JPH0321058Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to improvements in class D amplifiers.

In this specification, a class D amplifier refers to an amplifier that pulse-width-modulates an input audio signal, amplifies the power of the pulse-width-modulated signal, filters it, and outputs it.

A conventional class D amplifier was constructed as shown in FIG. In FIG. 1, 1 is a sawtooth wave or triangular wave modulated signal oscillator, and 2 is a comparator, which compares the input audio signal applied to input terminal a with the output of the modulated wave oscillator 1. In comparison, the input audio signal is pulse width modulated, the pulse width modulated wave is amplified into a large current, high voltage pulse width modulated wave by the power amplifier 3, and then filtered by the low pass filter 4 to obtain an audio signal. ing. Note that 5 is a load.

However, when using the above-mentioned conventional class D amplifier, there is a drawback that distortion occurs in the output signal due to accumulation, delay, etc. that occur when a large current is passed through the output stage amplification element of the power amplifier.

Further, due to the above, there was a problem in that an expensive element had to be used as the output stage amplifying element.

The present invention has been made in view of the above, and an object thereof is to provide a class D power amplifier that eliminates the above-mentioned drawbacks and problems.

The present invention will be explained below with reference to examples.

FIG. 2 is a block diagram of one embodiment of the present invention.

In FIG. 2, the same components as those of the conventional class D amplifier shown in FIG. 1 are designated with the same reference numerals.

One embodiment of the present invention is a balanced, transformerless (hereinafter referred to as BTL) output stage of the power amplifier 3 that constitutes the conventional class D amplifier shown in FIG.
It consists of a circuit and is indicated by 3 ₁ in FIG.
This _BTL power amplifier ₃₁ is composed of a first power amplifier _3A and a second power amplifier _3B . Amplify the signal as input,
The second power amplifier _3B receives the output of the modulated signal oscillator 1 as an input, and is configured to amplify the output of the second comparator _2B which switches the modulated signal without modulation.

The functions of the modulated signal generator 1, the first comparator 2, the first power amplifier _3A , and the low-pass filter 4 are the same as those of a conventional class D amplifier, and their explanation will be omitted. The output of the modulated signal oscillator 1 is subjected to non-modulated switching and power amplified by the second comparator _2B and the second power amplifier _3B . Now, the phase at this time is in phase with the switching phase of the class D amplifier, which is composed of the modulated signal oscillator 1, the first comparator 2, the first power amplifier _3A , the low-pass filter 4, and the load 5, when no modulation is performed. shall be.

Then, when the input audio signal is applied to the comparator 2, the output point b of the first power amplifier _3A is shown in FIG.
A pulse width modulated signal with a waveform shown in is output. On the other hand, an unmodulated signal having the waveform shown in FIG. 3d is outputted to the output point d of the second power amplifier _3B . When the waveforms shown in FIGS. 3b and 3d are combined, a signal waveform as shown in FIG. 3b-d is obtained. When the waveform signals shown in FIG. 3b-d pass through the low-pass filter 4, a power-amplified audio signal is obtained.

Next, distortion in one embodiment of the present invention will be explained. Figure 4 shows the waveform when a current flows through a pulse width modulated signal, Figure 4a is the waveform when the current is zero, Figure 4b is the waveform when the current is small, and Figure 4c. 4 shows the waveforms when the current is large, and in FIGS. 4b and 4c, the shaded areas are the parts that have collapsed due to the flow of current, and as is clear from FIGS. 4a to 4c, the waveforms change as the current increases. The degree of distortion is also large, which in turn causes distortion in conventional class D amplifiers.

However, D of an embodiment of the present invention shown in FIG.
According to the class amplifier, the current flowing to the output point b of the first power amplifier _3A as the current increases is (d-
1), (e-1), and (f-1), and the current flowing to the output point d of the second power amplifier _3B is (d-2), (e-2), and (f-1). It collapses as shown in -2). However, if elements with the same or similar characteristics are used as the output amplification elements of the first power amplifier _3A and the second power amplifier _3B , the currents flowing will be approximately equal and the waveforms will be distorted in the same way. Diagram e
The areas between the solid line and the broken line at and f are the same, and the distorted portions cancel each other out, eliminating the occurrence of distortion.

As explained above, according to the present invention, distortion caused by accumulation of output elements and delay is canceled out, and no distortion occurs.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional class D amplifier, Figure 2 is a block diagram of a conventional class D amplifier.
The figure is a block diagram of one embodiment of the present invention, FIG. 3 is a waveform diagram showing the operating principle of one embodiment of the present invention, and FIG. 4 is a waveform diagram for explaining the operation of one embodiment of the present invention. . 1... Modulated signal oscillator, 2 and 2 _B ... First and second comparators, 3 _A and 3 _B ... First and second power amplifiers, 4... Low pass filter, 5... Load.

Claims (1)

[Scope of utility model registration request] a first comparator that compares an input audio signal with a modulated signal obtained from a modulated wave signal generator and pulse-width-modulates the input audio signal; a first power amplifier that amplifies power; a second comparator that receives the modulated wave signal obtained from the modulated wave signal oscillator as input and obtains an unmodulated pulse width modulated wave; a second power amplifier for power amplifying the obtained pulse width modulated wave;
A class D amplifier, characterized in that a load is connected between the output point of the power amplifier and the output point of the second power amplifier.