JPS5917710A - Power amplifier - Google Patents

Abstract

PURPOSE:To improve the efficiency without degradation of tone quality and to reduce the noise and the distortion rate, by using a PCM digital signal as an input source in a high-efficiency power amplifier used for digital audio. CONSTITUTION:A PCM audio signal impressed to an input terminal 1a is inputted to class ''B'' amplifying parts 2, 3a, 3b and 4 of the first amplifying circuit through a ditial delay element 34. This signal is supplied as a switching signal to a switching power source 18 of the second amplifying circuit through a PWM converting part 50, and power is supplied to amplifying parts 2, 3a, 3b and 4. Thus, the PCM digital signal is used as the input source, and the second amplifier is provided, and its output is supplied as the collector voltage of the first amplifier, thereby obtaining a miniaturized, lightweight, and high- efficiency amplifier superior in tone quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a high efficiency power amplifier suitable for digital audio.

[Technical background of the invention and its problems]

The most commonly used audio amplifier in the past is the 8EPP amplifier of class A or class B operation shown in FIG. 1 is the input terminal, 2 is the drive circuit, 3a and 3b
is a transistor, 4 is a load, and 5a and 5b are DC power supplies. Whether this amplifier operates in class A or class B operation is determined by the idle current flowing through the transistors 3a and 3b caused by the bias circuit. Class A operation is of high quality, but the efficiency is much lower than that of class B operation, so most amplifiers operate in class B operation. The class 9 amplifier (PW) shown in Fig. 2 is still more efficient than the class 8 amplifier.
M amplifier). In this method, an input signal is converted into a PWM signal by a PWM signal converter 6, this is switched by a power switch 7, and demodulated by a low-pass fink 8.
Supply to load 4. Since the single power stage is an on/off switch operation, it is extremely efficient. Figure 3 shows the relationship between output and correction loss for class 8 and class 9 amplifiers.
It can be seen how the loss of 10 in a class 9 amplifier is smaller than the loss of 9 in a class 9 amplifier. However, this class D method contains a large amount of PWM Tsukugo's own signal, and the Jiro pass filter 8 cannot necessarily remove distortion sufficiently. In order to improve frequency characteristics and reduce distortion, G(Z
It is not used as an audio amplifier because it requires switching at high speeds, making it expensive despite its quality. The 4th class amplifier has traditionally been considered to be able to reduce the distortion of class 0 amplifiers and increase the efficiency of class 3 amplifiers at the same time.
This is the method shown in FIGS.

First, in Fig. 4, the AC100V input terminal 1181
11b, 1: The obtained AC is connected to the rectifier diode 12a
, 12b112c 112d rectify it and smooth it with a capacitor 13 to obtain a DC voltage, which is switched by a switching transistor 14 and then passed through a transformer 15 to a diode 16a.

The output of the section 18, which corresponds to a so-called switching power supply, is rectified by 16b and smoothed by capacitors 17a and 17b, and is connected to transistors 3a and 3b of a 5EPP amplifier.
is supplied as the power supply voltage to the collector of At this time, the switching wave of the switching transistor 14 is based on an M wave obtained by converting the input signal into an absolute value signal by an absolute value circuit 19, adding an appropriate direct current, and then obtaining an N modulation section 20. An example of the configuration of the m modulation section 20 is as shown in FIG.
Two waveforms are obtained using this output. Furthermore, this P
The switching transistor 4 is driven via the driver circuit 23 with the wM waveform. The voltage waveforms thus obtained supplied to the collectors of the transistors 3a and 13b are respectively 24a and 24b in FIG. 6, and the voltage waveform applied to the load 4 is 25. As can be seen in FIG. 6, the collector loss during operation of the transistor 3a13b is significantly reduced because the collector-emitter voltage is maintained at a constant value.

However, due to the fluctuation of the balance N, the switching operation, and the smoothing circuit, there is a time delay in the waveforms 24a and 24b compared to the input signal, so that the output waveform 25 is distorted, especially at high frequency and large amplitude. In order to improve this time delay, attempts have been made to insert an analog delay into the main signal section, but the analog delay causes significant deterioration in sound quality and impairs the sound quality of the amplifier. Next, the method shown in FIG. 7 is also a method that attempts to simultaneously achieve the high sound quality and high efficiency that have been seen in the past. In other words, the input signal is temperature-converted by the N conversion circuit 20, and the so-called "Ko" (amplifier 26 is driven), and its output is passed through the floating power supply 5a1 to the collector voltage of the final stage output transistors 3a and 3b of the conventional amplifier section. Therefore, the collector voltage is
As shown in the figure, it is possible to completely follow the output voltage 28 supplied to the load 4 (27a and 27b), especially when 3a and 3b operate in class A.
Yo, batL, 7 It's a, Ega.

There is a delay due to the smoothing circuit. Furthermore, the method shown in FIG. 9 is also a conventional example that attempts to achieve both high quality and high efficiency, and the input signal is subjected to P%I modulation in the rear field M modulation circuit 20 which adds an appropriate DC current to the switcher 14a114b. Smoothing circuits 30a, 31a and 30b131b
Smoothing is performed by the final stage transistor 3a of the amplifier section.

The collector'&L ratio is fully supplied to 3b. Here 29a,
29b is a clamper diode. In FIG. 10, the collector voltage of this system is shown at 32a, 32b, and the load end voltage is shown at 33. In this method as well, there is a delay in the same respects as in the above two methods, and sufficient characteristics cannot be obtained in terms of slew rate.

[Purpose of the invention]

The present invention was made to eliminate these drawbacks of conventional power amplifiers, and aims to provide a compact, lightweight, and highly efficient power amplifier that uses a PGvi digital signal as an input source, has excellent sound quality, and is compact, lightweight, and highly efficient. That is.

[Summary of the invention]

The present invention converts a digitized audio signal into an input signal, supplies this to a first amplifier circuit via a digital delay element, a D/A converter, and a low-pass filter, and converts the input signal into a clear signal. A conversion circuit that performs foot conversion and a second amplifier circuit that is switched by the obtained m signal are provided, and the second amplifier circuit supplies power to the first amplifier circuit.

[Embodiments of the invention]

FIG. 11 shows a first embodiment of a power amplifier according to the present invention. A PCM audio signal is input to the input terminal 1a. This input signal is converted into an analog signal by a D/A converter and a low-pass filter 35 via a digital delay element 34, and is converted into an analog signal by a conventional class 8 amplifier section (drive circuit 2, transistor 3a13b, load 4). As this digital delay element, dynamic RAM1 static RA
M, shift register ζ, etc. are suitable. On the other hand, the input signal passes through the product 1 converter 50 and is supplied to the switching power supply 18 as a switching signal. The circuit configuration of the circular conversion section 500 includes a binary geo. One is D/A as shown in Figure 12.
The signal is converted into an analog signal by a converter and a low-pass filter 35a, converted into an absolute value by an absolute value circuit 19, and converted into PVvM by a high modulation circuit 20, as in the example shown in FIG. Since the D/A converter 35a is used to obtain a signal for generating a power supply voltage for a class 8 amplifier using the switching power supply 18, high precision is not required, and 8 to 12 bits is sufficient. On the other hand 3
The D/A converter 5 is for the main signal section and requires the same number of bits as the input signal. The other method shown in FIG. 13 is to convert the PCM input signal into two while keeping it digital. First, the sign of the PCM input signal is converted into a folded binary code, and the sign bit (MSB) is set to a constant value '1.
, // , J or 'D'' to perform absolute value encoding. This digital absolute value encoding unit is 37.

Next, the signal passes through a digital adder 38 that adds an appropriate DC constant value, and then a PS'1M converter 39 converts the switching {M} signal from the digital signal. That is, as shown in FIG. 14, a serial/parallel converter 40 converts the signal into a parallel signal, the upper 8 bits of the signal are counted by programmable counters 42a and 42b, and a flip-flop 43 forms a PWM signal. 40.42a,
42b43 and all digital input signals clock 4
1. What should be noted here is the V of the main signal section.
It is necessary to take into consideration the phase rotation υ caused by the low-pass filter after A in the case of digital interpolation, and a phase equalizer 36 should be inserted as in the embodiment of FIG. This 36
In reality, a digital filter seems to be optimal. By the way, both of the two circuit configurations described above have advantages and disadvantages. IC
Although it can be said that the second circuit configuration is suitable for this purpose, due to the relationship of the clock frequency of the counter, the culm N signal is equal to or about the same as the sampling frequency of the PCM signal (50KE).
The first circuit configuration seems to be more appropriate for performing high-frequency switching. Because■
Since the χ signal reproduction band is 201G (up to Z), the cutoff of the smoothing sections 17a and 17b should be maintained up to 20IGJ7, and the waveform obtained through this smoothing section should have low ripple. This is because it is advantageous to increase the number of switching cycles.

1! FIG. 15 shows a second embodiment corresponding to the second conventional example according to the present invention. Similarly, a digital signal is input to the input terminal 1a, converted into an analog signal by the D/A converter and low-pass filter 35 via the digital delay element 34, and input to the main signal section of the amplifier. On the other hand, the FWM signal of the PWM amplifier is generated by a PWM converter 50 from a digital signal. For the culm conversion, the input signal is converted into an analog signal by the D/A converter and the low-pass filter 35a, and the culm modulation circuit 2
There is a first circuit configuration formed by comparing the voltage at 0 with a triangular wave using a voltage comparator, and a second circuit configuration formed by the method shown in FIG. 14 via a digital phase equalizer.

Furthermore, FIG. 16 shows a third embodiment of the present invention. 51 and 52 are P'R'M converters, and it is necessary to add a certain amount of direct current to each of them at the preceding stage. There are two ways to add direct current: analog or digital, as in the first embodiment. The subsequent modulation method can similarly be based on two methods: analog and digital.

〔Effect of the invention〕

As described above, according to the present invention, the first embodiment improves the efficiency of the class 8 amplifier without deteriorating the sound quality at least below 20 KIIz using digital input signals. This makes it possible to achieve higher efficiency in class A or class 8 amplifiers. Further, according to the present invention, since the amplifier main signal section and the switching section are separated in the digital signal section, switching noise does not propagate to the main signal section, and low noise and low distortion can also be achieved.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional class A or class B power amplifier, Figure 2 is a configuration diagram of a conventional D@power amplifier, and Figure 3 is a comparison of collector loss between a conventional class B power amplifier and a class D power amplifier. 4 is a circuit diagram of another conventional power amplifier, FIG. 5 is a circuit diagram of an h to M modulation section used in the power amplifier of FIG. 4, and FIG.
The figures are an explanatory diagram of the operation of the power amplifier of Fig. 4, Fig. 7 is a circuit diagram of yet another conventional power amplifier, Fig. 8 is an explanatory diagram of its operation, and Fig. 9 is an illustration of the conventional or still other power amplifier. The circuit diagram, FIG. 10 is an explanatory diagram of its operation, and FIG. 11 is the first circuit diagram according to the present invention.
FIG. 12 is a circuit diagram of the embodiment of R in the first embodiment.
■4 The first circuit example of the conversion unit, Figure 13 is the second circuit example of the PWM conversion unit in the first embodiment, Figure 14 is the circuit example of the ceramic conversion unit, and Figure 15 is the circuit example of the PWM conversion unit in the first embodiment. FIG. 16 is a circuit diagram of the third embodiment of the present invention. 1a...Input terminal 2...Drive circuit 3a
, 3b...Transistor 4...Load 18...Switching power supply 34...Digital delay element 35...
・D/A converter and low-pass filter 50... Yen conversion department representative Patent attorney Kensuke Chika (and 1 other person) Fig. 1 Fig. 2 Fig. 3 Pψ/mine No. 4 Fig. 7 Fig. 8 Figure 9 Figure 1I Figure 21 Re I Figure 2 , (!θ Figure 14 Figure 15

Claims (1)

[Claims] An input terminal that receives a digitized audio signal as an input signal, a digital delay element with one end connected to this input terminal, and a D/A converter and a low-pass filter connected to the other end of the digital delay element. Q-switching is performed by the PWM signal obtained by the PWM conversion circuit of the connected first amplifier circuit and the input signal range conversion circuit connected to the input terminal, and the input signal is Q-switched to the first amplifier circuit. A power amplifier comprising a second amplifier circuit using a switching method for supplying power.