Triangular wave generating method and triangular wave generating circuit applied to D-class audio frequency amplifier

Abstract

The invention discloses a triangular wave generating method and a triangular wave generating circuit applied to a D-class audio frequency amplifier. The triangular wave generating method includes forming first reference voltage and second reference voltage according to feedback parameters in proportion to power supply voltage at an output stage of the D-class audio frequency amplifier and first voltage with a preset value, and enabling values of the first reference voltage and the second reference voltage to be a difference value and a sum value of the value of the first voltage and a value of second voltage in proportion to the power supply voltage respectively; using charging current and discharging current to charge and discharge a charge-discharge capacitor respectively, and enabling the first reference voltage and the second reference voltage to be a wave valley and a wave peak of voltage on the charge-discharge voltage; acquiring triangular waves, with common mode voltage to be the first voltage constantly and with amplitude in proportion to the power supply voltage, at two ends of the charge-discharge capacitor. When the triangular waves generated by the method are applied to the D-class audio frequency amplifier, accuracy in outputting of PWM (pulse width modulation) signals can be guaranteed, stability of a loop can be ensured without sacrificing power consumption and area performance, and increasing of production cost is avoided.

Description

technical field [0001] The invention relates to the field of electronics, in particular to a method and circuit for generating a triangular wave applied to a Class D audio amplifier. Background technique [0002] In the class D audio amplifier, pulse width modulation technology, that is, PWM (Pulse-Width Modulation) technology is needed. After the audio signal is modulated by PWM, it is output to control the switching state of the switch tube in the output stage of the class D audio amplifier. Pulse signal. [0003] Such as figure 1 (a) and figure 1 As shown in (b), the audio signal V in The triangular wave signal V output by the triangular wave generating circuit tri The comparison is performed by the comparator Comp to generate a PWM signal whose output pulse width is proportional to the amplitude of the audio signal input to the comparator Comp. Therefore, an indispensable part in PWM modulation is a triangular wave generating circuit. The triangular wave signal gen...

AI Technical Summary

Problems solved by technology

[0004] In the prior art, when the triangular wave signal whose common-mode voltage changes is input to the comparator, if its common-mode voltage changes to exceed the common-mode voltage input range of the comparator, the comparator will fail to perform comparison or output a wrong signal. PWM signal, which affects the performance of the Class D audio amplifier

In addition, the PWM modulation transfer function G pwm The value is the amplitude of the output PWM signal and the triangle wave signal V tri The ratio of the magnitudes of G pwm It needs to be constant to ensure the stability of the class D audio amplifier. In practical applications, the switching action of the switching tube in the output stage will cause the transient current to affect the power supply voltage V of the output stage circuit in practical applications. DD (the power supply voltage of the output stage circuit) has a relatively large impact, making the power supply voltage V DD There will be fluctuations, that is, the amplitude of the PWM signal will change

therefore, figure 2 Such a constant-amplitude triangle wave signal as shown cannot make G pwm Constant to ensure the stability of the class D audio amplifier loop, which requires sacrificing the power consumption and area of ​​the class D audio amplifier to improve the stability of the loop, and at the same time increase the production cost

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