WO2022021505A1

WO2022021505A1 - Digital power amplifier for current feedback self-excited oscillation audio of filter capacitor

Info

Publication number: WO2022021505A1
Application number: PCT/CN2020/110399
Authority: WO
Inventors: 张金路
Original assignee: 张金路
Priority date: 2020-07-27
Filing date: 2020-08-21
Publication date: 2022-02-03
Also published as: CN111740714A

Abstract

A digital power amplifier for current feedback self-excited oscillation audio of a filter capacitor, which digital power amplifier relates to the field of digital power amplifiers. The digital power amplifier comprises: a voltage feedback outer-loop circuit, a current self-excited inner-loop circuit, an MOS driving circuit and an LC circuit, wherein an input end of the LC circuit is connected to an output end of the MOS driving circuit, an output end of the LC circuit is connected to the voltage feedback outer-loop circuit and provides output voltage feedback, and the capacitance current of the LC circuit serves as a feedback signal of the current self-excited inner-loop circuit; an input end of the voltage feedback outer-loop circuit is connected to an input voltage VIN, and an output end thereof outputs a control voltage VM to an input end of the current self-excited inner-loop circuit; and an output end of the current self-excited inner-loop circuit is connected to an input end of the MOS driving circuit. The digital power amplifier has the advantages of a high loop stability, an extremely small output impedance, an extremely high power supply rejection ratio and easy current sampling.

Description

Filter capacitor current feedback self-oscillating audio digital power amplifier

technical field

The invention relates to a digital power amplifier, in particular to a filter capacitor current feedback self-excited oscillation audio frequency digital power amplifier.

Background technique

Traditional Class D digital power amplifier, the principle used by most products on the market today, generally uses the voltage feedback before LC, generates an error signal and compares it with a triangular wave, obtains a PWM signal to drive the switch tube, and then filters the output by LC. This circuit does not directly control the output voltage, and the loop is difficult to adjust quickly, and the sound quality is worse than that of an analog power amplifier.

IR company's integrated chip principle, using LC front voltage feedback, self-excited to generate PWM signal to drive the switch tube, the performance is basically the same as the traditional class D digital power amplifier.

Patented circuit used in a foreign power amplifier: inventor Bruno Putzeys, company hypex, patent number 101814899, adopts output voltage feedback, uses LC oscillation characteristics and phase control, makes it self-excited at the operating frequency, and achieves extremely high-speed control characteristics and performance It is more than ten times higher than the traditional circuit, and the sound quality is extremely high.

The patents CN101517891A and CN101395793A applied by two foreign companies both obtain feedback signals from the front and rear of the LC at the same time, and generate a PWM signal through a complex combination of self-excitation. The performance is comparable to that of a power amplifier circuit disclosed in Patent No. 101814899.

Patent document CN1471758A discloses a power amplifier circuit, the output inductor current feedback self-excitation mode, the stability and dynamic performance can be very high, but the output impedance is an order of magnitude higher than the output impedance of the power amplifier circuit disclosed above, and the high frequency performance is not good. , which leaves insufficient control over the horn.

SUMMARY OF THE INVENTION

In order to solve the above technical problems existing in the prior art, the present invention discloses a filter capacitor current feedback self-excited oscillation audio digital power amplifier, the specific technical scheme of which is as follows.

A filter capacitor current feedback self-excited oscillation audio digital power amplifier, comprising a voltage feedback outer loop circuit, a MOS drive circuit, a current self-excited inner loop circuit and an LC circuit, the input end of the LC circuit is connected to the output end of the MOS drive circuit, The output end of the LC circuit is connected to the voltage feedback outer loop circuit and provides output voltage feedback, and the capacitor current of the LC circuit is used as the feedback signal of the current self-excited inner loop circuit; the input end of the voltage feedback outer loop circuit is connected to the input voltage VIN, and the output The terminal outputs the control voltage signal VM to the input terminal of the current self-excited inner loop circuit; the output terminal of the current self-excited inner loop circuit is connected to the input terminal of the MOS driving circuit.

Further, the LC circuit includes an output inductor L1, an output capacitor C3 and a load element RL, and the current through the output capacitor C3 is used as a current detection feedback signal to be input to the current self-excited inner loop circuit, and one end of the output inductor L1 is connected to a MOS drive. The output end of the circuit, the other end is connected to the same node with one end of the output capacitor C3 and one end of the load element RL, the same node is connected with the voltage feedback outer loop circuit, and the other end of the load element RL is connected with the other end of the output capacitor C3 back ground.

Further, the current of the output capacitor C3 is measured and obtained by the current detection sensor, and the current of the output capacitor C3 is measured as the feedback value of the current detection feedback signal or the current of the output inductor L1 and the current through the load element RL are measured, and the two are measured. The difference is used as the feedback value of the current detection feedback signal.

Further, the current detection sensor includes a high-frequency current transformer or a resistor or a high-frequency current detection chip.

Further, the voltage feedback outer loop circuit includes a resistor R1, a resistor R2, a resistor R3, an operational amplifier U1, a capacitor C1 and a capacitor C2; one end of the resistor R3 is connected to the input voltage VIN, and the other end is connected to the inverting phase of the operational amplifier U1. Input terminal; one end of resistor R1 is connected to one end of resistor R2 and then connected to the other end of resistor R3, the other end of resistor R1 is connected to one end of capacitor C1, the other end of capacitor C1 is connected to the other end of resistor R2 and then connected to the input terminal. The same node described above; one end of the capacitor C2 is connected to the node between the resistor R3 and the resistor R2.

Further, the current self-excited inner loop circuit includes a resistor R5, a resistor R6 and a comparator U2; one end of the resistor R5 is connected to the node between the other end of the capacitor C2 and the output end of the operational amplifier U1, and the other end is connected to the resistor. One end of R6 is connected to the non-inverting input end of the comparator U2; the other end of the resistor R6 is connected to the output end of the comparator U2.

Further, the current self-excited inner loop circuit utilizes the high-frequency fluctuation of the current of the output capacitor C3 to form self-excited oscillation through the comparator U2.

Further, the input end of the MOS drive circuit is connected to the node between the other end of the resistor R6 and the output end of the comparator U2, and the output end is connected to the input end of the LC circuit through the power switch circuit.

The filter capacitor current feedback self-excited oscillation audio digital power amplifier of the present invention has the advantages of high loop stability, extremely small output impedance, extremely high power supply suppression ratio and easy current sampling.

Description of drawings

1 is a schematic diagram of a circuit schematic diagram of the present invention;

Fig. 2 is the step response waveform diagram of the circuit of the present invention;

FIG. 3 is a response waveform diagram when the output of the present invention adds a 10KHZ trapezoidal wave perfusion current.

detailed description

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the filter capacitor current feedback self-excited oscillation audio digital power amplifier of the present invention includes a voltage feedback outer loop circuit, a MOS drive circuit, a current self-excited inner loop circuit and an LC circuit, and the input end of the LC circuit is connected to The output end of the MOS drive circuit and the output end of the LC circuit are connected to the voltage feedback outer loop circuit and provide output voltage feedback, and the capacitance current of the LC circuit is used as the feedback signal of the current self-excited inner loop circuit; the input end of the voltage feedback outer loop circuit The input voltage VIN is connected, and the output terminal outputs the control voltage signal VM to the input terminal of the current self-excited inner loop circuit; the output terminal of the current self-excited inner loop circuit is connected to the input terminal of the MOS driving circuit.

The LC circuit includes an output inductor L1, an output capacitor C3 and a load element RL, and the current through the output capacitor C3 is input to the current self-excited inner loop circuit as a current detection feedback signal, and one end of the output inductor L1 is connected to the output of the MOS drive circuit. The other end is connected to the same node with one end of the output capacitor C3 and one end of the load element RL, the same node is connected to the voltage feedback outer loop circuit, and the other end of the load element RL is connected to the other end of the output capacitor C3 and then grounded.

The current of the output capacitor C3 is measured and obtained by the current detection sensor, and the current of the output capacitor C3 is measured as the feedback value of the current detection feedback signal or the current of the output inductor L1 and the current through the load element RL are measured, and the difference between the two is calculated. As the feedback value of the current detection feedback signal, that is, the current of the output capacitor C3 is equal to the current of the output inductor L1 minus the current of the load element RL. The chip implementation is far simpler than measuring the output inductor L1, because the current flowing through the output capacitor C3 is AC and is at the ground terminal.

The voltage feedback outer loop circuit includes a resistor R1, a resistor R2, a resistor R3, an operational amplifier U1, a capacitor C1 and a capacitor C2; one end of the resistor R3 is connected to the input voltage VIN, and the other end is connected to the inverting input terminal of the operational amplifier U1; One end of resistor R1 is connected to one end of resistor R2 and then connected to the other end of resistor R3, the other end of resistor R1 is connected to one end of capacitor C1, and the other end of capacitor C1 is connected to the other end of resistor R2 and then connected to the same node ; One end of capacitor C2 is connected to the node between resistor R3 and resistor R2.

The current self-excited inner loop circuit includes a resistor R5, a resistor R6 and a comparator U2; one end of the resistor R5 is connected to the node between the other end of the capacitor C2 and the output end of the operational amplifier U1, and the other end is connected to one end of the resistor R6. After being connected, it is connected to the non-inverting input end of the comparator U2; the other end of the resistor R6 is connected to the output end of the comparator U2, the resistor R5, the resistor R6 and the comparator U2 form a hysteresis comparison together, and the hysteresis comparison is used to generate oscillation And make the current of the output capacitor C3 track the control voltage signal VM.

The current self-excited inner loop circuit utilizes the high-frequency fluctuation of the current of the output capacitor C3 to form self-excited oscillation through the comparator U2.

The input end of the MOS drive circuit is connected to the node between the other end of the resistor R6 and the output end of the comparator U2, and the output end is connected to the input end of the LC circuit through the power switch circuit.

Specifically, the key point of the filter capacitor current feedback self-excited oscillation audio digital power amplifier of the present invention is that the current self-excited inner loop circuit uses the current of the output capacitor C3 as the control amount, and the benefits are shown in the following two aspects:

Dynamic characteristics: The current self-excited inner loop circuit uses the comparator U2 to form self-excited oscillation by using the high-frequency fluctuation of the current of the output capacitor C3, and transforms the characteristics that are not easy to control in the LC circuit into the integral characteristics of the current source and capacitor, so that the voltage feedback outer loop The circuit can use very high loop control speed, stability and frequency response bandwidth can achieve very high performance. As shown in Figure 2, when the circuit operates at a frequency of 400KHZ, V(aim) is the ideal output waveform after the input signal is amplified by the amplifier, V(OUT) is the output voltage, I(L1) is the output inductor current, and the output is relatively smooth. In the case of overshoot, the response delay time is only 6us, which reflects the very high bandwidth of the circuit frequency response.

Output Impedance: The key benefit of using capacitive current control is that it incorporates the output current, a comparative integral control loop that is effectively equivalent to zero error inductor current and load current, and is very fast, allowing adjustment in a single cycle. That is to say, when the load current changes, the current self-excited inner loop circuit adjusts the inductor current so that the capacitor current does not change. In this process, the control voltage signal VM of the voltage feedback outer loop circuit does not need to respond. In theory, the full frequency range is zero output impedance; as shown in Figure 3, V(OUT) is the output voltage, I(I3) is the perfusion current applied to the OUT node, and I(L1) is the output inductor current. The figure shows that the inductor current follows well The effect of the perfusion current is quickly canceled, and the perturbation on V(OUT) is very small, reflecting a very low output impedance.

The voltage feedback outer loop circuit outputs the control voltage signal VM to the current self-excited inner loop circuit; the current waveform of the output capacitor C3 is sampled and fed back to the comparator U2 of the current self-excited inner loop circuit, and the control voltage signal is communicated with the control voltage signal through the comparator U2 VM is compared within a certain hysteresis value, so that the capacitor current fluctuates around the control voltage signal VM within the range of the hysteresis value. Originally, the output LC is a second-order characteristic, and the phase shift of the resonance point is close to 180 degrees, which makes the traditional loop very difficult to stabilize and cannot achieve high dynamic response speed. The current self-excited inner loop circuit has changed the original second-order characteristics into first-order characteristics, and the maximum phase shift is only 90 degrees, so the voltage feedback outer loop circuit can be stable even if it is very fast.

Claims

A filter capacitor current feedback self-excited oscillation audio digital power amplifier, comprising a voltage feedback outer loop circuit and a MOS drive circuit, characterized in that it also includes a current self-excited inner loop circuit and an LC circuit, and the input end of the LC circuit is connected to the MOS The output end of the drive circuit, the output end of the LC circuit is connected with the voltage feedback outer loop circuit and provides output voltage feedback, and the capacitance current of the LC circuit is used as the feedback signal of the current self-excited inner loop circuit; the input end of the voltage feedback outer loop circuit is connected to The input voltage VIN is input, and the output terminal outputs the control voltage signal VM to the input terminal of the current self-excited inner loop circuit; the output terminal of the current self-excited inner loop circuit is connected to the input terminal of the MOS driving circuit.
The filter capacitor current feedback self-oscillating audio digital power amplifier of claim 1, wherein the LC circuit includes an output inductor L1, an output capacitor C3 and a load element RL, and the current through the output capacitor C3 is used as a current detection feedback The signal is input to the current self-excited inner loop circuit. One end of the output inductor L1 is connected to the output end of the MOS drive circuit, and the other end is connected to the same node with one end of the output capacitor C3 and one end of the load element RL. The voltage feedback outer loop circuit is connected, and the other end of the load element RL is connected to the other end of the output capacitor C3 and then grounded.
The filter capacitor current feedback self-excited oscillation audio digital power amplifier according to claim 2, wherein the current of the output capacitor C3 is measured and obtained by a current detection sensor, and the current of the output capacitor C3 is measured as the feedback of the current detection feedback signal value or measure the current of the output inductor L1 and the current through the load element RL, and use the difference between the two as the feedback value of the current detection feedback signal.
The filter capacitor current feedback self-excited oscillation audio digital power amplifier according to claim 3, wherein the current detection sensor comprises a high frequency current transformer or a resistor or a high frequency current detection chip.
The filter capacitor current feedback self-excited oscillation audio digital power amplifier according to claim 2, wherein the voltage feedback outer loop circuit comprises a resistor R1, a resistor R2, a resistor R3, an operational amplifier U1, a capacitor C1 and a capacitor C2; One end of the resistor R3 is connected to the input voltage VIN, and the other end is connected to the inverting input end of the operational amplifier U1; one end of the resistor R1 is connected to one end of the resistor R2 and then connected to the other end of the resistor R3, and the other end of the resistor R1 is connected to the capacitor C1 One end of the capacitor C1 is connected to the other end of the resistor R2 and then connected to the same node; one end of the capacitor C2 is connected to the node between the resistor R3 and the resistor R2.
The filter capacitor current feedback self-excited oscillation audio digital power amplifier according to claim 5, wherein the current self-excited inner loop circuit comprises a resistor R5, a resistor R6 and a comparator U2; one end of the resistor R5 is connected to the The node between the other end of the capacitor C2 and the output end of the operational amplifier U1, the other end is connected to one end of the resistor R6 and then connected to the non-inverting input end of the comparator U2; the other end of the resistor R6 is connected to the output end of the comparator U2.
The filter capacitor current feedback self-excited oscillation audio digital power amplifier of claim 6, wherein the current self-excited inner loop circuit utilizes the high-frequency current fluctuation of the output capacitor C3 to form self-excited oscillation through the comparator U2.
The filter capacitor current feedback self-excited oscillation audio digital power amplifier according to claim 6, wherein the input end of the MOS drive circuit is connected to the node between the other end of the resistor R6 and the output end of the comparator U2, and the output The terminal is connected with the input terminal of the LC circuit through the power switch circuit.