JP5700697B2 - Digital / analog converter - Google Patents

Description

  The present invention relates to a digital-to-analog converter, and more particularly to a switched capacitor type digital-to-analog converter that converts a digital input signal into an analog output signal.

In general, in a digital / analog converter used in the audio field, a demand for distortion is severe, and a slight conversion error of an analog output signal causes deterioration of characteristics.
In the digital-analog converter, the capacitive element is charged according to the signal level of the digital input signal, and the operational amplifier outputs an analog output signal according to the charging voltage of the capacitive element. In the digital-analog converter having such a configuration, in order to realize low distortion, the connection between the input terminal of the digital input signal and the capacitive element and the output terminal of the operational amplifier when the capacitive element and the operational amplifier are connected. What is comprised so that it may connect is disclosed by patent document 1, for example.

  FIG. 1 is a circuit configuration diagram of a digital / analog converter disclosed in Patent Document 1. FIGS. 2A to 2D are control waveforms of switches in the digital / analog converter 100 shown in FIG. The vertical axis represents “H” or “L” of the level of the control clock signal CK1, and the horizontal axis represents time. 2A shows the waveform of the control clock signal CK1 input to the switch 110, FIG. 2B shows the waveform of the control clock signal CK2 input to the switch 120, and FIG. FIG. 2D shows the waveform of the control clock signal CK4 input to the switch 140. FIG. In the figure, reference numeral 1 denotes a control clock generator, and 2 denotes an operational amplifier.

  The switches 110 and 120 are turned on while CK1 and CK2 are “H”, and the sampling capacitor 150 is charged with a capacitance corresponding to the signal level of the digital input signal. Next, after the switches 110 and 120 are turned off, the switches 130 and 140 are turned on while the CK3 and CK4 are “H” to connect the sampling capacitor element 150 and the integrating capacitor element 160 in series, and the sampling capacitor The element Cs and the output terminal Vout of the operational amplifier are connected, and the potential of the output terminal Vout changes. In such a digital-analog converter, a configuration having a MOS transistor is generally used as a switch.

That is, the switch units included in the switches 110 and 140, the switches 120 and 130, are both turned on when the control signal is “H” and turned off when the control signal is “L”. A period during which the switches 110 and 120 are turned on is a first period, and a period during which the switches 130 and 140 are turned on is a second period.
The digital-analog converter 100 described above constitutes a direct transmission type digital-analog converter. The digital / analog converter 100 may perform digital / analog conversion after delta-sigma modulation of the digital input signal.

FIG. 3 is a diagram showing MOS transistors constituting each switch unit 14i (i = 1 to N) of the fourth switch shown in FIG. 1, and shows a feedback switch 140 that connects the capacitive element Cs and the output terminal Vout. The MOS transistor which comprises each switch unit is shown.
As shown in FIG. 3, each switch unit of the feedback switch 140 includes a P-type MOS transistor 140P (Tr1) and an N-type MOS transistor 140N (Tr2). The source terminals or drain terminals of the P-type MOS transistor 140P and the N-type MOS transistor 140N are connected to the output terminal of the operational amplifier 2.

The PMOS control waveform is CK-P, and the NMOS control waveform is CK-N. When CK-P becomes “L” level and CK-N becomes “H” level, SW4 is turned on. In general, the “L” level is the ground level, and the “H” level is the power supply voltage level.
The resistance values (on-resistances) when the switches 130 and 140 are in the on state are Rsw3 and Rsw4, the total capacitance of the sampling capacitor 150 is Cs, and the capacitance of the integration capacitor 160 is Ci. The output terminal Vout exhibits a transient characteristic depending on a time constant (Rsw3 + Rsw4) * Ci * Cs / (Ci + Cs) due to serial connection of Ci, Cs and Rsw3 and Rsw4. However, the on-resistance Rsw3 of the MOS transistor of the switch 130 does not change with respect to the potential of the output terminal Vout, but the on-resistance Rsw4 of the MOS transistor of the switch 140 is the potential of the output terminal Vout that is the source (or drain) terminal of the MOS. It is known to change depending on

JP-A-11-55121 (Patent No. 3852721)

However, as described in Patent Document 1 described above, the transient characteristics change due to fluctuations in the on-resistance value of the MOS transistor that constitutes the switch 140 that connects the capacitive element 150 and the output terminal Vout, thereby causing distortion. There is a problem that the characteristics deteriorate.
FIG. 4 is a graph showing changes in the on-resistance value Rsw4 of the MOS transistor constituting the switch 140 that connects the sampling capacitor 150 and the output terminal Vout. The graph shown in the lower part of FIG. 4 is a diagram showing how the voltage at the output terminal Vout fluctuates with a constant amplitude. The graph shown in the upper part of FIG. 4 is output like the graph shown in the lower part. It is a figure which shows the change of ON resistance value Rsw4 when the voltage of the terminal Vout changes. As shown in FIG. 4, when the voltage of Vout varies, the on-resistance value Rsw4 greatly changes accordingly.

  FIG. 5 is an enlarged graph showing the transient characteristics of the output terminal Vout when the on-resistance value Rsw4 of the MOS transistor shown in FIG. 4 is the maximum value “a” and the minimum value “b”. As shown in FIG. 4, “a” and “b” having different on-resistance values have different transient characteristics. In this way, the transient characteristic changes due to the change of the on-resistance value of the switch, and thereby the distortion characteristic deteriorates.

  That is, FIG. 5 is a diagram showing the relationship between the analog output signal Vout and time. The vertical axis represents the analog output signal Vout, and the horizontal axis represents time. A curve La in FIG. 5 shows the relationship between the analog output signal Vout and time when the on-resistance value Rsw4 of the switch 140 is indicated by the point a shown in FIG. A curve Lb shows the relationship between the analog output signal VAout and time when the on-resistance value Rsw4 of the switch 140 is indicated by the point b shown in FIG.

As is apparent from the curves La and Lb shown in FIG. 5, the transient characteristics differ when the on-resistance values of the switches used in the digital-analog converter are different. The degree of the difference between the transient characteristics is represented by a length d generated between the curve La and the curve Lb. Further, the difference in the transient characteristic of the analog output signal Vout appears as deterioration of the distortion characteristic of the digital / analog converter.
The present invention has been made in view of such problems, and an object of the present invention is to provide a digital circuit that can further suppress the occurrence of distortion of an analog output signal due to the on-resistance value of a switch with a simple circuit configuration. • To provide an analog converter.

The present invention has been made to achieve such an object, and the invention according to claim 1 is a digital / analog capable of suppressing the occurrence of distortion of the analog output signal due to the on-resistance value of the switch. A plurality of input terminals to which a plurality of bit signals constituting a digital signal are respectively input; a plurality of sampling capacitors (250) provided corresponding to the plurality of input terminals; A first switch unit (210) that switches connection and disconnection between one terminal of the sampling capacitor element (250) and the plurality of input terminals corresponding to the other terminal, and the other terminal of the plurality of sampling capacitor elements (250) A second switch (220) that switches connection and disconnection with the first reference voltage source (Vr1), and a second reference voltage of the second reference voltage source is applied to the non-inverting input terminal. The other terminal of the plurality of sampling capacitors (250) and the inverting input terminal of the operational amplifier according to disconnection and connection in switching the operational amplifier (12) and the first switch unit (210) A third switch (230) that switches connection and disconnection between the other terminal of the plurality of sampling capacitors (250) and one terminal of the integration capacitor element (260); Connection and disconnection of the one terminal of the sampling capacitor element (250), connection and disconnection of the one terminal of the plurality of sampling capacitor elements (250) and the output terminal of the operational amplifier, and the plurality A fourth switching circuit that switches connection and disconnection between the sampling capacitor (250) and the other capacitor capacitor (260). A clock for controlling the switch unit (240), the first switch unit (210), the second switch (220), the third switch (230), and the fourth switch unit (240) is generated. A control clock generator (11), and at least one of the plurality of PMOS transistors and the plurality of NMOS transistors constituting the fourth switch unit has different on-resistances having different threshold voltages Vth prepared in advance in a semiconductor process MOS transistor der each having is, the plurality of PMOS transistors configured in different PMOS transistor threshold voltage Vth, the plurality of NMOS transistors, characterized in that an NMOS transistor having a single threshold voltage Vth .

The invention according to claim 2 is a digital-to-analog converter capable of suppressing the occurrence of distortion of the analog output signal due to the on-resistance value of the switch, wherein a plurality of bit signals constituting the digital signal are provided. Connection between a plurality of input terminals respectively input, a plurality of sampling capacitors provided corresponding to the plurality of input terminals, and the plurality of input terminals corresponding to one terminal of the plurality of sampling capacitors A switch unit that switches between disconnection and disconnection, a second switch that switches connection and disconnection between the other terminal of the plurality of sampling capacitors and the first reference voltage source, and a second reference voltage source connected to the non-inverting input terminal. The plurality of sampling capacitor elements according to disconnection and connection in switching of the operational amplifier to which the reference voltage is applied and the first switch unit. A third switch for switching connection and disconnection between the other terminal of the operational amplifier and the inverting input terminal of the operational amplifier, and connection and disconnection between the other terminal of the plurality of sampling capacitors and one terminal of the integrating capacitor And connecting and disconnecting the one terminal of the plurality of sampling capacitors, connecting and disconnecting the one terminal of the plurality of sampling capacitors and the output terminal of the operational amplifier, and the plurality of samplings A fourth switch unit that switches connection and disconnection between the capacitive element and the other terminal of the integrating capacitive element; and controls the first switch unit, the second switch, the third switch, and the fourth switch unit. And a control clock generator for generating a clock for the second switch unit. At least one of the PMOS transistor and the plurality of NMOS transistors is a MOS transistor having threshold voltages Vth prepared in advance in a semiconductor process and having different on-resistances, and the plurality of PMOS transistors have a single threshold voltage Vth. The plurality of NMOS transistors are formed of NMOS transistors having different threshold voltages Vth .

According to a third aspect of the present invention, there is provided a digital-to-analog converter capable of suppressing the occurrence of distortion of the analog output signal due to the on-resistance value of the switch, wherein a plurality of bit signals constituting the digital signal are converted. And a plurality of input terminals (Dia, Div (i = 1 to N)) to which the corresponding signals are input, and a plurality of sampling capacitor elements (550a, 550b) provided corresponding to the plurality of input terminals, A plurality of first switch units (510a, 510b) for switching connection and disconnection between a plurality of input terminals corresponding to one terminal of the plurality of sampling capacitor elements (550a, 550b), and the plurality of samplings A plurality of second switches for switching connection and disconnection between the other terminal of the capacitive element portion (550a, 550b) and the reference voltage source (Vr1a, Vr1b). A switch (520a, 520b), an operational amplifier (42) in which the reference voltage source (Vr1a, Vr1b) is applied to a non-inverting input terminal (+) or an inverting input terminal (−), and the first switch (510a). , 510b) according to disconnection and connection in switching, connection and disconnection between the other terminal of the plurality of sampling capacitor elements (550a, 550b) and the inverting input terminal (−) of the operational amplifier, and the plurality of A plurality of third switches (530a, 530b) for switching connection and disconnection between the other terminal of the sampling capacitor elements (550a, 550b) and one terminal of the integrating capacitor elements (560a, 560b); Mutual connection and disconnection of the one terminals of the sampling capacitor elements (550a, 550b) and the plurality of samples Connection and disconnection of the one terminal of the capacitive element section (550a, 550b) and the output terminal of the operational amplifier, and the plurality of sampling capacitive element sections (550a, 550b) and the plurality of integral capacitive elements (560a, 560b) A plurality of fourth switch units (540a, 540b) for switching connection and disconnection with the other terminal, the first switch (510a, 510b), the second switch (520a, 520b), and the third switch Each of the plurality of fourth switch units (540a), and a control clock generator (41) for generating a clock for controlling the switches (530a, 530b) and the fourth switch (540a, 540b). 540b) of the plurality of PMOS transistors and the plurality of NMOS transistors Kutomo one hand, Ri MOS transistor der each having a pre-prepared by the threshold voltage Vth is different on-resistance together are a semiconductor process, a plurality of PMOS transistors configured in different PMOS transistor threshold voltage Vth, the plurality of The NMOS transistor is formed of an NMOS transistor having a single threshold voltage Vth .

Also, an invention according to claim 4, a digital-to-analog converter capable of suppressing the generation of distortion of the analog output signal by the on resistance of the switch, a plurality of bit signals constituting the digital signal A plurality of input terminals to which signals corresponding to each of them are input, a plurality of sampling capacitor elements provided corresponding to the plurality of input terminals, and the terminals corresponding to one terminal of the plurality of sampling capacitors A plurality of first switch units for switching connection and disconnection with a plurality of input terminals; a plurality of second switches for switching connection and disconnection between the other terminal of the plurality of sampling capacitor elements and a reference voltage source; In response to disconnection and connection in switching of the differential operational amplifier and the first switch unit, the other of the plurality of sampling capacitor elements A plurality of third switches for switching connection and disconnection between a child and an input terminal of the differential operational amplifier and connection and disconnection between the other terminal of the plurality of sampling capacitor elements and one terminal of the integrating capacitor element; The connection and disconnection of the one terminal of the plurality of sampling capacitor elements, the connection and disconnection of the one terminal of the plurality of sampling capacitor elements and the output terminal of the differential operational amplifier, and the plurality of the plurality of sampling capacitor elements A plurality of fourth switch units for switching connection and disconnection between the sampling capacitor element section and the other terminal of the plurality of integral capacitor elements; the plurality of first switch units; the second switch; and the third switch. A control clock generator for generating a clock for controlling the switch and the plurality of fourth switch units; At least one of the plurality of PMOS transistors and a plurality of NMOS transistors constituting each of the plurality of fourth switch unit, a MOS transistor having a threshold voltage Vth which is previously prepared by a semiconductor process each having different on-resistances from each other, wherein The plurality of PMOS transistors are composed of PMOS transistors having a single threshold voltage Vth, and the plurality of NMOS transistors are composed of a plurality of NMOS transistors having different threshold voltages Vth.

  According to the present invention, it is possible to obtain an effect of suppressing distortion and noise of an analog output signal due to a change in on-resistance value of a switch with a simple configuration. Further, distortion of the analog output signal can be prevented without affecting the response speed allowed in the digital / analog converter.

2 is a circuit configuration diagram of a digital / analog converter disclosed in Patent Document 1. FIG. (A) thru | or (d) is a figure which shows the control waveform of the switch in the digital-analog converter shown in FIG. It is a figure which shows the MOS transistor which comprises the 4th switch unit shown in FIG. (A), (b) is a figure which shows the change of ON resistance value Rsw4 of the MOS transistor which comprises switch SW4 which connects capacitive element Cs and the output terminal Vout in a graph. FIG. 5 is an enlarged graph showing the transient characteristics of the output terminal Vout when the on-resistance value Rsw4 of the MOS transistor shown in FIG. 4 is a maximum value “a” and a minimum value “b”. It is a circuit block diagram for demonstrating Example 1 of the digital-analog converter based on this invention. FIG. 7 is a circuit diagram of PMOS and NMOS transistors constituting a fourth switch unit in the digital-analog converter shown in FIG. 6. (A), (b) is the figure which showed the change of the ON resistance of the 4th switch used for the digital-analog converter shown by FIG. 6 in the graph. FIG. 9 is an enlarged graph showing transient characteristics of the output terminal Vout when the on-resistance value Rsw4 of the MOS transistor shown in FIG. 8 is a maximum value “a” and a minimum value “b”. It is a circuit block diagram for demonstrating Example 2 of the digital-analog converter based on this invention. FIG. 11 is a circuit diagram of PMOS and NMOS transistors constituting a fourth switch unit in the digital-analog converter shown in FIG. 10. FIG. 12 is a circuit diagram showing a schematic configuration of a circuit for generating a control clock for PMOS and NMOS transistors constituting the fourth switch unit shown in FIG. (A), (b) is a schematic circuit diagram which shows an example of the level adjustment circuit 1 in the control clock generation circuit shown in FIG. (A), (b) is a schematic circuit diagram which shows an example of the level adjustment circuit 2 in the control clock generation circuit shown in FIG. (A), (b) is the figure which showed the control clock which the control clock generation circuit shown in FIG. 12 outputs in the graph. It is a circuit block diagram for demonstrating Example 3 of the digital-analog converter based on this invention. FIG. 17 is a circuit diagram showing a schematic configuration of a circuit for generating a control clock for PMOS and NMOS transistors constituting the fourth switch unit shown in FIG. (A), (b) is the figure which showed the control clock which the control clock generation circuit shown in FIG. 17 outputs in the graph. It is a circuit block diagram for demonstrating Example 4 of the digital-analog converter based on this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 6 is a circuit configuration diagram for explaining the first embodiment of the digital-analog converter according to the present invention. In the figure, reference numeral 11 denotes a control clock generator, and 12 denotes an operational amplifier. The first switch 210 is composed of a switch unit 21i (i = 1 to N), the fourth switch 240 is composed of a switch unit 24i (i = 1 to N), and the sampling capacitor 250 is The capacitor 25i (i = 1 to N) is used.

The digital / analog converter 200 according to the present invention is a digital / analog converter capable of suppressing the occurrence of distortion of an analog output signal due to the on-resistance value of a switch.
A plurality of input terminals VDini (i = 1 to N) are input with signals corresponding to a plurality of bit signals constituting a digital signal, respectively. The plurality of sampling capacitors 25i are provided corresponding to the plurality of input terminals VDini.

The plurality of switch units 21i constituting the first switch 210 switches connection and disconnection between one terminal of the plurality of sampling capacitors 25i and a plurality of input terminals VDini corresponding thereto.
The second switch 220 switches connection and disconnection between the other terminal of the plurality of sampling capacitors 250 and the first reference voltage source Vr1. The operational amplifier 22 is applied with the second reference voltage of the second reference voltage source at the non-inverting input terminal.

In addition, the third switch 230 connects and disconnects the other terminal of the plurality of sampling capacitors 25i and the inverting input terminal of the operational amplifier according to disconnection and connection in switching the first switch 210, and a plurality of The connection and disconnection of the other terminal of the sampling capacitor 25i and one terminal of the integrating capacitor 260 are switched.
The plurality of switch units 24i constituting the fourth switch 240 are connected to and disconnected from one terminal of the plurality of sampling capacitors 25i, and one terminal of the plurality of sampling capacitors 25i and the output of the operational amplifier. The connection and disconnection between the terminals and the connection and disconnection between the plurality of sampling capacitors 25i and the other terminal of the integral capacitor 260 are switched.

In the operational amplifier 12, the second reference voltage Vr2 of the second reference voltage source is applied to the non-inverting input terminal.
The control clock generator 21 generates a clock for controlling the first switch 210, the second switch 220, the third switch 230, and the fourth switch 240.

Further, the plurality of switch units 24i constituting the fourth switch 240 are constituted by complementary MOS transistors. The complementary MOS transistors are configured to have different on-resistances. The complementary MOS transistors are configured to have different threshold values.
In the MOS transistors constituting the plurality of fourth switch units 24i, the PMOS transistors are composed of a plurality of PMOS transistors having different threshold voltages Vth, and the NMOS transistors are composed of a plurality of NMOS transistors having different threshold voltages Vth. .

In addition, the MOS transistors constituting the plurality of fourth switch units 24i are composed of a plurality of PMOS transistors having different threshold voltages Vth, and an NMOS transistor is composed of an NMOS transistor having a single threshold voltage Vth. Also good.
In addition, in the MOS transistors constituting the plurality of fourth switch units 24i, the PMOS transistor is composed of a PMOS transistor having a single threshold voltage Vth, and the NMOS transistor is composed of a plurality of NMOS transistors having different threshold voltages Vth. Also good.

The digital-to-analog converter of the present invention is a digital-to-analog converter that can suppress the occurrence of distortion of the analog output signal due to the on-resistance value of the switch.
With such a configuration, it is possible to realize a digital-analog converter that can suppress distortion of an analog output signal due to a change in the on-resistance value of the switch with a simple configuration.
That is, as shown in FIG. 6, the digital / analog converter 200 of the first embodiment is a switched capacitor type digital / analog converter. An input signal VDini (i = 1 to N) corresponding to digital data is input to the digital / analog converter 200, and an analog output signal Vout is output.

  The digital-analog converter 200 has a one-to-one correspondence with the input terminal Di (i = 1 to N) to which the input signal VDini (i = 1 to N) corresponding to the digital data is input and each of the input terminals Di. A plurality of sampling capacitors 25i (i = 1 to N) are provided. The sampling capacitor 25i is charged to the first reference voltage Vr1 according to the signal level (voltage Vref + or Vref−) of the bit signal input from the corresponding input terminal Di. A plurality of first switch units 21 i (i = 1 to N) for switching between connection and disconnection are also provided between the input terminal Di and the corresponding plurality of sampling capacitors 25 i, and the first reference voltage source Vr 1. And the other terminal of the sampling capacitor Csi is provided with a second switch 220 for switching between connection and disconnection, and each switch is constituted by a MOS transistor.

The sampling capacitors 25i (i = 1 to N) may all have the same capacitance (Cs1 = Cs2 =... CsN). Further, the capacitance may be set to Csi = 2 ⁱ⁻¹ Cs (i−1) so that the capacitance ratio of the sampling capacitive elements 251, 252,... 25N becomes a binary ratio (2 ⁱ⁻¹ times). . The sampling capacitor 25i (i = 1 to N) is connected to the switch 230 and the switch 220. The switch 220 connects and disconnects the plurality of sampling capacitors 25i and the power source, and the power source is a plurality of sampling units. A reference voltage Vr1 is applied to the capacitive element 25i.

The digital / analog converter 200 includes an operational amplifier 12. The switch 230 electrically connects and disconnects the inverting input terminal of the operational amplifier 12 and the plurality of sampling capacitors 25i. The switch 230 connected to the inverting input terminal is also referred to as a summing node switch.
A power source is connected to the non-inverting input terminal of the operational amplifier 12, and a reference voltage Vr2 is applied to the non-inverting input terminal by the power source. The output terminal of the operational amplifier 12 is connected to the output terminal of the digital / analog converter 200 and outputs an analog output signal Vout. The reference voltage Vr1 and the reference voltage Vr2 may be the same value.

  An integrating capacitive element 260 is provided between the output terminal and the inverting input terminal of the operational amplifier 12. The output terminal of the operational amplifier 12 is further connected between the plurality of switch units 21i (i = 1 to N) and the sampling capacitor 25i (i = 1 to N). A plurality of switch units 24i (i = 1 to N) are provided between the output terminal and the plurality of switch units 21i and the plurality of sampling capacitors 25i.

The plurality of switch units 24i that return the analog output signal Vout from the output terminal of the operational amplifier 12 to between the plurality of switch units 21i and the plurality of sampling capacitors 25i are also referred to as feedback switches.
In the above configuration, all the switches are configured using MOS transistors. The switch unit 21 i (i = 1 to N) is referred to as a switch 210. The switch unit 24i (i = 1 to N) is referred to as a switch 240. Further, the sampling capacitive element 25 i (i = 1 to N) is a sampling capacitive element 250.

  The switches 210, 220, 230, and 240 are turned on and off by control clock signals CK1 to CK4 generated by the control clock generator 11. At this time, the switch units 21i (i = 1 to N) included in the switch 210 are simultaneously turned on and off. The switch units 24i (i = 1 to N) included in the switch 240 are simultaneously turned on and off, and the on-resistance value Rsw4 when the plurality of switch units 24i are turned on is the plurality of switch units 24i (i = 1 to N). These on-resistance values are synthesized. The on-resistance value of the switch 230 is Rsw3.

In the digital-analog converter 200 shown in FIG. 6, a plurality of input terminals Di (i = 1 to N), a plurality of sampling capacitors 25i (i = 1 to N), and the first switch unit 21i ( i = 1 to N) and the title switch units 24i (i = 1 to N) are provided with the same number (N).
FIG. 7 is a circuit diagram of PMOS and NMOS transistors constituting the fourth switch unit in the digital-analog converter shown in FIG. FIG. 7 shows control clock generation for generating gate control clocks “CK_P” and “CK_N” of the MOS transistor.

  Next, the operation will be specifically described. By connecting the first switch 210 and the second switch 220, the sampling capacitor 250 is charged to the first quasi-voltage source Vr1 according to the signal level of the bit signal input from the input terminal Di (first voltage source Vr1). period). Next, when the first switch 210 and the second switch 220 are disconnected and the third switch 230 and the fourth switch 240 are connected, the analog output signal Vout is based on the charging voltage of the sampling capacitor 250. Changes (second period). The first period and the second period are alternately performed periodically.

  In the second period, the third switch 230, the fourth switch 240, the sampling capacitor 250, and the integrating capacitor 260 are connected in series to form a closed loop. The on-resistance of the MOS transistor constituting the third switch 230 is Rsw3, the combined on-resistance of all the MOS transistors constituting the fourth switch 240 is Rsw4, the total capacitance of the sampling capacitor 250 is Cs, and the capacitance of the integration capacitor 260 is Assuming that Ci, the time constant of the closed loop is (Rsw3 + Rsw4) * Ci * Cs / (Ci + Cs), and the analog output signal Vout exhibits a transient characteristic depending on the time constant of the closed loop.

  Here, the on-resistance Rsw3 of the MOS transistor constituting the third switch 230 will be described in more detail. In the second period of this embodiment, since the potentials of the source terminal and the drain terminal of the MOS transistor constituting the third switch 230 do not change depending on the signal level, the on-resistance value is a constant value.

  The combined on-resistance Rsw4 of all the MOS transistors constituting one fourth switch 240 will be described in detail. The fourth switch 240 includes N switch units 24i (i = 1 to N), and each switch unit 24i includes a PMOS transistor and an NMOS transistor. These MOS transistors have a characteristic that the on-resistance value decreases as the voltage between the gate terminal as the control terminal and the source terminal or drain terminal as the main terminal exceeds the threshold voltage of the MOS transistor (the voltage dependence of the on-resistance value). ). Therefore, in the second period of the present embodiment, when the fourth switch 240 is connected, the source terminal and the drain terminal of the MOS transistor constituting each switch unit 24i are at the potential of the analog output signal Vout. The resistance value changes depending on the potential of the analog output signal Vout.

The time constant of the closed loop is (Rsw3 + Rsw4) * Ci * Cs / (Ci + Cs). As Rsw4 changes depending on the potential of the analog output signal Vout, the time constant of the closed loop also changes, and the analog output signal Vout The transient characteristics change depending on the potential of Vout, leading to the generation of distortion.
Here, in this embodiment, each unit 24i of the fourth switch is composed of a plurality of MOS transistors having different threshold voltages. Each unit 24i of the fourth switch is composed of a PMOS transistor having M threshold voltages Vth_P_j (j = 1 to M) and an NMOS transistor having L threshold voltages Vth_N_k (k = 1 to L). To do. Since the potential of the gate terminal of the PMOS transistor in the second period of the present embodiment is the ground level VSS and the potential of the gate terminal of the NMOS transistor is the power supply voltage level VDD, the MOS transistors constituting each unit 24i of the fourth switch The on-resistance value suddenly increases when the potential of the analog output signal Vout, which is the potential of the source (drain) terminal, approaches VSS-Vth_P_j and VDD-Vth_N_k.

Here, when each unit 24i of the fourth switch is configured by a MOS transistor having a single threshold voltage as in the prior art, that is, when M = L = 1, the “c” and “a” in FIG. At the two points shown, the potential of the analog output signal Vout approaches VSS-Vth_P_1 and VDD-Vth_N_1, and the on-resistance Rsw4 increases rapidly, and as a result, the fluctuation range of the on-resistance Rsw4 increases. However, when each unit SW4xi of the fourth switch is configured by a plurality of MOS transistors having different threshold voltages as in the present invention, that is, when M> 1 and L> 1, the on-resistance Rsw4 increases rapidly. Since there are three or more of −Vth_P_j and VDD−Vth_N_k, the characteristics of the on-resistance Rsw4 are averaged, and the fluctuation range can be suppressed small.
The number of types of PMOS transistors (M) having different threshold voltages and the number of types (L) of NMOS transistors having different threshold voltages constituting each unit 24i of the fourth switch may be M> 1 and L> 1. Alternatively, M = 1 and L> 1 may be set, or M> 1 and L = 1 may be set.

FIGS. 8A and 8B are graphs showing changes in the ON resistance of the fourth switch used in the digital-analog converter shown in FIG.
As an example, a case where M = 2 and L = 2 will be described. (1) in FIG. 8 is a graph showing the on-resistance when each unit 24i of the fourth switch is configured by a PMOS transistor having a threshold voltage Vth_P_1 and an NMOS transistor having a threshold voltage Vth_N_1. 2) is a graph showing the on-resistance when each unit 24i of the fourth switch is configured by a PMOS transistor having a threshold voltage Vth_P_2 and an NMOS transistor having a threshold voltage Vth_N_2. When each unit 24i of the fourth switch is configured by PMOS transistors having threshold voltages Vth_P_1 and Vth_P_2 and NMOS transistors having threshold voltages Vth_N_1 and Vth_N_2 as in the present embodiment, the on-resistance is (1) in FIG. The characteristics shown in (3) in FIG. 8 are obtained by averaging (2) in FIG. Here, (1) in FIG. 8 and (2) in FIG. 8 are different in that the on-resistance rapidly increases. Therefore, the graph of (3) in FIG. 8 obtained by averaging these two graphs is different. In the graph, there are four points where the on-resistance rapidly increases, and the maximum value is lower, the minimum value is higher than (1) in FIG. 8 and (2) in FIG. 8, and the fluctuation range is suppressed.

In this way, by configuring each unit 24i of the fourth switch with a plurality of PMOS transistors and NMOS transistors having different threshold voltages, the characteristics of the on-resistance Rsw4 can be averaged and the fluctuation range can be suppressed small.
FIG. 9 is an enlarged graph showing the transient characteristics of the output terminal Vout when the on-resistance value Rsw4 of the MOS transistor shown in FIG. 8 is the maximum value “a” and the minimum value “b”. Thereby, as shown in FIG. 9, the change depending on the on-resistance Rsw4 of the analog signal output Vout can be suppressed, and the occurrence of distortion can be suppressed.

  That is, as is apparent from the curves La and Lb shown in FIG. 9, the length d1 generated between the curves La and Lb is the curves La and Lb of the digital-analog converter 100 shown in FIG. Shorter than the length d generated between the two. Therefore, the present embodiment can suppress the change in the transient characteristic of the analog output signal due to the change in the on-resistance value Rsw4 and suppress the occurrence of distortion.

As a method of providing a plurality of MOS transistors having different threshold voltages, MOS transistors having different threshold voltages prepared in the process may be used, or the threshold voltage is controlled by controlling the base potential of the MOS transistor. Also good.
In this embodiment, the integrating capacitive element 260 may not be provided between the output terminal and the inverting input terminal of the operational amplifier 12. In that case, the summing node switch 230 may be replaced with a resistor.

Thus, the present embodiment can suppress the occurrence of distortion with a simple configuration. Further, it is possible to prevent the distortion of the analog output signal from occurring without adversely affecting the response speed allowed in the digital / analog converter.
Further, according to the first embodiment, when the first switch 210 and the second switch 220 are connected, the plurality of sampling capacitors are charged according to the signal levels of the plurality of bit signals constituting the digital input signal, respectively. The After that, when the first switch 210 and the second switch 220 are disconnected and the third switch 230 and the fourth switch 240 are connected, the sampling capacitor 250, the integrating capacitor 260, and the operational amplifier 12 are connected. The operational amplifier 12 outputs a voltage corresponding to the charging voltage of all the sampling capacitance elements 250 as an analog output signal.

  At this time, if the on-resistance of the third switch 230 is Rsw3 and the combined on-resistance of all the units 24i of the fourth switch is Rsw4, the analog output signal is the integration capacitor Ci, the total capacitance Cs and Rsw3 of the sampling capacitor 25i, The transient characteristic depending on the time constant (Rsw3 + Rsw4) * Ci * Cs / (Ci + Cs) by the serial connection of Rsw4 is shown. Here, in this embodiment, since the PMOS transistor and the NMOS transistor configuring the fourth switch unit 24i are configured by a plurality of MOS transistors having different threshold voltages Vth, the combined on of all the units 24i of the fourth switch is performed. The resistor Rsw4 can be adjusted so that the fluctuation range changing with respect to the level of the analog output signal Vout is small, and the occurrence of distortion can be suppressed.

  Regarding the MOS transistors constituting the fourth switch unit 24i, the PMOS transistors are composed of a plurality of PMOS transistors having different threshold voltages Vth, and the NMOS transistors are composed of a plurality of NMOS transistors having different threshold voltages Vth. It is good. Alternatively, the PMOS transistor may be configured by a plurality of PMOS transistors having different threshold voltages Vth, and the NMOS transistor may be configured by an NMOS transistor having a single threshold voltage Vth. Alternatively, the PMOS transistor may be configured by a PMOS transistor having a single threshold voltage Vth, and the NMOS transistor may be configured by a plurality of NMOS transistors having different threshold voltages Vth.

  As a result, distortion of the analog output signal can be prevented without affecting the response speed allowed in the digital-analog converter with a simple configuration.

FIG. 10 is a circuit configuration diagram for explaining Example 2 of the digital-analog converter according to the present invention. In the figure, reference numeral 21 denotes a control clock generator, and 22 denotes an operational amplifier. In addition, the same code | symbol is attached | subjected to the component which has the same function as the component shown in FIG.
As shown in FIG. 10, the digital / analog converter 300 in the second embodiment is different from the first embodiment in that the fourth switch is 240 to 340, each unit is 24i to 34i, and the switch A control clock generator 21 for generating a clock for controlling the second switch 340 is provided, and a plurality of clocks for controlling the fourth switch 340 are provided.

FIG. 11 is a circuit diagram of PMOS and NMOS transistors constituting the fourth switch unit in the digital-analog converter shown in FIG.
Specifically, each unit 34i of the fourth switch 340 is composed of M PMOS transistors and L NMOS transistors, and the gate terminal of each PMOS transistor is connected to M different clocks CK-P_j (j = 1 to 1). M) and the gate terminal of each NMOS transistor are controlled by L different clocks CK-N_k (k = 1 to L). In the second period of the second embodiment in which the fourth switch SW4y is turned on, the clocks CK-P_j (j = 1 to M) have different “L” levels VG_P_j (j = 1 to M) and clocks CK-N_k. (K = 1 to L) are different “H” levels VG_N_k (k = 1 to L).

  The number of PMOS transistors (M) and the number of NMOS transistors (L) may be M> 1 and L> 1, M = 1 and L> 1, or M> 1 and L = It may be 1. The M PMOS transistors may be composed of PMOSs having different threshold voltages, or may be composed of PMOS transistors having the same threshold voltage. Further, the L NMOS transistors may be configured with NMOS having different threshold voltages, or may be configured with NMOS transistors having the same threshold voltage.

In this embodiment, the integrating capacitive element 360 may not be provided between the output terminal and the inverting input terminal of the operational amplifier 22. In that case, the summing node switch 330 may be replaced with a resistor.
FIG. 12 is a circuit diagram showing a schematic configuration of a circuit for generating control clocks for the PMOS and NMOS transistors constituting the fourth switch unit shown in FIG. In the figure, reference numeral 23a denotes a first level adjustment circuit, and 23b denotes a first level adjustment circuit.

  An example of a circuit for controlling the gate terminals of the PMOS transistors and the NMOS transistors constituting each unit 34i of the fourth switch 340 at different levels in the second period of the second embodiment will be described. A first level adjustment circuit (LVLSFT1_j (j = 1 to M) for outputting different “L” levels VG_P_j (j = 1 to M) to the generation units of the clock CK-P_j (j = 1 to M), respectively. )) 23a, and a second level adjustment circuit (LVLSFT2_k) for outputting different “H” level VG_N_k (k = 1 to L) to the generation unit of the clock CK-N_k (k = 1 to L), respectively. (K = 1 to L)) 23b.

  FIGS. 13A and 13B are schematic circuit diagrams illustrating an example of the first level adjustment circuit in the control clock generation circuit illustrated in FIG. An example of each LVLSFT1_j of the first level adjustment circuit 23a is shown. CK4 'shown in FIG. 12 is a clock that becomes "H" level in the second period of the second embodiment, and a clock CK4N' obtained by inverting CK4 'is input to the level adjustment circuit LVLFT1_j shown in FIG. The level adjustment circuit LVLSFT1_j includes a capacitor CP_j connected to the input CK4N ′, a switch that switches connection and disconnection between the other terminal CKP′_j of the capacitor CP_j and the third reference voltage Vr3_j, and the other of the capacitor CP_j. A switch that switches connection and disconnection between the terminal CKP′_j and the output terminal CK-P_j, and a switch that switches connection and disconnection between the output terminal CK-P_j and the power supply voltage VDD are provided. The level of the third reference voltage Vr3_j is an arbitrary voltage that differs for each LVLFT1_j.

  FIG. 13A shows a state in which CK4 'is "L" other than the second period in the second embodiment. At this time, the input CK4N ′ is at the “H” level, that is, the level of the power supply voltage VDD. During this time, the other terminal CKP′_j of the capacitor CP_j and the third reference voltage Vr3_j are connected, and a potential difference of VDD−Vr3_j is generated between both ends of the capacitor CP_j. The output terminal CK-P_j is disconnected from the other terminal CKP'_j of the capacitor CP_j and connected to the power supply voltage VDD, and outputs the level of VDD.

  Next, FIG. 13B shows a state in which the CK4 ′ in the second period of the second embodiment is “H”. At this time, the input CK4N ′ is at the “L” level, that is, the level of the ground VSS. At this time, the other terminal CKP'_j of the capacitive element CP_j and the third reference voltage Vr3_j, and the output terminal CK-P_j and the power supply voltage VDD are disconnected, and the other terminal CKP'_j of the capacitive element CP_j is disconnected. The output terminal CK-P_j is connected. Here, since the charge of the capacitor CP_j is ideally held, CKP′_j is at a level of VSS− (VDD−Vr3_j), and the output terminal CK−P_j connected to the CKP′_j is VSS− (VDD -Vr3_j) level is output. Accordingly, since the level of the third reference voltage Vr3_j differs for each LVLFSFT1_j, each clock CK-P_j outputs a different “L” level.

FIGS. 15A and 15B are graphs showing the control clock output from the control clock generation circuit shown in FIG.
FIG. 15A is a diagram showing an output waveform of the first level adjustment circuit. As described above, the first level adjustment circuit 23a outputs the “H” level of the clock CK-P_j for controlling the gate terminal of the PMOS transistor constituting each unit 34i of the fourth switch at the level of the power supply voltage VDD. , “L” level is output at a plurality of different levels. 12 and 13 are examples of the first level adjustment circuit, and the first level adjustment circuit 23a may be configured by other circuits having the same function.

FIGS. 14A and 14B are schematic circuit diagrams showing an example of the second level adjustment circuit in the control clock generation circuit shown in FIG.
Next, FIG. 14 shows an example of each LVLSFT2_k of the second level adjustment circuit 23b. The level adjustment circuit LVLSFT2_k shown in FIG. 14 receives the clock CK4 ′ that becomes “H” level in the second period of the second embodiment. The level adjustment circuit LVLFTFT2_k includes a capacitor CN_k connected to the input CK4 ′, a switch that switches connection and disconnection between the other terminal CKN′_k of the capacitor CN_k and the fourth reference voltage Vr4_k, and the other terminal of the capacitor CP A switch that switches connection and disconnection between CKN′_k and the output terminal CK-N_k, and a switch that switches connection and disconnection between the output terminal CK-N_k and the ground VSS are provided. The level of the fourth reference voltage Vr4_k is an arbitrary voltage that differs for each LVSLS2_k.

  FIG. 14A shows a state in which the CK4 'is “L” except for the second period in the second embodiment. At this time, the input CK4 'is at the level of the ground VSS. During this time, the other terminal CKN′_k of the capacitor CN_k and the fourth reference voltage Vr4_k are connected, and a potential difference of Vr4_k−VSS is generated at both ends of the capacitor CN_k. The output terminal CK-N_k is disconnected from the other terminal CKN′_k of the capacitor CN_k and connected to the ground VSS, and outputs the level of VSS.

  Next, FIG. 14B shows a state in which CK4 'in the second period of the second embodiment is “H”. At this time, the input is at the level of the power supply voltage VDD. At this time, the other terminal CKN′_k and the fourth reference voltage Vr4_k of the capacitor CN_k and the output terminal CK-N_k and the ground VSS are disconnected, and the other terminal CKN′_k and the output terminal CK of the capacitor CN_k are disconnected. -N_k is connected. Here, since the charge of the capacitor CN_k is ideally held, CKN′_k is at the level of VDD + (Vr4_k−VSS), and the output terminal CK−N connected to CKN′_k is at VDD + (Vr4_k−VSS). ) Level is output. Therefore, since the level of the fourth reference voltage Vr4_j is different for each LVLFTFT2_k, each clock CK-N_k outputs a different “H” level.

  FIG. 15B is a diagram showing an output waveform of the second level adjustment circuit. In this way, the second level adjustment circuit 23b outputs the “L” level of the clock CK-N_k that controls the gate terminal of the NMOS transistor constituting each unit 34i of the fourth switch at the level of the ground VSS. It has a function of outputting the “H” level at a plurality of different levels. 12 and 14 are examples of the second level adjustment circuit 23b, and the second level adjustment circuit 23b may be configured by other circuits having the same function.

  In the second embodiment, the case where the fourth switch unit 34i is configured by a PMOS transistor having a single threshold voltage Vth_P and an NMOS transistor having a single threshold voltage Vth_N is taken as an example. The combined on-resistance Rsw4 will be described. The on-resistance Rsw4 has a characteristic that the on-resistance value suddenly increases when the potential of the analog output signal Vout approaches VG_P_j-Vth_P and VG_N_k-Vth_N. In this embodiment, since at least one of VG_P_j and VG_N_k is plural, it has three or more points at which the on-resistance Rsw4 rapidly increases. As described in the first embodiment, the on-resistance Rsw4 These characteristics are averaged, and the fluctuation range is suppressed to be small. Thereby, as shown in FIG. 9, the change depending on the ON resistance Rsw4 of the analog signal output Vout can be suppressed, and the occurrence of distortion can be suppressed.

  Thus, this embodiment can suppress the occurrence of distortion with a simple configuration. Further, it is possible to prevent the distortion of the analog output signal from occurring without adversely affecting the response speed allowed in the digital / analog converter.

FIG. 16 is a circuit configuration diagram for explaining the third embodiment of the digital-analog converter according to the present invention. In the figure, reference numeral 31 denotes a control clock generator, and 32 denotes an operational amplifier. In addition, the same code | symbol is attached | subjected to the component which has the same function as the component shown in FIG.
As shown in FIG. 16, the digital-analog converter 400 in the third embodiment is different from the second embodiment in that a control clock generator 31 for generating a clock for controlling the switch is provided.

  Specifically, each unit 44i of the fourth switch 440 includes M PMOS transistors and L NMOS transistors, and M gates of the PMOS transistors are connected to M different clocks CK-P_j (j = 1 to 1). M), and the gate terminal of each NMOS transistor is controlled by L different clocks CK-N_k (k = 1 to L). The clock CK-P_j (j = 1 to M) has different falling edge timings, and the clock CK-N_k (k = 1 to L) has different rising edge timings.

  The number of PMOS transistors (M) and the number of NMOS transistors (L) may be M> 1 and L> 1, M = 1 and L> 1, or M> 1 and L = 1. Also good. The M PMOS transistors may be composed of PMOSs having different threshold voltages, or may be composed of PMOS transistors having the same threshold voltage. Further, the L NMOS transistors may be configured with NMOS having different threshold voltages, or may be configured with NMOS transistors having the same threshold voltage.

FIG. 17 is a circuit diagram showing a schematic configuration of a circuit for generating control clocks for the PMOS and NMOS transistors constituting the fourth switch unit shown in FIG. In the figure, reference numeral 33a denotes a first delay circuit, and 33b denotes a second delay circuit.
An example of a circuit that generates clocks CK-P_j (j = 1 to M) having different falling edge timings and clocks CK-N_k (k = 1 to L) having different rising edge timings is shown. The generation unit of the clock CK-P_j (j = 1 to M) includes first delay circuits (Delay_P_j (j = 1 to M)) 33a having different delay amounts, and the clock CK-N_k (k = 1 to M). The generation unit L) includes first delay circuits (Delay_N_k (k = 1 to L)) 33b having different delay amounts.

  18A is a graph showing an analog output waveform in the second period of the third embodiment, and FIG. 18B is an output clock CK-P_j (j) of the clock generation circuit shown in FIG. = 1 to M) and CK-N_k (k = 1 to L) are graphs. As shown in FIG. 18, the analog output waveform changes greatly at the beginning of the second period of the third embodiment, and the combined on-resistance Rsw4 of the fourth switch 440 at the initial operation shows the transient characteristics of the analog output waveform. It dominates and is greatly involved in the generation of distortion.

  In the third embodiment, an example in which the fourth switch unit 44i is configured by a PMOS transistor having a single threshold voltage Vth_P and an NMOS transistor having a single threshold voltage Vth_N is shown as an analog output shown in FIG. The combined on-resistance Rsw4 of the fourth switch 440 at the time (a) at the time of the initial movement when the waveform greatly changes will be described. When the potential of CK-P_j at time (a) is VG_P_j and the potential of CK-N_k is VG_N_k, the on-resistance Rsw4 at this time is when the potential of the analog output signal Vout approaches VG_P_j-Vth_P and VG_N_k-Vth_N. Shows the characteristic that the on-resistance value suddenly increases. Here, in the present embodiment, at least one of CK-P_j and CK-N_k has a plurality of clock edges as shown in FIG. 18B, and the clock potential VG_P_j or VG_N_k at time (a). At least one of these has a plurality of potentials. For this reason, there are three or more points at which the on-resistance Rsw4 rapidly increases, and as described in the first embodiment, the characteristics of the on-resistance Rsw4 are averaged and the fluctuation range is suppressed to be small. Thereby, the change depending on the ON resistance Rsw4 of the analog signal output Vout at the initial operation can be suppressed, and the occurrence of distortion can be suppressed.

FIG. 17 shows a circuit that generates clocks CK-P_j (j = 1 to M) having different falling edge timings and clocks CK-N_k (k = 1 to L) having different rising edge timings. It may be configured by a circuit as shown, or may be configured by another circuit having a similar function.
In this embodiment, the integrating capacitive element 460 may not be provided between the output terminal and the inverting input terminal of the operational amplifier 32. In that case, the summing node switch 430 may be replaced with a resistor.
Thus, the third embodiment can suppress the occurrence of distortion with a simple configuration. Further, it is possible to prevent the distortion of the analog output signal from occurring without adversely affecting the response speed allowed in the digital / analog converter.

FIG. 19 is a circuit configuration diagram for explaining a fourth embodiment of the digital-analog converter according to the present invention. In the figure, reference numeral 41 denotes a control clock generator, and 42 denotes an operational amplifier. In addition, the same code | symbol is attached | subjected to the component which has the same function as the component shown in FIG.
As shown in FIG. 19, the digital-to-analog converter 500 according to the fourth embodiment is different from the first embodiment in that the operational amplifier is a differential operational amplifier, and each of the two input terminals is connected to the first embodiment. The same charging voltage is input.

  Specifically, the inverting input terminal of the differential operational amplifier has the same configuration as that of the first embodiment (displayed by adding a to each symbol in FIG. 19), and the bit signal Dia ( The charging voltage of the sampling capacitor 55ia (i = 1 to N) is input according to i = 1 to N), and the non-inverting analog output signal Vout + is output from the non-inverting output terminal of the differential operational amplifier. Also, the non-inverting input terminal of the differential operational amplifier also has the same configuration as in the first embodiment (shown by adding b to each symbol in FIG. 19), so that the same bit signal Dib (i = 1 to N), the charging voltage of the sampling capacitor 55ib (i = 1 to N) is input, and the inverted analog output signal Vout− is output from the inverting output terminal of the differential operational amplifier.

The digital / analog converter 500 (500A, 500B) according to the present invention is a digital / analog converter capable of suppressing the occurrence of distortion of an analog output signal due to the on-resistance value of a switch.
Signals corresponding to a plurality of bit signals constituting a digital signal are input to the plurality of input terminals Dia and Div, respectively. The sampling capacitor elements 55ia and 55ib are provided corresponding to the plurality of input terminals Dia and Div.

  The plurality of first switch units 51 ia and 51 ib (i = 1 to N) switch connection and disconnection between the plurality of input terminals Dia and Div corresponding to one terminal of the plurality of sampling capacitor elements 55 ia 55 ib. The plurality of second switches 520a and 520b switch connection and disconnection between the other terminals of the plurality of sampling capacitor elements 55ia and 55ib and the reference voltage sources Vr1a and Vr1b.

  The third switches 530a and 530b are connected to the other of the plurality of sampling capacitor elements 55ia and 55ib according to disconnection and connection in switching of the plurality of first switch units 51ia and 51ib (i = 1 to N). The connection and disconnection between the terminal and the inverting input terminal (−) of the operational amplifier 42 and the connection and disconnection between the other terminals of the plurality of sampling capacitor elements 55 ia and 55 ib and one terminal of the integrating capacitor element 560 are switched.

  The plurality of fourth switch units 54 ia and 54 ib (i = 1 to N) are connected to and disconnected from one terminal of the plurality of sampling capacitor elements 55 ia and 55 ib and the plurality of sampling capacitor elements 55 ia and 55 ib. Switching between connection and disconnection of one of the terminals and the output terminal of the operational amplifier 22 and connection and disconnection between the plurality of sampling capacitor elements 55ia and 55ib and the other terminals of the plurality of integral capacitor elements 560a and 560b.

  The first switches 510a and 510b include a plurality of first switch units 51ia and 51ib (i = 1 to N), and the fourth switches 540a and 540b include a plurality of fourth switch units 54ia and 54ib (i = 1 to N), and the sampling capacitor elements 550a and 550b are composed of a plurality of sampling capacitor elements 55ia and 55ib (i = 1 to N), and the same number N is provided.

Further, an integrating capacitive element 560a is provided between the non-inverting output terminal and the inverting input terminal of the operational amplifier 42, and an integrating capacitive element 560b is provided between the inverting output terminal and the non-inverting input terminal of the operational amplifier 42. .
The control clock generator 41 generates a clock for controlling the first switches 510a and 510b, the second switches 520a and 520b, the third switches 520a and 520b, and the fourth switches 540a and 540b. .

In this way, by configuring a fully differential digital-to-analog converter, in-phase noise can be removed, and digital-to-analog conversion can be performed with higher accuracy.
In the fourth embodiment, each of the units 54ia and 54ib of the fourth switch is composed of a plurality of MOS transistors having different threshold voltages. Each unit 54ia and 54ib of the fourth switch is composed of a PMOS transistor having M threshold voltages Vth_P_j (j = 1 to M) and an NMOS transistor having L threshold voltages Vth_N_k (k = 1 to L). Suppose that Since the potential of the gate terminal of the PMOS transistor in the second period of the present embodiment is the ground level VSS and the potential of the gate terminal of the NMOS transistor is the power supply voltage level VDD, each unit 54ia and 54ib of the fourth switch is configured. The on-resistance value suddenly increases when the potential of the analog output signal Vout which is the potential of the source (drain) terminal of the MOS transistor approaches VSS-Vth_P_j and VDD-Vth_N_k.

  Here, when each of the units 54ia and 54ib of the fourth switch is configured by a plurality of MOS transistors having different threshold voltages as in the present invention, that is, when M> 1 and L> 1, the on resistances Rsw4a and Rsw4b are suddenly increased. Thus, there are three or more points VSS-Vth_P_j and VDD-Vth_N_k, and the characteristics of the on-resistances Rsw4a and Rsw4b are averaged, and the fluctuation range can be suppressed small. Thereby, the change depending on the on resistances Rsw4a and Rsw4b of the analog signal output can be suppressed, and the occurrence of distortion can be suppressed.

Regarding the number of types (M) of PMOS transistors having different threshold voltages and the number of types (L) of NMOS transistors having different threshold voltages constituting the units 54ia and 54ib of the fourth switch, M> 1 and L> 1 Alternatively, M = 1 and L> 1 may be set, or M> 1 and L = 1 may be set.
In addition, as a method including a plurality of MOS transistors having different threshold voltages, MOS transistors having different threshold voltages prepared in the process may be used, or the threshold voltage is controlled by controlling the base potential of the MOS transistor. May be.

In this embodiment, the integrating capacitive element 560a is provided between the non-inverting output terminal and the inverting input terminal of the operational amplifier 42, and the integrating capacitor is provided between the inverting output terminal and the non-inverting input terminal of the operational amplifier 42. The element 560b may not be provided. In that case, the summing node switches 530a and 530b may be replaced with resistors.
Thus, the fourth embodiment can suppress the occurrence of distortion with a simple configuration. Further, it is possible to prevent the distortion of the analog output signal from occurring without adversely affecting the response speed allowed in the digital / analog converter.

Example 5 of the digital-analog converter according to the present invention is an improvement of Example 2, in which the operational amplifier is a differential operational amplifier, and the same charging voltage as in the second embodiment is applied to each of the two input terminals. It is configured to be input.
Specifically, the charging voltage of the sampling capacitor 35ia is input to the inverting input terminal of the differential operational amplifier according to the bit signal Dia constituting the digital input signal by the same configuration as in the second embodiment. A non-inverted analog output signal Vout + is output from the non-inverted output terminal of the dynamic operational amplifier. Also, the non-inverting input terminal of the differential operational amplifier has the same configuration as that of the second embodiment, and the charging voltage of the sampling capacitor 35 ib is input in accordance with the same bit signal Dib as that on the inverting input terminal side. An inverted analog output signal Vout− is output from the inverted output terminal of the amplifier.

In this way, by configuring a fully differential digital-to-analog converter, in-phase noise can be removed, and digital-to-analog conversion can be performed with higher accuracy.
In the fifth embodiment, each unit 34 ia and 34 ib of the fourth switch is composed of M PMOS transistors and L NMOS transistors, and M different clocks CK-P_j (j = 1 to M) and the gate terminal of each NMOS transistor is controlled by L different clocks CK-N_k (k = 1 to L). In the second period of the fifth embodiment in which the fourth switches SW4ya and SW4yb are turned on, the clock CK-P_j (j = 1 to M) has different “L” levels VG_P_j (j = 1 to M) and the clock CK. -N_k (k = 1 to L) is a different “H” level VG_N_k (k = 1 to L).

  The number of PMOS transistors (M) and the number of NMOS transistors (L) may be M> 1 and L> 1, M = 1 and L> 1, or M> 1 and L = 1. Also good. The M PMOS transistors may be composed of PMOSs having different threshold voltages, or may be composed of PMOS transistors having the same threshold voltage. Further, the L NMOS transistors may be configured with NMOS having different threshold voltages, or may be configured with NMOS transistors having the same threshold voltage.

  FIG. 12 described above is an example of a circuit for controlling the gate terminals of the PMOS transistors and the NMOS transistors constituting the units 34ia and 34ib of the fourth switch at different levels in the second period of the fifth embodiment. FIG. The level adjustment circuit 1 (LVLSFT1_j (j = 1 to M)) for outputting different “L” levels VG_P_j (j = 1 to M) to the generation units of the clock CK-P_j (j = 1 to M) And the level adjustment circuit 2 (LVLSFT2_k (k = 1) for outputting different “H” levels VG_N_k (k = 1 to L) to the generation unit of the clock CK-N_k (k = 1 to L), respectively. To L)).

  FIG. 15A shows an output waveform of the level adjustment circuit 1. In this way, the level adjustment circuit 1 outputs the “H” level of the clock CK-P_j that controls the gate terminals of the PMOS transistors constituting the units 34 ia and 34 ib of the fourth switch at the level of the power supply voltage VDD, It has a function of outputting the “L” level at a plurality of different levels. The level adjustment circuit 1 may be configured by using circuit examples as shown in FIGS. 12 and 13, or the level adjustment circuit 1 may be configured by other circuits having the same function.

FIG. 15B shows an output waveform of the level adjustment circuit 2. In this way, the level adjustment circuit 2 outputs the “L” level of the clock CK-N_k that controls the gate terminals of the NMOS transistors constituting the units 34 ia and 34 ib of the fourth switch as the level of the ground VSS. It has a function of outputting the H ″ level at a plurality of different levels. The level adjustment circuit 2 may be configured by using circuit examples as shown in FIGS. 12 and 14, or the level adjustment circuit 1 may be configured by other circuits having similar functions. .
In this embodiment, an integrating capacitive element between the non-inverting output terminal and the inverting input terminal of the operational amplifier and an integrating capacitive element between the inverting output terminal and the non-inverting input terminal of the operational amplifier are provided. It is good also as not providing. In the case where the integration capacitor element is not provided, the summing node switch may be replaced with a resistor.

In the fifth embodiment, since at least one of the clock level VG_P_j and the clock level VG_N_k is plural, the on-resistances Rsw4a and Rsw4b have three or more points that increase rapidly. As described, the characteristics of the on-resistances Rsw4a and Rsw4b are averaged and the fluctuation range is suppressed to be small. Thereby, the change depending on the on resistances Rsw4a and Rsw4b of the analog signal output can be suppressed, and the occurrence of distortion can be suppressed.
Thus, Example 5 can suppress the occurrence of distortion with a simple configuration. Further, it is possible to prevent the distortion of the analog output signal from occurring without adversely affecting the response speed allowed in the digital / analog converter.

  The fifth embodiment of the digital-analog converter according to the present invention is an improvement of the third embodiment. The operational amplifier is a differential operational amplifier, and a charging voltage similar to that of the third embodiment is input to each of the two input terminals. Is to be configured. Specifically, the charging voltage of the sampling capacitor 45ia is input to the inverting input terminal of the differential operational amplifier in accordance with the bit signal Dia constituting the digital input signal by the same configuration as in the third embodiment. A non-inverted analog output signal Vout + is output from the non-inverted output terminal of the operational amplifier. Also, the non-inverting input terminal of the differential operational amplifier has the same configuration as that of the third embodiment, and the charging voltage of the sampling capacitor 45ib is input in accordance with the same bit signal Dib as that on the inverting input terminal side. An inverted analog output signal Vout− is output from the inverted output terminal of the amplifier.

In this way, by configuring a fully differential digital-to-analog converter, in-phase noise can be removed, and digital-to-analog conversion can be performed with higher accuracy.
In the sixth embodiment, each unit 44 ia and 44 ib of the fourth switch is composed of M PMOS transistors and L NMOS transistors, and the gate terminal of each PMOS transistor is M different clocks CK-P_j (j = 1 to M), and the gate terminal of each NMOS transistor is controlled by L different clocks CK-N_k (k = 1 to L). The clock CK-P_j (j = 1 to M) has different falling edge timings, and the clock CK-N_k (k = 1 to L) has different rising edge timings.

  The number of PMOS transistors (M) and the number of NMOS transistors (L) may be M> 1 and L> 1, M = 1 and L> 1, or M> 1 and L = 1. Also good. The M PMOS transistors may be composed of PMOSs having different threshold voltages, or may be composed of PMOS transistors having the same threshold voltage. Further, the L NMOS transistors may be configured with NMOS having different threshold voltages, or may be configured with NMOS transistors having the same threshold voltage.

FIG. 17 shows a circuit that generates clocks CK-P_j (j = 1 to M) having different falling edge timings and clocks CK-N_k (k = 1 to L) having different rising edge timings. It may be configured with such a circuit, or may be configured with another circuit having a similar function.
In this embodiment, an integrating capacitive element between the non-inverting output terminal and the inverting input terminal of the operational amplifier and an integrating capacitive element between the inverting output terminal and the non-inverting input terminal of the operational amplifier are provided. It is good also as not providing. In the case where the integration capacitor element is not provided, the summing node switch may be replaced with a resistor.

  FIG. 18A is a graph showing an analog output waveform in the second period of the sixth embodiment, and FIG. 18B is a diagram showing the output clock CK-P_j (of the clock generation circuit shown in FIG. It is the figure which showed the example of j = 1-M) and CK-N_k (k = 1-L) on the graph. As shown in FIG. 18, the analog output waveform changes greatly at the beginning of the second period of the sixth embodiment, and the combined on-resistances Rsw4a and Rsw4b of the fourth switches 440a and 440b at the initial operation are the analog output waveforms. It greatly governs the transient characteristics of and greatly contributes to the generation of distortion.

  In the sixth embodiment, assuming that the potential of CK-P_j and the potential of CK-N_k at the time (a) at the time of the initial operation when the analog output waveform shown in FIG. 18 changes greatly are VG_N_k, the potential of the clock at this time At least one of VG_P_j and VG_N_k has a plurality of potentials. For this reason, there are three or more points where the on-resistances Rsw4a and Rsw4b increase rapidly, and as described in the first embodiment, the characteristics of the on-resistances Rsw4a and Rsw4b are averaged and the fluctuation range is suppressed to be small. . Thereby, the change depending on the ON resistances Rsw4a and Rsw4b of the analog signal output Vout at the initial operation can be suppressed, and the occurrence of distortion can be suppressed.

  As described above, the sixth embodiment can suppress the occurrence of distortion with a simple configuration. Further, it is possible to prevent the distortion of the analog output signal from occurring without adversely affecting the response speed allowed in the digital / analog converter.

1, 11, 21, 31, 41 Control clock generator (first to fourth switch control clock generation circuit)
2, 12, 22, 32, 42 operational amplifier 23a first level adjustment circuit 23b first level adjustment circuit 33a first delay circuit 33b second delay circuit 100, 200, 300, 400, 500A, 500B Analog converter 110,210,310,410,510,310b 1st switch unit 120,220,320,420,520a, 520b 2nd switch 130,230,330,430,530a, 530b 3rd switch 140,240, 340, 440, 540a, 540b Fourth switch unit 150, 250, 350, 450, 550a, 550b All sampling capacitors 151 to 15N, 251 to 25N, 351 to 35N, 451 to 45N, 551a to 55Na, 551b to 551b Grayed capacitive element 160,260,360,460,560a, 560b integrating capacitor Vr1 first reference voltage source Vr2 second reference voltage source Di, Dia, Dib (i = 1~N) a plurality of bit signals (digital input signal)
Rsw3, Rsw3a, Rsw3b Synthetic on-resistance Rsw4, Rsw4a, Rsw4b of the third switch Synthetic on-resistance CK1 of the fourth switch CK1 First switch unit control clock signal CK2 Second switch control clock signal CK3 Third switch control clock signal CK4 Fourth switch Unit control clock signal Vout, Vout +, Vout- Analog output signal CK-P PMOS control clock signal CK-N constituting the fourth switch unit NMOS control clock signal VG_P CK-P constituting the fourth switch unit "L""H" level VG_N CK-N level Vr3 Third reference voltage source Vr4 in LVLFTFT Fourth reference voltage source CP in LVSFT2 Capacitance element CN in LVLFTFT1 Capacitance element in CLVLSFT2

Claims (4)

A digital-to-analog converter capable of suppressing the occurrence of distortion of the analog output signal due to the on-resistance value of the switch,
A plurality of input terminals to which a plurality of bit signals constituting a digital signal are respectively input;
A plurality of sampling capacitors provided corresponding to the plurality of input terminals;
A switch unit that switches connection and disconnection between the plurality of input terminals corresponding to one terminal of the plurality of sampling capacitors;
A second switch for switching connection and disconnection between the other terminal of the plurality of sampling capacitors and the first reference voltage source;
An operational amplifier in which the second reference voltage of the second reference voltage source is applied to the non-inverting input terminal;
According to disconnection and connection in switching of the first switch unit, connection and disconnection of the other terminal of the plurality of sampling capacitors and the inverting input terminal of the operational amplifier, and the sampling capacitors of the plurality of sampling capacitors A third switch for switching connection and disconnection between the other terminal and one terminal of the integrating capacitive element;
Mutual connection and disconnection of the one terminals of the plurality of sampling capacitor elements, connection and disconnection of the one terminal of the plurality of sampling capacitor elements and the output terminal of the operational amplifier, and the plurality of sampling capacitor elements And a fourth switch unit that switches connection and disconnection between the integration capacitor element and the other terminal of the integration capacitor element;
A control clock generator for generating a clock for controlling the first switch unit, the second switch, the third switch, and the fourth switch unit;
Wherein at least one of the plurality of PMOS transistors and a plurality of NMOS transistors constituting the fourth switch unit, Ri MOS transistor der the threshold voltage Vth which is previously prepared by a semiconductor process each having different on-resistances from each other,
The digital-analog converter characterized in that the plurality of PMOS transistors are composed of PMOS transistors having different threshold voltages Vth, and the plurality of NMOS transistors are composed of NMOS transistors having a single threshold voltage Vth . A digital-to-analog converter capable of suppressing the occurrence of distortion of the analog output signal due to the on-resistance value of the switch,
A plurality of input terminals to which a plurality of bit signals constituting a digital signal are respectively input;
A plurality of sampling capacitors provided corresponding to the plurality of input terminals;
A switch unit that switches connection and disconnection between the plurality of input terminals corresponding to one terminal of the plurality of sampling capacitors;
A second switch for switching connection and disconnection between the other terminal of the plurality of sampling capacitors and the first reference voltage source;
An operational amplifier in which the second reference voltage of the second reference voltage source is applied to the non-inverting input terminal;
According to disconnection and connection in switching of the first switch unit, connection and disconnection of the other terminal of the plurality of sampling capacitors and the inverting input terminal of the operational amplifier, and the sampling capacitors of the plurality of sampling capacitors A third switch for switching connection and disconnection between the other terminal and one terminal of the integrating capacitive element;
Mutual connection and disconnection of the one terminals of the plurality of sampling capacitor elements, connection and disconnection of the one terminal of the plurality of sampling capacitor elements and the output terminal of the operational amplifier, and the plurality of sampling capacitor elements And a fourth switch unit that switches connection and disconnection between the integration capacitor element and the other terminal of the integration capacitor element;
A control clock generator for generating a clock for controlling the first switch unit, the second switch, the third switch, and the fourth switch unit;
At least one of the plurality of PMOS transistors and the plurality of NMOS transistors constituting the fourth switch unit is a MOS transistor having threshold voltages Vth prepared in advance in a semiconductor process and having different on-resistances, respectively.
Wherein the plurality of PMOS transistors is a PMOS transistor having a single threshold voltage Vth, features and to Lud digital-to-analog converter to be configured in different NMOS transistors of the plurality of NMOS transistors the threshold voltage Vth. A digital-to-analog converter capable of suppressing the occurrence of distortion of the analog output signal due to the on-resistance value of the switch,
A plurality of input terminals to which signals corresponding to a plurality of bit signals constituting the digital signal are respectively input;
A plurality of sampling capacitor elements provided corresponding to the plurality of input terminals;
A plurality of first switch units for switching connection and disconnection with the plurality of input terminals corresponding to one terminal of the plurality of sampling capacitor elements;
A plurality of second switches for switching connection and disconnection between the other terminals of the plurality of sampling capacitor elements and a reference voltage source;
A differential operational amplifier;
According to disconnection and connection in switching of the first switch unit, connection and disconnection between the other terminal of the plurality of sampling capacitor elements and an input terminal of the differential operational amplifier, and the plurality of sampling capacitor elements A plurality of third switches for switching connection and disconnection between the other terminal and one terminal of the integrating capacitive element;
Mutual connection and disconnection of the one terminal of the plurality of sampling capacitor elements, connection and disconnection of the one terminal of the plurality of sampling capacitor elements and the output terminal of the differential operational amplifier, and the plurality of sampling A plurality of fourth switch units for switching connection and disconnection between the capacitive element section and the other terminal of the plurality of integrating capacitive elements;
A control clock generator for generating a clock for controlling the plurality of first switch units, the second switch, the third switch, and the plurality of fourth switch units;
At least one of the plurality of PMOS transistors and a plurality of NMOS transistors constituting the plurality of the fourth switch unit, Ri MOS transistor der the threshold voltage Vth which is previously prepared by a semiconductor process each having different on-resistances from each other ,
The digital-analog converter characterized in that the plurality of PMOS transistors are composed of PMOS transistors having different threshold voltages Vth, and the plurality of NMOS transistors are composed of NMOS transistors having a single threshold voltage Vth . A digital-to-analog converter capable of suppressing the occurrence of distortion of the analog output signal due to the on-resistance value of the switch,
A plurality of input terminals to which signals corresponding to a plurality of bit signals constituting the digital signal are respectively input;
A plurality of sampling capacitor elements provided corresponding to the plurality of input terminals;
A plurality of first switch units for switching connection and disconnection with the plurality of input terminals corresponding to one terminal of the plurality of sampling capacitor elements;
A plurality of second switches for switching connection and disconnection between the other terminals of the plurality of sampling capacitor elements and a reference voltage source;
A differential operational amplifier;
According to disconnection and connection in switching of the first switch unit, connection and disconnection between the other terminal of the plurality of sampling capacitor elements and an input terminal of the differential operational amplifier, and the plurality of sampling capacitor elements A plurality of third switches for switching connection and disconnection between the other terminal and one terminal of the integrating capacitive element;
Mutual connection and disconnection of the one terminal of the plurality of sampling capacitor elements, connection and disconnection of the one terminal of the plurality of sampling capacitor elements and the output terminal of the differential operational amplifier, and the plurality of sampling A plurality of fourth switch units for switching connection and disconnection between the capacitive element section and the other terminal of the plurality of integrating capacitive elements;
A control clock generator for generating a clock for controlling the plurality of first switch units, the second switch, the third switch, and the plurality of fourth switch units;
At least one of the plurality of PMOS transistors and the plurality of NMOS transistors constituting each of the plurality of fourth switch units is a MOS transistor having an on-resistance having different threshold voltages Vth prepared in advance in a semiconductor process,
Wherein the plurality of PMOS transistors is a PMOS transistor having a single threshold voltage Vth, features and to Lud digital-to-analog converter to be configured in different NMOS transistors threshold voltage Vth of the plurality of NMOS transistors .

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