JP3461263B2 - Delta-sigma modulation amplifier - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to measures against unwanted radiation noise in a delta-sigma modulation amplifier. In particular, it relates to a circuit for avoiding tuner interference.

[0002]

2. Description of the Related Art Conventionally, as a delta-sigma modulation amplifier, the one described in Japanese Patent Application Laid-Open No. 05-63457 is known.

FIG. 3 is a block diagram of a conventional delta-sigma modulation amplifier, in which 1 is an input terminal to which analog signals are sequentially input, 2 is a feedback signal which is sequentially fed back with an acoustic signal of an input analog signal. A differential integrator that sequentially outputs a differential integrated signal obtained by integrating the difference between the 3 and 1 is a 1-bit quantizer that determines the polarity of the differential integrated signal and sequentially outputs a 1-bit digital signal, and 4 is a 1-bit quantizer. A pulse amplifier that amplifies digital signals sequentially output from 3 to output a power pulse signal, 5 is a low-pass filter that passes only frequency components in the audio band of the power pulse signal, and 7 is a power pulse signal as a feedback signal A feedback circuit for sending to the difference integrator 2 and a time constant controller 8 for determining an integration time constant of the difference integrator 2.

The operation of the delta-sigma modulation amplifier configured as described above will be described below.

First, the differential integrator 2 has an analog input signal such as a music signal which is sequentially input from the input terminal 1 and a feedback circuit 7.
Integrate the difference with the power pulse signal that is sequentially fed back from
The difference integration signals obtained as a result are sequentially output.

The integration time constant of the time difference integrator 2 is determined by the time constant controller 8 and is composed of, for example, a quadratic difference integrator as shown in FIG.

Next, the 1-bit quantizer 3 sequentially determines the polarities of the differential integration signals output from the differential integrator 2, and, for example, when the polarity is positive, the value is 1 and when it is negative, the value is 0. By sequentially outputting, a 1-bit digital signal can be obtained. Here, the 1-bit quantizer 3 is, for example, a comparator,
It is composed of a device such as a D-type flip-flop.

Next, the pulse amplifier 4 power-amplifies the sequentially input digital signals and converts them into power pulse signals. Here, as a device used for the pulse amplifier 4, a power MOSFE having a small voltage drop because the loss of the amplitude of the power pulse signal with respect to the power supply voltage causes a loss.
It is preferable to use T.

The low-pass filter 5 sequentially outputs analog power signals obtained after passing only the audio frequency band component of the power pulse signal supplied from the pulse amplifier 4 as an audio output signal from the output terminal.

On the other hand, the power pulse signals sequentially output from the pulse amplification section 4 are sequentially fed through the feedback circuit 7 to the differential integrator 2
Of the analog input signal sequentially input from the input terminal 1 and integrated.
By this negative feedback loop, self-excited oscillation is performed centering on the frequency according to the time constant determined by the time constant control unit 8, and as a result, noise included in the 1-bit digital signal output from the 1-bit quantizer 3 is generated. As for the component, since the differential integrator 2 is a second-order integrator, it increases as the frequency increases to 2
The curve becomes the following curve, and the amount of noise in a low frequency band such as an audio frequency band can be suppressed.

[0011]

In this conventional delta-sigma modulation amplifier, the self-excited oscillation frequency is set sufficiently high in order to reduce the amount of noise in the audio frequency band, that is, to improve the audio characteristics such as the SN ratio and the distortion rate. Therefore, the harmonic component contained in the power pulse signal causes reception interference of the tuner and the like, and the cost is inevitable because a strong shield case or the like is used as a countermeasure.

It is an object of the present invention to reduce unnecessary high frequency noise which may interfere with reception of a tuner without deteriorating audio characteristics.

[0013]

In order to solve the above-mentioned problems, a delta-sigma modulation amplifier according to the present invention has an analog input signal sequentially input from an input terminal and a power pulse signal supplied as a feedback signal. A differential integrator that outputs a differential integrated signal obtained by integrating the difference between the signal and the feedback signal; a quantizer that determines the polarity of the differential integrated signal and outputs a digital signal as a quantized signal; A power amplifier for amplifying power to output a power pulse signal, a high frequency removing unit for removing frequency components in the power pulse signal that are equal to or higher than the local oscillation frequency band of the tuner, and a power pulse signal output from the high frequency removing unit. A feedback circuit for transmitting to the differential integrator as a feedback signal, and an audio band of the power pulse signal connected to the high frequency removing unit. And a low pass filter for passing only frequency components.

With this configuration, the power pulse signal from which the high frequency component contained in the power pulse signal that causes the tuner interference is removed is negatively fed back, and the power pulse signal that interferes with the reception of the tuner is obtained without deteriorating the audio characteristics. It is possible to reduce the noise of the included high frequency component.

In order to solve the above-mentioned problems, a delta-sigma modulation amplifier according to the present invention is provided with an analog input signal sequentially input from an input terminal and a power pulse signal as a feedback signal, and the analog input signal and the feedback signal. A difference integrator that outputs a difference integration signal that integrates the difference with the signal, a quantizer that determines the polarity of the difference integration signal and outputs a digital signal as a quantized signal, and power-amplifies the quantized signal. And a high-frequency phase control unit for attenuating the amplitude of the local oscillation frequency band component of the tuner of the power pulse signal and controlling the phase of the power pulse signal in the high frequency band. A feedback circuit that sends the power pulse signal output from the high frequency phase control unit to the difference integrator as a feedback signal, and the high frequency phase And a low pass filter for passing only frequency components of the audio band of the connected to the control unit power pulse signal.

With this configuration, harmonic components contained in the power pulse signal that cause tuner interference are removed,
Since the signal that controls the phase of the pulse signal in the high frequency band is negatively fed back and the phase rotation in the high frequency band can be limited to prevent the self-excited oscillation frequency from decreasing, it is possible to adjust without the time constant. It is possible to reduce high frequency noise without deteriorating the audio characteristics.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a block diagram of a delta-sigma modulation amplifier according to the first embodiment. In FIG. 1, 1 is an input terminal to which analog input signals are sequentially input, 2 is a difference integrator which is supplied with a power pulse signal as a feedback signal and which outputs a difference integration signal obtained by integrating the difference between the analog input signal and the feedback signal, Reference numeral 8 is a time constant control unit that determines the integration time constant of the differential integrator 2, 3 is a 1-bit quantizer that determines the polarity of the differential integration signal, and outputs a 1-bit digital signal as a quantized signal, and 4 is a quantum A pulse amplifier for power-amplifying the converted signal and outputting a power pulse signal, 9 is a high frequency removing unit for removing frequency components in the power pulse signal above the local oscillation frequency band of the tuner, and 7 is power output from the high frequency removing unit. A feedback circuit 5 for sending the pulse signal as a feedback signal to the difference integrator 2 is connected to the high frequency removing unit 9 and passes only the frequency component in the audio band of the power pulse signal. To a low-pass filter.

The operation of the delta-sigma modulation amplifier according to the first embodiment constructed as above will be described below.

First, the difference integrator 2 integrates the difference between an analog input signal such as a music signal that is sequentially input and the high frequency attenuation pulse signal that is sequentially fed back from the feedback circuit 7, and sequentially outputs the resulting difference integration signal. To do. At this time, the integration time constant of the time difference integrator 2 is determined by the time constant control unit 8 and is composed of, for example, a second-order difference integrator shown in FIG. Next, the 1-bit quantizer 3 sequentially determines the polarity of the difference integration signal output from the difference integrator 2 and outputs a value of 1 when the polarity is positive and a value of 0 when the polarity is negative, for example. As a result, a 1-bit digital signal is output. Here, 1-bit quantizer 3
Is composed of devices such as a comparator and a D-type flip-flop.

Next, the pulse amplifier 4 power-amplifies the sequentially input digital signals and sequentially converts them into power pulse signals. Here, as the device used for the pulse amplifier 4, it is preferable to use a power MOSFET capable of high-speed switching operation and having a small voltage drop because the area of the power pulse signal whose amplitude is dropped with respect to the power supply voltage causes a loss. The high-frequency removing section 9 removes frequency components of the tuner's local oscillation frequency or more from the sequentially output power pulse signals, and the result is sequentially sent to the low-pass filter 5 as a high-frequency attenuated pulse signal. The high frequency removing unit 9 is composed of an LC circuit of a coil and a capacitor, and it is preferable to set the frequency around 100 MHz because the interference of the harmonic components included in the power pulse signal is large especially in the FM radio band. Further, in order to shorten the mounting distance between the pulse amplifier 4 and the low-pass filter 5 as much as possible to achieve low noise, it is better to use ferrite beads for the coil L, and the capacitor C is a non-inductive winding film capacitor having good high frequency characteristics. Is preferred.

Further, the low-pass filter 5 is a passive filter composed of a coil L and a capacitor C, and the core used for the coil is preferably a toroidal type in order to suppress noise emission, and further linearity in the audio frequency band, that is, distortion rate. In order to prevent the deterioration of the magnetic field, it is preferable that the magnetic permeability μ is low, and the value is 2 digits or less. Next, the low-pass filter 5 sequentially outputs the analog power signal obtained after passing only the component in the audio frequency band of the high frequency attenuated pulse signal as an audio output signal from the output terminal. The cutoff frequency of this low-pass filter is preferably set to about 30 kHz in consideration of the attenuation characteristic of the filter.

On the other hand, the high frequency attenuation pulse signals sequentially output from the high frequency removing section 9 are sequentially input to the negative side terminal of the difference integrator 2 via the feedback circuit 7 and the analog input signal sequentially input from the input terminal. The difference will be integrated.

(Second Embodiment) FIG. 2 shows a block diagram of a delta-sigma modulation amplifier according to a second embodiment. In FIG. 2, reference numeral 10 designates an amplitude of a local oscillation frequency band component of a tuner in a power pulse signal, and This is a high frequency phase control unit for controlling the phase of the power pulse signal in the high frequency band, and for example, FIG. 2 shows an example using a choke coil. Other configurations are similar to those of the first embodiment.

The operation of the delta-sigma modulation amplifier according to the second embodiment having the above configuration will be described below.

First, the difference integrator 2 integrates the difference between an analog input signal such as a music signal that is sequentially input and the high frequency phase control pulse signal that is sequentially fed back from the feedback circuit 7, and obtains a difference integral signal obtained as a result. Output sequentially. The integration time constant of the difference integrator 2 is determined by the time constant controller 8 and is composed of, for example, a second-order difference integrator.

Next, the 1-bit quantizer 3 sequentially determines the polarity of the difference integration signal output from the difference integrator 2 as in the first embodiment. For example, when the polarity is positive, a value of 1 is set and when the polarity is negative, At that time, a 1-bit digital signal can be obtained by sequentially outputting a value of 0. Here, the 1-bit quantizer 3 is composed of devices such as a comparator and a D-type flip-flop. Next, the pulse amplifier 4 power-amplifies the sequentially input digital signals and sequentially converts them into power pulse signals. Here, as the device used for the pulse amplifier 4, it is preferable to use a power MOSFET capable of high-speed switching operation and having a small voltage drop because the area of the power pulse signal whose amplitude is dropped with respect to the power supply voltage causes a loss.

Next, the high-frequency phase control unit 10 attenuates the frequency components near the local oscillation frequency of the tuner of the sequentially output power pulse signals, and the result is sequentially transmitted to the low-pass filter 5 as a high-frequency phase control pulse signal. To be done.
This high frequency phase control unit 10 is composed of a coil L, and is particularly 100 MHz of the harmonic components included in the power pulse signal.
The frequency components in the vicinity can be attenuated, and the sharp phase rotation in the high frequency band, that is, the phase delay can be reduced. Further, in order to minimize the mounting distance between the pulse amplifier 4 and the low-pass filter 5 and reduce noise, it is better to use ferrite beads for the coil L.

The low-pass filter 5 is a passive filter composed of a coil L and a capacitor C, and the core used for the coil is a toroidal type in order to suppress noise emission, and the linearity in the audio frequency band, that is, the distortion factor is deteriorated. In order to prevent it, it is preferable that the magnetic permeability μ is low, and the value is preferably 2 digits or less.

Next, the low-pass filter 5 sequentially outputs from the output terminal the analog power signal obtained after passing only the audio frequency band component of the high frequency phase control pulse signal as an audio output signal. The cutoff frequency of this low-pass filter is preferably set to about 30 kHz in consideration of the attenuation characteristic of the filter.

On the other hand, the high frequency phase control pulse signals sequentially output from the high frequency phase control unit 10 are sequentially input to the negative terminal of the differential integrator 2 via the feedback circuit 7 and sequentially input from the analog input terminals. The difference from the input signal will be integrated.

In the above description, the differential integrator is a second-order integrator, but a multi-order integrator may be used. In that case, the quantizer is connected to multiple bits and a plurality of pulse amplifiers are connected in parallel. You can do it.

[0033]

According to the present invention, the frequency component of the audio band is removed by the low pass filter from the high frequency attenuated pulse signal in which the frequency band component higher than the local oscillation frequency of the tuner contained in the power pulse signal of the pulse amplifier is removed by the high frequency removing unit. Only the noise can be taken out, and since the high-frequency elimination part is in the negative feedback loop, it is possible to avoid the reception interference of the tuner without deteriorating the audio characteristics, especially the distortion rate, and the cost for noise measures such as shielding. Can be reduced.

Further, according to the present invention, the local oscillation frequency band component of the tuner included in the power pulse signal of the pulse amplifier can be attenuated by the high frequency phase control unit without causing a phase delay in the high frequency band. In addition, since it is possible to prevent the self-excited oscillation frequency from being lowered by the time constant control unit, it is not necessary to reset the time constant, and the trouble of adjustment after mounting can be saved. Further, since the high frequency phase control unit is in the negative feedback loop, it is possible to avoid tuner reception interference without deteriorating the audio characteristics, especially the distortion rate, and reduce the cost for noise countermeasures such as shielding. it can.

[Brief description of drawings]

FIG. 1 is a block diagram of a delta-sigma modulation amplifier according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a delta-sigma modulation amplifier according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional delta-sigma modulation amplifier.

[Explanation of symbols]

1 input terminal 2 Difference integrator 3 1-bit quantizer 4 pulse amplifier 5 Low pass filter 6 output terminals 7 Feedback circuit 8 Time constant control unit 9 High frequency removal section 10 High frequency phase controller

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-52-113666 (JP, A) JP-A-5-1552867 (JP, A) JP-A-5-63457 (JP, A) JP-A-6- 29757 (JP, A) Actual development Sho 53-66048 (JP, U) Japanese Patent Publication 7-105666 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03F 1/00-3 / 72

Claims (2)

(57) [Claims] 1. An analog signal input terminal, a difference integrator which is supplied with a power pulse signal as a feedback signal, and outputs a difference integration signal obtained by integrating a difference between the analog signal and the feedback signal, and a polarity of the difference integration signal. A quantizer for determining a digital signal as a quantized signal and outputting the quantized signal as a quantized signal, a pulse amplifier for power-amplifying the quantized signal to output a power pulse signal, and a tuner local oscillation frequency band of the power pulse signal or more A high-frequency removing unit for removing the frequency component of, a feedback circuit for sending the power pulse signal output from the high-frequency removing unit to the difference integrator as a feedback signal,
A delta-sigma modulation amplifier, comprising: a low-pass filter that is connected to the high-frequency removing unit and passes only a frequency component in an audio band of the power pulse signal. 2. An analog signal input terminal, a difference integrator that outputs a difference integration signal obtained by integrating a difference between the analog signal and the feedback signal when a power pulse signal is supplied as a feedback signal, and a polarity of the difference integration signal. A quantizer that outputs a digital signal as a quantized signal, a pulse amplifier that power-amplifies the quantized signal and outputs a power pulse signal, and a local oscillation frequency band component of the tuner of the power pulse signal. To the difference integrator as a feedback signal, a high frequency phase control unit that attenuates the amplitude of the power pulse signal and controls the phase in the high frequency band of the power pulse signal, and a power pulse signal output from the high frequency phase control unit. A feedback circuit for sending out, and a low-pass filter connected to the high frequency phase control unit for passing only the frequency component of the audio band of the power pulse signal. Delta-sigma modulation amplifier with.