JPS59183510A - Distortion correcting circuit - Google Patents

Abstract

PURPOSE:To reduce distortion by detecting and correcting a distorted component generated in a power amplifier PWM-converting directly a digital signal of PCM audio by means of an A/D converter, an operating circuit and a memory. CONSTITUTION:An output of a subtractor 15 operating subtraction between a PCM digital signal applied to an input terminal 13 and an output of the A/D converter 14 is stored in the memory 16. An adder 17 adds data of the memory 16 and PCM digital signal data. The data becoming an analog signal via the adder 17, a PWM converter 11 and a low-pass filter 12 becomes again a digital signal data by a converter 14. The analog signal applied to a speaker 7 becomes a signal correcting distortion generated by the PWM converter 11 and a sound signal with low distortion is reproduced.

Description

Detailed Description of the Invention (Field of Application) The present invention relates to a distortion correction circuit for a power amplifier for PCM audio, and in particular to a distortion correction circuit suitable for reducing distortion in a power amplifier that performs direct PWM conversion of a PCM digital signal. Regarding.

(Background) In the field of audio equipment and equipment, PCM recording and playback equipment that converts analog signals into digital signals and records and plays them back is becoming popular.
Due to its good performance, it is being introduced for consumer use. In these devices, an analog signal is regenerated from a digital signal and is added to a power amplifier to drive a speaker.

FIG. 1 shows an example of a conventional analog power amplifier used in such a device. 1 is an input terminal, 2 is a power amplifier circuit, 6 and 4 are output terminals, 5 and 6 are speaker input terminals, 7 is a speaker, 8 and 9 are feedback input terminals, 10
is a feedback circuit.

The feedback input terminal 8 is connected to the speaker input terminal 5, and the feedback input terminal 9 is connected to the speaker input terminal B. With such a connection, both ends of the speaker 70 are included in the feedback loop, and noises caused by the impedance of the speaker cord connecting between the terminals 6.5 and 4.6 are reduced.

However, this analog power amplifier does not have a means for detecting distortion caused by nonlinearity of the speaker and feeding it back. Therefore, this power amplifier has a drawback in that the distortion cannot be reduced. Furthermore, the conventional analog power amplifier shown in FIG. 1 has the disadvantage of high loss when attempting to obtain large power.

On the other hand, when using a PCM digital signal as the source,
Although digital signals are converted into analog signals and applied to power amplifiers via control amplifiers, it is being considered to perform power amplification as digital signals. The power amplifier in this case is configured by once converting a digital signal into a PWM signal and turning on/off the I)WM multiplied signal power supply.

FIG. 2 shows a block diagram of an example. In FIG. 2, 1( is a PWM converter, IIA is an output signal of the PWM converter 11, 12 is a low-pass filter, and 16 is a PCM digital signal input terminal.

In FIG. 2, PCM digital signal data applied to a terminal 16 is generated by a PWM converter 11 to have a pulse width corresponding to the data, and the power is controlled on/off using the pulse signal.

The output of this PWM converter 11 has a shape in which the pulse width changes momentarily, as shown in FIG. The output signal with such a shape is passed through the low-pass filter 1.
2, an analog signal is generated, and the speaker 7 is driven by this signal. From this example, the loss of the power amplifier is reduced.

However, the output +1A of the PWM converter 11 is
The waveform becomes dull as shown by JIB in the figure. For this reason, there was a drawback that the analog signal applied to the speaker was distorted. Further, in such a circuit configuration, since the input is a digital signal and the output is an analog signal, there is a drawback that it is not possible to provide a feedback circuit to reduce the distortion. Furthermore, similar to the conventional circuit shown in FIG. 1, there is a drawback in that it is not possible to reduce noise caused by non-linearity in the speaker.

(Objective) An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a distortion correction circuit that can reduce distortion even in a power amplifier using PWM conversion. Also,
Another object of the present invention is to provide a distortion correction circuit capable of reducing distortion caused by nonlinearity of a speaker.

(Overview) The features of the present invention include a power amplifier that receives a PCM digital signal as input and directly PWM-converts the digital signal, an analog-to-digital conversion means that converts an analog signal output from the power amplifier into a digital signal, and a power amplifier that converts an analog signal output from the power amplifier into a digital signal. - A subtraction means for comparing the output of the digital conversion means and the PCM digital signal input, a storage means for storing the output data of the subtraction means, and a means for calculating the read data of the storage means into the PCM digital signal input. , by using the output data of the arithmetic means as input to the power amplifier, the distortion of the power amplifier is reduced. Another feature is that in a power amplifier that receives a PCM digital signal as an input and obtains an analog signal for driving a speaker, a detection means for detecting an audio signal reproduced by the speaker is provided, and this detection output is sent to the analog-to-digital conversion means. The point is that the input signal is taken as the input signal.

An embodiment of the present invention will be described below with reference to FIG. In the figure, 14 is an analog-to-digital converter (A/D converter) that converts an analog signal into a digital signal; +
A subtractor 5.5 takes the difference between the PCM digital signal applied to the input terminal t6 and the output of the A/D converter 15. ! 6 is P
A memory 17 uses the CM digital signal input as an address and inputs the output data of the subtracter 15, and 17 is an adder that adds the data in the memory 16 and the PCM digital signal data. Note that other symbols indicate the same or equivalent parts as in FIGS. 1 and 2.

Next, the operation of this embodiment will be explained in detail using the timing chart of FIG. As shown in Figure 85, data is applied to the input terminal 16 in the order of D2, D3. At this time, the adder +7. PWMi exchange i+1
．． The data that has become an analog signal through the low-pass filter 12 becomes digital signal data again at the A/D converter 14. This data is input data Dl + D
2+D3, and becomes digital signal data 0DIOIOD201 0D30 including distortion generated in the circuit. Furthermore, digital signal data QDIO, 0D20
1 oD3o is input data D+.

D2. D3 is delayed by the A/D converter 14 and the like. In FIG. 5, this delay is treated as a time of two samples.

The subtracter 15 calculates the difference between the data obtained by delaying the signal of the PCM digital signal input 16 by two samples and the output of the A/D converter 14. As a result, the output of the subtractor 15 is:
Data Ds + D2.

ΔD10+ ΔD20 which is the calculation result corresponding to D3
+ΔD30 is obtained. This difference, input data Dlr
It is written into the memory 16 at the address corresponding to D2+D3.

After that, when data D is added from the input terminal 16,
The memory 16 stores data ΔI corresponding to the input data D,
outputs to to the adder circuit 17. The adder circuit 17 adds the input data D1 and the data ΔDIG. As a result, the digital signal data applied to the PWM converter 11 is
This is the input data D1 plus the previous input/output difference ΔDIO, which is the correction data for the cup.

The corrected data, that is, DI + ΔDIO, passes through the low-pass filter 12 and becomes an analog signal, which is then converted into an analog signal.
The signal is again converted into a digital signal by the /D converter 14. At this time, the corresponding data appearing at the output of the A/D converter 14 is assumed to be oDl. The subtraction circuit 15 performs subtraction between this data oDu and the input PCM digital signal data D] to obtain the difference ΔD11. Next, in the memory 16, the previous correction data ΔI)to is read out from the memory 16, and the correction data ΔDlO is added to this difference ΔD1□. Then, the data is written into the memory 16 again as new correction data.

In this way, each time the input data D1 is added to the input terminal 16 of the 5 IC, an operation is performed in which the correction data is corrected. As a result, the correction data at the n-th input becomes as shown by the following equation.

Such a correction operation is performed not only for the data D1 but also for all patterns applied to the input terminal 16.

Therefore, the analog signal applied to the speaker 7 is PW
The signal is obtained by correcting the distortion generated in the M converter 11, and has the effect of being able to reproduce a low-frequency audio signal.

Although FIG. 5 shows that the input data D1 to D3 are input periodically, it goes without saying that the input data is generally input aperiodically. . It is obvious that this embodiment is effective in this case as well. FIG. 6 shows a middle embodiment of the present invention. This example is
In addition to the effects of the first embodiment, it is also possible to correct the nonlinearity of the speaker.

First, the configuration of this embodiment will be explained. In the figure, 18 is a microphone for detecting the output pleasure signal of the speaker 7;
9 is a microphone input terminal 5; 20 is an amplifier for amplifying the signal detected by the microphone 18; the output thereof is applied to the A/D converter 14; The numeral numeral indicates the same as or equivalent to that in FIG.

Next, the operation of this embodiment will be explained. The music signal played by the speaker 7 is detected by the microphone 18, and the A/D converter 1
4, it is converted into a digital signal.

This digital signal and the PCM applied to the input terminal 16
The digital signals are compared by a subtracter 15, and a signal corresponding to the difference is input to a memory 16.

The operation after this is the same as in the case of Fig. 4.C゛,
The explanation will be omitted. In this embodiment K, the double voltage A signal reproduced by the speaker 7 is fed back to perform the correction operation of A).
'(-, PWM transformation teI device + 1 It has the effect of being able to generate Fru 1 [Zocha・Sode 11'] generated in Oyohisbeeka 7.

The embodiment shown in Figure 1.6 has been explained using an example using 'rat force amplification power amplification - [, P WM conversion r: +y I I, but 1) WM converter 11 and C-bus filter 12 ((replacement゛[,I'), ,A converter and')-
Pro, use the gummy power increase 1 @ device in combination V and also ゛℃,
Figure 6 and Mr. I+'11 1. [Speaker 7' (111!4
The effect of being able to stop children 1 or 9 is 3゜(result).The present invention IC, j fth A, increases the power of interviewing PCM child/shield signal by converting PWλ1.・It is said that it is possible to detect the distortion components generated in the amplifier by using an A, -'D converter, a Wakuj9S circuit, and a memory, and to create a power amplifier with low distortion. effective.

Another advantage is that distortion caused by the nonlinearity of the speaker can be reduced by detecting the speaker output with a microphone, A/D converting it, comparing it with the input digital signal, and correcting it.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional analog power amplifier, Figure 2 is a block diagram of a conventional analog power amplifier.
The figure shows a block diagram of a conventional power amplifier that directly PWM-converts a PCM digital signal. A block diagram of one embodiment, FIG. 5 is a timing chart showing the operation of FIG. 4. 11... PWM converter, 14... A/D converter, 15... Subtractor, 16. ...Memory, 1
7...Adder, 18...Mike Dairanukito Patent Attorney Hiraki Michihito'A-1 Zusai 2 Shoga 4 Zuyo 5 Enclosure

Claims (1)

[Claims] (A power amplifier that receives an 11PCM digital signal as an input and directly PWM-converts the digital signal, an analog-to-digital conversion means for converting an analog signal output from the power amplifier into a digital signal, and an analog-to-digital conversion means for converting an analog signal output from the power amplifier into a digital signal. A subtraction means for comparing the output of the means with the PCM digital signal input, a storage means for storing data of the subtraction means, and a means for calculating read data of the storage means and the PCM digital signal input, By inputting the output data of the calculation means to the power amplifier,
A distortion correction circuit characterized in that the distortion of the power amplifier is reduced. (A power amplifier that receives a 21PCM digital signal as an input and obtains an analog signal to drive a speaker, a detection means that detects the audio signal reproduced by the two listeners, and an analog/digital amplifier that converts the output of the detection means into a digital signal. a conversion means, a subtraction means for comparing the output of the analog-to-digital conversion means and the PCM digital signal input, a storage means for storing the output data of the subtraction means, and a calculation between the read data of the storage means and the PCM digital signal input. A distortion correction circuit characterized in that the output data of the calculation means is used as input data of a power amplifier that obtains an analog signal for driving the speaker, and distortion of the power amplifier and the speaker is reduced. .