significant digit of the digital output d (k ⁇ 1) of the stage S (k ⁇ 1) in a binary system. Further, based on the addition result (added value), the most significant digit of d (k ⁇ 1) and the least significant digit of the digital output d (k ⁇ 2) of stage S (k ⁇ 2) are also binary-coded. Add by the method. Such processing is repeated to add up the least significant digit of the digital output d1 of the stage S1 and the most significant digit of the digital output d2 of the stage S2. The final result of the addition is output as a digital output signal Dout.
- FIG. 16 is a diagram for illustrating the calculation for calculating the digital output signal Dout described above.
- Embodiments 1-1 and 1-2 will be described as specific examples of the sampling circuit of Embodiment 1.
- the embodiment 1-1 is a sampling circuit that uses clock signals ⁇ 1 and ⁇ 2 that do not include jitter and clock signals ⁇ 1 ′ and ⁇ 2 ′ that include jitter as clock signals.
- the embodiment 1-2 is a sampling circuit using a clock signal ⁇ 1 ′′ in which jitter is added only at the rising edge of the clock signal ⁇ 1 in addition to the clock signals ⁇ 1, ⁇ 2, ⁇ 1 ′, ⁇ 2 ′.
- the basic configuration of the sampling circuit is the same.
- FIG. 17 is a diagram for explaining the sampling circuit of the embodiment 1-1, showing the sampling circuit 801 in FIG. 15, and simultaneously showing a control circuit 139 common to a plurality of A / D converters.
- a sampling circuit 140 (corresponding to the sampling circuit 801 in FIG. 15) shown in FIG. 17 intermittently samples the analog input signal Ain input by the continuous unit 130a for inputting the analog input signal Ain and the continuous unit 130a, And a sample and hold unit 130b for holding and transferring the sampled signal.
- the memory 803 and the arithmetic circuit 804 illustrated in FIG. 15 function as a digital unit 130c illustrated in FIG.
- the control circuit 139 common to each stage of the pipeline type A / D converter has clock signals ⁇ 1 and ⁇ 2 not including jitter, clock signals ⁇ 1 ′ and ⁇ 2 ′ to which jitter is added, and only at the rising edge of the clock signal ⁇ 1.
- a jitter-added clock signal ⁇ 1 ′′ is generated.
- the clock signal ⁇ 1 is input to the continuous unit 130a
- the clock signal ⁇ 2 ′ is input to the sample and hold unit 130b.
- the continuous unit 130a includes a switch 131 and a switch 135, and the switch 131 and the switch 135 are turned on and off according to the clock signal ⁇ 1.
- the analog input signal Ain is sampled and becomes the input signal Vin.
- the sample and hold unit 130b includes a capacitor 132 that samples the input signal Vin, holds the charge generated by the input signal Vin, and a switch 133 that transfers the charge held in the capacitor 132 to a subsequent stage.
- the switch 133 performs a switching operation according to the clock signal ⁇ 2 ′.
- the continuous unit 130a is operated by the clock signal ⁇ 1
- the sample / hold unit 130b is operated by the clock signal ⁇ 2 'to which jitter is added.
- the embodiment 1-1 is not limited to such a configuration.
- the switch 131 and the switch 135 may be operated by different clock signals, and a clock signal in which jitter is added to the clock signal. May be operated. In this case, however, jitter should not be added to the switch that is switched off first.
- the clock signal ⁇ 1 that does not add jitter is used for the clock that operates the switch 135, and the clock signal that adds jitter is used for the clock that operates the switch 131.
- ⁇ 1 ′ may be used.
- FIG. 18 is a functional block diagram for explaining an A / D converter (referred to as ADC in the drawing) including the sampling circuit 140 and the control circuit 139 shown in FIG.
- the control circuit 139 supplies a non-jittered clock signal ⁇ 1 to the continuous unit 130a, and supplies a jittered clock signal ⁇ 2 ′ to the digital unit 130c, and a sample and hold unit 130b. Is supplied with a jittered clock signal ⁇ 2 ′.
- the clock supplied to the digital unit 130c may be a clock signal ⁇ 1 ′ whose phase relationship with the clock supplied to the sample and hold unit 130b is inverted.
- the control circuit 139 includes a clock signal generation unit 143, a jitter generation unit (denoted as Jitter_Gen. In FIG. 18) 141, and a jitter selection unit (denoted as Jitter_Sel. In FIG. 18) 142. .
- the clock signal generator 143 generates a clock signal ⁇ 1 and a non-overlapping clock signal ⁇ 2 of opposite phase that does not become High at the same time as the clock signal ⁇ 1.
- the jitter generator 141 adds jitter to the clock signal ⁇ 1 to generate a clock signal ⁇ 1 ′, adds jitter to the clock signal ⁇ 2 and does not become high simultaneously with the clock signal ⁇ 1 ′, and has a non-overlapping non-overlap including jitter.
- a clock signal ⁇ 2 ′ is generated.
- jitter is added only to the rising edge of the clock signal ⁇ 1 to generate the clock signal ⁇ 1 ′′.
- This clock signal ⁇ 1 ′′ does not become high simultaneously with respect to each of the clock signals ⁇ 2 and ⁇ 2 ′. Clock signal.
- the clock signal ⁇ 1 and the clock signals ⁇ 1 ′ and ⁇ 1 ′′ generated by adding jitter to the clock signal ⁇ 1 and the clock signals ⁇ 2 and ⁇ 2 ′ do not become high at the same time, and have a reversed phase and overlapping relationship. is there.
- the clock signal ⁇ 2 ′ including the jitter generated by the jitter generating unit 141 is output to the sample and hold unit 130b, the clock signal ⁇ 1 without adding jitter is output to the continuous unit 130a, and the clock signal ⁇ 2 ′ including the jitter is output. It operates to output to the digital unit 130c.
- the jitter generation unit 141 can be configured relatively easily by a delay circuit or the like that delays the clock signal.
- FIGS. 19A to 19E are timing charts of clock signals ⁇ 1, ⁇ 1 ′, ⁇ 2, ⁇ 2 ′, and ⁇ 1 ′′.
- 19A shows a timing chart of the clock signal ⁇ 1
- FIG. 19B shows a timing chart of the clock signal ⁇ 1 ′
- FIG. 19C shows a timing chart of the clock signal ⁇ 1 ′′
- FIG. A timing chart of the signal ⁇ 2 is shown
- (e) shows a timing chart of the clock signal ⁇ 2 ′.
- the switch to which each clock signal is supplied is driven so that the switch is turned on during a period when the clock signal is High and turned off during a period when the clock signal is Low.
- the clock signal ⁇ 1 ′′ to which jitter is added only at the rising edge of the clock signal is generated, for example, by inputting the clock signal ⁇ 1 and the clock signal ⁇ 1 ′ to the AND circuit.
- FIG. 20 is a diagram for explaining a specific configuration of jitter selecting section 142 shown in FIG.
- the jitter selecting unit 142 includes switch units 1301, 1302, and 1303 each including five switches.
- the switch unit 1301 selects a clock signal output to the continuous unit 130a.
- the switch unit 1302 selects a clock signal output to the sample and hold unit 130b.
- the switch unit 1303 selects a clock signal output to the digital unit 130c.
- the clock signals ⁇ 1 ′ and ⁇ 2 ′ with added jitter are output to the jitter selector 142.
- the jitter selection unit 142 also receives clock signals ⁇ 1 and ⁇ 2 to which no jitter is added.
- the jitter selection unit 142 selects the clock signal ⁇ 1 from the clock signals ⁇ 1, ⁇ 2, ⁇ 1 ′, ⁇ 2 ′, ⁇ 1 ′′, and outputs the selected clock signal ⁇ 2 ′ to the continuous unit 130a.
- the clock signal ⁇ 2 ′ is selected and output to the digital unit 130c.
- the jitter selection unit 142 is eliminated, the clock signal ⁇ 1 is directly output from the clock signal generation unit 143 to the continuous unit 130a, and the clock signal ⁇ 2 ′ is output from the jitter generation unit 141 to the sample and hold unit 130b. You may output directly to the digital part 130c.
- the sample and hold unit 130b transmits the sampled signal, and the signal component is a DC component. Therefore, the signal component is modulated by jitter applied to the operation clock. It does not take. However, since periodic noise mixed from the A / D converter itself or other electronic devices is an AC component, the noise component is modulated by jitter applied to the operation clock, and a noise diffusion effect is obtained. In other words, it does not change to STF (Signal Transfer Function), only NTF (Noise Transfer Function) can be modulated by jitter, and mixed periodic noise can be efficiently separated from signal components. Therefore, the jitter generation unit can also be referred to as a frequency modulation signal generation unit that generates a signal for frequency modulation. Jitter can also be said to be a signal whose frequency varies. For this reason, without adding noise to the signal to be transmitted, only the noise in the in-band can be dispersed and the peak of the spectrum can be reduced.
- STF Signal Transfer Function
- NTF Noise Transfer Function
- the embodiment 1-1 described above it is possible to enhance the resistance to noise of the A / D converter itself, instead of reducing noise generated from devices around the A / D converter. For this reason, the influence of noise on the A / D converter can be reduced by changing only the A / D converter without changing the configuration of other devices around the A / D converter.
- the embodiment 1-1 can be realized only by adding a circuit for adding jitter to the clock signal. This eliminates the need for advanced semiconductor process technology and the increase in the number of pins on the chip, thereby preventing the A / D converter from increasing in cost. Furthermore, according to Embodiment 1-1, since the A / D converter can be disposed in close proximity to other devices without considering the influence of noise, the size of the device including the A / D converter can be reduced. Has an effect on
- Embodiment 1-1 it is possible to reduce the noise suppression requirement for a decoupling capacitor that is generally provided for the purpose of reducing noise generated from devices around the A / D converter. . Further, according to Embodiment 1-1, since the noise suppression requirement for the decoupling capacitor can be reduced, it may be considered that the decoupling capacitor itself is unnecessary.
- the digital unit 130c is operated by the clock signal ⁇ 2 'to which jitter is added.
- the embodiment 1-1 is not limited to such a configuration, and the noise of the A / D converter itself may be input even when the clock signal ⁇ 2 to which no jitter is added is input to the digital unit 130c. The effect of enhancing the resistance to is not impaired at all. If jitter is added to the clock signal of the digital unit 130c, the noise peak of the signal output from the A / D converter is reduced, and the A / D converter reduces the influence of noise on other devices. Can do.
- Embodiment 1-1 when the A / D converter is configured as a single unit, the control circuit 139 shown in FIG. 15 is provided in association with one sampling circuit.
- the clock signal generation unit 143 of the A / D converter may be provided outside the A / D converter.
- the control circuit 139 when the sampling circuit of the A / D converter shown in FIGS. 17 and 18 is configured as another device, the control circuit 139 may be provided outside the device.
- Embodiment 1-2 of the present invention and an A / D converter using this sampling circuit will be described.
- the difference between the embodiment 1-2 and the embodiment 1-1 described above is that the radiation signal due to the inrush current generated in the continuous portion is diffused, and therefore the clock signal ⁇ 1 ′′ with jitter added to the continuous portion is input. Then, jitter is added to the edge that is a trigger for determining the operation start time of the clock signal input to the continuous section, and jitter is added to the edge that is the trigger for determining the operation end time.
- the radiation noise caused by the inrush current of the analog unit can be diffused to further effectively suppress the radiation noise.
- FIG. 21 is a diagram for explaining the sampling circuit of the embodiment 1-2, and shows the sampling circuit 801 in FIG. 15 and a control circuit 139 common to a plurality of A / D converters.
- the sampling circuit 140 in the embodiment 1-2 shown in FIG. 21 is input by the continuous unit 130a for inputting the analog input signal Ain and the continuous unit 130a, like the sampling circuit 140 in the embodiment 1-1.
- a sample-and-hold unit 130b that intermittently samples the analog input signal Ain and holds and transfers the sampled signal.
- the memory 803 and the arithmetic circuit 804 shown in FIG. 15 function as a digital unit 130c shown in FIG.
- the control circuit 139 generates a clock signal ⁇ 1 ′ with jitter added to the rising and falling edges of the clock signal ⁇ 1, a clock signal ⁇ 1 with jitter added to the rising edge of the clock signal ⁇ 1, and no jitter added to the falling edge.
- a clock signal ⁇ 2 ′ in which jitter is added to the rising and falling edges of the clock signal ⁇ 2 which is a non-overlapping signal and does not become high simultaneously with the clock signal ⁇ 1 is generated and output.
- the control circuit 139 supplies a clock signal ⁇ 1 ′′ to which the jitter is added at the rising edge and the jitter is not added to the falling edge to the continuous part 130a, and the digital part 130c.
- An arbitrary clock signal can be supplied to the unit 130c. For example, it is conceivable to supply a clock signal ⁇ 1 ′ whose phase relationship is inverted with respect to the clock signal supplied to the sample and hold unit 130b.
- the continuous unit 130a includes a switch 131 that is turned on and off in accordance with the clock signal ⁇ 1 ′′ and a switch 135.
- the on / off operation of the switch 131 and the switch 135 causes an analog input signal Ain to be input. It becomes the signal Vin.
- the sample and hold unit 130b includes a capacitor 132 that samples the input signal Vin, holds the charge generated by the input signal Vin, and a switch 133 that transfers the charge held in the capacitor 132 to a subsequent stage.
- the switch 133 performs a switching operation according to the clock signal ⁇ 2 ′.
- the continuous unit 130a is operated with the clock signal ⁇ 1 ′′
- the sample / hold unit 130b is operated with the clock signal ⁇ 2 ′.
- the switch 131 and the switch 135 may be operated by different clock signals, or may be operated by a clock signal obtained by adding jitter to the clock signal. Jitter should not be added to the switch that switches off first, that is, when switch 135 is turned off first and switch 131 is turned off later, the clock that operates switch 135 is not jittered at the rising edge. The falling edge is set to the clock signal ⁇ 1 ”with no jitter added, and the switch 131 is operated. Or as a clock signal .phi.1 'plus jitter to the clock to be.
- FIG. 22 is a functional block diagram for explaining an A / D converter (referred to as ADC in the figure) including the sampling circuit 140 and the control circuit 139 shown in FIG.
- the control circuit 139 includes a clock signal generator 143, a jitter generator (denoted as Jitter_Gen. In FIG. 22) 141, and a jitter selector (denoted as Jitter_Sel. In FIG. 22) 142.
- the clock signal generator 143 generates clock signals ⁇ 1 and ⁇ 2 that do not add jitter.
- the jitter generator 141 adds jitter to the clock signals ⁇ 1 ′ and ⁇ 2 ′ obtained by adding jitter to the clock signals ⁇ 1 and ⁇ 2 and the rising edge which is a trigger for determining the operation start time of the clock signal ⁇ 1.
- a clock signal ⁇ 1 ′′ to which no jitter is added is generated at the falling edge that is a trigger for determining the end time.
- the jitter selector 142 generates clock signals ⁇ 1, ⁇ 2, ⁇ 1 ′, ⁇ 2 ′, ⁇ 1.
- the clock signal ⁇ 2 ′ generated by the jitter generator 141 is selected and output to the sample and hold unit 130b and the digital unit 130c, and the clock signal ⁇ 1” is selected and output to the continuous unit 130a.
- the clock signals ⁇ 1, ⁇ 2, ⁇ 1 ′, ⁇ 2 ′, ⁇ 1 ′′ are clearly shown in FIGS. 19A to 19 E, and the clock signals ⁇ 1 ′, ⁇ 2 ′ are Jitter is added to the falling edge. However, jitter is added only to the rising edge of the clock signal in the clock signal ⁇ 1 ′′.
- the clock signal ⁇ 2 ′ is selected and supplied to the sample and hold unit 130b and the digital unit 130c shown in FIG. Then, the clock signal ⁇ 1 ′′ is supplied to the continuous unit 130a shown in FIG.
- the signal component in the sample and hold operation of the continuous unit 130a is an AC component
- the signal component is not added by adding jitter to the edge that is a trigger for determining the operation end time of the operation clock signal. No modulation is applied.
- the edge which is a trigger for determining the start of operation
- radiation noise caused by inrush current that occurs at the start of the sample and hold operation of the continuous part is diffused, and radiation noise is more effectively suppressed. can do.
- the noise generated from the A / D converter itself is reduced, the resistance to the noise of the A / D converter itself is enhanced, and in addition, the inrush current generated in the continuous portion.
- the resulting radiation noise is also diffused, and the noise can be further reduced. For this reason, the influence of noise on the A / D converter can be reduced by changing only the A / D converter without changing the configuration of other devices around the A / D converter.
- the digital unit 130c is operated by the clock signal ⁇ 2 'to which jitter is added.
- the present embodiment is not limited to such a configuration, and even if the clock signal ⁇ 2 to which no jitter is added is input to the digital unit 130c, the A / D converter itself is resistant to noise. The effect of strengthening is not impaired at all. If jitter is added to the clock signal of the digital unit 130c, the noise peak of the signal output from the A / D converter is reduced, and the A / D converter reduces the influence of noise on other devices. Can do.
- the clock signal generation unit 143 may be provided outside the A / D converter.
- the control circuit 139 may be provided outside the A / D converter.
- the control circuit 139 generates the clock signals ⁇ 1, ⁇ 2, ⁇ 1 ′, ⁇ 2 ′, and ⁇ 1 ′′, and the jitter selection unit 142 selects one of these five types of clock signals. Therefore, the sampling circuit is operated without using the clock signal ⁇ 1 ′′ as in the embodiment 1-1, and the clock signal ⁇ 1 ′′ is supplied to the continuous unit 130a as in the embodiment 1-2. In the first embodiment 1-1, since the clock signal ⁇ 1 ′′ is not used, the control circuit 139 uses the clock signal ⁇ 1, ⁇ 2, ⁇ 1 ′, and ⁇ 2 ′ may be generated, and the jitter selection unit 142 may select any one of the four types of clock signals.
- Embodiment 2 will be described.
- the sampling circuit of the present invention is applied to a D / A converter.
- Embodiments 2-1 and 2-2 will be described as specific examples of the sampling circuit of Embodiment 2.
- the embodiment 2-1 is a sampling circuit using clock signals ⁇ 11 and ⁇ 12 not including jitter and clock signals ⁇ 11 ′ and ⁇ 12 ′ including jitter as clock signals.
- the embodiment 2-2 is a sampling circuit using a clock signal ⁇ 11 ′′ in which jitter is added only at the rising edge of the clock signal ⁇ 11 in addition to the clock signals ⁇ 11, ⁇ 12, ⁇ 11 ′, and ⁇ 12 ′.
- FIG. 23 is a diagram for explaining the D / A converter according to the embodiment 2-1.
- the illustrated D / A converter includes a sampling circuit 160 and a control circuit 159-1.
- the sampling circuit 160 intermittently samples an input signal (reference signal Vref, the sampled reference signal Vref is referred to as an input signal Vin) based on the input digital signal Din, and holds and transfers the sampled signal.
- a hold unit 150b and a continuous unit 150a that outputs the signal transferred by the sample and hold unit 150b as an analog signal Aout are included.
- the control circuit 159-1 generates and outputs clock signals ⁇ 11 and ⁇ 12 which do not include jitter and clock signals ⁇ 11 ′ and ⁇ 12 ′ to which jitter is added.
- the clock signal ⁇ 12 to which no jitter is added is input to the continuous unit 150a, and the clock signal ⁇ 11 ′ to which jitter is added is input to the sample and hold unit 150b.
- the sample-and-hold unit 150 b includes a capacitor 152 that accumulates charges generated by the input signal Vin, a switch 151 that accumulates in the capacitor 152, and a switch 153.
- the switch 151 and the switch 153 perform a switching operation according to the clock signal ⁇ 11 ′.
- the continuous unit 150a includes an operational amplifier 155, a feedback path 158 that inputs the analog output signal Aout of the operational amplifier 155 to the inverting input terminal, a capacitor 154 that accumulates charges generated by the analog output signal Aout on the feedback path 158, and a capacitor A switch 156 for transferring the charge accumulated in 152 to the analog output signal Aout and a switch 157 are included.
- a clock signal ⁇ 12 having no jitter is output to the switches 156 and 157 of the continuous unit 150a, and the continuous unit 150a is operated by the clock signal ⁇ 12.
- the continuous part 150 a further includes a capacitor 154.
- This capacitor 154 forms an LPF, and the cutoff frequency of the LPF is determined by the capacitance ratio of the capacitors 154 and 152 and the switching frequency.
- FIG. 24 is a diagram for explaining a D / A converter (denoted as DAC in the drawing) including the sampling circuit 160 and the control circuit 159-1 shown in FIG.
- the control circuit 159-1 supplies a clock signal ⁇ 12 without adding jitter to the continuous unit 150a, and supplies a clock signal ⁇ 11 ′ with added jitter to the digital unit 150c.
- a clock signal ⁇ 11 ′ with jitter added is supplied.
- the control circuit 159-1 includes a clock signal generation unit 163 that generates clock signals ⁇ 11 and ⁇ 12 without adding jitter, and a jitter generation unit that generates clock signals ⁇ 11 ′ and ⁇ 12 ′ with addition of jitter (in FIG. 24).
- 161 and a clock signal ⁇ 11, ⁇ 12, ⁇ 11 ′, ⁇ 12 ′ are input, the clock signal ⁇ 11 ′ generated by the jitter generator 161 is selected and output to the sample and hold unit 150b, and the clock signal a jitter selection unit (denoted as Jitter_Sel. in FIG. 24) 162-1 that operates to select ⁇ 11 ′ and output it to the digital unit 150c, and select the clock signal ⁇ 12 and output it to the continuous unit 150a. It is out.
- the jitter selection unit 162-1 is eliminated, the clock signal ⁇ 11 ′ is directly output from the jitter generation unit 161 to the sample and hold unit 150b and the digital unit 150c, and the clock signal ⁇ 12 is directly output from the clock signal generation unit 163 to the continuous unit 150a. It may be output.
- the embodiment 2-1 as in the embodiment 1-1, it is possible to modulate only the noise transfer function without modulating the signal transfer function of the D / A converter. For this reason, without adding noise to the signal to be transmitted, only the noise in the in-band can be dispersed and the peak of the spectrum can be reduced. Note that the feedback path via the capacitor 154 may be eliminated.
- 25 (a) to 25 (d) are timing charts of the clock signals ⁇ 11, ⁇ 11 ′, ⁇ 12, and ⁇ 12 ′ described with reference to FIGS. 25A shows a timing chart of the clock signal ⁇ 11
- FIG. 25B shows a timing chart of the clock signal ⁇ 11 ′
- FIG. 25C shows a timing chart of the clock signal ⁇ 12
- FIG. d) represents a timing chart of the clock signal ⁇ 12 ′.
- the switch to which each clock signal is supplied is driven so as to be turned on when the clock signal is High and turned off when the clock signal is Low.
- the jitters of the clock signals ⁇ 11 ′ and ⁇ 12 ′ are added only at the rise and fall of the clock signal ⁇ 11 and the clock signal ⁇ 12.
- the rising edges of the clock signals ⁇ 11, ⁇ 12, ⁇ 11 ′, and ⁇ 12 ′ serve as triggers for determining the operation start times of the circuit elements that operate according to the clock signals.
- the falling edge of each clock signal serves as an operation end time determination trigger for circuit elements that operate according to each clock signal.
- the clock signal ⁇ 12 is a non-overlapping clock signal that does not become high simultaneously with the clock signal ⁇ 11.
- the clock signal ⁇ 12 ' is a non-overlapping clock signal that does not become high at the same time as the clock signal ⁇ 11'.
- These clock signals are the clock signal ⁇ 11 and the clock signal ⁇ 11 ′ generated by adding jitter to the clock signal ⁇ 11, and the clock signal ⁇ 12 and the clock signal ⁇ 12 ′ generated by adding jitter to the clock signal ⁇ 12, At the same time, it is in a non-overlapping relationship of reverse phase that does not become high.
- FIG. 26 is a diagram for explaining a specific configuration of the jitter selector 162-1 shown in FIG.
- the jitter selection unit 162-1 includes switch units 1501-1, 1502-1, and 1503-1 each including four switches.
- the switch unit 1501-1 selects a clock signal output to the continuous unit 150a.
- the switch unit 1502-1 selects a clock signal output to the sample / hold unit 150b, and the switch unit 1503-1 selects a clock signal output to the digital unit 150c.
- the clock signal ⁇ 12 is selected from the clock signals ⁇ 11, ⁇ 11 ′, ⁇ 12, and ⁇ 12 ′ and supplied to the continuous unit 150a shown in FIG.
- the clock signal ⁇ 11 ′ is selected from the clock signals ⁇ 1, ⁇ 1 ′, ⁇ 2, and ⁇ 2 ′, and is supplied to the sample and hold unit 150b shown in FIG. 24, and the clock signals ⁇ 11, ⁇ 11 ′, ⁇ 12, and ⁇ 12 ′ are clock signals.
- ⁇ 11 ′ is selected and supplied to the digital unit 150c shown in FIG.
- the embodiment 2-1 can be realized only by adding a circuit for adding jitter to the clock signal. This eliminates the need for advanced semiconductor process technology and the increase in the number of pins on the chip, thereby preventing an increase in cost of the D / A converter. Furthermore, according to Embodiment 2-1, since the D / A converter can be arranged close to other devices without considering the influence of noise, the size of the device including the D / A converter can be reduced. Has an effect.
- the embodiment 2-1 it is possible to reduce a noise suppression request to a decoupling capacitor generally provided for the purpose of reducing noise generated from devices around the D / A converter. . Further, according to the embodiment 2-1, since the noise suppression requirement for the decoupling capacitor can be reduced, it can be considered that the decoupling capacitor itself is not required.
- the embodiment 2-1 is not limited to the one that inputs the clock signal ⁇ 11 ′ with jitter added to the digital unit 150c. Even if the clock signal ⁇ 11 that does not add jitter is input to the digital unit 150c, the effect of enhancing the resistance to noise of the D / A converter itself is not impaired at all. Further, also in the embodiment 2-1, the clock signal generation unit 163 may be provided outside the D / A converter. Further, when the sampling circuit of the D / A converter shown in FIGS. 23 and 24 is configured as another device, the control circuit 159-1 may be provided outside the device.
- the continuous unit 150a starts to output the signal transferred by the sample and hold unit 150b as an analog signal Aout at the rising edge that is a trigger for determining the operation start time, and determines the operation end time. At the falling edge as a trigger, the analog signal Aout at the operation end time is sampled and held until the next operation starts. Similar to the sampling circuit described above, when periodic noise is superimposed during sampling and holding at the operation end time, the noise is folded back into the analog signal Aout.
- the present embodiment 2-2 is made to diffuse and reduce noise mixed in the continuous part.
- the difference between the present embodiment 2-2 and the above-described embodiment 2-1 is that a noise-added clock signal is input to the continuous portion in order to diffuse noise mixed in the continuous portion.
- jitter is not added to the edge that is a trigger for determining the operation start time of the clock signal input to the continuous unit, but jitter is added to the edge that is the trigger for determining the operation end time.
- it is possible to efficiently separate the mixed periodic noise and the signal component by modulating only the periodic noise by the jitter without modulating the signal component of the analog output signal Aout.
- FIG. 27 is a diagram for explaining the D / A converter of the embodiment 2-2.
- the same components as those shown in the drawings used in the description of the embodiment 2-1 described above are given the same reference numerals. The description will be partially omitted.
- the illustrated D / A converter includes a sampling circuit 160 and a control circuit 159-2.
- the sampling circuit 160 describes an input signal (a reference signal is Vref and a sampled reference signal Vref is an input signal Vin) based on a digital signal Din (not shown) input to a digital unit (not shown in FIG. 27). ) Intermittently, and a sample / hold unit 150b that holds and transfers the sampled signal, and a continuous unit 150a that outputs the signal transferred by the sample / hold unit 150b as an analog signal Aout. Yes.
- the continuous unit 150a includes an operational amplifier 155, a feedback path 158 that inputs the analog output signal Aout of the operational amplifier 155 to the inverting input terminal, a capacitor 154 that accumulates charges generated by the analog output signal Aout on the feedback path 158, and a capacitor A switch 156 for transferring the charge accumulated in 152 to the analog output signal Aout and a switch 157 are included.
- the clock signal ⁇ 12 ′′ is input to the switches 156 and 157 of the continuous unit 150a, and the continuous unit 150a is operated by the clock signal ⁇ 12 ′′.
- an LPF Low Pass Filter
- the cutoff frequency of the LPF is determined by the capacitance ratio of the capacitor 154 and the capacitor 152 and the switching frequency.
- such a capacitor 154 may not be provided.
- the sample and hold unit 150b includes a capacitor 152 that accumulates charges generated by the input signal Vin, a switch 151 that accumulates in the capacitor 152, and a switch 153.
- the switch 151 and the switch 153 perform a switching operation according to the clock signal ⁇ 11 '.
- the control circuit 159-2 includes a clock signal ⁇ 11 ′ in which jitter is added to the rising and falling edges of the clock signal ⁇ 11, a clock signal ⁇ 12 ′ in which jitter is added to the rising and falling edges of the clock signal ⁇ 12, and the rising edge thereof. Generates a clock signal ⁇ 12 ′′ with no jitter and jitter at the falling edge.
- the clock signal ⁇ 12 ′′ is output to the switches 156 and 157 of the continuous unit 150a, and the continuous unit 150a receives the clock.
- the clock signal ⁇ 11 ′ is input to the switches 151 and 153 of the sample and hold unit 150b.
- FIG. 28 is a functional block diagram for explaining a D / A converter (denoted as DAC in the figure) including the sampling circuit 160 and the control circuit 159-2 shown in FIG.
- the control circuit 159-2 determines the clock signal generation unit 163 that generates the clock signals ⁇ 11 and ⁇ 12 that do not add jitter, the clock signals ⁇ 11 ′ and ⁇ 12 ′ that add jitter to the clock signals ⁇ 11 and ⁇ 12, and the operation start time.
- a jitter generator (see FIG. 28) generates a clock signal ⁇ 12 ′′ in which jitter is not added to the rising edge, which is a trigger for the operation, and jitter is added to the falling edge, which is a trigger for determining the operation end time.
- the jitter selecting unit operates to output to 150c, select the clock signal ⁇ 12 "and output to the continuous unit 150a.
- the clock signal ⁇ 12 ′′ whose jitter appears only at the falling edge of the signal is generated.
- the clock signal ⁇ 12 is a non-overlapping clock signal that does not become high simultaneously with the clock signal ⁇ 11.
- the clock signal ⁇ 12 ' is a non-overlapping clock signal that does not become high at the same time as the clock signal ⁇ 11'.
- These clock signals include a clock signal ⁇ 11 and a clock signal ⁇ 11 ′ generated by adding jitter to the clock signal ⁇ 11, and a clock signal ⁇ 12 ′ and ⁇ 12 ′′ generated by adding jitter to the clock signal ⁇ 12 and the clock signal ⁇ 12. Is a non-overlapping relationship of opposite phase that does not become High at the same time.
- the signal component in the sample / hold operation of the continuous unit 150a is a DC component
- the signal component is not modulated by jitter added to the operation clock signal.
- periodic noise mixed from the D / A converter itself or other electronic equipment is an AC component
- the noise component is modulated by jitter applied to the operation clock signal, and a noise diffusion effect is obtained.
- Embodiment 2-2 does not change to STF, but can modulate only NTF by jitter, and efficiently separates periodic noise mixed in an analog output signal from signal components. Can do. For this reason, in the present embodiment 2-2, only the noise in the in-band can be dispersed without adding noise to the signal to be transmitted, and the peak of the noise spectrum can be reduced.
- FIGS. 29A to 29E are timing charts of the clock signals ⁇ 11, ⁇ 11 ′, ⁇ 12, ⁇ 12 ′, and ⁇ 12 ′′ described in FIG. 27 and
- FIG. 29A shows a timing chart of the clock signal ⁇ 11
- FIG. 29B shows a timing chart of the clock signal ⁇ 11 ′
- FIG. 29C shows a timing chart of the clock signal ⁇ 12
- FIG. ) Represents a timing chart of the clock signal ⁇ 12 ′
- FIG. 29E represents a timing chart of the clock signal ⁇ 12 ′′.
- the switch to which each clock signal is supplied is driven so that the switch is turned on during a period when the clock signal is High and turned off during a period when the clock signal is Low.
- the clock signals ⁇ 11 ′ and ⁇ 12 ′ have jitter added to the rising and falling edges of the clock signal.
- jitter is added to the clock signal ⁇ 12 ′′ only at the falling edge of the clock signal.
- the fluctuation of the start time of the operation of outputting the signal transferred by the sample / hold unit 150b as the analog signal Aout causes frequency modulation of the signal component.
- the switches 156 and 157 of the continuous unit 150a By operating the switches 156 and 157 of the continuous unit 150a by the signal ⁇ 12 ′′, the start of the operation of outputting the signal transferred by the sample and hold unit 150b as the analog signal Aout is not affected by jitter. Therefore, the clock signal ⁇ 12 ′′ does not modulate the signal component of the analog output signal Aout.
- ⁇ 12 ′′ is diffused by jitter at the timing when the end of the operation is determined, the mixed periodic noise can be diffused by jitter.
- FIG. 30 is a diagram for explaining a specific configuration of the jitter selector 162-2 shown in FIG.
- the jitter selecting unit 162-2 includes switch units 1501-2, 1502-2, and 1503-2 each including five switches.
- the switch unit 1501-2 selects a clock signal output to the continuous unit 150a.
- the switch unit 1502-2 selects a clock signal output to the sample and hold unit 150b.
- the switch unit 1503-2 selects a clock signal output to the digital unit 150c.
- the clock signal ⁇ 11 ′ is selected and supplied to the sample and hold unit 150b and the digital unit 150c shown in FIG.
- the clock signal ⁇ 12 ′′ is supplied to the continuous unit 150a shown in FIG.
- the present embodiment 2-2 described above does not reduce noise generated from devices around the D / A converter, like the sampling circuit and D / A converter of the embodiment 2-1 described above.
- the resistance of the D / A converter itself to noise can be enhanced. For this reason, the influence of noise on the D / A converter can be reduced by changing only the D / A converter without changing the configuration of other devices around the D / A converter.
- the embodiment 2-2 can be realized only by adding a circuit for adding jitter to the clock signal. This eliminates the need for advanced semiconductor process technology and the increase in the number of pins on the chip, thereby preventing an increase in cost of the D / A converter. Furthermore, since the D / A converter can be disposed close to other devices without considering the influence of noise in the present embodiment 2-2, it is possible to reduce the size of the device including the D / A converter. There is an effect.
- the present embodiment 2-2 it is possible to reduce the noise suppression requirement for a decoupling capacitor generally provided for the purpose of reducing noise generated from devices around the D / A converter. Become. Moreover, according to this embodiment, since the noise suppression requirement for the decoupling capacitor can be reduced, it may be considered that the decoupling capacitor itself is unnecessary.
- the present embodiment 2-2 also diffuses the periodic noise generated by the sample and hold operation in the continuous portion 150a because the clock signal ⁇ 12 ′′ with jitter added is also input to the continuous portion 150a.
- noise is not superimposed on the analog output signal Aout by not adding jitter to the rising edge of the clock signal ⁇ 12 ′′.
- the embodiment 2-2 is not limited to the one that inputs the clock signal ⁇ 11 ′ to which the jitter is added to the digital unit 150c. That is, even if the clock signal ⁇ 11 without adding jitter is input to the digital unit 150c, the effect of enhancing the resistance to noise of the D / A converter itself is not impaired at all.
- the clock signal generation unit 163 may be provided outside the D / A converter.
- the control circuit 159-2 may be provided outside the D / A converter.
- the embodiment 2-2 is a sampling circuit using the clock signals ⁇ 11, ⁇ 12, ⁇ 11 ′, ⁇ 12 ′ and the clock signal ⁇ 11 ′′ in which jitter is added only to the rising edge of the clock signal ⁇ 11
- the sampling circuit of the embodiment 2-1 can be realized by using only the clock signals ⁇ 11, ⁇ 12, ⁇ 11 ′, and ⁇ 12 ′ and switching the output destination.
- the third embodiment is a codec (CODEC) in which the A / D converter described in the first embodiment and the D / A converter described in the second embodiment are mixedly mounted.
- CODEC codec
- FIG. 31 is a diagram for explaining the CODEC of the embodiment 3-1.
- the same reference numerals as those described in the embodiments 1-1 and 2-1 denote the same reference numerals, and a description thereof will be omitted.
- both the A / D converter and the D / A converter operate the sample and hold unit with a clock signal to which jitter has been added. Periodic noise caused by inrush current can be effectively diffused, and generation of dominant radiation noise itself can be suppressed.
- both the A / D converter and the D / A converter operate the sample and hold unit with a clock signal added with jitter, so that the STF has By applying modulation only to the NTF without applying modulation, it is possible to suppress the influence of radiation noise generated by the A / D converter and D / A converter itself, and to perform D / A conversion. And the influence of the radiation noise generated by the A / D converter from others can be suppressed. Therefore, a synergistic noise suppressing effect by suppressing the generation of radiation noise and enhancing the resistance to radiation noise can be expected.
- Embodiment 3-1 is advantageous for configuring a small CODEC.
- it is possible to reduce the noise suppression requirement for a decoupling capacitor that is generally provided for the purpose of reducing noise generated from CODEC peripheral devices.
- the noise suppression requirement for the decoupling capacitor can be reduced, it may be considered that the decoupling capacitor itself is unnecessary.
- FIGS. 32A and 32B are diagrams for explaining the effect of the embodiment 3-1.
- FIG. 32B shows an example in which a clock signal added with jitter is input to the digital part together with the sample and hold part.
- FIG. 32A is a diagram for explaining the characteristics of the conventional CODEC.
- FIG. 32B is a diagram for explaining the CODEC characteristics of the embodiment 3-1.
- the vertical axis THD + N indicates the distortion of the CODEC output signal (the ratio of the signal portion of the output signal to noise at 20 Hz to 20 kHz).
- 32A and 32B show the frequency difference between the sampling frequency of the A / D converter (sampling operation frequency) and the sampling frequency of the D / A converter.
- the CODEC of Embodiment 3-1 has the same sampling frequency between the A / D converter and the D / A converter (the difference between the operating frequency on the horizontal axis). 0), even if the sampling frequency of the A / D converter and the D / A converter has a difference of about ⁇ 25 Hz, the distortion of the output signal is smaller than that of the prior art.
- Embodiment 3-1 as described above both the asynchronous CODEC in which the A / D converter and the D / A converter operate with different sampling clocks, and the synchronous CODEC in which the same sampling clock operates, The distortion of the output signal can be reduced as compared with the prior art.
- the frequency of the jitter added to the operation clock is 48 kHz to 384 kHz.
- the embodiment 3-1 was able to reduce the distortion of the output signal as compared with the prior art, similarly to the result shown in FIG.
- FIG. 31 illustrates a case where a codec in which the A / D converter described in the embodiment 1-1 and the D / A converter described in the embodiment 2-1 are mixed is described. And a codec in which the A / D converter described in the embodiment 1-2 and the D / A converter described in the embodiment 2-2 are mixedly supplied so as to supply a clock signal with jitter added. Is also possible.
- FIG. 33 is a diagram for explaining the CODEC of the embodiment 3-2.
- the embodiment 3-2 includes a jitter selection unit in a codec (CODEC) in which the A / D converter described in the embodiment 1-1 and the D / A converter described in the embodiment 2-1 are mixedly mounted. 142 and 162-1 are not provided. Even in this form, the same effect as the CODEC of Embodiment 3-1 can be obtained.
- CODEC codec
- the sampling circuit of the present invention is not limited to the one configured as an A / D converter, a D / A converter, and a CODEC, and may be used for, for example, a charge pump. Can do.
- the scope of the present invention is not limited to the exemplary embodiments shown and described above, but includes all embodiments that bring about effects equivalent to those intended by the present invention.
- the scope of the invention is not limited to the combinations of features of the invention defined by the claims, but may be defined by any desired combination of particular features among all the disclosed features. .
- the present invention can be used for all electronic devices having D / A conversion and A / D conversion functions in addition to A / D converters, D / A converters, and CODECs.
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Abstract
Description
このような従来技術は、A/D変換器、D/A変換器が発生する輻射ノイズを低減させ、ノイズの他の機器に対する影響を低減するという発想に基づいてなされたものである。
また、従来技術はデジタル部にのみジッタを加えるため、アナログ部の突入電流起因の周期ノイズを拡散することはできない。このため、従来技術の拡散効果は限定的なものになる。
前記コンテニアス部(例えば図18に示すコンテニアス部130a)は第2のクロック信号(例えば図18に示すクロック信号φ1)に基づいて動作し、前記第2のクロック信号は、基になるクロック信号にジッタが加えられていない信号であり、つまり基になるクロック信号そのものであり、さらに前記第1のクロック信号(例えば図18に示すクロック信号φ2’)と前記第2のクロック信号とは逆相でありかつノンオーバーラップの関係にあってよい。
前記A/D変換器と前記D/A変換器とは非同期動作するものであってよい。
さらに、ジッタが加えられたクロック信号に基づいてコンテニアス部を動作させることで、アナログ部の突入電流起因の輻射ノイズを拡散できるため、輻射ノイズを効果的に抑制できる。
まず、本発明の実施形態の説明に先立って、本発明のサンプリング回路の考え方について説明する。なお、この説明では、本実施形態のサンプリング回路を適用したD/A変換器を例にする。
以下、デジタル部は一般的なデジタル回路を備え、、量子化され、標本化された信号を伝達する。サンプル・ホールド部は一般的なスイッチトキャパシタ回路(SC回路)を備え、量子化されず、標本化された信号を伝達する。コンテニアス部は一般的な連続信号回路(Continuous回路)を備え、量子化されず、標本化されていない信号を伝達する。
図1に示したサンプリング回路は、信号をサンプル、ホールドするサンプル・ホールド部とアナログ信号を処理するコンテニアス部とを有し、キャパシタ111-1、112、113と、演算増幅器121-1と、を含んでいる。図1において、デジタル信号を扱うデジタル部は図示していない。
図2(a)は参照信号Vrefのサンプリングタイミングを示している。図2(b)はキャパシタ111-1が入力信号Vinによって蓄積された電荷をホールド、放出するタイミングを示し、図2(c)は直流電圧である参照信号Vrefを示し、図2(d)は演算増幅器121-1から出力される、アナログ信号である出力信号Voutを示している。なお、図2(d)において、実線で示した信号がキャパシタ111-1から転送されてきた電荷によって生じる入力信号Vinであり、キャパシタ112を介したフィードバックによって破線で示した出力信号Voutが生成される。
図3中、グラフ(b)はキャパシタ111-1が入力信号Vinによって蓄積された電荷をホールド、放出するタイミングを律するクロックをフーリエ変換により周波数軸に変換したスペクトルを示し、図3中、グラフ(c)は出力信号Voutをフーリエ変換により周波数軸に変換したスペクトルを示している。
図3中、グラフ(a)に示したように、キャパシタ111-1から出力された信号(図中にスペクトルp1で示す)は一定の周波数を有している。スペクトルqは入力信号Vinにおけるノイズシェープされたフロアノイズを示す。スペクトルp1、qがスイッチ101-1、102-1によってサンプリングされ、ホールド、放出されると、畳み込みによってグラフ(c)に示す出力信号Voutが生成される。出力信号Voutにおいて、スペクトルp1、qが、グラフ(c)中に示す破線を軸として対称にミラーされている。
図4(a)~(d)は、図1に示したサンプリング回路において、参照信号Vrefに周期ノイズがある場合のD/A変換器の動作を説明するための図である。
図4(a)は参照信号Vrefのサンプリングタイミングを示している。
図4(b)はキャパシタ111-1が参照信号Vrefによって蓄積された電荷をホールド、放出するタイミングを示している。図4(a)、(b)に示すクロック信号が供給されるスイッチは、クロック信号がHighである区間でオンとなり、クロック信号がLowである区間でオフされるよう駆動される。
図4(c)に示す周期ノイズN1が参照信号Vrefに発生している場合、D/A変換器では、図4(d)に示す出力信号Voutにも周期ノイズN1に対応する周期ノイズN2が発生することになる。
図5は、入力信号Vinと、周期ノイズと、の出力信号Voutへの表れ方を説明するための図である。図5中、グラフ(a)は、図1に示したキャパシタ111-1から出力される信号を説明するための図であり、入力信号Vinをフーリエ変換により周波数軸に変換したスペクトルを示す。
図5中の、グラフ(a)、(b)、(c)のいずれにおいても、縦軸は信号のスペクトルの強度を示し、横軸は周波数を示している。グラフ(a)、(b)、(c)の各グラフ中に矢線で示した縦軸の位置は、周波数の基準(「0」)を示している。
A/D変換器、D/A変換器は、非連続的な信号であるデジタル信号を処理するデジタル部、信号をサンプル、ホールドするサンプル・ホールド部(S/H部)、連続的な信号であるアナログ信号を処理するコンテニアス部(Continuous部)、を備えるサンプリング回路を含んでいる。
図6中、グラフ(a)は、図1に示したキャパシタ111-1から出力される信号を説明するための図であり、入力信号Vinをフーリエ変換により周波数軸に変換したスペクトルを示す。
図6中の、グラフ(a)、(b)、(c)のいずれにおいても、縦軸は信号のスペクトルの強度を示し、横軸は周波数を示している。また、グラフ(a)、(b)、(c)中に矢線で示した縦軸の位置は、周波数の基準(「0」)を示している。
第1態様は、上記した目的を実現するため、D/A変換器のサンプル・ホールド部のクロック信号にジッタを加えるようにした。
図7中の、グラフ(a)は、図1に示したキャパシタ111-1から出力される信号を説明するための図であり、入力信号Vinをフーリエ変換により周波数軸に変換したスペクトルを示す。
グラフ(a)、(b)、(c)のいずれにおいても、縦軸は信号のスペクトルの強度を示し、横軸は周波数を示している。また、グラフ(a)、(b)、(c)中に矢線で示した縦軸の位置は、周波数の基準(「0」)を示している。
図8に示したサンプリング回路は、本実施形態の基礎となる態様(以下、「第2態様」とも示す)のサンプリング回路である。
このサンプリング回路は、コンテニアス部と、サンプル・ホールド部と、デジタル部と、を有している。このような構成のうち、デジタル部は、一般的なデジタル回路を有し、量子化され、標本化された信号を出力する。サンプル・ホールド部は、一般的なスイッチトキャパシタ回路(SC回路)を有し、量子化されず、標本化された信号を出力する。また、コンテニアス部は、一般的な連続信号回路(Continuous回路)を有し、量子化されず、標本化されていない信号を出力する。
図9(a)はアナログ入力信号Ainのサンプリングタイミングを示している。
図9(b)はキャパシタ111-2がアナログ入力信号Ainによって蓄積された電荷をホールド、放出するタイミングを示している。
図9(c)はアナログ入力信号Ainを示し、図9(d)は直流電圧である基準信号Vcomを示し、図9(e)はキャパシタ111-2から転送されてきた電荷によって生じるアナログ信号Vinを示している。
図9(f)は、演算増幅器121-2から出力されるアナログ信号である出力信号VAinを示している。
図10中のグラフ(b)は、演算増幅器121-2の出力信号であるVAinをフーリエ変換により周波数軸に変換したスペクトルを示している。
図10中のグラフ(a)に示したように、キャパシタ111-2から出力された信号(図中にスペクトルP2で示す)は一定の周波数を有している。スペクトルP2がスイッチ101-2、102-2、103によってサンプリングされ、ホールド、放出されると、図10中のグラフ(b)に示す出力信号VAin(図中にスペクトルp2で示す)が生成される。
図11(a)~(f)は、図8に示したサンプリング回路の、基準信号Vcomに周期ノイズがある場合の動作を説明するための図である。
図11(a)はアナログ入力信号Ainのサンプリングタイミングを示している。
図11(b)はキャパシタ111-2がアナログ入力信号Ainによって蓄積された電荷をホールド、放出するタイミングを示している。
図11(f)は、演算増幅器121-2から出力されるアナログ信号である出力信号VAinを示している。
図11(d)に示す周期ノイズN11が基準信号Vcomに発生している場合、サンプリング回路では、周期ノイズN11を、演算増幅器121-2を介して出力信号Vinに重畳することになる。そのため周期ノイズを含んだ出力信号Vinをサンプル、ホールドすると出力信号VAinにも周期ノイズN11に対応する周期ノイズN12が発生する。
図11(d)、(e)、(f)に示した周期ノイズを、図12に示すグラフ(a)、(b)を使って説明する。
図12中(b)に示したグラフは演算増幅器121-2の出力信号であるVAinをフーリエ変換により周波数軸に変換したスペクトルp2を示している。
図12中、グラフ(a)で示したスペクトルを図8に示したスイッチ101-2、102-2、103でサンプリングし、ホールド、放出すると、周期ノイズN12は折り返され、図12(b)に示すように周期ノイズN12’がDC付近に現れる。周期ノイズN12’は、A/D変換器が例えばオーディオ機器に用いられる場合、出力音声に使用される周波数領域、すなわちin-band内に現れる。
A/D変換器は、コンテニアス部(Continuous部)と、サンプル・ホールド部(S/H部)と、デジタル部と、を備えるサンプリング回路を含んでいる。ここでは、図8に示したサンプリング回路をA/D変換器が備えるものとして説明する。
図13中、グラフ(a)及び(b)は、A/D変換器において、デジタル部を動作させるクロック信号にジッタを加えた場合の、周期ノイズについて説明するための図である。
図13に示すグラフ(b)は演算増幅器121-2の出力信号であるVAinをフーリエ変換により周波数軸に変換したスペクトルp2を示している。
図13中、(a)及び(b)に示したグラフのいずれにおいても、縦軸は信号のスペクトルの強度を示し、横軸は周波数を示している。図13中のグラフ(a)及び(b)中に矢線で示した縦軸の位置は、周波数の基準(「0」)を示している。
第2態様は、上記した目的を実現するため、A/D変換器のサンプル・ホールド部のクロック信号にジッタを加えるようにした。
図14中の、グラフ(a)は、図8に示したキャパシタ111-2から出力される信号を説明するための図であり、アナログ信号Vinをフーリエ変換により周波数軸に変換したスペクトルP2を示す。
図14中のグラフ(a)、(b)のいずれにおいても、縦軸は信号のスペクトルの強度を示し、横軸は周波数を示している。図14に示すグラフ(a)、(b)中に矢線で示した縦軸の位置は、周波数の基準(「0」)を示している。
まず、本発明のサンプリング回路を適用した実施形態1のA/D変換器を説明する。実施形態1では、A/D変換器をパイプライン型A/D変換器として構成している。
図15は、実施形態1のパイプライン型A/D変換器を示した図である。
ステージS1~Skは直列に接続され、各々入力される入力信号VAinに基づいてn桁のデジタル出力信号djをメモリ803に送出する。また、各ステージでは、前段から入力信号VAinが入力され、デジタル出力信号djと入力信号VAinとによって生成されたアナログの出力信号VAoutが、次のステージに出力される。図中にステージS1を基準にした入力信号VAin、出力信号VAoutを示す。
演算回路804は、メモリ803に格納されたデジタル出力信号djに基づいて演算し、N桁のデジタル出力信号Doutを出力する。デジタル出力信号Doutを算出するための演算は、次のように行われる。
このような処理を繰り返し、ステージS1のデジタル出力d1の最下位桁とステージS2のデジタル出力d2の最上位桁までを足し合わせる。足し合わされた最終的な結果は、デジタル出力信号Doutとして出力される。
図16の例では、4個のステージS1~S4があって、各ステージS1~S4が、3桁のデジタル出力d1~d4をそれぞれ図15に示したメモリ803に出力するものとする。より具体的には、デジタル出力d1~d4の値を、以下のように定める。
d1=001、d2=100、d3=101、d4=111
図16の例では、隣接するステージによって出力されるデジタル出力の最上位桁と最下位桁とを加算した結果、デジタル出力信号Doutとして、「010011011」の値が得られる。
図17に示したサンプリング回路140(図15のサンプリング回路801に対応)は、アナログ入力信号Ainを入力するコンテニアス部130aと、コンテニアス部130aによって入力されたアナログ入力信号Ainを間欠的にサンプリングし、サンプリングされた信号をホールド、転送するサンプル・ホールド部130bと、を含んでいる。このような実施形態1では、図15に示したメモリ803と演算回路804とが、後述の図18に示すデジタル部130cとして機能する。
サンプル・ホールド部130bは、入力信号Vinをサンプリングし、入力信号Vinによって生じた電荷を保持するキャパシタ132と、キャパシタ132に保持された電荷を後段のステージに転送するスイッチ133と、を含む。スイッチ133は、クロック信号φ2’にしたがってスイッチング動作を行っている。
制御回路139は、コンテニアス部130aに対しては、ジッタを加えていないクロック信号φ1を供給し、デジタル部130cに対しては、ジッタを加えたクロック信号φ2’を供給し、サンプル・ホールド部130bに対しては、ジッタを加えたクロック信号φ2’を供給する。また、デジタル部130cに供給されるクロックはサンプル・ホールド部130bに供給されるクロックとの位相関係が反転であるクロック信号φ1’であっても良い。
図19(a)~(e)は、クロック信号φ1、φ1’、φ2、φ2’、φ1”のタイミングチャートを表した図である。
図19において、(a)はクロック信号φ1のタイミングチャートを表し、(b)はクロック信号φ1’のタイミングチャートを表し、(c)はクロック信号φ1”のタイミングチャートを表し、(d)はクロック信号φ2のタイミングチャートを表し、(e)はクロック信号φ2’のタイミングチャートを表す。
なお、クロック信号の立ち上りにのみジッタが付加されるクロック信号φ1”は、例えば、クロック信号φ1とクロック信号φ1’とをAND回路に入力することによって生成される。
図20に示したように、ジッタ選択部142は、各々が5つのスイッチを含むスイッチユニット1301、1302及び1303を備えている。スイッチユニット1301はコンテニアス部130aに出力されるクロック信号を選択する。スイッチユニット1302はサンプル・ホールド部130bに出力されるクロック信号を選択する。スイッチユニット1303はデジタル部130cに出力されるクロック信号を選択する。
ジッタ選択部142は、クロック信号φ1、φ2、φ1’、φ2’、φ1”、からクロック信号φ1を選択し、コンテニアス部130aに出力する。また、クロック信号φ2’を選択し、サンプル・ホールド部130bに出力し、クロック信号φ2’を選択し、デジタル部130cに出力する。
このため、伝達すべき信号にノイズを加えることなく、in-band内のノイズだけを分散し、そのスペクトルのピークを低減することができる。
実施形態1-2と上記した実施形態1-1との相違は、コンテニアス部で発生する突入電流起因の輻射ノイズを拡散するため、コンテニアス部にもジッタを加えたクロック信号φ1”を入力させる点である。そして、コンテニアス部に入力させるクロック信号の動作開始時刻を確定するためのトリガであるエッジにはジッタが加えられ、動作終了時刻を確定するためのトリガであるエッジにジッタを加えられていないことにより、アナログ部の突入電流起因の輻射ノイズを拡散し輻射ノイズをさらに効果的に抑制することができるものにした点である。
図21に示した、実施形態1-2におけるサンプリング回路140は、上記実施形態1-1におけるサンプリング回路140と同様に、アナログ入力信号Ainを入力するコンテニアス部130aと、コンテニアス部130aによって入力されたアナログ入力信号Ainを間欠的にサンプリングし、サンプリングされた信号をホールド、転送するサンプル・ホールド部130bと、を含んでいる。このような実施形態1-2では、図15に示したメモリ803と、演算回路804とが、後述の図22に示すデジタル部130cとして機能する。
サンプル・ホールド部130bは、入力信号Vinをサンプリングし、入力信号Vinによって生じた電荷を保持するキャパシタ132と、キャパシタ132に保持された電荷を後段のステージに転送するスイッチ133と、を含む。スイッチ133は、クロック信号φ2’にしたがってスイッチング動作を行っている。
制御回路139は、クロック信号生成部143と、ジッタ生成部(図22中にJitter_Gen.と記す)141と、ジッタ選択部(図22中にJitter_Sel.と記す)142と、を含んでいる。クロック信号生成部143は、ジッタを加えないクロック信号φ1、φ2を生成する。ジッタ生成部141は、クロック信号φ1、φ2にジッタを加えたクロック信号φ1’、φ2’と、クロック信号φ1の動作開始時刻を確定するためのトリガである立ち上りエッジにはジッタが加えられ、動作終了時刻を確定するためのトリガである立ち下りエッジにはジッタが加えられていないクロック信号φ1”と、を生成する。ジッタ選択部142は、クロック信号φ1、φ2、φ1’、φ2’、φ1”、を入力し、ジッタ生成部141によって生成されたクロック信号φ2’を選択してサンプル・ホールド部130b及びデジタル部130cに出力し、クロック信号φ1”を選択してコンテニアス部130aに出力するように動作する。
実施形態2は、本発明のサンプリング回路を、D/A変換器に適用したものである。
実施形態2のサンプリング回路の具体例として、実施形態2-1、及び実施形態2-2について説明する。実施形態2-1は、クロック信号として、ジッタを含まないクロック信号φ11、φ12と、ジッタを含むクロック信号φ11’、φ12’とを用いるサンプリング回路である。実施形態2-2は、上記クロック信号φ11、φ12、φ11’、φ12’に加えて、さらにクロック信号φ11の立ち上がりにのみジッタを加えたクロック信号φ11”も用いたサンプリング回路である。
図示したD/A変換器は、サンプリング回路160と、制御回路159-1と、を備えている。
サンプリング回路160は、入力されたデジタル信号Dinに基づく入力信号(参照信号Vref、サンプリング後の参照信号Vrefを入力信号Vinと記す)を間欠的にサンプリングし、サンプリングされた信号をホールド、転送するサンプル・ホールド部150bと、サンプル・ホールド部150bによって転送された信号を、アナログ信号Aoutとして出力するコンテニアス部150aと、を含んでいる。
サンプル・ホールド部150bは、入力信号Vinによって生じる電荷を蓄積するキャパシタ152と、キャパシタ152に蓄積するスイッチ151と、スイッチ153と、を含む。スイッチ151と、スイッチ153と、は、クロック信号φ11’にしたがってスイッチング動作を行っている。
制御回路159-1は、コンテニアス部150aに対しては、ジッタを加えないクロック信号φ12を供給し、デジタル部150cに対しては、ジッタを加えたクロック信号φ11’を供給し、サンプル・ホールド部150bに対しては、ジッタを加えたクロック信号φ11’を供給する。
このような実施形態2-1によれば、実施形態1-1と同様に、D/A変換器の信号伝達関数には変調をかけず、ノイズ伝達関数にだけ変調をかけることができる。このため、伝達すべき信号にノイズを加えることなく、in-band内のノイズだけを分散し、そのスペクトルのピークを低減することができる。
なお、キャパシタ154を介したフィードバック経路はなくしてもよい。
図25(a)は、クロック信号φ11のタイミングチャートを表し、図25(b)はクロック信号φ11’のタイミングチャートを表し、図25(c)はクロック信号φ12のタイミングチャートを表し、図25(d)はクロック信号φ12’のタイミングチャートを表す。
図26に示したように、ジッタ選択部162-1は、各々が4つのスイッチを含むスイッチユニット1501-1、1502-1、1503-1を備えている。スイッチユニット1501-1は、コンテニアス部150aに出力されるクロック信号を選択する。スイッチユニット1502-1はサンプル・ホールド部150bに出力されるクロック信号、スイッチユニット1503-1はデジタル部150cに出力されるクロック信号を選択する。ジッタ選択部162-1によれば、クロック信号φ11、φ11’、φ12、φ12’からクロック信号φ12が選択され、図24に示したコンテニアス部150aに供給される。また、クロック信号φ1、φ1’、φ2、φ2’からクロック信号φ11’が選択され、図24に示したサンプル・ホールド部150bに供給され、クロック信号φ11、φ11’、φ12、φ12’からクロック信号φ11’が選択され、図24に示したデジタル部150cに供給される。
さらに、実施形態2-1においても、クロック信号生成部163はD/A変換器の外部に設けられるものであってもよい。また、図23、24に示したD/A変換器のサンプリング回路を他の機器として構成する場合、制御回路159-1を機器の外部に設けるものであってもよい。
本発明のサンプリング回路、D/A変換器の発明者等は、その後、実施形態2-1のサンプリング回路のコンテニアス部における信号のサンプル、ホールド動作においてもD/A変換器自身、または、他の電子機器から混入する周期ノイズが折り返されることを発見した。コンテニアス部150aは、動作開始時刻を確定するためのトリガである立ち上がりエッジでは、サンプル・ホールド部150bによって転送された信号をアナログ信号Aoutとして出力することを開始し、動作終了時刻を確定するためのトリガである立ち下りエッジでは、動作終了時刻のアナログ信号Aoutを次の動作開始までサンプル、ホールドする。前記したサンプリング回路同様、動作終了時刻におけるサンプル、ホールド時に周期ノイズが重畳すると、アナログ信号Aoutにノイズが折り返す。
本実施形態2-2と上記した実施形態2-1との相違は、コンテニアス部で混入するノイズを拡散するため、コンテニアス部にもジッタを加えたクロック信号を入力させる点である。そして、コンテニアス部に入力させるクロック信号の動作開始時刻を確定するためのトリガであるエッジにはジッタが加えられず動作終了時刻を確定するためのトリガであるエッジにジッタを加える。これによりアナログ出力信号Aoutの信号成分に変調をかけることなく、周期ノイズのみにジッタによる変調をかけることで、混入する周期ノイズと信号成分とを効率的に分離することができる。
なお、本実施形態2-2で示した図面に記された構成のうち、上記した実施形態2-1の説明に用いた図面に記された構成と同様の構成については同様の符号を付し、その説明を一部略すものとする。
制御回路159-2は、ジッタを加えないクロック信号φ11、φ12を生成するクロック信号生成部163と、クロック信号φ11、φ12にジッタを加えたクロック信号φ11’、φ12’、動作開始時刻を確定するためのトリガである立ち上がりエッジにはジッタが加えられず動作終了時刻を確定するためのトリガである立下りエッジにはジッタが加えられたクロック信号φ12”を生成するジッタ生成部(図28中にJitter_Gen.と記す)161と、クロック信号φ11、φ12、φ11’、φ12’、φ12”を入力し、ジッタ生成部161によって生成されたクロック信号φ11’を選択してサンプル・ホールド部150b及びデジタル部150cに出力し、クロック信号φ12”を選択してコンテニアス部150aに出力するように動作するジッタ選択部(図28中にJitter_Sel.と記す)162-2と、を含んでいる。一例として、クロック信号φ12とクロック信号φ12’とをOR回路に入力することにより、信号の立ち下りにのみジッタが表れるクロック信号φ12”が生成される。
一方、D/A変換器自身、または、他の電子機器から混入する周期ノイズはAC成分であるため、動作クロック信号に加えられたジッタによりノイズ成分に変調がかかり、ノイズ拡散効果が得られる。
図29(a)はクロック信号φ11のタイミングチャートを表し、図29(b)はクロック信号φ11’のタイミングチャートを表し、図29(c)はクロック信号φ12のタイミングチャートを表し、図29(d)はクロック信号φ12’のタイミングチャートを表し、図29(e)はクロック信号φ12”のタイミングチャートを表す。
図29(a)~(e)より明らかなように、クロック信号φ11’、φ12’は、いずれもクロック信号の立ち上り及び立ち下りにジッタが付加されている。しかし、クロック信号φ12”には、クロック信号の立ち下りにのみジッタが付加されている。
図30に示したように、ジッタ選択部162-2は、各々が5つのスイッチを含むスイッチユニット1501-2、1502-2、1503-2と、を備えている。スイッチユニット1501-2はコンテニアス部150aに出力されるクロック信号を選択する。スイッチユニット1502-2はサンプル・ホールド部150bに出力されるクロック信号を選択する。スイッチユニット1503-2はデジタル部150cに出力されるクロック信号を選択する。
ジッタ選択部162-2によれば、クロック信号φ11’が選択され、図28に示したサンプル・ホールド部150b、デジタル部150cに供給される。そして、クロック信号φ12”が図28に示したコンテニアス部150aに供給される。
さらに、クロック信号生成部163は、D/A変換器の外部に設けられるものであってもよい。また、図27、図28に示したD/A変換器のサンプリング回路を他の機器として構成する場合、制御回路159-2をD/A変換器の外部に設けるようにしてもよい。
実施形態3は、実施形態1で説明したA/D変換器と、実施形態2で説明したD/A変換器とを混載した、コーデック(CODEC)である。
まず、実施形態3-1にかかるCODECを説明する。
図31は、実施形態3-1のCODECを説明するための図である。
図31において、実施形態1-1、実施形態2-1で先に説明した構成と同様の符号には同様の符号を付し、その説明を略すものとする。
しかし、実施形態3-1のCODECによれば、A/D変換器、D/A変換器のいずれもが、サンプル・ホールド部を、ジッタを加えたクロック信号で動作させることにより、アナログ部の突入電流起因の周期ノイズを効果的に拡散することができ、支配的な輻射ノイズの発生そのものを抑制することができる。
また、実施形態3-1では、CODEC周辺の機器から発生するノイズを低減することを目的として一般的に具備されるデカップリングコンデンサへのノイズ抑制要求を低減することが可能となる。また、実施形態3-1によれば、デカップリングコンデンサへのノイズ抑制要求を低減できることから、デカップリングコンデンサそのものを不要とすることも考えられる。
なお、図32(b)は、サンプル・ホールド部とともに、デジタル部にもジッタを加えたクロック信号を入力した例である。
図32(a)は従来技術のCODECの特性を説明するための図である。
また、図32(b)は、実施形態3-1のCODECの特性を説明するための図である。
なお、図31では、実施形態1-1で説明したA/D変換器と実施形態2-1で説明したD/A変換器とを混載したコーデックを構成した場合について説明したが、コンテニアス部へもジッタを付加したクロック信号を供給するようにした、実施形態1-2で説明したA/D変換器及び実施形態2-2で説明したD/A変換器とを混載したコーデックを構成することも可能である。
図33は、実施形態3-2のCODECを説明するための図である。
この実施形態3-2は、実施形態1-1で説明したA/D変換器と、実施形態2-1で説明したD/A変換器とを混載した、コーデック(CODEC)において、ジッタ選択部142、162-1がない構成となっている。この形態であっても、実施形態3-1のCODECと同様の効果が得られる。
また、本発明の範囲は、以上図示され、記載された例示的な実施形態に限定されるものではなく、本発明が目的とするものと均等な効果をもたらすすべての実施形態をも含む。さらに、本発明の範囲は、各請求項により画される発明の特徴の組み合わせに限定されるものではなく、すべての開示されたそれぞれの特徴のうち特定の特徴のあらゆる所望する組み合わせによって画されうる。
111-1、111-2、112、113、132、152、154、161 キャパシタ
121-1、121-2、134、155 演算増幅器
130a、150a コンテニアス部
130b、150b サンプル・ホールド部
130c、150c デジタル部
138、158 フィードバック経路
139、159-1、159-2 制御回路
140、160 サンプリング回路
141、161 ジッタ生成部
142、162-1、162-2 ジッタ選択部
143、163 クロック信号生成部
Claims (21)
- 連続的な信号を伝達するコンテニアス部と、
第1のクロック信号に基づいて動作し、前記コンテニアス部に接続され、標本化されかつ量子化されていない信号を伝達するサンプル・ホールド部と、
前記サンプル・ホールド部に接続され、標本化及び量子化がされた信号を伝達するデジタル部と、
を備え、
前記第1のクロック信号は、基になるクロック信号にジッタが加えられた信号であることを特徴とするサンプリング回路。 - 前記コンテニアス部は入力されたアナログ信号をサンプリングし、
前記サンプル・ホールド部は、前記コンテニアス部によってサンプリングされた信号を保持することを特徴とする請求項1に記載のサンプリング回路。 - 前記コンテニアス部は第2のクロック信号に基づいて動作し、
前記第2のクロック信号は、基になるクロック信号にジッタが加えられていない信号であり、
さらに前記第1のクロック信号と前記第2のクロック信号とは逆相でありかつノンオーバーラップの関係にあることを特徴とする請求項2に記載のサンプリング回路。 - 前記コンテニアス部は第2のクロック信号に基づいて動作し、
前記第2のクロック信号は、基になるクロック信号の、動作開始時刻を確定するためのトリガであるエッジにはジッタが加えられ、かつ動作終了時刻を確定するためのトリガであるエッジにはジッタが加えられていない信号であり、
さらに前記第1のクロック信号と前記第2のクロック信号とは逆相でありかつノンオーバーラップの関係にあることを特徴とする請求項2に記載のサンプリング回路。 - 前記サンプル・ホールド部は、前記デジタル部からのデジタル信号に基づく基準信号をサンプリングし、
前記コンテニアス部は、前記サンプル・ホールド部によってサンプリングされた信号をアナログ信号として転送することを特徴とする請求項1に記載のサンプリング回路。 - 前記コンテニアス部は第2のクロック信号に基づいて動作し、
前記第2のクロック信号は、基になるクロック信号にジッタが加えられていない信号であり、
さらに前記第1のクロック信号と前記第2のクロック信号とは逆相でありかつノンオーバーラップの関係にあることを特徴とする請求項5に記載のサンプリング回路。 - 前記コンテニアス部は第2のクロック信号に基づいて動作し、
前記第2のクロック信号は、基になるクロック信号の、動作開始時刻を確定するためのトリガであるエッジにはジッタが加えられず、動作終了時刻を確定するためのトリガであるエッジにはジッタが加えられた信号であり、
さらに前記第1のクロック信号と前記第2のクロック信号とは逆相でありかつノンオーバーラップの関係にあることを特徴とする請求項5に記載のサンプリング回路。 - 入力されたアナログ信号をサンプリングするコンテニアス部と、前記コンテニアス部によってサンプリングされた信号を保持するサンプル・ホールド部と、前記サンプル・ホールド部からの信号をデジタル信号として出力するデジタル部と、を含むサンプリング回路、及び前記サンプル・ホールド部に第1のクロック信号を供給するクロック信号供給部を備え、
前記第1のクロック信号は、基になるクロック信号にジッタが加えられた信号であることを特徴とするA/D変換器。 - 前記クロック信号供給部は、前記コンテニアス部に第2のクロック信号を供給し、
前記第2のクロック信号は、基になるクロック信号にジッタが加えられていない信号であり、
さらに、前記第1のクロック信号と前記第2のクロック信号とは逆相でありかつノンオーバーラップの関係にあることを特徴とする請求項8に記載のA/D変換器。 - 前記サンプル・ホールド部は、前記アナログ信号によって生じる電荷を蓄積する容量素子と、前記容量素子に蓄積された電荷を保持し、前記デジタル部に転送する第1のスイッチング素子と、を含み、
前記第1のスイッチング素子は、前記第1のクロック信号にしたがってオン動作及びオフ動作をすることを特徴とする請求項8または請求項9に記載のA/D変換器。 - 前記クロック信号供給部は、前記コンテニアス部に第2のクロック信号を供給し、
前記第2のクロック信号は、基になるクロック信号の、動作開始時刻を確定するためのトリガであるエッジにはジッタが加えられ、動作終了時刻を確定するためのトリガであるエッジにはジッタが加えられていない信号であることを特徴とする請求項8に記載のA/D変換器。 - 前記サンプル・ホールド部は、前記アナログ信号によって生じる電荷を蓄積する容量素子と、前記容量素子に蓄積された電荷を保持し、前記デジタル部に転送する第1のスイッチング素子と、を含み、
前記第1のスイッチング素子は、前記第1のクロック信号によってオン動作及びオフ動作し、
前記コンテニアス部は、前記容量素子に電荷を蓄積する第2のスイッチング素子を含み、
前記第2のスイッチング素子は、前記第2のクロック信号によってオン動作及びオフ動作をすることを特徴とする請求項11に記載のA/D変換器。 - 前記クロック信号供給部は、前記デジタル部に前記第1のクロック信号を供給することを特徴とする請求項8から請求項12のいずれか1項に記載のA/D変換器。
- デジタル信号を出力するデジタル部と、前記デジタル信号に基づく基準信号をサンプリングするサンプル・ホールド部と、前記サンプル・ホールド部によってサンプリングされた信号をアナログ信号として転送するコンテニアス部と、を含むサンプリング回路、及び前記サンプル・ホールド部に第1のクロック信号を供給するクロック信号供給部を備え、
前記第1のクロック信号は、基になるクロック信号にジッタが加えられた信号であることを特徴とするD/A変換器。 - 前記クロック信号供給部は、前記コンテニアス部に第2のクロック信号を供給し、
前記クロック信号は、基になるクロック信号にジッタが加えられていない信号であり、
さらに前記第1のクロック信号と前記第2のクロック信号とは逆相でありかつノンオーバーラップの関係にあることを特徴とする請求項14に記載のD/A変換器。 - 前記サンプル・ホールド部は、前記基準信号によって生じる電荷を蓄積する容量素子と、前記容量素子に電荷を蓄積する第1のスイッチング素子と、を含み、
前記第1のスイッチング素子は、前記第1のクロック信号にしたがってオン動作及びオフ動作をすることを特徴とする請求項14または請求項15に記載のD/A変換器。 - 前記クロック信号供給部は、前記コンテニアス部に第2のクロック信号を供給し、
前記第2のクロック信号は、基になるクロック信号の、動作開始時刻を確定するためのトリガであるエッジにはジッタが加えられず、動作終了時刻を確定するためのトリガであるエッジにはジッタが加えられた信号であり、
さらに前記第1のクロック信号と前記第2のクロック信号とは逆相でありかつノンオーバーラップの関係にあることを特徴とする請求項14に記載のD/A変換器。 - 前記サンプル・ホールド部は、前記基準信号によって生じる電荷を蓄積する容量素子と、前記容量素子に電荷を蓄積する第1のスイッチング素子と、を含み、
前記第1のスイッチング素子は、前記第1のクロック信号にしたがってオン動作及びオフ動作し、
前記コンテニアス部は、前記容量素子に蓄積された電荷を転送する第2のスイッチング素子を含み、
前記第2のスイッチング素子は、前記第2のクロック信号によってオン動作及びオフ動作をすることを特徴とする請求項17に記載のD/A変換器。 - 前記クロック信号供給部は、前記デジタル部に前記第1のクロック信号を供給することを特徴とする請求項14から請求項18のいずれか1項に記載のD/A変換器。
- 請求項8から請求項13のいずれか1項に記載のA/D変換器と、請求項14から請求項19のいずれか1項に記載のD/A変換器と、を混載したことを特徴とするCODEC。
- 前記A/D変換器と前記D/A変換器とは非同期動作することを特徴とする請求項20に記載のCODEC。
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