JP4699300B2 - Oscillator - Google Patents

Description

  The present invention relates to an oscillation device, and more particularly to an oscillation device capable of obtaining a digital output signal.

  Analog oscillators can be easily and inexpensively configured simply by combining an amplifier and a feedback circuit including a phase shifter or a filter, and are therefore often used even today when digital signal processing has become popular. In an analog oscillator, the condition for establishing oscillation is that the gain in the feedback loop (loop gain) is 1 or more and that the phase change when the feedback loop is made is 360 degrees or more. This condition can be satisfied relatively easily by a combination of electronic elements.

  As an amplifier, in addition to a general analog amplifier, in recent years, an amplifier using a switching operation has been frequently used. For such switching operation, for example, a PWM (Pulse Width Modulation) method is used. The PWM system is a system that compares an input signal with a reference signal that changes over time, and obtains a switching output from the comparison result, and by changing the pulse width or the duty of the pulse signal according to the input signal level, It becomes possible to control the average value of the signal in each bit. An input signal can be amplified by passing the switching output obtained by this method through a low-pass filter. Power amplifiers using this method are widely used for audio signal reproduction, mechanical actuator control, and the like.

  In addition, 1-bit signals (1-bit digital signals) obtained from ΔΣ (delta sigma) modulators are used not only for recording audio signals and for transmission between devices, but also for power amplification. Is done. For example, a demodulated analog signal with power amplification can be obtained by inputting a 1-bit signal as it is to a semiconductor power amplifier and supplying the obtained high-voltage switching pulse to a low-pass filter. Moreover, in this case, the semiconductor power amplifying element is not used in the linear region (unsaturated region) as in the conventional amplifier, but is used in the nonlinear region (saturated region). For this reason, switching amplifiers using ΔΣ modulation have the advantage that power amplification can be performed with extremely high efficiency, and are used in various products.

  A technique using the characteristic that a 1-bit signal including the output of the ΔΣ modulator is a digital signal and includes an analog signal component (analog signal waveform) is also disclosed in Patent Documents 1, 2, and 3 below. It is disclosed. Patent Documents 1 and 2 below disclose techniques for driving a speaker by adding the output of a ΔΣ modulator to a switching circuit. Patent Document 3 below discloses a DC-DC converter that employs a configuration in which the output of a ΔΣ modulator is added to a switching circuit.

JP-A-5-176387 JP-A-6-335082 JP 2002-300771 A

  By the way, various oscillators that can obtain a digital signal as an output have been developed as oscillators that can be applied to various applications.

  As a method for obtaining a digital output signal from an oscillator, there is a method using digital signal processing such as a method using a counter alone or a combination of a counter and a ROM (Read Only Memory), a method using an M-sequence signal, and the like. . However, in order to obtain an arbitrary waveform by digital signal processing, it is necessary to prepare an output signal in the ROM in advance. Therefore, when this type of method is employed, the circuit scale and development system become large.

  For this reason, as another method for obtaining a digital output signal from an oscillator, a method of using an analog oscillator and an A / D converter in combination is often used.

  As described above, an analog oscillator is configured by combining an amplifier and a phase shifter or a filter. In particular, in an analog sine wave oscillator, in order to obtain a low distortion oscillation signal, the amplification factor of the amplifier is precisely controlled. There is a need to. Conventionally, the amplification factor of an amplifier has been controlled for the purpose of realizing a low distortion sine wave oscillator. However, in order to control the amplification factor, an FET (Field effect transistor) or a light bulb is used as a variable resistance element. In principle, there is a problem that non-linearity is unavoidably superimposed on the variable amplification factor. Non-linearity in the variable amplification factor increases the distortion of the oscillation signal.

  In order to keep the oscillation frequency at a desired frequency with high accuracy, it is necessary to stably maintain the characteristics of the amplifier and the characteristics of the phase shifter or filter over a long period of time. However, since these characteristics are likely to change due to external factors such as temperature and humidity, it is difficult to construct an oscillator having stable characteristics over a long period of time.

  Note that none of the techniques described in Patent Documents 1 to 3 are applied to an oscillator, and are not intended to extract a digital signal as an output.

  In view of the above points, an object of the present invention is to provide an oscillation device that can extract a digital output signal and contributes to improvement in characteristics.

  As oscillators for achieving the above object, first, second, third and fourth oscillators according to the present invention are shown below. The first oscillation device corresponds to, for example, FIGS. 1 and 2, the second oscillation device corresponds to, for example, FIGS. 4, 5, 7, and 8, and the third oscillation device includes, for example, Corresponding to FIG. 3, the fourth oscillation device corresponds to FIGS. 6 and 9, for example.

  A first oscillation device according to the present invention includes an A / D converter for A / D converting an analog input signal, a D / A converter for D / A converting an output signal of the A / D converter, Phase-shifting means for phase-shifting the output signal of the D / A converter and outputting the phase-shifted signal obtained by the phase-shifting to the A / D converter; and the output signal of the A / D converter Output means for outputting as a digital output signal of the oscillation device, and the output signal of the D / A converter is amplified with respect to the input signal to the A / D converter.

  A digital amplifier can be realized by combining the A / D converter and the D / A converter. By changing the operation reference voltage of the A / D converter and / or the D / A converter, the digital amplifier can be realized. The amplification factor can be changed. In order to realize the change of the amplification factor, it is not necessary to provide a variable resistance element in the signal path as in the prior art, so that a low distortion variable amplification factor amplifier can be realized. This contributes to lower distortion of the oscillation signal.

  Further, by adopting a configuration in which the output of the D / A converter is returned to the A / D converter via the phase shift means, noise generated in the D / A converter is reduced by the phase shift means. It is also possible.

  In the first oscillation device, for example, a noise shaping type A / D converter may be used as the A / D converter.

  When a noise shaping type A / D converter is used, the D / A converter can be formed by a low-pass filter that extracts an analog signal component included in a digital signal. As a result, the configuration for D / A conversion can be simplified and the number of parts can be reduced.

  A second oscillation device according to the present invention includes an A / D converter that performs A / D conversion on an analog input signal, and a digital signal processing unit that performs predetermined digital signal processing on an output signal of the A / D converter. The D / A converter for D / A converting the output signal of the digital signal processing unit, and the output signal of the D / A converter are phase shifted, and the phase shift signal obtained by the phase shift is converted to the A / A Phase shift means for outputting to the D converter, and output means for outputting the output signal of the A / D converter as a digital output signal of the oscillation device, and for the input signal to the A / D converter The output signal of the D / A converter is amplified.

  The same effect as that of the first oscillation device can be expected by the second oscillation device. In addition, the gain of the digital amplifier can be changed by the digital signal processing unit. In addition, various waveform processing can be performed by the digital signal processing unit, which is useful for obtaining a desired oscillation waveform.

  In the second oscillation device, for example, a noise shaping type A / D converter may be used as the A / D converter.

  As a result, the configuration for D / A conversion can be simplified and the number of parts can be reduced. Even if the A / D converter is not a noise shaping type, the same effect can be expected by performing noise shaping processing in the digital signal processing unit.

  In the second oscillation device, for example, control means for controlling the output signal of the D / A converter by controlling the digital signal processing unit based on the output signal of the A / D converter is further provided. You may make it prepare.

  By providing control means and appropriately controlling the digital signal processing unit with reference to the output signal of the A / D converter, for example, it compensates for changes in the oscillation waveform caused by changes in the characteristics of the components of the oscillation device. Thus, the oscillation waveform can be maintained at a desired waveform. Thereby, improvement of the characteristics of the oscillation device (such as improvement of long-term stability) can be expected.

  A third oscillation device according to the present invention includes a noise shaping type A / D converter for A / D converting an analog input signal, and a D / A conversion of the output signal of the A / D converter. Phase shifting means for outputting the phase shift signal obtained by the phase shift to the A / D converter, and output means for outputting the output signal of the A / D converter as a digital output signal of the oscillation device The gain of the signal after D / A conversion by the phase shift means with respect to the input signal to the A / D converter is 1 or more.

  The same effect as that of the first oscillation device can be expected by the third oscillation device. Further, by utilizing the characteristics of the output signal of the noise shaping type A / D converter and integrating the D / A conversion function in the phase shift means, the number of parts can be further reduced.

  A fourth oscillation device according to the present invention includes an A / D converter that performs A / D conversion on an analog input signal, and a digital signal processing unit that performs predetermined digital signal processing on an output signal of the A / D converter. Phase-shifting means for phase-shifting the output signal of the digital signal processing unit while D / A converting, and outputting the phase-shifted signal obtained by the phase-shifting to the A / D converter, and the A / D conversion Output means for outputting the output signal of the oscillator as a digital output signal of the oscillation device, and at least one of the A / D converter and the digital signal processing unit is subjected to noise shaping processing, and the A The gain of the signal after D / A conversion by the phase shift means with respect to the input signal to the / D converter is 1 or more.

  According to the fourth oscillation device, the same effect as that of the first oscillation device can be expected, and the same effect as that of the second oscillation device can be expected by providing the digital signal processing unit. Furthermore, the number of parts can be further reduced by consolidating the D / A conversion function in the phase shift means using noise shaping processing.

  In the fourth oscillation device, for example, control for controlling the signal after D / A conversion by the phase shift means by controlling the digital signal processing unit based on the output signal of the A / D converter. You may make it further provide a means.

  By providing control means and appropriately controlling the digital signal processing unit with reference to the output signal of the A / D converter, for example, it compensates for changes in the oscillation waveform caused by changes in the characteristics of the components of the oscillation device. Thus, the oscillation waveform can be maintained at a desired waveform. Thereby, improvement of the characteristics of the oscillation device (such as improvement of long-term stability) can be expected.

  In the first, second, third, or fourth oscillation device, specifically, for example, the A / D converter ΔΣ modulates an input signal to itself and outputs a ΔΣ modulation signal. It is a ΔΣ modulator.

  According to the present invention, it is possible to configure an oscillation device that can extract a digital output signal and contribute to improvement in characteristics.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In each of the drawings to be referred to, the same part is denoted by the same reference numeral, and redundant description of the same part is omitted in principle.

<< First Embodiment >>
First, a first embodiment of the present invention will be described. FIG. 1 is a block diagram showing the configuration of an oscillation circuit (oscillation device) according to the first embodiment of the present invention.

  The oscillation circuit of FIG. 1 includes an A / D converter 11, a D / A converter 13, and a phase shifter 14 as a feedback circuit. In this embodiment and each embodiment described later, a digital amplifier is used as the oscillation amplifier. In a digital amplifier, signal format conversion from analog to digital is performed in the signal amplification process. In the present embodiment, a digital amplifier 101 is formed by the A / D converter 11 and the D / A converter 13.

  The A / D converter 11 converts an analog input signal to itself into a multi-bit digital signal and outputs it. The D / A converter 13 converts the digital output signal from the A / D converter 11 into an analog signal and outputs the analog signal.

  The phase shifter 14 receives an analog output signal from the D / A converter 13 and shifts the phase of the signal. That is, the phase of the output signal of the D / A converter 13 is changed. A signal obtained by phase shifting the output signal of the D / A converter 13 is referred to as a phase shift signal. The phase shift signal output from the phase shifter 14 is given to the A / D converter 11 as an input signal to the A / D converter 11. As is well known, the phase shifter 14 changes the phase of the output signal of the D / A converter 13 using an electrical or mechanical method, for example, using a combination of a resistor and a capacitor.

  Thus, the output signal of the D / A converter 13 is fed back to the A / D converter 11 via the phase shifter 14 as a feedback circuit. The output signal of the D / A converter 13 (that is, the output signal of the digital amplifier 101) is amplified with respect to the input signal of the A / D converter 11 (that is, the input signal of the digital amplifier 101). For this reason, the gain (loop gain) in the feedback loop is 1 or more.

  For example, an analog signal of 0 to 5 V (volt) is converted into a digital signal having a value of 0 to 255 by the A / D converter 11, and a digital signal having a value of 0 to 255 is converted to 0 by the D / A converter 13. The above amplification is realized by converting the analog signal to -10V.

  Further, the phase shifter 14 receives an input signal (the output signal of the D / A converter 13 in the present embodiment) to itself so that the phase change when it makes a round in the feedback loop becomes 360 degrees or more. Phase shift. Thereby, the oscillation condition is satisfied, and for example, an analog sine wave oscillation signal is obtained from the phase shifter 14 as an analog output signal of the oscillation circuit.

  In FIG. 1, the output signal of the A / D converter 11 is guided to the outside of the oscillation circuit via a terminal 16 as a digital output signal of the oscillation circuit.

  The phase shifter 14 also has a function as a filter that attenuates a signal having an unnecessary frequency. For this reason, white noise (noise caused by quantization error, etc.) and harmonics generated by the D / A converter 13 are oscillated at the oscillation frequency (oscillation signal of the oscillation circuit) due to the filter effect of the phase shifter 14. It works to be reduced as it gets farther away. That is, by adopting a configuration in which the output signal of the D / A converter is returned to the A / D converter via the phase shifter, an effect of suppressing noise inevitably generated in the D / A converter is obtained. As a result, an oscillation signal with excellent characteristics can be obtained.

  In addition, the digital amplifier 101 is formed by the A / D converter 11 and the D / A converter 13, and the operation reference voltage of the A / D converter 11 and / or the operation reference voltage of the D / A converter 13 is changed. By changing the gain, the amplification factor of the digital amplifier 101 can be changed. When changing the amplification factor, it is not necessary to provide a variable resistance element in the analog signal system, so that a low distortion variable amplification amplifier can be realized as compared with a conventional variable amplification factor analog amplifier.

  The operation reference voltage (reference voltage) of the A / D converter 11 is a voltage that defines the relationship between the input signal and the output signal in the A / D converter 11, and the operation reference voltage ( Reference voltage) is a voltage that defines the relationship between an input signal and an output signal in the D / A converter 13. In the A / D converter 11, when the operation reference voltage is changed, the output signal for the same input signal is changed. In the D / A converter 13, if the operation reference voltage is changed, the output signal for the same input signal changes.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing the configuration of the oscillation circuit according to the second embodiment of the present invention.

  The oscillation circuit in FIG. 2 includes an A / D converter 11a, a D / A converter 13a, and a phase shifter 14 as a feedback circuit. A digital amplifier 102 is formed by the A / D converter 11a and the D / A converter 13a.

  The A / D converter 11a in the present embodiment is a noise shaping type A / D converter, whereby the digital amplifier 102 is a noise shaping type digital amplifier.

  Specifically, for example, the A / D converter 11a modulates an analog input signal to the A / D converter 11a by ΔΣ modulation, so that a modulation signal that is distributed more as the quantization noise becomes higher, that is, noise. The shaped ΔΣ modulation signal is output. In this case, the A / D converter 11a can also be called a ΔΣ modulator. By ΔΣ modulation, an analog input signal to the A / D converter 11a is subjected to pulse density modulation (PDM) depending on the amplitude of the analog input signal to the A / D converter 11a with a period of a predetermined sampling frequency as a unit pulse width. The resulting ΔΣ modulation signal is a 1-bit PDM (Pulse Density Modulation) signal, which is a digital signal but contains an analog signal component (analog signal waveform) as it is, so it is interpreted as an analog signal. You can also This 1-bit PDM signal is a so-called 1-bit signal (1-bit digital signal) often used in an audio device or the like.

  The D / A converter 13a converts the output signal of the A / D converter 11a into an analog signal and outputs it. By using the noise shaping type A / D converter as the A / D converter 11a, the D / A converter 13a can be formed by a low-pass filter that extracts an analog signal component included in the digital signal. It becomes.

  FIG. 10 shows an example of an internal circuit of a D / A converter that can be used as the D / A converter 13a. The D / A converter shown in FIG. 10 includes a power source 21 that outputs a DC voltage, a switching element 22 formed of an FET (field effect transistor), a resistor 23, a capacitor 24, and a PDM signal. An input terminal 25 that is received as an input signal to the A converter and an output terminal 26 at which the output signal of the D / A converter appears are configured.

  The switching element 22 includes a first terminal 22a and a second terminal 22b, a common terminal 22c that is alternatively connected to the first terminal 22a or the second terminal 22b according to the PDM signal applied to the input terminal 25, Have At the timing when the PDM signal becomes positive, the common terminal 22c is connected to the first terminal 22a, and at the timing when the PDM signal becomes negative, the common terminal 22c is connected to the second terminal 22b.

  A positive output voltage from the power supply 21 is applied to the first terminal 22a, and a negative output voltage from the power supply 21 is applied to the second terminal 22b. The common terminal 22 c is commonly connected to one end of the capacitor 24 and the output terminal 26 via the resistor 23. The other end of the capacitor 24 is connected to the reference potential point of the D / A converter of FIG.

  When the D / A converter shown in FIG. 10 is used as the D / A converter 13a of FIG. 2, the PDM signal to the input terminal 25 is supplied from the A / D converter 11a. 10 may be provided in the A / D converter 11a, and the voltage appearing at the common terminal 22c may be used as the output signal of the A / D converter 11a. In this case, the D / A converter 13a can be formed only by a resistor and a capacitor (for example, the resistor 23 and the capacitor 24).

  The A / D converter 11a and the D / A converter 13a are configured such that the output signal of the D / A converter 13a is amplified with respect to the input signal of the A / D converter 11a. For example, the magnitude of the output voltage of the power supply 21 is set so that the output signal of the D / A converter 13a is amplified with respect to the input signal of the A / D converter 11a. Thereby, the gain (loop gain) in the feedback loop becomes 1 or more. Note that the magnitude of the output voltage of the power source 21 may be changeable.

  The phase shifter 14 provides the A / D converter 11a with a phase shift signal obtained by shifting the phase of the output signal of the D / A converter 13a. At this time, the phase shifter 14 shifts the phase of the input signal to itself so that the change of the phase when it goes around in the feedback loop becomes 360 degrees or more. Thereby, the oscillation condition is satisfied, and for example, an analog sine wave oscillation signal is obtained from the phase shifter 14 as an analog output signal of the oscillation circuit.

  In FIG. 2, the output signal of the A / D converter 11a is guided to the outside of the oscillation circuit via the terminal 16 as a digital output signal of the oscillation circuit.

  In the oscillation circuit of FIG. 2, the same effect as that of the oscillation circuit of FIG. 1 can be obtained. Further, by making the A / D converter a noise shaping type, the D / A converter can be formed by a low-pass filter that extracts an analog signal component included in the digital signal. That is, it is not necessary to use a special semiconductor element (dedicated component) as the D / A converter, and the configuration can be simplified and the number of components can be reduced.

<< Third Embodiment >>
Further, low-pass filters that function as D / A converters may be integrated into a phase shifter located outside the digital amplifier. As a result, the number of parts can be further reduced. A modification of the second embodiment in which the modification related to the aggregation is performed will be described as a third embodiment.

  FIG. 3 is a block diagram showing the configuration of the oscillation circuit according to the third embodiment of the present invention. The oscillation circuit of FIG. 3 includes an A / D converter 11a and a phase shifter 14a as a feedback circuit. A digital amplifier 103 is formed by the A / D converter 11a. In the present embodiment, the output signal (ΔΣ modulation signal) of the A / D converter 11a is directly supplied to the phase shifter 14a.

  FIG. 11 shows an internal circuit example of the phase shifter 14a. The phase shifter shown in FIG. 11 includes a phase inverter (inverter) 31, a first low-pass filter composed of a resistor 32 and a capacitor 33, a second low-pass filter composed of a resistor 34 and a capacitor 35, a resistor 36 and a capacitor. 37, a third low-pass filter. The first, second and third low pass filters are cascaded and they form a third order low pass filter.

  The phase inverter 31 receives the output signal (ΔΣ modulation signal) of the A / D converter 11a and changes its phase by 180 degrees. The output signal of the phase inverter 31 is given to the A / D converter 11a via the first, second and third low pass filters. In the first, second, and third low-pass filters, D / A conversion is performed by removing the high-frequency component of the output signal of the phase inverter 31, while the signal is phase-shifted at the same time.

  Further, the A / D converter so that the gain of the signal after the D / A conversion in the phase shifter 14a with respect to the input signal of the A / D converter 11a (that is, the output signal of the phase shifter 14a) becomes 1 or more. 11a and the phase shifter 14a are comprised. For example, the voltage amplitudes of the output signals of the A / D converter 11a and the phase inverter 31 are set so that the gain becomes 1 or more. Thereby, the gain (loop gain) in the feedback loop becomes 1 or more. As is well known, a stable sine wave generation condition is that the gain of the entire system is as close to 1 as possible after compensating for the insertion loss of the phase shifter. Therefore, in all the embodiments including this embodiment, the gain of the output signal of the phase shifter (14 or 14a) with respect to the input signal of the A / D converter (11 or 11a) is one or more close to 1 as much as possible. A value is desirable.

  In addition, the phase shifter 14a shifts the phase of the input signal to itself so that the phase change when it goes around the feedback loop is 360 degrees or more. Thereby, the oscillation condition is satisfied, and for example, an analog sine wave oscillation signal is obtained from the phase shifter 14a as an analog output signal of the oscillation circuit.

  In FIG. 3, the output signal of the A / D converter 11a is led to the outside of the oscillation circuit via the terminal 16 as a digital output signal of the oscillation circuit.

<< Fourth Embodiment >>
Further, a digital signal processing circuit may be inserted between the A / D converter 11 and the D / A converter 13 in the oscillation circuit of FIG. The modification of 1st Embodiment which performed this insertion is demonstrated as 4th Embodiment.

  FIG. 4 is a block diagram showing the configuration of the oscillation circuit according to the fourth embodiment of the present invention. The oscillation circuit in FIG. 4 includes an A / D converter 11, a digital signal processing circuit 12, a D / A converter 13, and a phase shifter 14 as a feedback circuit. A digital amplifier 104 is formed by the A / D converter 11, the digital signal processing circuit 12, and the D / A converter 13. Except for the digital signal processing circuit 12, the operations of the components of the oscillation circuit of FIG. 4 are the same as those of FIG.

  In FIG. 4, an A / D converter 11 converts an analog input signal to itself into a digital signal of a plurality of bits and outputs it. The digital signal processing circuit 12 performs predetermined digital signal processing on the output signal of the A / D converter 11 and outputs the digital signal after this digital signal processing to the D / A converter 13. The D / A converter 13 converts the output signal of the digital signal processing circuit 12 into an analog signal and outputs the analog signal. The phase shifter 14 provides the A / D converter 11 with a phase shift signal obtained by shifting the phase of the output signal of the D / A converter 13.

  As in the oscillation circuit of FIG. 1, the output signal of the D / A converter 13 is amplified with respect to the input signal of the A / D converter 11 in the oscillation circuit of FIG. 4. For this reason, the gain (loop gain) in the feedback loop is 1 or more. In addition, the phase shifter 14 shifts the phase of the input signal to itself so that the phase change when it makes a round in the feedback loop becomes 360 degrees or more. Thereby, the oscillation condition is satisfied, and for example, an analog sine wave oscillation signal is obtained from the phase shifter 14 as an analog output signal of the oscillation circuit. In FIG. 4, the output signal of the A / D converter 11 is led to the outside of the oscillation circuit via the terminal 16 as a digital output signal of the oscillation circuit.

  By providing the digital signal processing circuit 12, functions that are normally difficult to achieve in an analog circuit can be realized, and the degree of freedom in the configuration of the oscillation circuit is improved.

  For example, by inserting a multiplier (not shown) for multiplying the signal to a signal line for transmitting the signal from the A / D converter 11 to the D / A converter 13, the A / D converter 11. Is multiplied by a coefficient before being supplied to the D / A converter 13. Thereby, the amplification factor of the output signal of the D / A converter 13 with respect to the input signal of the A / D converter 11 can be controlled (changed) by changing the value of the coefficient. The above multiplier is provided in the digital signal processing circuit 12.

  In addition to changing the amplification factor, the digital signal processing circuit 12 can perform waveform processing including non-linear processing, and the digital signal processing circuit 12 can be effectively used to obtain a desired oscillation waveform. Is possible. For example, a time delay element can be realized by inserting a delayer (not shown) for delaying the signal into the signal line. Thereby, the oscillation cycle of the oscillation circuit can be delayed (that is, the oscillation frequency can be lowered). The delay device is provided in the digital signal processing circuit 12. Further, for example, waveform processing such as polarity determination processing for outputting a signal corresponding to the polarity of the input signal and correction processing for distortion generated in the signal processing system can be realized.

<< Fifth Embodiment >>
Similarly to the modification of the oscillation circuit of FIG. 1 to the oscillation circuit of FIG. 4, a digital signal processing circuit can be provided in the oscillation circuit of FIG. 2 according to the second embodiment. A fifth embodiment will be described as an embodiment showing a modification of the oscillation circuit of FIG.

  FIG. 5 is a block diagram showing the configuration of the oscillation circuit according to the fifth embodiment of the present invention. The oscillation circuit in FIG. 5 includes an A / D converter 11a, a digital signal processing circuit 12a, a D / A converter 13a, and a phase shifter 14 as a feedback circuit. A digital amplifier 105 is formed by the A / D converter 11a, the digital signal processing circuit 12a, and the D / A converter 13a. Except for the digital signal processing circuit 12a, the operations of the components of the oscillation circuit of FIG. 5 are the same as those of FIG.

  In FIG. 5, the A / D converter 11a is a noise shaping type A / D converter. Specifically, for example, the A / D converter 11a performs ΔΣ modulation on an analog input signal to the A / D converter 11a, thereby outputting a noise-shaped ΔΣ modulation signal. The digital signal processing circuit 12a performs predetermined digital signal processing on the output signal of the A / D converter 11a, and outputs the digital signal after the digital signal processing to the D / A converter 13a. The D / A converter 13a converts the output signal of the digital signal processing circuit 12a into an analog signal and outputs the analog signal. The phase shifter 14 provides the A / D converter 11a with a phase shift signal obtained by shifting the phase of the output signal of the D / A converter 13a.

  Similarly to the oscillation circuit of FIG. 2, in the oscillation circuit of FIG. 5, the output signal of the D / A converter 13a is amplified with respect to the input signal of the A / D converter 11a. For this reason, the gain (loop gain) in the feedback loop is 1 or more. In addition, the phase shifter 14 shifts the phase of the input signal to itself so that the phase change when it makes a round in the feedback loop becomes 360 degrees or more. Thereby, the oscillation condition is satisfied, and for example, an analog sine wave oscillation signal is obtained from the phase shifter 14 as an analog output signal of the oscillation circuit. In FIG. 5, the output signal of the A / D converter 11a is led to the outside of the oscillation circuit via the terminal 16 as a digital output signal of the oscillation circuit.

  By using a noise shaping type A / D converter, as is well known (by oversampling technology), the quantization noise is driven from a predetermined target signal band to a high frequency band, and as a result, as a D / A converter It is possible to simplify the configuration of the functioning low-pass filter. However, in reality, the improvement in the operation speed of the A / D converter is limited, and thus the noise shaping process of the A / D converter may be insufficient.

  In such a case, a digital filter (not shown) provided in the digital signal processing circuit 12a realizes a low-pass filter having a steep attenuation characteristic, and after removing a quantization noise component outside the target signal band, Furthermore, noise shaping processing is performed to push quantization noise to a higher frequency band. As a result, the configuration of the low-pass filter in the analog signal processing stage, that is, the configuration of the D / A converter 13a can be further simplified.

  The noise shaping process in the digital signal processing circuit 12a is typically realized by ΔΣ modulation, and the output signal of the digital signal processing circuit 12a becomes a ΔΣ modulation signal expressed as a 1-bit pulse density modulation signal. However, the noise shaping process in the digital signal processing circuit 12a can be realized by adopting various other modulation methods such as PWM (pulse width modulation).

  When the noise shaping process is performed in the digital signal processing circuit 12a, the A / D converter 11a is an A / D converter that outputs a multi-bit digital signal, like the A / D converter 11 in FIG. It can also be a container. When the noise shaping process is performed by the A / D converter 11a, the noise shaping process by the digital signal processing circuit 12a can be omitted.

  Also, the digital signal processing circuit 12a can be provided with the same functions (multiplier and delay function) as those of the digital signal processing circuit 12 of FIG. 4, and thereby the oscillation circuit according to the fourth embodiment. The same effect can be obtained.

<< Sixth Embodiment >>
Similar to the modification of the oscillation circuit of FIG. 1 (FIG. 2) to the oscillation circuit of FIG. 4 (FIG. 5), the oscillation circuit of FIG. 3 according to the third embodiment can be modified. A sixth embodiment will be described as an embodiment showing a modification of the oscillation circuit of FIG.

  FIG. 6 is a block diagram showing the configuration of the oscillation circuit according to the sixth embodiment of the present invention. The oscillation circuit in FIG. 6 includes an A / D converter 11a, a digital signal processing circuit 12a, and a phase shifter 14a as a feedback circuit. A digital amplifier 106 is formed by the A / D converter 11a and the digital signal processing circuit 12a. Except for the digital signal processing circuit 12a, the operations of the components of the oscillation circuit of FIG. 6 are the same as those of FIG. The digital signal processing circuit 12a is the same as that in FIG.

  In the present embodiment, the output signal of the digital signal processing circuit 12a is directly given to the phase shifter 14a. The phase shifter 14a of FIG. 6 is configured in the same manner as that of FIG. 3, and the phase shifter 14a performs D / A conversion of the output signal of the digital signal processing circuit 12a and performs signal phase shift. Is called. That is, the low-pass filters that function as the D / A converter 13a in FIG. 5 are collected in the phase shifter 14a. And the request | requirement with respect to the function of the low-pass filter in the phase shifter 14a can be eased by the digital signal processing (specifically noise shaping process) of the digital signal processing circuit 12a.

  In other words, with the provision of the digital signal processing circuit, the demand for the function of the low-pass filter (such as the steepness of attenuation) is relaxed, and as a result, the low-pass filter can be concentrated in the phase shifter. It can also be said.

  Also in FIG. 6, the output signal (phase shift signal) of the phase shifter 14a is given to the A / D converter 11a. As in the oscillation circuit of FIG. 3, in the oscillation circuit of FIG. 6, the signal after D / A conversion in the phase shifter 14a with respect to the input signal of the A / D converter 11a (ie, the output signal of the phase shifter 14a). The gain is set to 1 or more. That is, the gain (loop gain) in the feedback loop is 1 or more. In addition, the phase shifter 14a shifts the phase of the input signal to itself so that the phase change when it goes around the feedback loop is 360 degrees or more. Thereby, the oscillation condition is satisfied, and for example, an analog sine wave oscillation signal is obtained from the phase shifter 14a as an analog output signal of the oscillation circuit. In FIG. 6, the output signal of the A / D converter 11a is led to the outside of the oscillation circuit via the terminal 16 as a digital output signal of the oscillation circuit.

<< Seventh Embodiment >>
A control circuit for controlling the contents of digital signal processing in the digital signal processing circuit may be added to the oscillation circuit of FIG. An embodiment in which a control circuit is added to the oscillation circuit of FIG. 4 will be described as a seventh embodiment.

  FIG. 7 is a block diagram showing the configuration of the oscillation circuit according to the seventh embodiment of the present invention. The oscillation circuit of FIG. 7 is different from the oscillation circuit of FIG. 4 in that a control circuit 15 is added, and the oscillation circuits of FIGS. 4 and 7 are the same in other points. The explanation will focus on the differences between the two.

  The control circuit 15 includes waveform observation means for observing the output signal waveform of the oscillation circuit provided outside the loop for generating the oscillation signal. The control circuit 15 controls the digital signal processing circuit 12 so as to maintain a desired waveform while observing the waveform of the output signal of the oscillation circuit.

  Specifically, in the oscillation circuit of FIG. 7, the control circuit 15 refers to the output signal of the A / D converter 11 and controls the content of the signal processing by the digital signal processing circuit 12 based on this output signal. As a result, the output signal of the D / A converter 13 is controlled. Thus, it can be said that the output signal of the phase shifter 14 or the output signal of the A / D converter 11 is controlled.

  By performing the control by the control circuit 15, the characteristics of the oscillation circuit can be improved in various points. The characteristics here include amplitude stability, frequency stability, harmonic characteristic stability, and the like. Here, the harmonic characteristic stability is an index indicating whether or not the harmonic component in the oscillation signal increases with time.

  For example, the control circuit 15 generates an oscillation signal (for example, a sine output from the phase shifter 14) obtained based on a predetermined reference voltage as a reference for the amplitude of the oscillation signal and the output signal of the A / D converter 11. The amplitude signal of the wave oscillation signal) is sequentially compared, and the digital signal processing circuit 12 is controlled so that the state in which both are equal is maintained. For example, by changing the coefficient in the multiplier (see the fourth embodiment) provided in the digital signal processing circuit 12 as necessary, both are kept equal. Further, the operation reference voltage of the A / D converter 11 and / or the operation reference voltage of the D / A converter 13 may be controlled so that both are kept equal. By performing these controls, the amplitude stability of the oscillation circuit is improved.

  For example, let us consider a case where the oscillation circuit of FIG. 7 functions as a sine wave oscillation circuit for generating a sine wave oscillation signal. In this case, the control circuit 15 observes the distortion rate of an oscillation signal (for example, a sine wave oscillation signal output from the phase shifter 14) obtained based on the output signal of the A / D converter 11, and the distortion rate Is increased, the gain of the digital amplifier 104 is decreased by controlling the digital signal processing circuit 12 in order to suppress this increase. This makes it possible to reduce the distortion rate.

  In addition, for example, the control circuit 15 may generate an oscillation frequency (for example, a phase shifter 14) obtained based on a predetermined reference frequency as a reference of the oscillation frequency (frequency of the oscillation signal) and the output signal of the A / D converter 11. And the digital signal processing circuit 12 are controlled so that the two are kept equal. For example, by changing the delay amount of the signal by the delay device (see the fourth embodiment) provided in the digital signal processing circuit 12 as necessary, both are kept equal. Alternatively, for example, when the oscillation frequency is higher than the reference frequency, the delay device provided in the digital signal processing circuit 12 is caused to function to lower the oscillation frequency. By performing these controls, the frequency stability of the oscillation circuit is improved.

  Further, for example, the control circuit 15 observes the waveform of an oscillation signal (for example, a sine wave oscillation signal output from the phase shifter 14) obtained based on the output signal of the A / D converter 11, and converts it into the oscillation signal. Monitor the included harmonic components. When the harmonic component increases, for example, the digital signal processing circuit 12 is controlled to control the amplification factor of the digital amplifier 104, thereby reducing the harmonic component. Further, if a harmonic component is generated due to nonlinearity in the signal processing of the digital signal processing circuit 12, the digital signal processing circuit 12 is caused to perform a process for correcting the harmonic component. For example, the inverse characteristics of the nonlinearity are superimposed on the signal. This is realized by, for example, a convolution calculation by a DSP (Digital Signal Processor). By performing these controls, the harmonic characteristic stability is improved and the noise characteristic is also improved.

<< Eighth Embodiment >>
Similar to the configuration of the oscillation circuit of FIG. 7 by adding the control circuit 15 to the oscillation circuit of FIG. 4, a similar control circuit may be added to the oscillation circuit of FIG. An embodiment in which a control circuit is added to the oscillation circuit of FIG. 5 will be described as an eighth embodiment.

  FIG. 8 is a configuration block diagram of an oscillation circuit according to the eighth embodiment of the present invention. The oscillation circuit of FIG. 8 is different from the oscillation circuit of FIG. 5 in that a control circuit 15 is added, and the oscillation circuits of FIGS. 5 and 8 are the same in other points.

  The control circuit 15 provided in the oscillation circuit of FIG. 8 has the same function as that of the control circuit 15 of FIG. 7, and all items described in the seventh embodiment are the same as in the present embodiment unless there is a contradiction. Also applies. Of course, when the matters described in the seventh embodiment are applied to this embodiment, the difference between 11 and 11a, the difference between 12 and 12a, the difference between 13 and 13a, and the difference between 104 and 105 are It will be ignored.

<< Ninth Embodiment >>
Similar to the configuration of the oscillation circuit of FIG. 7 by adding the control circuit 15 to the oscillation circuit of FIG. 4, a similar control circuit may be added to the oscillation circuit of FIG. An embodiment in which a control circuit is added to the oscillation circuit of FIG. 6 will be described as a ninth embodiment.

  FIG. 9 is a configuration block diagram of an oscillation circuit according to the ninth embodiment of the present invention. The oscillation circuit of FIG. 9 is different from the oscillation circuit of FIG. 6 in that a control circuit 15 is added, and the oscillation circuits of FIGS. 6 and 9 are the same in other points.

  The control circuit 15 provided in the oscillation circuit of FIG. 9 has the same function as that of the control circuit 15 of FIG. 7, and all the items described in the seventh embodiment are the same as in the present embodiment unless there is a contradiction. Also applies. Of course, when the matters described in the seventh embodiment are applied to this embodiment, the difference between 11 and 11a, the difference between 12 and 12a, the difference between 14 and 14a, and the difference between 104 and 106 are It will be ignored.

<< Common items of each embodiment >>
Hereinafter, common items of the above-described embodiments will be described.

  The digital output signal obtained from the oscillation circuit of each embodiment described above is used in various forms as a stable digital oscillation signal. For example, it is used for electronic musical instruments and experimental signal generators. Further, when the digital output signal is a multi-bit digital signal, there are advantages such that it can be directly supplied to a computer or can be easily placed on a digital audio interface. When the digital output signal is a 1-bit PDM signal, a high-efficiency amplifier (power amplifier) can be formed by driving the switching circuit with the digital output signal.

  The phase shifters (14 and 14a) also have a function as a filter that attenuates a signal having an unnecessary frequency. For this reason, white noise (noise caused by quantization error, etc.) and harmonics generated in a D / A converter or digital signal processing circuit are separated from the oscillation frequency by the filter effect of the phase shifter. (In the phase shifter of FIG. 11, the higher the frequency, the lower the frequency). That is, by adopting a configuration in which the D / A converter (and the digital signal processing circuit) and the phase shifter are cascade-connected and the output signal of the phase shifter is returned to the A / D converter, the D / A converter ( In addition, it is possible to obtain an effect of suppressing noise inevitably generated in the digital signal processing circuit), and as a result, an oscillation signal having excellent characteristics can be obtained.

  In addition, noise shaping processing is performed inside the digital amplifier, and signal processing is performed with a noise shaping bitstream signal typified by a 1-bit signal, so that the noise shaping bitstream signal is a digital signal and analog. The D / A conversion function can be realized by a simple low-pass filter by taking advantage of the characteristic of including the signal component (analog signal waveform). As a result, it is possible to omit a dedicated component (such as a comparator) for realizing the D / A converter, thereby simplifying the configuration and reducing the number of components.

  The phase shifter, which is a component of the oscillation circuit, is generally composed of a capacitor and a resistor, and the component circuit is substantially the same as that of the low-pass filter. Therefore, when a noise shaping bitstream signal is handled, a low-pass filter for realizing the D / A conversion function can be provided in the phase shifter to further reduce the number of parts.

  In addition, the oscillation circuit (oscillation device) according to the present invention can be configured as various types of oscillation circuits. For example, it can be configured as a phase-shifting oscillation circuit, or can be configured as a Wien bridge oscillation circuit. In the Wien bridge oscillation circuit, a band-pass filter is used as a feedback circuit. Therefore, the band-pass filter may have a function as a low-pass filter for realizing a D / A conversion function.

  In addition, since there is a section processed with a digital signal in the feedback loop (feedback loop) of the oscillation circuit, the digital signal processing circuit can be inserted into that section. As a result, functions that are normally difficult to realize can be realized in the analog circuit, and the degree of freedom in the configuration of the oscillation circuit is improved.

  In addition, by observing the output signal of the oscillation circuit and providing a control circuit for changing the characteristics of the digital amplifier based on the observation result, the characteristics as the analog oscillation circuit can be changed. Various characteristics can be improved by appropriate control by the control circuit.

1 is a configuration block diagram of an oscillation circuit according to a first embodiment of the present invention. FIG. 5 is a configuration block diagram of an oscillation circuit according to a second embodiment of the present invention. FIG. 6 is a configuration block diagram of an oscillation circuit according to a third embodiment of the present invention. FIG. 6 is a configuration block diagram of an oscillation circuit according to a fourth embodiment of the present invention. FIG. 10 is a configuration block diagram of an oscillation circuit according to a fifth embodiment of the present invention. FIG. 10 is a configuration block diagram of an oscillation circuit according to a sixth embodiment of the present invention. FIG. 10 is a configuration block diagram of an oscillation circuit according to a seventh embodiment of the present invention. FIG. 10 is a configuration block diagram of an oscillation circuit according to an eighth embodiment of the present invention. FIG. 10 is a configuration block diagram of an oscillation circuit according to a ninth embodiment of the present invention. It is a figure which shows the example of an internal circuit of the D / A converter which can be utilized as a D / A converter of FIG. It is a figure which shows the example of an internal circuit of the phase shifter of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 11a A / D converter 12, 12a Digital signal processing circuit 13, 13a D / A converter 14, 14a Phase shifter 15 Control circuit 16 Terminal 101-106 Digital amplifier

Claims (9)

An A / D converter for A / D converting an analog input signal;
A D / A converter for D / A converting the output signal of the A / D converter;
Phase-shifting means for phase-shifting the output signal of the D / A converter and outputting the phase-shifted signal obtained by the phase-shifting to the A / D converter;
Output means for outputting the output signal of the A / D converter as a digital output signal of the oscillation device,
An oscillation apparatus, wherein an output signal of the D / A converter is amplified with respect to an input signal to the A / D converter. 2. The oscillation device according to claim 1, wherein a noise shaping type A / D converter is used as the A / D converter. An A / D converter for A / D converting an analog input signal;
A digital signal processing unit that performs predetermined digital signal processing on the output signal of the A / D converter;
A D / A converter for D / A converting the output signal of the digital signal processing unit;
Phase-shifting means for phase-shifting the output signal of the D / A converter and outputting the phase-shifted signal obtained by the phase-shifting to the A / D converter;
Output means for outputting the output signal of the A / D converter as a digital output signal of the oscillation device,
An oscillation apparatus, wherein an output signal of the D / A converter is amplified with respect to an input signal to the A / D converter. 4. The oscillation device according to claim 3, wherein a noise shaping type A / D converter is used as the A / D converter. 4. A control means for controlling the output signal of the D / A converter by controlling the digital signal processor based on the output signal of the A / D converter. The oscillation device according to claim 4. A noise shaping type A / D converter for A / D converting an analog input signal;
Phase-shifting means for phase-shifting the output signal of the A / D converter while performing D / A conversion, and outputting the phase-shifted signal obtained by the phase shift to the A / D converter;
Output means for outputting the output signal of the A / D converter as a digital output signal of the oscillation device,
An oscillation device characterized in that a gain of a signal after D / A conversion by the phase shift means with respect to an input signal to the A / D converter is 1 or more. An A / D converter for A / D converting an analog input signal;
A digital signal processing unit that performs predetermined digital signal processing on the output signal of the A / D converter;
Phase-shifting means for phase-shifting the output signal of the digital signal processing unit while performing D / A conversion, and outputting the phase-shifted signal obtained by the phase-shifting to the A / D converter;
Output means for outputting the output signal of the A / D converter as a digital output signal of the oscillation device,
Noise shaping processing is performed in at least one of the A / D converter and the digital signal processing unit,
An oscillation device characterized in that a gain of a signal after D / A conversion by the phase shift means with respect to an input signal to the A / D converter is 1 or more. The digital signal processing unit is further controlled based on an output signal of the A / D converter to further control a signal after D / A conversion by the phase shift means. Item 8. The oscillation device according to Item 7. The A / D converter is a ΔΣ modulator that ΔΣ modulates an input signal to itself and outputs a ΔΣ modulation signal. The oscillation device according to claim 8.

Images