CN201181929Y

CN201181929Y - Output stage structure for reducing switch output transient noise of audio frequency power amplifier

Info

Publication number: CN201181929Y
Application number: CNU200720077661XU
Authority: CN
Inventors: 陶园林
Original assignee: SHANGHAI ECRANIC ELECTRONIC CO Ltd
Current assignee: Haide Zhongye Technology Innovate Engineering Co., Ltd., Shanghai; SHANGHAI ECRANIC MICROELECTRONICS CO., LTD.
Priority date: 2007-12-28
Filing date: 2007-12-28
Publication date: 2009-01-14
Anticipated expiration: 2017-12-28

Abstract

The utility model relates to an output stage structure capable of reducing the transient noise of the switching output of an audio power amplifier, which is composed of a class AB output stage, an auxiliary output transistor and a switch controlling the operating mode of a class AB output stage output transistor. The output stage structure ensures that when the power of the class AB audio power amplifier is on or down or the class AB audio power amplifier is switched on or off, the current flowing through an external load can be reduced by reducing the effective size of the output stage output transistor, so that the voltages at both ends of the load are gentle and can be nearly consistently increased or reduced to final voltages. Consequently, the direct-current voltage difference at both ends of the external load can be effectively reduced in the switching process, and thereby, an audio system can be prevented from emitting noise.

Description

A kind of output stage structure that reduces audio-frequency power amplifier switch output transient noise

Technical field:

The utility model relates to power amplifier field, be specifically related to a kind of output stage structure that reduces audio-frequency power amplifier switch output transient noise, be a kind of can effectively reduce " Pi " that the AB genus audio power amplifier produces in power or power-down, unlatching or when turn-offing, " " a kind of modified model AB class output stage structure of noise.

Background technology:

BTL (bridge joint) load connected mode is a kind of system configuration that is widely used in audio-frequency power amplifier, as shown in Figure 1.The advantage of this structure is that power output is big, and has the ability of common-mode noise inhibition preferably.But because the existence of input coupling capacitance Ci and common mode electrical level shunt capacitance Cb, and because positive and negative output stage Vo+, Vo-are unsymmetric structure, so when circuit is powering on and when power down, unlatching and shutoff, because the charge-discharge velocity difference of electric capacity causes can producing an instantaneous potential pulse at the load two ends of output stage.When this potential pulse amplitude during greater than 15mV, audio system will produce similar " Pi ", " " switching noise.

Summary of the invention:

The purpose of this utility model is to provide a kind of output stage structure that reduces audio-frequency power amplifier switch output transient noise.

To achieve these goals, the technical solution of the utility model is as follows: a kind of output stage structure that reduces audio-frequency power amplifier switch output transient noise, it is characterized in that this circuit is made up of the switch of AB class output stage, auxiliary efferent duct, control AB class output stage efferent duct mode of operation.

Output stage structure of the present utility model makes the AB genus audio power amplifier when power or power-down, unlatching or shutoff, by reducing the effective dimensions of output stage efferent duct, thereby the electric current of the external load that reduces to flow through, make increase that the voltage at load two ends is mild and intimate consistent or reduce, until reaching final voltage.So just can effectively reduce the DC voltage difference at external load two ends in switching process, thus avoid audio system send " Pi ", " " noise.

Description of drawings:

Fig. 1 is bridge joint (BTL) pattern of audio-frequency power amplifier

Fig. 2 is a modified model AB class output stage structure

Fig. 3 is the work wave of modified model AB class output stage

(a) S1, S2 switch controlling signal

(b) circuit start, shutoff control signal

(c) audio-frequency power amplifier forward output waveform

(d) audio-frequency power amplifier negative sense output waveform

(e) the positive negative sense output end voltage of audio-frequency power amplifier difference waveform

Embodiment:

Below in conjunction with drawings and Examples the utility model is elaborated.

This circuit structure comprises four parts: AB class output stage, switch S 1, switch S 2 and auxiliary efferent duct MO.Signal output function when AB class output stage is finished the circuit operate as normal, the efferent duct of switch S 1 control AB class output stage enters shutdown mode when circuit is opened or turn-off, the efferent duct operate as normal of switch S 2 control circuits AB class output stage when entering normal mode of operation, the physical dimension of auxiliary efferent duct corresponding efferent duct in the AB class output stage, it replaces the efferent duct work in the AB class output stage when circuit is opened or turn-off, reach the purpose that reduces output current.

Fig. 2 is the schematic diagram of a kind of embodiment of modified model AB class export structure proposed by the invention.As shown in Figure 2, the first efferent duct metal-oxide-semiconductor MA, the second efferent duct metal-oxide-semiconductor MB constitute normal AB class output-stage circuit, and metal-oxide-semiconductor MO is auxiliary efferent duct, and first switch S 1, second switch S2 are control switch.This output stage structure comprises the first efferent duct MA and the second efferent duct MB, it is characterized in that the first efferent duct MA and the second efferent duct MB are connected in series forms AB class output stage, one end of this AB output stage is connected with power supply, the other end ground connection of this AB output stage, be provided with auxiliary efferent duct MO between the first efferent duct MA and the second efferent duct MB and the power supply, be provided with first switch S 1 between the control end of the first efferent duct MA and the power supply, be provided with second switch S2 between the control end of auxiliary efferent duct MO and the control end of the first efferent duct MA.The source electrode of the first efferent duct MA connects positive source, the drain electrode of the first efferent duct MA is connected with the drain electrode of the second efferent duct MB, the source ground of the second efferent duct MB, the grid of the first efferent duct MA is connected with positive source by first switch S 1, the grid of the first efferent duct MA is connected with the grid of auxiliary efferent duct MO by second switch S2, the source electrode of auxiliary efferent duct MO connects positive source, the drain electrode of auxiliary efferent duct MO is connected with the drain electrode of the second efferent duct MB, the grid of auxiliary efferent duct MO meets the first voltage end Va, and the grid of the second efferent duct MB meets the second voltage end Vb.When voicefrequency circuit powers on or opens, 1 conducting of first switch S, second switch S2 turn-offs, thus the MA pipe ends, the MO operate as normal.Because the breadth length ratio of MO pipe is managed much smaller than MA, the electric current that the electric current of external load will be when MA manages conducting so flow through this moment, thus the voltage at load two ends is mild and be close to consistent rising, until arriving the syntype bias level.Va is first voltage end, and Vb is second voltage end, turn-offs S1 this moment again, connects S2, makes output stage enter normal operating conditions.In like manner, when voicefrequency circuit power down or shutoff, connect S1 earlier, turn-off S2, make the voltage at external load two ends also be close to consistent decline gently, until arriving power supply ground.As shown in Figure 3, waveform (a) is S1, S2 switch controlling signal, and waveform (b) is circuit start, turn-offs control signal, and waveform (c), (d) are respectively audio-frequency power amplifier anode and negative terminal output waveform, and waveform (e) is the difference of positive negative sense output end voltage.As can be seen from the figure, adopt modified model AB class output stage structure, the voltage difference at AB genus audio power amplifier load two ends when power or power-down, unlatching or shutoff is less than 10mV.

The follow-on AB class of this kind output stage structure can be applied to the MOS circuit, also can be applied to ambipolar circuit, forms device accordingly and promptly adopts metal-oxide-semiconductor circuit and ambipolar circuit.Auxiliary efferent duct can only be applied to the power supply of AB class output stage to output, also can only be applied to end with outputing to, can also output to the application simultaneously of power supply and ground, and increase corresponding ON-OFF control circuit.Auxiliary efferent duct can only be made of a metal-oxide-semiconductor or bipolar tube, also can be made of one group of metal-oxide-semiconductor or bipolar tube; These auxiliary MOS transistor or bipolar tube can have identical physical dimension simultaneously, also can have different physical dimensions.The switch of control AB class output stage efferent duct mode of operation can be made of single tube MOS or bipolar circuit, also can be made of other combination of devices circuit of CMOS or bipolar integrated circuit; Simultaneously control switch can constitute by one group, also can constitute by some groups; Auxiliary efferent duct can turn-off when the circuit operate as normal, also can not turn-off.Switch controlling signal can be identical, also can be different; Can produce by external timer, also can produce by comparator.

Claims

1. one kind effectively reduces the output stage structure that the audio-frequency power amplifier switch is exported transient noise, comprise first efferent duct and second efferent duct, it is characterized in that first efferent duct and second efferent duct are connected in series forms AB class output stage, one end of this AB output stage is connected with power supply, the other end ground connection of this AB output stage, be provided with auxiliary efferent duct between first efferent duct and second efferent duct and the power supply, be provided with first switch between the control end of first efferent duct and the power supply, be provided with second switch between the control end of auxiliary efferent duct and the control end of first efferent duct.

2. output stage structure as claimed in claim 1, it is characterized in that first efferent duct, second efferent duct and auxiliary efferent duct are metal-oxide-semiconductor, the source electrode of first efferent duct connects positive source, the drain electrode of first efferent duct is connected with the drain electrode of second efferent duct, the source ground of second efferent duct, the grid of first efferent duct is connected with positive source by first switch, the grid of first efferent duct is connected with the grid of auxiliary efferent duct by second switch, the source electrode of auxiliary efferent duct connects positive source, the drain electrode of auxiliary efferent duct is connected with the drain electrode of second efferent duct, the grid of auxiliary efferent duct connects first voltage end, and the grid of second efferent duct connects second voltage end.