JPS6139708A - Power supply voltage fluctuation correcting method in pulse width modulation amplifier - Google Patents

Abstract

PURPOSE:To eliminate output fluctuation due to power supply voltage fluctuation by detecting the fluctuation of a power supply voltage fed to a power amplifier circuit, converting the detected signal into a digital signal and using the digital signal so as to correct an input signal. CONSTITUTION:When an input signal Sin is an analog signal, a level adjusting circuit 5 adjusts a level of a power supply voltage + or -V fed to a power amplifier circuit 2 from a power supply 4 and detects the fluctuation. That is, the level of a power supply voltage +V is decreased by a DELTAV, the power voltage is set to a level (a) when it is a specified voltage to a sawtooth reference pulse CP so that the upper limit of the expected fluctuation is a level (b) and the lower limit is within a level (c), and the fluctuated voltage DELTAV is inputted to a pulse width modulation (PWM) circuit 6. The PWM circuit 6 applies the pulse width modulation to the fluctuated voltage DELTAV to convert it into a digital signal. That is, the fluctuated voltage DELTAV is compared with the reference pulse Cp to output a signal A of pulse width modulation waveform going to ''H'' only at DELTAV>Cp. The duty of the signal A is selected to 10% at, e.g., the specified voltage so as to attain level adjustment by the level adjusting circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply voltage fluctuation correction method in a pulse width modulation amplifier (hereinafter abbreviated as "PWM amplifier").

[Conventional technology]

A PWM amplifier converts the level of an input signal into a pulse width modulated wave represented by the duty of a pulse waveform and amplifies the power. For example, as shown in Fig. 4, a pulse width modulation (PWM) circuit 1 and a power amplifier circuit are used. 2, a low-pass filter 3, and a power supply 4.

The PWM circuit 1 uses, for example, a comparator like the one shown in FIG. S, and compares the analog input signal Sin as shown in FIG. When Sin>CP, the output is “H=, 5in(C
When p, the output is set to L'' and converted into a pulse width modulated wave signal Sp↓ as shown in FIG.

The duty T■/T of this signal SpwI11 corresponds to the input signal level.

The power amplifier circuit 2 includes, for example, NPN type and PNP type power transistors Ql' connected in series as shown in FIG.
Q2 is connected between the positive and negative power supplies, and this power 1 is controlled by the pulse-modulated wave signal Sp%1I11 from the PWM circuit 1.
On/off control of transistors Ql and Q2 (S ptrm
When is “H”, Ql is on and Q2 is off, Spt
When im is T-'', Q2 is on and QI is off), and the sixth transistor is connected from the emitter connection point of transistor Q+ and Q2.
An output signal Spa as a power amplified pulse width modulated wave as shown in FIG. 3(C) is obtained.

When this output signal Spo is passed through a low-pass filter 3, high frequency components are removed, and as shown in FIG. With this signal, the output level becomes 0 when the unity is 50%.

Note that when this output signal drives a speaker, for example, the voice coil serves as a low-pass filter, so that the output signal of the power amplifier circuit 2 can be directly supplied to the speaker.

In addition, if the input signal Sin is a pulse-encoded digital signal (PCM signal), the PWM circuit
The signal may be converted into a pulse width modulated wave signal using a CM/PWM converter.

This kind of PWM amplifier has a simple circuit configuration.

Moreover, since power amplification is performed by switching on and off of power transistors, the efficiency is always approximately 1.
00%, and its usefulness is attracting attention.

[Problem that the invention seeks to solve]

However, as described above, such a PWM amplifier performs power amplification by the switching operation of the power transistor, and always outputs the power supply voltage by pulse width modulation. Therefore, when the power supply voltage fluctuates, for example, the
As shown by the broken line in Figure (C), there is a problem in that the effect of this effect is directly reflected in the output signal waveform at all signal levels.

To solve this problem, PWM is applied to the input side of the power transistor of the power amplifier circuit so as not to turn it on completely.
Although there is a method of limiting the amplitude of the signal, this method reduces the efficiency of the output stage, resulting in a reduction in the greatest advantage of the PWM amplifier.

[Means for solving problems]

In order to solve the above-mentioned problems, this method of correcting power supply voltage fluctuations in pulse width modulation amplifiers based on this proposal detects fluctuations in the power supply voltage supplied to the power amplifier circuit, converts it into a digital signal, and inputs the digital signal using the digital signal. The signal or its pulse width modulated wave is corrected to eliminate output fluctuations due to power supply voltage fluctuations.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 is a block configuration diagram of a PWM amplifier showing an example in which the input signal Sjn is an analog signal.
The same parts as in the conventional example in the figure are given the same reference numerals, and their explanation will be omitted.

The level adjustment circuit 5 has the role of adjusting the level of the power supply voltage ±V supplied from the power supply 4 to the power amplifier circuit 2 and detecting the variation.

Since the absolute values of the power supply voltages +■ and -■ are equal, the level of one of the voltages, 10 V, is lowered as shown by ΔV in Figure 2 (A), and the power supply voltage is When the voltage is at the specified voltage, it will be at the level a, and the expected fluctuation will be
- Make sure that the eye is within the level b and the lower limit is within the level C, and input this fluctuating voltage ΔV to the PWM circuit 6.

The PWM circuit 6 serves to pulse width modulate this fluctuating voltage ΔV and convert it into a digital signal.

That is, as shown in FIG. 2 (a), the fluctuating voltage ΔV is compared with the reference pulse Cp, and as shown in FIG.
>Cp, a signal A with a pulse width modulation waveform that becomes H'' is output.

The level adjustment is performed by the level adjustment circuit described above so that the tute of this signal A changes, for example, between 0 and 20% due to fluctuations in the power supply voltage, and becomes 10% at the specified voltage.

This signal A is inverted by the inverter 7 and is
A digital signal B having a pulse waveform with a duty varying between 80 and 100% as shown in c) is generated and inputted to the AND circuit 8.

AND 8 combines this signal B with a pulse width modulated signal S p as shown in FIG. 2 (d) input from the PWM circuit 1.
As shown in the same figure (e), the pulse width of the signal Spwm is H'' is reduced by the period that the signal B is L'', and the duty is corrected. Let them input.

This correction amount changes to offset fluctuations in the power supply voltage, and when the power supply voltage becomes larger than the specified value, the duty of the output signal Spo is reduced by 10% or more, and when the power supply voltage becomes smaller than the specified value, it decreases by 10% or less. do.

Since the power of the output signal Sout passed through the low-pass filter 3 is proportional to the product of the amplitude and duty of the output signal Spo of the power amplifier circuit 2, the power of the output signal Sout that has passed through the low-pass filter 3 is
Even if the amplitude of the output signal Spo changes as shown by the broken line in FIG.

According to this embodiment, even when the power supply voltage is at the specified value, the duty of the pulse width modulated wave signal input to the power amplifier circuit 2 is reduced by a certain amount (for example, 10%), so the dynamic range is reduced accordingly. However, since the fluctuation range of the power supply voltage is not that large, there is no practical problem.

Furthermore, in order to improve this point, if a circuit is provided for increasing the pulse width by a certain duty (for example, 10%) in the output signal S pwm' of the AND circuit 8 in FIG. The duty of the output signal Spwm' can be made to be the same as the duty of the output signal Spwm of the PWM circuit 1 when the value of the output signal Spwm' is the same as that of the output signal Spwm of the PWM circuit 1.

Next, according to FIG. 3, the input signal Sjn is converted into a digital signal (
An example in which the signal is a PCM signal will be described.

In this case, the absolute value of the power supply voltage supplied from the power supply 4 to the power amplifier circuit 2 is compared with a specified value, and the variation ΔV is detected by the voltage fluctuation detection circuit 10.

This variation ΔVt1 is converted into a digital signal Dv similar to the input signal Sin by inverting the sign and negative by the A/D converter.

This digital signal Dv is input to the adder 12.

The adder 12 adds the input signal Sin and the digital signal Dv according to this voltage fluctuation (when the power supply voltage becomes larger than a specified value, a negative value is added; when it becomes smaller than the specified value, a negative value is added; (adding a positive value), the digital value of the input signal Sin is corrected.

The corrected input signal ^in' is input to the PCM/PWM converter 13' and converted into a pulse width modulated wave signal Spw+e, which is power amplified by the power amplifier circuit 2 and outputted through the low-pass filter '3.

Ck is a clock pulse for synchronizing the operation timings of the A/D converter 11 and the PCM/PWM converter 13.

In this way, when the input signal Sin is a digital signal, the voltage fluctuation is converted into a digital signal, and it is directly added (or subtracted) to the input signal Sin to correct the output fluctuation due to the power supply voltage fluctuation. can be eliminated.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reliably correct the variation in power supply voltage and eliminate the influence on the output signal without reducing the amplification efficiency of the power amplifier circuit in the PWM amplifier. ”

[Brief explanation of drawings]

FIG. 1 is a schematic drawing of a PWM amplifier showing an embodiment of the present invention, and FIG. It is a boot storage block diagram of the PWM amplifier which shows the Example of :-. FIG. 4 is a block diagram showing an example of a conventional PW'M amplifier. FIG. 5 is a circuit diagram showing a specific example of the PWM circuit and the power amplifier circuit, and FIG. 6 is a signal waveform diagram of each part for explaining the operation of the conventional/conventional example of FIG. 1...PWM circuit 2...Power amplifier circuit 3
... Low pass filter 4 ... Power supply 5 ... Level adjustment circuit 6 ... PWM circuit 7 ... Inverter 8 ... AND circuit 10 ... Voltage fluctuation detection circuit 11 ... A/D conversion Device 12... Adder 13...
・PCM/PWM converter

Claims (1)

[Claims] 1 In a pulse width modulation amplifier that amplifies power by converting an input signal into a pulse width modulation wave and controlling on/off of a power transistor of a power width amplification circuit, fluctuations in the power supply voltage supplied to the power amplification circuit are A method for correcting power supply voltage fluctuations, comprising: detecting the input signal and converting it into a digital signal, and correcting the input signal or its pulse width modulated wave using the digital signal to eliminate output fluctuations due to fluctuations in the power supply voltage.