JPS6345907A - Power amplifier - Google Patents

Abstract

PURPOSE:To realize low noise and high efficiency of an amplifier by connecting an audio signal in opposite phase and a carrier signal in phase, a balanced transformerless (BTL) fashion and connecting a capacitor in parallel with a load. CONSTITUTION:In extracting a pulse signal subjected to power amplification via a low-pass filter 5, a low frequency output signal similar to an audio input signal from which a signal component corresponding to a carrier signal is eliminated is fed to one terminal of the load. In extracting the signal via a low-pass filter 5', since the signal passes through an inverting circuit 8, the low frequency output signal of opposite phase is fed to the other terminal of the load. That is, because of BTL connection, a low frequency signal having a double output voltage is extracted across the load. Then the signal through the low-pass filters 5, 5' is fed back to preamplifier circuits 1, 1' via feedback circuits 6, 6'. Further, a leaked carrier signal component after the low-pass filters 5, 5' is cut off by a capacitor 9 connected in parallel with the load 7.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a PWM (Pulse Width Modulation) type power amplifier that pulses an analog input signal and amplifies the vane force.

Conventional technology Conventionally, class A amplifiers have been used as audio amplifiers.

Class B amplifiers are known, and when emphasis is placed on acoustic characteristics such as distortion rate, class A amplifiers are often used, and from the standpoint of amplifier efficiency, class B amplifiers are often used. However, in the car audio field where power supply capacity is limited, higher output is being promoted, and amplifier efficiency is becoming increasingly important. The actual efficiency at low output is extremely poor.

Therefore, in consideration of the poor efficiency of conventional amplifiers, emphasis has recently been placed on high-efficiency amplifiers based on pulse width modulation, so-called so-called class D amplifiers.

Hereinafter, a conventional class D amplifier will be explained with reference to FIG.

In Figure 2, 1 is a preamplifier circuit, 2 is a triangular wave generation circuit, 3 is a comparison circuit, 4 is an output amplifier circuit, 5 is a low-pass filter consisting of a coil and a capacitor, 6 is a feedback circuit, and 7 is a load. It is.

The operation of the class D amplifier configured as described above will be explained below.

First, an audio input signal is applied to the preamplifier circuit 1 and input to one input terminal of the comparator circuit 3. Further, the other input terminal of the comparison circuit 3 receives a triangular wave which is a carrier signal generated by the triangular wave generation circuit 2, and the comparison circuit 3
A pulse signal whose pulse width is modulated according to the amplitude of the audio input signal is output from the input signal. That is, a pulse signal whose period is equal to that of the carrier signal and whose pulse duty ratio changes depending on the amplitude of the audio input signal is obtained. This pulse signal is supplied to the output amplifier circuit 4,
Power is amplified by driving the switching elements in the output amplification circuit 4. When the power-amplified pulse signal is extracted through the low-pass filter 6, the signal component corresponding to the carrier signal is removed, and a low-frequency output signal similar to the audio input signal is supplied to the load 7. Furthermore, by feeding back the signal that has passed through the low-pass filter 6 to the preamplifier circuit 1 via the feedback circuit 6, the modulation characteristics and overall characteristics can be improved.

Problems to be Solved by the Invention However, if the maximum transmission frequency of the audio signal band is 20 KHz, the carrier frequency is usually selected to be 5 times or more, or 100 KHz or more.

A low-pass filter is required to remove this carrier frequency component, but you can increase the value of the coil and capacitor, or connect multiple stages of low-pass filters in series, but if the value is increased, the reproduction band will become narrower. become, again,
If multiple stages are connected in series, there is a problem that feedback cannot be stably applied due to the phase rotation of the signal. There is also the problem of increasing output in the car audio field, where power supply capacity is limited. Solving both of these problems is important for practical use as an audio amplifier.

The present invention provides a high-efficiency, large-output, class D power amplifier that solves the above problems.

Means for Solving the Problems To achieve this object, the power amplifier of the present invention includes a comparator circuit that compares the output signal of the preamplifier circuit to which the 5-page analog signal is applied and the output signal of the triangular wave generator circuit. B T is a class D power amplification system consisting of an output amplification circuit that amplifies the power of the pulse width modulation signal output from this comparison circuit, a low-pass filter that removes the carrier signal component, and a feedback circuit.
L (Balanced Transformer L
A load is connected between the outputs of the low-pass filters of the 6th system, and a capacitor is connected in parallel with this load.

Function: With this configuration, the leakage carrier signal component after passing through the low-pass filter is cut by the capacitor.

In addition, since the low-pass filter is one stage (ie, a second-order filter), there is little phase rotation, and feedback can be stably applied.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a power amplifier in one embodiment of the present invention. In Figure 1, 1 and 1' are preamplifier circuits to which A6 page analog signals are applied in positive and negative phase, respectively, 2 is a triangular wave generation circuit, and 3 and 3' are preamplifier circuits 1.
, 1' and the triangular wave generation circuit 2.
, 2' are applied and compared with the triangular wave signals output from the comparator circuits 3, 4', and 4, 4' drive the switching elements with the output pulses of the pulse width modulation signals output from the comparator circuits 3, 3', and generate power. Output amplification circuits 5 and 5' have capacitors and coils, and the output pulses of output amplification circuits 4 and 4' are integrated through low-pass filters, 6 and 6', and outputs of halo-pass filters 6 and 6' are passed through. The feedback circuit that feeds back to the stationary amplifier circuits 1 and 1' constitutes a class D power amplification system. 7 is a load connected between the outputs of the low-pass filters 5 and 5', 8 is an inverting circuit, and 9 is a capacitor connected in parallel with the load 7.

The operation of the power amplifier configured as above will be explained below.

First, one of the audio input signals is input to the preamplifier circuit 1, and its output is input to one input terminal of the comparator circuit 3. The other seven pages of audio input signals are input to a preamplifier circuit 1' through an inversion circuit 8, and the output thereof is input to one input terminal of a comparator circuit 3'.

The triangular wave, which is a carrier signal generated by the triangular wave generating circuit 2, is input to the other input terminal of each comparator circuit 3, 3', and the signal is output from each comparator circuit 3, 3' according to the amplitude of the in-phase audio input signal. A pulse width modulated pulse signal is output. This pulse signal is supplied to each output amplification circuit 4, 4' and is amplified by driving the switching elements in each output amplification circuit 4, 4'. When the power-amplified pulse signal is extracted through the low-pass filter 5, the signal component corresponding to the carrier signal is removed, and a low-frequency output signal similar to the audio input signal is supplied to one of the loads.

Further, when the signal is taken out through the low-pass filter 5', a low-frequency output signal with an opposite phase is supplied to the other side of the load because it is passed through the inverting circuit 8. In other words, because of the BTL connection, a low frequency signal with twice the output voltage can be extracted at both ends of the load. Next, the signals that have passed through the low-pass filters 5 and 5' are sent to the preamplifier circuits 1 and 1 via the feedback circuits 6 and 6'.
Return to '. Meanwhile, the leakage carrier signal component after passing through each =3-pass filter 5, 5' is cut by a capacitor 9 connected in parallel with a load 7.

According to this embodiment, as shown in μ, the capacitor 9 is connected to the load 7.
By connecting in parallel with the low-pass filters 5, 5
' has a simple configuration, and since carrier signal components can be removed, noise can be reduced.

Effects of the Invention In the present invention, since the audio signal is in reverse phase and the carrier signal is in the same phase for BTL connection, the carrier components cancel each other out, but there is no leakage carrier signal generated due to variations in the output amplifier circuit and low-pass filter elements. Since the component is cut by the capacitor connected in parallel with the load,
Carrier components can be completely removed, making it possible to reduce noise. Furthermore, since the low-pass filter can be configured with a simple single stage, phase rotation is less likely to occur and feedback can be stably applied. Further, while taking advantage of the high efficiency of class D amplification, the output voltage is doubled, and the output power is 4 times as much as 9 pages, making it possible to increase the output even when the power supply capacity is limited. Therefore, it is possible to realize an excellent power amplifier that can achieve the effects of high output, high efficiency, and low noise required for audio amplifiers.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a power amplifier according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional power amplifier. 1.1'...Preamplifier circuit, 2...Triangular wave generation circuit, 3,3'...Comparison circuit, 4,4
'...Output amplifier circuit, 5.5'...Low pass filter, 7...Load, 8...
Inverting circuit, 9... Capacitor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (1)

[Claims] a preamplification circuit to which an analog signal is applied; a triangular wave generation circuit; a comparison circuit to which a modulated input signal output from the preamplification circuit and an output triangular wave signal of the triangular wave generation circuit are applied; and the comparison circuit. The switching element is driven by the output pulse of the pulse width modulation signal output from the
A class D power amplification system is BTL-connected, and includes an output amplification circuit that performs power amplification, a low-pass filter that integrates output pulses of the output amplification circuit, and a feedback circuit that returns the output of the low-pass filter to the preamplification circuit. , A power amplifier characterized in that a load is connected between the outputs of the low-pass filters of each system, and a capacitor is connected in parallel with the load.