TWI407688B - Pwm modulator for a class-d amplifier and class-d amplifier adaptive to analog and digital input by using the same - Google Patents

Abstract

A PWM modulator for a class-D amplifier has a discharge element connected to an input terminal of its operation amplifier to establish a discharge path and therefore, the class-D amplifier can be directly driven by an analog or digital input signal, without input driving circuit.

Description

PWM modulator for Class D amplifiers and Class D amplifiers that use this PWM modulator to accommodate analog and digital inputs

This invention relates to a class D amplifier, and more particularly to a class D amplifier that can be directly driven by analog and digital input signals.

1 is a conventional analog input differential class D amplifier. After the analog input signal 32 enters from a pair of differential input terminals 10 and 12, signals Cbr1 and Cbr2 are generated via the input drive circuit 13, and are modulated by the pulse width modulator 18. Pulse Width Modulation (PWM) signals SpwmP and SpwmN are generated for power stages 20 and 22, which in turn generate differential output signals VoP and VoN to drive load 24. In order to obtain a more stable output, the class D amplifier further includes feedback networks 14 and 16 respectively detecting signals VoP and VoN to generate feedback signals VfbP and VfbN to the PWM modulator 18. In the PWM modulator 18, the resistor R1, the capacitor C1 and the operational amplifier 26 form an integrator to integrate the signal Cbr1 to generate a signal VinP, the resistor R2, the capacitor C2 and the operational amplifier 28 form an integrator to integrate the signal Cbr2 to generate a signal VinN, PWM generation The device 30 generates signals SpwmP and SpwmN based on the signals VinP and VinN and the carrier signal. The feedback networks 14 and 16, the power stages 20 and 22, and the PWM generator 30 are all well-established techniques, and their circuits and operations can be found in many documents, such as U.S. Patent Nos. 7,183,840 and 7,262,658. Since there is no path for the negative input terminals of operational amplifiers 26 and 28 to bleed charge, in order to prevent the negative input terminals of operational amplifiers 26 and 28 from continuously accumulating charges, their DC voltage levels continue to rise, and operational amplifiers 26 and 28 are positive. The input receives the common mode voltage Vcm to clamp the DC voltage level at its negative input. In order to prevent the PWM modulator 18 from operating due to the difference between the DC bias of the analog input signal 32 and the common mode voltage Vcm, the input drive circuit 13 includes capacitors Cin1 and Cin2 that filter the DC bias of the analog input signal 32. However, the DC limiting capacitors Cin1 and Cin2 block the digital signal, so the Class D amplifier cannot be driven by the digital input signal.

2 is a conventional digital differential input class D amplifier, except for the input drive circuit 13, the other circuits are the same as in FIG. Since the high and low levels of the digital signals are not necessarily the same, the input driving circuit 13 includes buffers 36 and 38 for converting the digital input signal 34 into signals Cbr1 and Cbr2 having high and low levels of VDD and 0, respectively. Because of the presence of buffers 36 and 38, this class D amplifier cannot be driven by analog input signals.

Although there are also Class D amplifiers that can be driven by analog and digital input signals, the input driver circuit requires the detector to detect the input signal in addition to the DC limiting capacitors Cin1 and Cin2 of Figure 1 and the buffers 36 and 38 of Figure 2. An analog or digital signal to switch the Class D amplifier to an analog input mode or a digital input mode.

One of the objects of the present invention is to provide a class D amplifier that can be driven by an analog or digital input signal without requiring an input driver circuit.

One of the objects of the present invention is to provide a PWM regulator that allows a Class D amplifier to be directly driven by an analog or digital input signal.

In accordance with the present invention, a PWM modulator for a Class D amplifier is coupled to a discharge element at the input of its operational amplifier to establish a discharge path such that the Class D amplifier can be driven by an analog or digital input signal without the need for an input drive circuit.

In single-ended load applications, the other input of the op amp of the PWM modulator is floating.

For differential input applications, the PWM modulator uses a dual output op amp or two op amps with another input floating.

3 is a differential input class D amplifier to which the present invention is applied, which is based on the circuit of FIGS. 1 and 2, and the PWM modulator 18 does not need to input the drive circuit 13 as an input interface, so the class D The amplifier can be directly driven by the analog input signal 32 or the digital input signal 34. In PWM modulator 18, the positive inputs of operational amplifiers 26 and 28 are both floating, and the negative inputs respectively add discharge elements 40 and 42 to establish a discharge path for discharging charge. In this embodiment, the discharge element 40 includes a resistor R3 connected between the negative input terminal of the operational amplifier 26 and the ground GND. The discharge element 42 includes a resistor R4 connected between the negative input terminal of the operational amplifier 28 and the ground GND. In other embodiments, discharge elements 40 and 42 may establish a discharge path with other electronic components or circuits. This class D amplifier accommodates the analog input signal 32 and the digital input signal 34 due to the removal of the DC limiting capacitors Cin1 and Cin2 and the buffers 36 and 38. When the analog input signal 32 or the digital input signal 34 is applied to the class D amplifier, the resistors R1 and R3 divide the voltage at the positive input terminal 10 into a signal Sd1, and the resistors R2 and R4 divide the voltage at the negative input terminal 12 into a signal. Sd2. Since the positive inputs of operational amplifiers 26 and 28 are both floating, the DC voltage levels at the negative inputs of operational amplifiers 26 and 28 are determined by signals Sd1 and Sd2, respectively. As the DC voltage level of the analog input signal 32 or the digital input signal 34 changes, the DC voltage level at the negative input of the operational amplifiers 26 and 28 automatically changes.

Further, as shown in FIG. 4, the operational amplifiers 26 and 28 of FIG. 3 can be replaced with dual output operational amplifiers 44. The positive input terminal of the operational amplifier 44 is connected to the resistor R1 and the discharge element 40, the negative input terminal is connected to the resistor R2 and the discharge element 42, the capacitor C1 is connected between the positive input terminal and the negative output terminal, and the capacitor is connected between the negative input terminal and the positive output terminal. C2. The positive and negative outputs of operational amplifier 44 provide signals VinN and VinP to PWM generator 30, respectively.

5 is an embodiment of the power stages 20 and 22 of FIG. 3, including the MOSFETs M1 and M2 being controlled by the PWM signal SpwmP or SpwmN, and switching the switching node LX to the power supply terminal VDD and the ground GND, switching the node LX The voltage is filtered by LC filter 46 to produce an output signal VoP or VoN. In some embodiments, the signals VoP and VoN may be applied directly to the load without the use of the LC filter 46.

Figure 6 is an embodiment applied to a single-ended load. The operation of the circuit is the same as that of the embodiment of Figure 3, but the input and output of the Class D amplifier are single, not differential.

The above description of the preferred embodiments of the present invention is intended to be illustrative, and is not intended to limit the scope of the invention to the disclosed embodiments. It is possible to make modifications or variations based on the above teachings or learning from the embodiments of the present invention. The embodiments are described and illustrated in the practical application of the present invention in various embodiments, and the technical idea of the present invention is intended to be equivalent to the scope of the following claims. Decide.

10. . . Positive input

12. . . Negative input

13. . . Input drive circuit

14. . . Feedback network

16. . . Feedback network

18. . . PWM modulator

20. . . Power level

twenty two. . . Power level

twenty four. . . load

26. . . Operational Amplifier

28. . . Operational Amplifier

30. . . PWM generator

32. . . Analog input signal

34. . . Digital input signal

36. . . buffer

38. . . buffer

40. . . Discharge element

42. . . Discharge element

44. . . Operational Amplifier

46. . . LC filter

Figure 1 is a conventional analog input class D amplifier;

Figure 2 is a conventional digital input class D amplifier;

Figure 3 is a differential input class D amplifier to which the present invention is applied;

Figure 4 is another embodiment in accordance with the present invention;

Figure 5 is an embodiment of the power stage of Figure 3;

Figure 6 is an embodiment of the invention applied to a single ended load.

10. . . Positive input

12. . . Negative input

14. . . Feedback network

16. . . Feedback network

18. . . PWM modulator

20. . . Power level

twenty two. . . Power level

twenty four. . . load

26. . . Operational Amplifier

28. . . Operational Amplifier

30. . . PWM generator

32. . . Analog input signal

34. . . Digital input signal

40. . . Discharge element

42. . . Discharge element

Claims (10)

A differential input class D amplifier for generating two differential output signals, the class D amplifier comprising: a pair of differential inputs for receiving analog or digital input signals; a first operational amplifier having a first input, floating a second input terminal and an output terminal; a first resistor connected between the positive input terminal of the pair of differential input terminals and the first input terminal of the first operational amplifier; a first discharge element connected to the first operational amplifier a first input terminal for establishing a discharge path; a second operational amplifier having a first input terminal, a floating second input terminal and an output terminal; a second resistor coupled to the negative input terminal of the pair of differential input terminals and the a first input end of the second operational amplifier; a second discharge element coupled to the first input of the second operational amplifier to establish a discharge path; a PWM generator coupled to the output of the first and second operational amplifiers a second pulse width modulation signal is generated according to the carrier signal and the output of the first and second operational amplifiers; and the second power stage is connected to the PWM generator, respectively, according to the two pulse width modulation signal The two differential output signals. The class D amplifier of claim 1, wherein the first discharge element comprises a third resistor connected between the first input terminal and the ground terminal of the first operational amplifier. The class D amplifier of claim 1, wherein the second discharge element comprises a third resistor connected between the first input terminal and the ground terminal of the second operational amplifier. A class D amplifier includes: an operational amplifier having a first input terminal, a floating second input terminal, and an output terminal; a first resistor coupled to the input terminal of the class D amplifier and the first input terminal of the operational amplifier a discharge element is coupled to the first input of the operational amplifier to establish a discharge path; a PWM generator is coupled to the output of the operational amplifier to generate a pulse width modulated signal based on the carrier signal and the output of the operational amplifier; A power stage is coupled to the PWM generator to generate an output signal based on the pulse width modulation signal. A class D amplifier of claim 4, wherein the discharge element comprises a second resistor coupled between the first input of the operational amplifier and the ground. A PWM modulator for a class D amplifier having a pair of differential inputs for receiving an analog or digital input signal, the PWM modulator comprising: a first operational amplifier having a first input and floating a second input terminal; a first resistor connected between the positive input terminal of the pair of differential input terminals and the first input terminal of the first operational amplifier; a first discharge element connected to the first of the first operational amplifier Input terminal for which a discharge path is established; a second operational amplifier has a first input terminal and a floating second input terminal; a second resistor is coupled between the negative input terminal of the pair of differential input terminals and the first input terminal of the second operational amplifier; A second discharge element is coupled to the first input of the second operational amplifier to establish a discharge path therewith. The PWM modulator of claim 6, wherein the first discharge element comprises a third resistor connected between the first input terminal and the ground terminal of the first operational amplifier. The PWM modulator of claim 6, wherein the second discharge element comprises a third resistor connected between the first input terminal and the ground terminal of the second operational amplifier. A PWM modulator for a class D amplifier, comprising: an operational amplifier having a first input and a floating second input; a resistor coupled to the input of the class D amplifier and the first input of the operational amplifier And a discharge element is coupled to the first input of the operational amplifier for establishing a discharge path. The PWM modulator of claim 9, wherein the discharge element comprises a second resistor connected between the first input terminal and the ground terminal of the operational amplifier.