JPH07105666B2 - 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 a delta-sigma modulation amplifier for highly efficient power amplification of an acoustic signal.

[0002]

2. Description of the Related Art In recent years, two-state modulation has been used as a signal processing method for high-efficiency power amplifiers for acoustic signals, and has the advantage that particularly high-level power can be processed with high efficiency.

A conventional signal processing method of a two-state modulation amplifier for the purpose of highly efficient power amplification is disclosed in, for example, Japanese Patent Laid-Open No. 2-1776.
No. 06 publication.

The signal processing method of the conventional two-state modulation power amplifier will be described below. FIG. 4 is a block diagram of a pulse width modulation amplifier which is the conventional two-state modulation amplifier. In FIG. 4, 9 is an analog signal input terminal, 10 is a comparator, 11 is a drive amplifier, 12
Is a pulse amplifier, 13 and 14 are coils and capacitors forming a low-pass filter, 15 is an output terminal, 16 is a load, 17 is a triangular wave signal generator, 18 is an FM modulator, 1
Reference numeral 9 is a basic signal oscillator, and 20 is a random signal oscillator.

The operation of the pulse width modulation amplifier configured as described above will be described below.

First, the acoustic signal input to the analog signal input terminal 9 is input to the (-) input terminal of the comparator 10, and the triangular wave signal is input from the triangular wave signal oscillator 9 to the (+) input terminal of the comparator 10. It Amplitudes of these two types of signals are compared by a comparator 10 and converted into a 1-bit digital signal. That is, the output C _{out of the} comparator 10 is C _out = when the acoustic signal> the triangular wave signal
0 When acoustic signal <triangular wave signal C _out =
It becomes 1. From this, it can be seen that C _out is converted into a pulse width modulation signal using the frequency of the triangular wave signal as a carrier.

The output C _{out of the} comparator 10 is amplified by the drive amplifier 11 and further power-amplified by the pulse amplifier 12. An unnecessary component is removed from the power-amplified pulse width modulation signal by a low-pass filter including a coil 13 and a capacitor 14, and an acoustic signal is output from the output terminal 15. Further, in order to improve the characteristics of the amplifier, the output of the pulse amplifier 12 is changed to the comparator 10
Feedback is applied to the (-) input terminal of the via a resistor.

On the other hand, the triangular wave signal is generated by the basic signal generated by the basic signal oscillator 19 and the random signal oscillator 2.
The random signal generated at 0 is FM-modulated by the FM modulator 18, and the output signal of the FM modulator 18 is converted into a triangular wave signal by the triangular wave generator 17. As a result, the carrier signal for converting the acoustic signal input to the analog signal input terminal 9 into a pulse width modulation signal is energy diffused,
The degree of interference with other electronic and electric devices can be reduced.

[0009]

However, the above-mentioned conventional configuration requires a basic signal oscillator, a random signal oscillator, an FM modulator and a triangular wave generator in order to obtain a triangular wave signal capable of energy-spreading a carrier signal. However, there was a problem that the structure had to be complicated.

The present invention solves the above-mentioned conventional problems, and obtains a pulse density modulation signal by subjecting an analog signal (or two-state modulation signal) to delta sigma modulation, and energy-spreading the carrier signal, An object of the present invention is to provide a highly efficient delta-sigma modulation amplifier capable of reducing the degree of interference with other electronic and electric devices with a simple configuration.

[0011]

In order to achieve this object, a delta-sigma modulation amplifier of the present invention outputs a difference integration signal obtained by integrating the difference between an analog signal (or two-state modulation signal) and a feedback signal. A differential integrator, a 1-bit quantizer that determines the polarity of the differential integrated signal and outputs a 1-bit digital signal, and a delay that delays the digital output signal of the 1-bit quantizer with a clock of an arbitrary frequency Device, a pulse amplifier for power-amplifying the digital signal output from the delay device, a feedback circuit for sending the digital output signal of the pulse amplifier as the feedback signal to the difference integrator, and the output of the pulse amplifier And a low-pass filter that passes only the necessary frequency band.

[0012]

The present invention has the above-mentioned configuration and has a differential integrator,
A closed-loop circuit is composed of a bit quantizer, delay device, pulse amplifier, and feedback circuit. This closed loop circuit is in a negative feedback state in the low frequency region and a positive feedback state in the high frequency region mainly due to the phase delay of the differential integrator and the delay device,
It oscillates in the high frequency range. The oscillation frequency is not a constant frequency because the closed loop circuit and the feedback circuit are configured to correct the 1-bit quantization error in the low frequency range. As a result, the oscillation frequency of the feedback circuit, that is, the frequency of the carrier signal constantly changes, and the energy of the carrier signal is diffused without being concentrated on a single frequency and its harmonics.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a delta-sigma modulation amplifier according to an embodiment of the present invention. In FIG. 1, reference numeral 1 is an input terminal, and 2 is an acoustic signal (analog signal or two-state modulation signal) input to the input terminal 1 and a feedback signal as inputs, and a difference integration is performed by integrating a difference value between these two signals. A differential integrator that outputs a signal, 3 is a 1-bit quantizer that converts the differential integrated signal into a digital signal, and 4 is a delay device that delays the digital output signal of the 1-bit quantizer 3 with a clock of an arbitrary frequency. , A D-type flip-flop or the like, 5 is a clock oscillator that generates a clock pulse of an arbitrary frequency, 6 is a pulse amplifier that power-amplifies the digital output signal of the delay device 4, and 7 is an output signal of the pulse amplifier 6. A filter for removing unnecessary signal components, and 8 is an output terminal.

The operation of the delta-sigma modulation amplifier of this embodiment constructed as above will be described below. When an acoustic signal enters the input terminal 1, the pulse amplifier 6
The difference integrator 2 integrates the difference value between the two signals with the output signal of 1 to output a difference integration signal. The difference integration signal is input to the 1-bit quantizer 3 and converted into a 1-bit digital signal by the 1-bit quantizer 3. The 1-bit digital signal is input to the delay unit 4 and delayed by a time corresponding to the repetition cycle of the clock supplied from the clock oscillator 5. The delay-processed digital signal is the pulse amplifier 6
Power is amplified by. The output signal of the pulse amplifier 6 is
It is input to the difference integrator 2 via the feedback circuit 30. Further, the output signal of the pulse amplifier 6 is input to the filter 7 including a coil and a capacitor, unnecessary signal components are removed, and the output signal is output from the output terminal 8.

The closed circuit loop composed of the differential integrator 2, the 1-bit quantizer 3, the delay device 4, the pulse amplifier 6 and the feedback circuit 30 is constructed so as to be a negative feedback in the low frequency range. In the frequency range, the positive feedback is provided due to the phase delay caused by the difference integrator 2 and the delay device 4. Therefore, the closed circuit loop is oscillated in a high frequency range (carrier oscillation), but its oscillation frequency is lower than the clock frequency of the clock oscillator 5.

Here, a description of the delta-sigma modulator will be given with reference to FIG.
Do with FIG. 2 is a block diagram of a second-order delta-sigma modulator, in which T is a delay device for delaying the input signal by one sample clock period. The delta-sigma modulator of FIG. 2 can be expressed by the following Z conversion formula.

Vo (z) = − αVin (z) [2-Z ⁻¹ ] + [2Z ⁻¹ −Z ⁻² ] [Vo (z) −αYo (z)] (1) The delta shown in FIG. The block diagram of the sigma modulation amplifier is
The configuration is changed based on the above formula.

Next, it will be shown that the delta-sigma modulation amplifier shown in FIG. 1 is equivalent to the delta-sigma modulator shown in FIG.

The input / output characteristics of the differential integrator 2 must be the characteristics shown in the following equation.

[0021]

[Equation 1]

However, T = sampling period, Vs = difference integrator input signal, and Vo = difference integrator output signal.

If this is expressed by the Z conversion formula, the following formula is obtained. Vo (z) =-α [2Vs (z) -Z^-1Vs (z) ＋ 2Z^-1Vo (z) -Z^-2Vo (z)] (3) If the output of the 1-bit quantizer 3 is Yo, pulse amplification
Since the output of the device 6 has a time delay of T at the delay device 4,
^-1It becomes Yo (z). Output signal Z of pulse amplifier 6 ^-1Yo (z)
And Vs (z) is represented by the signal Vin applied to the input terminal 1,
It becomes an expression.

Vs (z) = Vin (z) + Z ⁻¹ Yo (z) (4) If formula (4) is used to represent formula (3), the following formula is obtained.

Vo (z) = − αVin (z) [2-Z ⁻¹ ] + [2Z ⁻¹ −Z ⁻² ] [Vo (z) −αYo (z)] (5) Formula (5) is a formula It is the same as (1), and it can be seen that the delta-sigma modulation amplifier shown in FIG. 1 and the delta-sigma modulator shown in FIG. 2 operate in the same manner.

FIG. 3 shows the signal and quantization noise spectrum of the delta-sigma modulator. Although the quantization noise by the 1-bit quantizer is considered to be white noise, a peak of the quantization noise appears near 1/2 of the sampling frequency (clock frequency of the delay device) fs due to the noise shaping characteristic of delta-sigma modulation. Similarly, the delta-sigma modulation amplifier also exhibits noise shaping characteristics. Also, the sampling frequency is the frequency of the clock supplied to the delay device 4, as in the delta-sigma modulator.

Here, the frequency at which the closed circuit loop of FIG. 1 oscillates in a high frequency range (carrier oscillation) is not constant because it acts to reduce the quantization error.

As described above, according to this embodiment, the difference integrator (2) for outputting the difference integration signal obtained by integrating the difference between the analog signal (or the two-state modulation signal) and the feedback signal,
A 1-bit quantizer (3) that determines the polarity of the difference integration signal and outputs a 1-bit digital signal, and a delay device (which delays the digital output signal of the 1-bit quantizer with a clock of an arbitrary frequency ( 4) and a pulse amplifier (6) for power-amplifying the digital signal which is the output of the delay device,
By providing a feedback circuit (30) for sending the digital output signal of the pulse amplifier as a feedback signal to the difference integrator, the closed circuit loop has a noise shaping characteristic and the carrier oscillation frequency is not constant. Therefore, the energy of the carrier signal can be diffused with a simple structure, and the ratio of the oscillation frequency of the clock oscillator 5 to the carrier frequency or the sampling frequency of the two-state modulation signal is set to an integer ratio so that the two-state modulation signal can be obtained. (For example, the pulse width modulation signal and the pulse density modulation signal) and the carrier signal do not cause a beat.

[0029]

As described above, the present invention provides a differential integrator, 1
By configuring the closed loop circuit with the bit quantizer, delay device, pulse amplifier, and feedback circuit, the closed circuit loop has noise shaping characteristics, and the carrier oscillation frequency is not constant. Therefore, the energy of the carrier signal can be diffused with a simple configuration, and by making the ratio of the oscillation frequency of the clock oscillator and the carrier frequency or sampling frequency of the two-state modulation signal an integer ratio,
The two-state modulation signal (for example, pulse width modulation signal, pulse density modulation signal) and the carrier signal do not cause a beat.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a delta-sigma modulation amplifier in the example.

FIG. 3 is a frequency spectrum diagram showing a signal and a quantization noise spectrum of the delta sigma modulation amplifier in the example.

FIG. 4 is a block diagram showing a configuration of a conventional pulse width modulation amplifier.

[Explanation of symbols]

 1 input terminal 2 differential integrator 3 1-bit quantizer 4 delay device 5 clock oscillator 6 pulse amplifier 7 filter 8 output terminal

Claims (1)

[Claims] 1. An analog signal or a two-state modulated signal,
A difference integrator that outputs a difference integration signal that integrates the difference with a feedback signal, a 1-bit quantizer that determines the polarity of the difference integration signal and outputs a 1-bit digital signal, and the 1-bit quantizer A delay unit that delays the digital output signal of the digital signal with a clock of an arbitrary frequency, a pulse amplifier that power-amplifies the digital signal that is the output of the delay unit, and a digital output signal of the pulse amplifier to the difference integrator as a feedback signal A delta-sigma modulation amplifier comprising: a feedback circuit for sending out; and a low-pass filter that receives an output of the pulse amplifier as an input and passes only a necessary frequency band.