JP2000059153A - Digital switching amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the power efficiency of pulse amplification when the amplitude level of input analog signals is minute and to improve an S/N. SOLUTION: In this switching amplifier, after the difference value S1' of the input analog signals S1 inputted to an input terminal 1 and feedback signals S5 negatively fed back by a feedback circuit FC is integrated in a difference integrator 2, it is converted to a quantized output signal S3 in a quantizer 3. At the time, the input analog signals S1 are also inputted to an input level detection part 9 and the amplitude level is detected and outputted to a constant voltage control part 6 as an input level detection signal S9. The constant voltage control part 6 sets the voltage level of the constant voltage V of a pulse amplifier 4 based on the input level detection signal S9 and outputs a constant voltage signal S6 to the pulse amplifier 4. Thus, the pulse amplifier 4 pulse-amplifies the quantized output signals 33 by the constant voltage V of the voltage level corresponding to the amplitude level of the input analog signals S1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier for amplifying an analog signal such as an audio signal, and more particularly to a digital switching amplifier for pulse-amplifying a quantized signal obtained by delta-sigma modulation as a switching control signal. Things.

[0002]

2. Description of the Related Art In recent years, as a signal processing method of a high-efficiency power amplifier for an acoustic signal realizing a small size, large output, and high S / N,
A digital switching amplifier using delta-sigma modulation has been provided. This is based on pulse density modulation (PD) by delta-sigma modulation of the input analog signal.
M) By obtaining a signal and spreading the energy of the carrier signal, power can be efficiently amplified with a simple configuration.

A conventional high efficiency power amplifier to which delta sigma modulation is applied is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-63457.

Here, a digital switching amplifier as a power amplifier to which delta sigma modulation according to the prior art is applied will be described with reference to FIG.

As shown in FIG. 10, the digital switching amplifier comprises an input terminal 81, a differential integrator 82,
Bit quantizer 83, pulse amplifier 84, attenuator 85,
Delay device 90, clock oscillator 91, low-pass filter 8
7. The output terminal 88 is provided. The delta-sigma modulation unit AD is composed of the difference integrator 82 and the one-bit quantizer 83. Also, the pulse amplifier 84
A feedback circuit FC for negatively feeding back the output signal of the differential integrator 82 as an input signal of the differential integrator 82 is configured.
Above the attenuator 85 and the delay unit 90 are provided.

The difference integrator 82 uses the input analog signal (audio signal) S81 input to the input terminal 81 and the feedback signal S90 from the feedback circuit FC as input signals, and integrates the difference value S81 'between these two signals. It is an integrator / adder group that outputs the difference integration signal S82.

The one-bit quantizer 83 determines the polarity of the difference integrated signal S82 and outputs a quantized signal S83 converted into a binary (1 bit) digital signal.

[0008] The pulse amplifier 84 has a quantized output signal S8 which is a digital output signal of the 1-bit quantizer 83.
3 is a high-speed switching pulse amplifier that amplifies power with a constant voltage V as a switching control signal and outputs a pulse amplified signal S84.

The low-pass filter 87 is a filter that generates an output signal S87 by removing unnecessary signal components from the amplified pulse signal S84 output from the pulse amplifier 84, and includes, for example, a coil and a capacitor.

The attenuator 85 and the delay unit 90 are provided on a feedback circuit FC for negatively feeding the pulse amplified signal S84 to the input side of the difference integrator 82. The pulse amplified signal S84 input to the attenuator 85 is attenuated to the attenuated signal S85 and input to the delay unit 90. The delay unit 90 delays the attenuated pulse amplified signal S84 (attenuated signal S85) with a clock having an arbitrary frequency, and is configured by, for example, a D-type flip-flop. Here, a clock pulse of an arbitrary frequency is supplied from the clock oscillator 91 to the delay unit 90.

[0011] The digital switching amplifier to which the delta-sigma modulation configured as described above is applied operates as follows.

When the input analog signal S81 is input to the input terminal 81, the pulse amplified signal S84 output from the pulse amplifier 84 is fed back by the feedback circuit FC through the attenuator 85 and the delay unit 90 to the negative feedback signal S90. Is integrated by the difference integrator 82 to output a difference integration signal S82. The difference integration signal S82 is 1
The signal is converted into a quantized signal S83 which is a 1-bit digital signal by the bit quantizer 83. Quantized signal S83
Is power-amplified by the pulse amplifier 84 and converted into a pulse amplified signal S84. Unnecessary signal components are removed from the pulse amplified signal S84 by a low-pass filter 87 and output from an output terminal 88 as an output signal S87. At the same time, the pulse amplified signal S84 is
5 and is input to the delay unit 90 and delayed by a time corresponding to the repetition period of the clock supplied from the clock oscillator 91. A feedback signal S90, which is a digital signal subjected to the delay processing, is passed through a feedback circuit FC to a high-order differential integrator 82.
Negative feedback.

[0013]

However, in the digital switching amplifier having the above-mentioned conventional structure, the quantized output signal is always pulse-amplified at a constant voltage of a certain voltage level regardless of the amplitude level of the input analog signal. Therefore, when the amplitude level of the input analog signal is small, the power efficiency is poor, and when the voltage level of the switching constant voltage is high, the noise level increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to improve the power efficiency of pulse amplification when the amplitude level of an input analog signal is very small and to reduce the S / N. It is to provide a digital switching amplifier that can be improved.

[0015]

According to a first aspect of the present invention, there is provided a digital switching amplifier, comprising: a delta-sigma modulator for generating a quantized output signal by performing a delta-sigma modulation on an input analog signal; A power amplifying unit that generates a pulse-amplified switching signal by switching a constant voltage application based on the quantized output signal, wherein a constant voltage control unit that sets a voltage level of the constant voltage is provided. It is characterized by having.

With the above configuration, the voltage level of the constant voltage that is switched based on the quantized output signal in the power amplifier can be changed by the constant voltage controller according to desired conditions.

Therefore, by setting the voltage level of the constant voltage in accordance with the amplitude level of the input analog signal and performing pulse amplification, power efficiency can be improved and S / N can be improved. In addition, the volume can be adjusted with a simple configuration.

According to a second aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the first aspect, the constant voltage control unit is configured to control the constant voltage control unit in proportion to an amplitude level of the input analog signal. A constant voltage control circuit for setting a voltage level of the constant voltage is provided.

According to the above configuration, in addition to the operation of the first aspect, when the amplitude level of the input analog signal is large, the constant voltage of the power amplifying unit is increased to correspond to the amplitude level of the input analog signal. When the amplitude level is low, the constant voltage of the power amplifier can be set to a low voltage level.

Therefore, in the power amplifier, the input analog signal having a small amplitude level is pulse-amplified by a constant voltage having a low voltage level, thereby improving the power efficiency when the amplitude level of the input analog signal is small, and
Noise can be reduced and S / N can be improved.

According to a third aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the first or second aspect, the digital switching amplifier detects an amplitude level of the input analog signal, and the constant voltage control section performs An input level detection unit for outputting an input level detection signal serving as a reference for setting the voltage level of the constant voltage is provided.

According to the above configuration, in addition to the function of the first or second aspect, the input level detection section detects the amplitude level of the input analog signal and outputs an input level detection signal. Based on this, the voltage level of the constant voltage of the power amplification unit can be set by the constant voltage control unit.

Therefore, the voltage level of the constant voltage can be automatically set according to the amplitude level of the input analog signal, so that power efficiency can be improved and
Noise when the amplitude level of the input analog signal is small can be reduced, and S / N can be improved.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] The following will describe one embodiment of the present invention with reference to FIGS.

The digital switching amplifier according to the present embodiment is a circuit for performing pulse amplification by applying delta-sigma modulation. In particular, a constant voltage for performing pulse amplification is automatically set according to the amplitude level of an input analog signal. Circuit.

As shown in FIG. 1, the digital switching amplifier includes an input terminal 1, a difference integrator 2, a quantizer 3, a pulse amplifier (power amplifier) 4, an attenuator 5, a constant voltage controller 6, a low-pass controller. It comprises a filter 7, an output terminal 8, and an input level detector 9. The delta-sigma modulation unit AD is composed of the difference integrator 2 and the quantizer 3 described above. Further, a feedback circuit FC for negatively feeding back the output signal of the pulse amplifier 4 as an input signal of the difference integrator 2 is configured, and the attenuator 5 is provided on the feedback circuit FC.

The difference integrator 2 receives the input analog signal (audio signal) S1 input to the input terminal 1 and the feedback signal S5 as input signals, and calculates a difference value S between these two signals.
This is a high-order difference integrator composed of an integrator / adder group that outputs a difference integration signal S2 obtained by integrating 1 'to the quantizer 3.

The quantizer 3 determines the polarity of the difference integration signal S2 input from the difference integrator 2, converts the polarity into a quantized output signal S3 which is a binary digital signal, and converts the signal into a delta-sigma modulator AD. Is output to the pulse amplifier 4 as an output signal. Note that the quantization threshold value of the quantization output signal S3 is set optimally for the assumed sampling frequency.

The pulse amplifier 4 performs high-speed switching by using the quantized output signal S3 input from the delta-sigma modulation section AD as a switching control signal.
This is a high-speed switching pulse amplifier that amplifies power with a constant voltage V. Then, the obtained pulse amplified signal (switching signal) S4 is input to the low-pass filter 7 and the attenuator 5 on the feedback circuit FC. Here, the constant voltage V
Is set at a voltage level by the constant voltage control unit 6, and is supplied as a constant voltage signal S6.

The attenuator 5 is provided on the feedback circuit FC, and outputs the amplified pulse signal S4 output from the pulse amplifier 4.
Is fed back as an input signal to the difference integrator 2.

The low-pass filter 7 is a filter that outputs to the output terminal 8 an output signal S7 obtained by removing unnecessary signal components from the pulse amplified signal S4 input from the pulse amplifier 4, and includes, for example, a coil and a capacitor. Etc.

The input level detecting section 9 is a circuit for outputting to the constant voltage control section 6 an input level detecting signal S9 which detects the amplitude level of the input analog signal S1 inputted from the input terminal 1. It is composed mainly of an IC such as a level meter driver.

The constant voltage control section 6 performs the following based on the input level detection signal S9 input from the input level detection section 9.
The voltage level of the constant voltage V of the pulse amplifier 4 is set and controlled. The constant voltage V at the voltage level set by the constant voltage control unit 6 is input to the pulse amplifier 4 as a constant voltage signal S6.

The operation of the digital switching amplifier configured as described above will be described as follows.

In the above digital switching amplifier,
Input analog signal S such as audio signal to input terminal 1
1 and a feedback signal S5 negatively fed back via the attenuator 5 by the feedback circuit FC, a difference integrator 2 integrates a difference value S1 'between the two signals to generate a difference integration signal S2. The quantizer 3 converts the differential integration signal S2 into a quantized output signal S3 which is a digital signal.

The input analog signal S1 is also input to the input level detector 9. The input level detector 9 detects the amplitude level of the input analog signal S1 and outputs the input level detection signal S9 so that the constant voltage V of the corresponding voltage level is automatically set by the constant voltage controller 6. Then, in the constant voltage control unit 6, the first constant voltage control circuit (constant voltage control circuit) 6a (FIG. 2) converts the constant voltage signal S6 of the voltage level set in two stages based on the input level detection signal S9. Output to the pulse amplifier 4.

Thus, the pulse amplifier 4 pulse-amplifies the quantized output signal S3 with the constant voltage V by the constant voltage signal S6 to generate a pulse amplified signal S4.

The low-pass filter 7 outputs the pulse amplified signal S
The output signal S7 is output to the output terminal 8 after removing unnecessary signal components from the output signal S4. Further, the pulse amplification signal S4 is input to the attenuator 5 and the feedback signal S5 is input to the difference integrator 2 by the feedback circuit FC.

The switching frequency, that is, the sampling frequency of the 1-bit signal is, for example, 16 × 44.1 kHz in order to obtain a desired frequency characteristic and dynamic range.
= 0.7056 MHz, 32 x 44.1 kHz = 1.4112 MHz, 64 x 44.1 kHz
z can be set to 2.8224 MHz.

Further, details of the operation of the constant voltage control section 6 will be described with reference to FIGS.

The constant voltage control section 6 of the digital switching amplifier according to the present embodiment is provided with a first constant voltage control circuit (constant voltage control circuit) 6a.

As shown in FIG. 2, when the amplitude level of the input analog signal S1 is large based on the input level detection signal S9 which detects the amplitude level of the input analog signal S1, Sets the constant voltage V to a high voltage level, and sets the constant voltage V to a low voltage level when the amplitude level is small.

For example, the first constant voltage control circuit 6a
The input analog signal S1 is 1 for the maximum input signal level.
If / 以上 8 or more, the voltage level of the constant voltage V is set to V0, and if it is 1 / √8 or less with respect to the maximum input signal level, the voltage level of the constant voltage is set to V0 / √8. Can be

The above switching method is based on music information. That is, it is known that, when the input analog signal S1 is music information, the output is about 1/8 W of the maximum output on average even at the maximum output. Therefore, the voltage level of the constant voltage V necessary for the pulse amplification of the music information is V0 / $ 8. Therefore, the first constant voltage control circuit 6a determines whether the input analog signal S1 is music information or non-music information.
When switching the voltage levels of the above. That is, pulse amplification of music information can be performed with ideal power efficiency. Further, since the noise level at the time of pulse amplification of music information can be greatly reduced, the S / N can be improved.

Then, the constant voltage control section 6 outputs a constant voltage V of the voltage level set by the first constant voltage control circuit 6a.
Is supplied to the pulse amplifier 4 as a constant voltage signal S6.

The attenuator 5 works in conjunction with the first constant voltage control circuit 6a of the constant voltage control section 6 to keep the feedback amount of the pulse amplified signal S4 constant according to the voltage level of the constant voltage V. To be adjusted. That is,
When the voltage level of the constant voltage V of the pulse amplifier 4 is V0, the attenuation is adjusted so as to reduce the feedback amount of the pulse amplified signal S4, and when the voltage level is V0 / 8, the feedback amount of the pulse amplified signal S4 is reduced. Adjust the attenuation to increase.

As described above, when the volume is controlled by the constant voltage adjustment, the amount of feedback of the pulse amplified signal S4 is set to the value of the constant voltage V by setting the amount of attenuation in accordance with the amount of amplification (constant voltage V). It can be kept constant regardless of Therefore, even if the value of the constant voltage V changes, the analog value included in the quantized output signal S3 does not change.

Here, FIG. 3 to FIG. 5 show signal levels when a 1 kHz sine wave small signal is pulse-amplified by the above digital switching amplifier at a constant voltage V of voltage levels V0, V0 / 8, V0 / 8, respectively. 3 shows a graph of noise level distribution. V0 is 35V.

As can be seen from the distribution diagram, the lower the voltage level of the constant voltage V, the lower the noise level. That is, the noise level is lower by about 10 dB when the pulse is amplified at the voltage level V0 / √8 than when the pulse is amplified at the voltage level V0 (FIG. 3) (FIG. 4), and the pulse is amplified at the voltage level V0 / 8. It can be seen that the noise level is further reduced by performing (FIG. 5).

In the graphs of the distribution of the signal level and the noise level (FIGS. 3 to 5), as described above, the feedback amount of the pulse amplified signal S4 is kept constant according to the amplification amount (constant voltage V). By setting optimally as described above, almost the same graph can be obtained regardless of the constant voltage V.

As described above, the digital switching amplifier according to the present embodiment includes a delta-sigma modulation unit AD that generates a quantized output signal S3 by delta-sigma-modulating the input analog signal S1 and a quantized output signal S3. A voltage level of the constant voltage V is set in a digital switching amplifier having a pulse amplifier (power amplifying unit) 4 that generates a pulse amplified signal (switching signal) S4 by switching the application of the constant voltage V based on the pulse. Constant voltage control section 6 and input analog signal S1
Of the input level detection signal S, which serves as a reference for setting the voltage level of the constant voltage V
9 is provided.

Thus, the constant voltage controller 6 can automatically set the voltage level of the constant voltage V according to the amplitude level of the input analog signal S1.

Therefore, by changing the voltage level of the constant voltage V, which is switched by the pulse amplifier 4 based on the quantized output signal S3, according to desired conditions, power efficiency can be improved and noise can be reduced. do it,
S / N can be improved.

Further, in the digital switching amplifier according to the present embodiment, the constant voltage controller 6 controls the input analog signal S1 in proportion to the amplitude level of the input analog signal S1.
1 is a constant voltage control circuit that sets the constant voltage V of the pulse amplifier 4 to a high voltage level when the amplitude level is large, and sets the constant voltage V of the pulse amplifier 4 to a low voltage level when the amplitude level is small. 6a.

Thus, the voltage level of the constant voltage V of the pulse amplifier 4 can be set in proportion to the amplitude level of the input analog signal S1.

Therefore, in the pulse amplifier 4, the power efficiency when the amplitude level of the input analog signal S1 is small is improved by pulse-amplifying the input analog signal S1 having a small amplitude level with the constant voltage V having a low voltage level. , Noise, and S / N can be improved.

By arranging the variable resistor immediately after the input terminal 1, the volume can be adjusted.

Embodiment 2 Another embodiment of the present invention is described below with reference to FIGS. 1 and 6. For the sake of convenience, the same members as those described in the first embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

The digital switching amplifier according to the present embodiment differs from the digital switching amplifier according to the first embodiment in that the input level detection unit 9 finely detects the amplitude level of the input analog signal S1.
In this configuration, the voltage level of the constant voltage V at which switching is performed by the pulse amplifier 4 is finely and automatically set by the constant voltage control unit 6.

As shown in FIG. 1, the digital switching amplifier comprises an input terminal 1, a difference integrator 2, a quantizer 3, a pulse amplifier (power amplifier) 4, an attenuator 5, a constant voltage controller 6, It comprises a low-pass filter 7, an output terminal 8, and an input level detector 9. It should be noted that the delta-sigma modulator AD is obtained from the difference integrator 2 and the quantizer 3.
Is configured. Further, a feedback circuit FC for negatively feeding back the output signal of the pulse amplifier 4 as an input signal of the difference integrator 2 is configured, and the attenuator 5 is provided on the feedback circuit FC.

In particular, the constant voltage control section 6 of the digital switching amplifier according to the present embodiment is provided with a second constant voltage control circuit (constant voltage control circuit) 6b (FIG. 6).

As shown in FIG. 6, the second constant voltage control circuit 6b detects the input level of the input analog signal S1 in multiple stages.
9, the constant voltage V is divided into voltage levels V0, V
1,..., Vn (V0> Vn). That is, the second constant voltage control circuit 6b sets the voltage level V0 if the amplitude level of the input analog signal S1 is the maximum input signal level in the input level detection section 9, and the input signal levels lower than that are in proportion. The voltage levels V1,..., Vn are set. Thereby, the constant voltage control unit 6 supplies the constant voltage V of the voltage level set by the second constant voltage control circuit 6b to the pulse amplifier 4 as the constant voltage signal S6.

For example, if the input level detecting section 9 detects a signal having a dynamic range of 90 dB by 2 dB and outputs an input level detecting signal S9, the constant voltage controlling section 6
Thus, the constant voltage V can be controlled to 45 voltage levels in proportion to the amplitude level of the input level detection signal S9. And, the finer the voltage level of the constant voltage V, the smoother the difference in volume.

The operation of the above-described digital switching amplifier will be described below.

In the above digital switching amplifier,
Input analog signal S such as audio signal to input terminal 1
1 and a feedback signal S5 negatively fed back via the attenuator 5 by the feedback circuit FC, a difference integrator 2 integrates a difference value S1 'between the two signals to generate a difference integration signal S2. The quantizer 3 determines the polarity of the difference integration signal S2 and converts it to a quantization output signal S3 which is a binary (1 bit) digital signal.

The input analog signal S1 is also input to the input level detector 9 to detect the amplitude level finely.
An input level detection signal S9 is output so that the constant voltage control section 6 automatically sets a constant voltage V having a voltage level proportional to the amplitude level. The constant voltage control section 6 outputs a constant voltage signal S6 having a voltage level set in the second constant voltage control circuit 6b based on the input level detection signal S9.

As a result, the pulse amplifier 4 pulse-amplifies the quantized output signal S3 with the constant voltage V based on the constant voltage signal S6.

The low-pass filter 7 removes unnecessary signal components from the amplified pulse signal (switching signal) S 4 and outputs the output signal S 7 to the output terminal 8. The feedback circuit FC inputs the pulse amplified signal S4 to the attenuator 5 and inputs the feedback signal S5 to the difference integrator 2.

The attenuator 5 works in conjunction with the second constant voltage control circuit 6b of the constant voltage control unit 6 to keep the feedback amount of the pulse amplified signal S4 constant according to the voltage level of the constant voltage V. To be adjusted. For example, when the voltage level of the constant voltage V of the pulse amplifier 4 is changed to increase, the attenuator 5 adjusts the amount of attenuation in a direction to reduce the feedback amount of the pulse amplified signal S4 in conjunction therewith.

As described above, when controlling the volume by adjusting the constant voltage, the amount of feedback of the pulse amplified signal S4 is set to the value of the constant voltage V by setting the amount of attenuation according to the amount of amplification (constant voltage V). It can be kept constant regardless of Therefore, even if the value of the constant voltage V changes, the analog value included in the quantized output signal S3 does not change.

As described above, the digital switching amplifier according to the present embodiment outputs the input level detection signal S9 in which the amplitude level of the input analog signal S1 is finely detected in multiple steps by the input level detection section 9, and outputs the constant voltage. Control unit 6
In this configuration, a multi-step voltage level corresponding to the amplitude level of the input analog signal S1 is automatically set to the constant voltage V based on the input level detection signal S9.

As described above, the detection level of the amplitude level of the input analog signal S1 is made fine, and the voltage level of the constant voltage V is set finely, so that the sound volume difference in the sense of hearing becomes smooth.

Further, since the voltage level of the constant voltage V can always be set automatically and optimally in accordance with the amplitude level of the input analog signal S1, power efficiency can be improved and the amplitude level of the input analog signal S1 can be improved. Is small, the S / N can be improved.

Third Embodiment Still another embodiment of the present invention will be described below with reference to FIGS. Note that, for convenience of explanation, Embodiment 1
The same members as those described in the second embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The digital switching amplifier according to the present embodiment differs from the digital switching amplifiers of the first and second embodiments in that the input level detecting section 9 is not provided, and the voltage level of the constant voltage V can be set steplessly. The volume is adjusted by manually setting the voltage level of the constant voltage control unit 6 including the third constant voltage control circuit (constant voltage control circuit) 6c.

As shown in FIG. 7, the digital switching amplifier includes an input terminal 1, a difference integrator 2, a quantizer 3, a pulse amplifier (power amplifying unit) 4, an attenuator 5, a constant voltage control unit 6, a low-pass control unit. It comprises a filter 7 and an output terminal 8. The difference integrator 2 and the quantizer 3
A delta-sigma modulation unit AD is constituted by these. The output signal of the pulse amplifier 4 is divided by the difference integrator 2
A feedback circuit FC for performing a negative feedback as an input signal is provided, and the attenuator 5 is provided on the feedback circuit FC.

In particular, the constant voltage control section 6 of the digital switching amplifier according to the present embodiment is provided with a third constant voltage control circuit 6c (FIG. 8).

As shown in FIG. 8, the third constant voltage control circuit 6c includes a variable resistor 31 whose one end is grounded. The third constant voltage control circuit 6c includes a variable resistor 31
Is manually set, the voltage level of the constant voltage V can be set steplessly from 0 to V0. Thereby, the constant voltage control unit 6 supplies the pulse amplifier 4 with the constant voltage of the voltage level set by the third constant voltage control circuit 6c as the constant voltage signal S6.

For example, when the volume for adjusting the volume is linked to the variable resistor 31, the voltage level is set by the volume so that the volume can be adjusted even if the amplitude level of the input analog signal S1 is fixed. And noise can be reduced when the volume is low.

Here, as shown in FIG. 9, the attenuator 5
A variable resistor 32 provided with one terminal is provided, and the amount of feedback of the pulse amplification signal (switching signal) S4 can be adjusted by resistance division. Further, the variable resistor 32 is connected to the variable resistor 31 of the constant voltage controller 6.
In conjunction with, the feedback amount of the pulse amplified signal S4 is set to be kept constant.

For example, the variable resistor 31 of the constant voltage controller 6 and the variable resistor 32 of the attenuator 5 can be provided in a two-circuit one-package. Then, when the resistance value of the variable resistor 31 is changed in the direction of increasing the constant voltage V of the pulse amplifier 4, the resistance value of the variable resistor 32 on the feedback circuit FC is changed in the direction to decrease the feedback amount of the pulse amplified signal S4. Can be set to change.

As described above, when the volume is controlled by the constant voltage adjustment, the amount of attenuation (the resistance value of the variable resistor 32) is set in accordance with the amount of amplification (constant voltage V), so that the pulse amplified signal S4 is controlled. Feedback amount is constant voltage V
Can be kept constant regardless of the value of. Therefore, even if the value of the constant voltage V changes, the analog value included in the quantized output signal S3 does not change.

As described above, the digital switching amplifier according to the present embodiment is provided with the third constant voltage control circuit 6c in which the constant voltage control section 6 can set the voltage level of the constant voltage V steplessly. Configuration.

As a result, the voltage level of constant voltage V can always be optimally set according to the amplitude level of input analog signal S1, so that power efficiency can be improved and the amplitude level of input analog signal S1 can be improved. Is small, the S / N can be improved.

Further, the digital switching amplifier according to the present embodiment has a constant voltage V
Is set manually.

As a result, the input analog signal S1 can be amplified at an arbitrary gain. That is, the volume can be freely adjusted. Here, it is not necessary to detect the amplitude level of the input analog signal S1, and the amplitude level of the input analog signal S1 may be fixed. For example, by setting the voltage level with the volume, the amplitude level of the input analog signal S1 is fixed, the volume can be adjusted, and noise when the volume is low can be reduced.

The above embodiments do not limit the scope of the present invention, and various modifications can be made within the scope of the present invention.

[0088]

As described above, the digital switching amplifier according to the first aspect of the present invention is based on a delta-sigma modulation section that generates a quantized output signal by performing a delta-sigma modulation on an input analog signal and a quantized output signal. And a power amplifier for generating a pulse-amplified switching signal by switching the application of a constant voltage by using a constant voltage controller for setting the voltage level of the constant voltage.

Therefore, by setting the voltage level of the constant voltage corresponding to the amplitude level of the input analog signal and performing pulse amplification, the power efficiency can be improved and the S / N can be improved. Play. Further, there is an effect that the volume can be adjusted with a simple configuration.

According to the digital switching amplifier of the second aspect of the present invention, as described above, in addition to the configuration of the first aspect, the constant voltage control section controls the constant voltage in proportion to the amplitude level of the input analog signal. Is provided with a constant voltage control circuit for setting the voltage level.

Therefore, in addition to the effect of the configuration of claim 1, the power amplifier amplifies the input analog signal having a small amplitude level with a constant voltage of a low voltage level so that the amplitude level of the input analog signal is reduced. This has the effect of improving power efficiency when small, reducing noise, and improving S / N.

According to a third aspect of the present invention, a digital switching amplifier detects the amplitude level of the input analog signal in addition to the configuration of the first or second aspect.
The constant voltage control unit may include an input level detection unit that outputs an input level detection signal serving as a reference for setting the voltage level of the constant voltage.

Therefore, in addition to the effect of the first or second aspect, the voltage level of the constant voltage can be automatically set according to the amplitude level of the input analog signal. Therefore, the power efficiency can be improved, and the noise when the amplitude level of the input analog signal is small can be reduced, so that the S / N can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a configuration of a digital switching amplifier including a constant voltage control circuit shown in FIGS. 2 and 6.

FIG. 2 is an explanatory diagram schematically showing a configuration of a constant voltage control circuit provided in a constant voltage control unit of the digital switching amplifier according to one embodiment of the present invention.

3 is a graph showing signal level and noise level distributions when a 1 kHz sine wave small signal is pulse-amplified at a constant voltage V0 by the digital switching amplifier of FIG. 1 having the constant voltage control circuit shown in FIG. is there.

FIG. 4 shows the distribution of signal level and noise level when a 1 kHz sine wave small signal is pulse-amplified at a constant voltage V0 / √8 by the digital switching amplifier of FIG. 1 having the constant voltage control circuit shown in FIG. It is a graph shown.

5 shows signal level and noise level distributions when a 1 kHz sine wave small signal is pulse-amplified at a constant voltage V0 / 8 by the digital switching amplifier of FIG. 1 having the constant voltage control circuit shown in FIG. It is a graph.

FIG. 6 is an explanatory diagram schematically showing a configuration of a constant voltage control circuit provided in a constant voltage control unit of a digital switching amplifier according to another embodiment of the present invention.

7 is a block diagram schematically showing a configuration of a digital switching amplifier including the constant voltage control circuit shown in FIG.

FIG. 8 is an explanatory diagram schematically showing a configuration of a constant voltage control circuit provided in a constant voltage control unit of a digital switching amplifier according to another embodiment of the present invention.

FIG. 9 is an explanatory view schematically showing a configuration of an attenuator of the digital switching amplifier shown in FIG. 7;

FIG. 10 is a block diagram schematically showing a configuration of a digital switching amplifier according to a conventional technique.

[Explanation of symbols]

 AD delta sigma modulation unit 4 pulse amplifier (power amplification unit) 6 constant voltage control unit 6a constant voltage control circuit (constant voltage control circuit) 6b second constant voltage control circuit (constant voltage control circuit) 6c third constant voltage control Circuit (constant voltage control circuit) 9 Input level detector S1 Input analog signal S3 Quantized output signal S4 Pulse amplification signal (switching signal) S9 Input level detection signal V Constant voltage

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J064 AA02 BA03 BB02 BB07 BB12 BC08 BC11 BC16 BC19 BD02 5J091 AA01 AA24 AA41 CA36 CA41 FA02 HA26 HA29 HA33 KA15 KA17 KA23 KA31 KA32 KA42 KA53 MA13 SA05 TA01 A03 CA09 FA02 GR01 HA26 HA29 HA33 KA15 KA17 KA23 KA31 KA32 KA42 KA53 MA13 SA05 TA01 TA03 VL08

Claims (3)

[Claims] 1. A delta-sigma modulator for generating a quantized output signal by delta-sigma modulating an input analog signal, and generating a pulse-amplified switching signal by switching a constant voltage application based on the quantized output signal. A digital switching amplifier, comprising: a power amplifier configured to set a voltage level of the constant voltage. 2. The constant voltage control section according to claim 1, wherein said constant voltage control section includes a constant voltage control circuit for setting a voltage level of said constant voltage in proportion to an amplitude level of said input analog signal. Digital switching amplifier. 3. An input level detection section for detecting an amplitude level of the input analog signal and outputting an input level detection signal serving as a reference from which the constant voltage control section sets the voltage level of the constant voltage. 2. The method according to claim 1, wherein
Or the digital switching amplifier according to 2.