CN1681203A

CN1681203A - Low distortion and radiation D-type amplifier

Info

Publication number: CN1681203A
Application number: CN 200410002112
Authority: CN
Inventors: 李相前
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-01-09
Filing date: 2004-01-08
Publication date: 2005-10-12

Abstract

The invention introduces generative feedback at the input and output terminal of the comparator which largely reduces the distortion.

Description

Low distortion hangs down radiation D class A amplifier A

Affiliated technical field

The present invention relates to a kind of D class A amplifier A.Be used for the power amplification of the power amplification of signal, particularly audio signal.

Technical background

Existing D class A amplifier A has two kinds of citation forms, wherein a kind of principle one literary composition of seeing practical electronics digest fifth phase D in 1998 class A amplifier A comprises a comparator, adder and integrator, low pass filter, a PWM wave power amplification output stage and exports low pass filter.The PWM ripple of power output stage output relatively modulates the PWM ripple through low pass filter and input signal addition by integrator input comparator and triangular signal.Another kind of circuit comprises comparator, adder integrator, PWM wave power output stage, reaches the output low pass filter.Input signal modulates the PWM ripple by adder, integrator with the triangular wave input comparator, and by power output stage output, power output PWM ripple feeds back to adder and finishes negative feedback.The distortion of two kinds of D class A amplifier As is all bigger, the noise that the main source of distortion is that the power output stage transistor exists that conducting is delayed, diode drop produced when power supply was gone in the tube voltage drop during the output transistor conducting and the feedback of output low pass filter inductive current.The depth of feedback of D class A amplifier A is subjected to the restriction of switching frequency, and these distortions can not be effectively suppressed by negative feedback, especially high frequency distortion.Exporting low pass filter in addition is Bart's Olds filter of cascade, because adding magnetic core and shielding can make the non-linear of inductance increase greatly, is difficult to meet the demands.

Summary of the invention

The technical problem to be solved in the present invention is: reduce the distortion of D class A amplifier A, improve the Electro Magnetic Compatibility of amplifier.The technical solution adopted in the present invention is as follows:

1, triangular wave and input signal relatively modulate the PWM ripple in comparator, take out the input of the positive and negative feed-in comparator of fundamental signal from the PWM ripple of comparator output, promptly introduce positive feedback at the output and the input of comparator.This scheme can realize with digital circuit, also can realize with analog circuit.Comparator can be regarded the PWM wave modulator of a linearity as, the PWM ripple duty ratio of output is directly proportional with incoming signal level, can regard the amplifier of a linearity as for the input signal comparator, by positive feedback, the multiplication factor of this amplifier is increased, the whole amplification loop gain that comprises power output stage is improved, thereby the closed loop distortion is minimized.As positive feedback coefficient F therewith during the product AF=1 of the open loop multiplication factor A of amplifier, gaining is infinity.Draw the input formation closed loop of negative feedback from final stage, distortion is reduced to comparator.Can realize positive feedback with following way.PWM ripple by comparator output obtains the PWM ripple of an and constant amplitude identical with its duty ratio, (this can by obtaining) than the PWM ripple amplitude limit of device output with this PWM ripple by a low pass filter after the positive and negative input that is fed to comparator, it is minimum for distortion is reduced to, should make this regenerative circuit of AF=1. owing to there is low pass filter, make the high frequency feedback coefficient descend and the generation phase shift, so high frequency distortion is bigger.

Description of drawings

Fig. 1 is the schematic diagram of a kind of D class A amplifier A embodiment.

Fig. 2 is the schematic diagram of a kind of D class A amplifier A embodiment.

Embodiment

Fig. 1 is the schematic diagram of the embodiment of a D class A amplifier A, and the PWM ripple of comparator output is sent into the input of comparator by behind the amplitude limiter amplitude limit among the figure after low pass filter filtering, has realized positive feedback.

Fig. 2 is the schematic diagram of the embodiment of a D class A amplifier A, and among the figure, the PWM ripple of comparator output via exporting by amplifier A1 buffering after the low pass filter filtering of R2, C2, formation, is sent into comparator and finished positive feedback behind diode D1, D2 amplitude limit.

Claims

1, a kind of D class A amplifier A comprises comparator, adder integrator, the defeated level of PWM wave power, reaches the output low pass filter, triangular wave and input signal relatively modulate the PWM ripple in comparator, it is characterized in that: from the PWM ripple of comparator output, take out the input of the positive and negative feed-in comparator of fundamental signal, promptly introduce positive feedback at the output and the input of comparator.

2, according to the described D class A amplifier A of claim 1, it is characterized in that: the PWM ripple by comparator output obtains the PWM ripple of an and constant amplitude identical with its duty ratio, with this PWM ripple by a low pass filter after the positive and negative input that is fed to comparator.