CN101325401A - Circuit for restraining start-up and closedown noise of whole difference audio power amplifier - Google Patents
Circuit for restraining start-up and closedown noise of whole difference audio power amplifier Download PDFInfo
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- CN101325401A CN101325401A CNA2007100419072A CN200710041907A CN101325401A CN 101325401 A CN101325401 A CN 101325401A CN A2007100419072 A CNA2007100419072 A CN A2007100419072A CN 200710041907 A CN200710041907 A CN 200710041907A CN 101325401 A CN101325401 A CN 101325401A
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Abstract
A full difference audio power amplifier switch/shutdown noise suppression circuit is composed of a full differential operational amplifier, a fast charging circuit, a high and low voltage comparator, a switch/shutdown control circuit, a common mode bias circuit. The positive and negative difference audio signals are connected with the positive and negative common mode input pins of the full differential operational amplifier through a control switch, and the output voltage of the common mode bias circuit is connected with a voltage input pin of the full differential operational amplifier through an RC filter. When starting the power amplifier, the common mode voltage first charges each node in the system flatly, builds the inner working point of the operational amplifier, then starts the output power pipe; when closing the power amplifier, the common mode voltage discharges through a ground resistance, when the common mode voltage drops down to certain degree, then the output power pipe is closed. The invention effectively restrains the noises of the switch and shutdown in the audio power amplifier, advances the power-supply restraint ratio of the system and increases the amplifying quality of the audio signals.
Description
[technical field]
The present invention is used for the circuit that whole difference audio power amplifier suppresses the switching on and shutting down noise.
[background technology]
The inhibition technology of switching on and shutting down noise (Pop Click) mainly concentrates in the audio-frequency power amplifier of master-slaver structure.In when start master and slaver AB class amplifier all are connected into the form of buffer,, the inner quiescent point of class ab ammplifier were set up before common-mode voltage reaches setting simultaneously to the shunt capacitance quick charge.In shutdown or when quiet,, utilize it to discharge into certain level at a slow speed and close class ab ammplifier again because shunt capacitance has stored a large amount of electric charges.
Fig. 1 is traditional whole difference audio power amplifier circuit structure, because the fully differential amplifier has generally acknowledged symmetry, thereby to how eliminating the few of its switching on and shutting down noise research.In fact, in the sort circuit structure, the parasitic capacitance of power output pipe is bigger, all can produce bigger voltge surge at each output during switching on and shutting down, when difference appears in symmetry, also can occur tangible switching on and shutting down noise in the load.
Shown in Figure 2 is syntype bias circuit among Fig. 1, and the common-mode voltage of fully differential amplifier (operational amplifier) is directly to use the power supply dividing potential drop resultant, and power supply is not had inhibitory action.Fully differential AB class amplifier has higher requirement to common-mode voltage, and the fluctuation of common-mode voltage is the Another reason that produces noise at output.
The method that solves the switching on and shutting down noise problem now has: a class is that the circuit of output is opened in time constant or the increase time-delay of adjusting biasings at different levels, their problem is the bad control of the time constant of biasings at different levels, increased the difficulty of design, and can not deal with problems up hill and dale; Another kind of is to adopt outside mute circuit, when the operational amplifier switch that in a flash, adopt external signal to remove mute swap switch machine noise, its problem is the complexity and the cost of increase system.
[summary of the invention]
The switching on and shutting down generating noise is because more inner big electric capacity output node chargings of circuit and discharge cause.As long as when opening power amplifier, earlier each node in the system is smoothly charged, set up the working point of computing amplifier inside, common-mode voltage is charged to certain value, opens the power output pipe again, the noise that produces in the time of so just can suppressing to start shooting effectively; When closing power amplifier, to the common-mode voltage discharge, when waiting common-mode voltage to drop to a certain degree, close the power output pipe more earlier, can effectively suppress the noise that shuts down and produce.
According to above-mentioned analysis, the circuit for restraining start-up and closedown noise of whole difference audio power amplifier of the present invention's design is:
Positive and negative difference audio input signal connects the positive and negative common mode input pin of fully differential operational amplifier (can be called for short fully differential amplifier or operational amplifier), and positive and negative difference audio output signal connects the positive and negative common mode output connecting pin of fully differential fortune amplifier; The syntype bias circuit is composed in series successively by first divider resistance, second divider resistance, the 3rd divider resistance, the 4th divider resistance, shunt capacitance, first divider resistance connects power supply, shunt capacitance ground connection, the junction common-mode voltage of second divider resistance, the 3rd divider resistance is connected to the voltage input pin of fully differential operational amplifier, it is characterized in that, minus tolerance divides the audio frequency input signal to import pin through the negative common mode that the 5th switch connects the fully differential operational amplifier, and the positive differential audio input signal connects the positive common mode input pin of fully differential operational amplifier through the 6th switch; The negative common mode input pin of fully differential operational amplifier first switch and first of connecting successively discharges and recharges ground connection behind the resistance, and the positive common mode input pin of the fully differential operational amplifier second switch and second of connecting successively discharges and recharges ground connection behind the resistance; The junction that first switch and first discharges and recharges resistance the 3rd switch and the 3rd of connecting successively discharges and recharges the positive common mode output connecting pin that connects the fully differential operational amplifier behind the resistance, and the junction that second switch and second discharges and recharges resistance the 4th switch and the 4th of connecting successively discharges and recharges the negative common mode output connecting pin that connects the fully differential operational amplifier behind the resistance;
The output of the high low-voltage comparator of a default comparison value is connected to the input on a charging quickly road, and high low-voltage comparator input and charging quickly road output are connected between the 4th divider resistance and shunt capacitance of syntype bias circuit.
The present invention can be by controlling closing and disconnecting and realize following function of each switch: when opening power amplifier, common-mode voltage smoothly charges to each node in the system earlier, set up the working point of computing amplifier inside, be charged to certain value, open the power output pipe again, the noise that produces in the time of so just can suppressing to start shooting effectively; When closing power amplifier, common-mode voltage discharges by earth resistance, when waiting common-mode voltage to drop to a certain degree, closes the power output pipe again, can effectively suppress the noise that shuts down and produce.
[description of drawings]
Fig. 1 is the circuit structure of traditional whole difference audio power amplifier.
Fig. 2 is a syntype bias circuit among Fig. 1.
Fig. 3 is a circuit for restraining start-up and closedown noise of whole difference audio power amplifier of the present invention.
Fig. 4 is the syntype bias circuit among Fig. 3.
[embodiment]
Below in conjunction with description of drawings the specific embodiment of the present invention.
See Fig. 3, circuit for restraining start-up and closedown noise of whole difference audio power amplifier of the present invention shown in Figure 4, positive and negative difference audio input signal IN+, IN-connect the positive and negative common mode input pin of fully differential amplifier 1, and positive and negative difference audio output signal Vo+, Vo-connect the positive and negative common mode output connecting pin of fully differential amplifier 1; Syntype bias circuit 8 is composed in series successively by the first divider resistance R1, the second divider resistance R2, the 3rd divider resistance R3, the 4th divider resistance R4, shunt capacitance 9, the first divider resistance R1 meets power supply Vdd, shunt capacitance 9 ground connection, the common-mode voltage Vcom that the junction of the second divider resistance R2, the 3rd divider resistance R3 obtains is connected to the voltage input pin of fully differential amplifier 1.These circuit structures are the same with prior art.Different being characterised in that: minus tolerance divides audio frequency input signal IN-to import pin through the negative common mode that the 5th switch S 5 connects fully differential amplifier 1, and positive differential audio input signal IN+ connects the positive common mode input pin of fully differential amplifier 1 through the 6th switch S 6; The negative common mode input pin of fully differential amplifier 1 first switch S 1 and first of connecting successively discharges and recharges resistance 7 back ground connection, and the positive common mode input pin of the fully differential amplifier 1 second switch S2 and second that connects successively discharges and recharges resistance 5 back ground connection; The junction that first switch S 1 and first discharges and recharges resistance 7 the 3rd switch S 3 and the 3rd of connecting successively discharges and recharges the positive common mode output connecting pin that connects fully differential amplifier 1 behind the resistance 6, and the junction that second switch S2 and second discharges and recharges resistance 5 the 4th switch S 4 and the 4th of connecting successively discharges and recharges the negative common mode output connecting pin that connects fully differential amplifier 1 behind the resistance 4.
The output of the high low-voltage comparator 3 of a default comparison value is connected to the input on a charging quickly road 2, default comparison value is 90% of supply voltage Vdd 1/2nd, and high low-voltage comparator 3 inputs and charging quickly road 2 outputs are connected in the 4th divider resistance R4 of syntype bias circuit 8 and the contact cin between the shunt capacitance 9.High low-voltage comparator 3 and charging quickly road 2 are existing known circuits module.
For making fully differential amplifier 1 positive-negative output end, the fluctuation that overcomes common-mode voltage Vcom produces noise, as improvement of the present invention, the common-mode voltage Vcom of syntype bias circuit 8 outputs is connected to the voltage input pin (see figure 4) of fully differential amplifier 1 through a RC filter of being made up of resistance and electric capacity.Ripple on the RC filter filter out power, the common-mode voltage Vcom that obtains has very high Power Supply Rejection Ratio PSRR.
The operation principle that the present invention suppresses the switching on and shutting down noise is as follows:
When system opened, common-mode voltage Vcom was lower.Disconnect the 5th switch S 5 and the 6th switch S 6, fully differential transport and placing device 1 disconnects with input signal IN-and IN+.Close first to fourth switch S, 1～S4,2 pairs of fully differential amplifier 1 charge internal nodes in charging quickly road are set up working point (mainly be the power tube of output, parasitic capacitance can up to 50pF), simultaneously to external capacitive (mainly being shunt capacitance 9) quick charge.After built up the working point of fully differential amplifier 1 internal components, external capacitive (mainly being shunt capacitance 9) also was charged to certain voltage.The height of comparator 3 monitoring contact Cin voltages, when contact Cin arrive default comparison value be Vdd/2 90% the time close charging quickly road 2.Delay a period of time allows contact Cin be charged to Vdd/2, close the 5th switch S 5 and the 6th switch S 6, fully differential amplifier 1 is connected input signal IN-and IN+, disconnects first to fourth switch S, 1～S4 switch, fully differential amplifier 1 operate as normal, the noise that produces when suppressing start so effectively.
When system closing, common-mode voltage Vcom is higher.When external bypass capacitors 9 discharges into very low level, as 600mV, disconnect the 5th switch S 5 and the 6th switch S 6, fully differential transport and placing device 1 disconnects with input signal IN-and IN+.Close first to fourth switch S, 1～S4 this moment, fully differential amplifier 1 internal node is by earth resistance 4～7 discharges.The noise that produces when suppressing shutdown so effectively.
In sum, the present invention can suppress the Pop Click noise of start in the audio-frequency power amplifier, shutdown generation effectively, improves the Power Supply Rejection Ratio PSRR of system, improves the amplification quality of audio signal.
Claims (2)
1. circuit for restraining start-up and closedown noise of whole difference audio power amplifier, positive and negative difference audio input signal connects the positive and negative common mode input pin of fully differential operational amplifier, and positive and negative difference audio output signal connects the positive and negative common mode output connecting pin of fully differential operational amplifier; The syntype bias circuit is composed in series successively by first divider resistance, second divider resistance, the 3rd divider resistance, the 4th divider resistance, shunt capacitance, first divider resistance connects power supply, shunt capacitance ground connection, the junction common-mode voltage of second divider resistance, the 3rd divider resistance is connected to the voltage input pin of fully differential operational amplifier, it is characterized in that, minus tolerance divides the audio frequency input signal to import pin through the negative common mode that the 5th switch connects the fully differential operational amplifier, and the positive differential audio input signal connects the positive common mode input pin of fully differential operational amplifier through the 6th switch; The negative common mode input pin of fully differential operational amplifier first switch and first of connecting successively discharges and recharges ground connection behind the resistance, and the positive common mode input pin of the fully differential operational amplifier second switch and second of connecting successively discharges and recharges ground connection behind the resistance; The junction that first switch and first discharges and recharges resistance the 3rd switch and the 3rd of connecting successively discharges and recharges the positive common mode output connecting pin that connects the fully differential operational amplifier behind the resistance, and the junction that second switch and second discharges and recharges resistance the 4th switch and the 4th of connecting successively discharges and recharges the negative common mode output connecting pin that connects the fully differential operational amplifier behind the resistance;
The output of the high low-voltage comparator of a default comparison value is connected to the input on a charging quickly road, and high low-voltage comparator input and charging quickly road output are connected between the 4th divider resistance and shunt capacitance of syntype bias circuit.
2. circuit for restraining start-up and closedown noise of whole difference audio power amplifier according to claim 1 is characterized in that the common-mode voltage of syntype bias circuit output is connected to the voltage input pin of fully differential operational amplifier through a RC filter.
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| CN2007100419072A CN101325401B (en) | 2007-06-12 | 2007-06-12 | Circuit for restraining start-up and closedown noise of whole difference audio power amplifier |
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| CN2007100419072A CN101325401B (en) | 2007-06-12 | 2007-06-12 | Circuit for restraining start-up and closedown noise of whole difference audio power amplifier |
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| CN101325401B CN101325401B (en) | 2012-05-02 |
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| CN102783017A (en) * | 2010-01-07 | 2012-11-14 | 德州仪器公司 | Amplifier with improved input resistance and controlled common mode |
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Effective date of registration: 20151203 Address after: 330114, 399, Lake Avenue, Airport Economic Zone, Nanchang, Jiangxi Patentee after: Jiangxi Star core Microelectronics Co. Ltd. Address before: 201199 Shanghai city Minhang District No. 6269 humin road Yinxiao building B building room 1704 Patentee before: Xiao Guoqing |