TWI352501B - Audio signal amplyfing circuit and bypass volatge - Google Patents

Description

1352501 IX. Description of the Invention: [Technical Field] The present invention relates to an audio amplifying circuit, and more particularly to a reference voltage control circuit for an audio amplifying circuit. [Prior Art] Many electronic products have audio amplifier circuits, such as mobile phones, portable music, audio, and the like. The audio amplification circuit amplifies the voltage and current of a small (e.g., a few microvolts) source signal, so that the amplified source signal is sufficient to drive a load circuit such as a slapstick or a headphone. The first figure is a conventional audio amplifying circuit 100. The audio amplifier circuit 100 includes an input capacitor Ci 110, an output capacitor Co 112 , a bypass capacitor Cb 114 , an input resistor Ri 120 , a feedback resistor Rf 122 , a voltage dividing resistor R1 - R2 124 - 126 , an operational amplifier 130 , and a load 140 . The source signal Vs is input from the input capacitor Ci 110. Input resistor Ri 120 and feedback resistor Rf 122 • Determine the magnification. The voltage dividing resistors R1-R2 124-126 determine the bias voltage of the reference voltage Vref at the positive terminal of the operational amplifier 130 and the output terminal. To obtain the maximum output signal swing, the reference voltage Vref at the positive terminal of the operational amplifier 130 and the bias voltage at the output terminal can be designed as VDD/^VDD as the positive power supply of the audio amplifying circuit 100. The bypass capacitor Cb 114 is used to stabilize the reference voltage Vref. When using the audio amplifier circuit 100, we often encounter a problem. When the power supply (VDD) of the audio amplifier circuit 100 is turned off, or when the power supply voltage of the audio amplifier circuit 100 suddenly drops, the load 140 (pass)

Client’s Docket No,: TT’s Docket No: 0975-A41241-TW/fmal/林璟辉/2007_9-14 1352501 It is often La. Eight or headphones) often make annoying noises. The reason for the appearance of the storm will be detailed below. When VDD drops rapidly, the bias voltage of the internal circuitry of operational amplifier 13 也 also changes rapidly. However, at this time, the reference voltage Vref is still maintained at VDD/2 by the bypass capacitor Cb 114. We can see that the gate of the transistor (not shown in Figure 1) at the input of the operational amplifier 130 is still maintained at VDD/2, and the source and drain bias of the transistor change rapidly as VDD rapidly decreases. . Then the transistor at the input enters the saturation mode (saturati〇n mode) from the original active mode, and the violent phenomenon occurs at this moment. Therefore, in order to avoid the noise, we need to control the reference voltage to avoid the transistor going from active mode to saturation mode when the VDD changes instantaneously. SUMMARY OF THE INVENTION One aspect of the present invention is an audio amplifying circuit. The audio amplification circuit includes an operational amplifier, a feedback resistor, an input resistor, a bypass capacitor, a first comparator, a latch and a first switch. The operational amplifier has a positive input coupled to a first reference voltage and a negative input. The feedback resistor is coupled between an output of the operational amplifier and the negative input. The input resistor is connected to the negative input terminal and receives the sound hole to be amplified. The bypass capacitor handle is connected to the positive input terminal to stabilize the first reference voltage. The first comparator compares a second reference voltage with a voltage of the bypass capacitor to perform a first comparison signal. The latch issues a switching signal based on the setting of the first comparison signal. The first switch selectively couples the bypass capacitor to the ground according to the switching signal to perform adjustment of the first reference voltage. Another aspect of the present invention is a bypass voltage control of an audio amplifying circuit

Client's Docket No.: TT's Docket No:0975-A41241-TW/fmal/林璟辉/2007-9-14 1352501 - The method, wherein the audio amplifier circuit comprises an operational amplifier having a positive input terminal a reference voltage and a negative wheel input terminal; a feedback resistor is lightly connected between the output terminal and the negative input terminal. An input resistor is coupled to the negative input terminal to receive the amplification An audio signal is coupled to the positive input terminal to stabilize the first reference voltage. The method includes the steps of: coupling a power supply of the audio amplifier by a voltage resistor to determine a second reference voltage and a third reference voltage; and when a second reference voltage is lowered to the voltage of the bypass capacitor The bypass capacitor is discharged to a third reference voltage. [Embodiment] Fig. 2 is an audio amplifying circuit 200 according to a conventional embodiment of the present invention. For the sake of brevity, the following description will be combined with FIG. The audio amplifying circuit 2 includes a conventional audio amplifying circuit 100, a first comparator 210, a latch 220 switch 230, a resistor 241-249, a second comparator 250, and an offset voltage 252 °. • The first comparator 210 The positive terminal couples the bypass capacitor Cb 114 of the conventional audio amplifier circuit 1 and the voltage is VCb. The negative terminal of the first comparator 210 is connected to a second reference voltage. The second reference voltage is determined by switching one of the voltage resistors (R3, R4, R5) of one of the power sources (VDD) of the audio amplifier circuit 200, for example, in an actual circuit, in order to reduce components, Rl can be shared. , R2, R3, R4, R5 part of the resistance. When the power supply VDD of the audio amplifier 200 is turned off, or when the power supply VDD suddenly drops, the value of the power supply VDD drops rapidly, for example, from 5V to 3V. As mentioned earlier, in order to avoid the storm, we need to control the

Client's Docket No.: XT’s Docket No: 〇975-A41241-TW/fmal/林珠辉/2007-9-14 1352501 The bypass capacitor Cb 114 is maintained at a certain reference voltage, VCb. The first comparator 210 compares VCb with (VDD' is the present value of the power supply when falling) to issue a first comparison signal. When VCb>, the first comparator 210 sends the first comparison signal to control the switch 230 to couple the bypass capacitor Cb 114 to the ground. That is, the bypass capacitor Cb 114 is discharged to lower the VCb. In order to ensure a smooth discharge, a latch 220 is used to generate a switching signal according to the setting of the first comparison signal. The switch signal is used to control the switch 230' to couple the bypass capacitor Cb 114 to the ground. The discharge resistor Rd on the discharge path of the bypass capacitor Cb 114 can be used to control the discharge rate, and Rd can be coupled between the switch 230 and the bypass capacitor Cb 114 or between the switch 230 and the ground. As a result, when VDD drops rapidly, VCb also drops, so you can avoid violent noise. To further ensure that the operational amplifier 130 does not emit any signals, the switch control signal can also be used to turn off the bias current source (not shown) of the operational amplifier 130 or to control another switch (not shown) to short the feedback resistor Rf. Further, for example, when VDD returns to normal, in order to enable the audio amplifier 200 to operate normally again, when the bypass capacitor Cb 114 is discharged to a certain voltage value, the discharge path is released, and the bypass capacitor Cb 114 is stopped. The negative terminal of the second comparator 250 is coupled to the bypass capacitor Cb 114, and the positive terminal is coupled to a third reference voltage. The third reference voltage may be determined by a voltage resistor (R3, R4, R5) coupled to one of the power supplies VDD, such as VDD/2. The R6 243 can increase the ability to withstand noise from the power supply VDD. The second comparator 250 compares the third reference voltage with the voltage VCb of the bypass capacitor Cb 114 and outputs a second comparison signal for resetting

Client's Docket No.: TT’s Docket No: 0975-A41241-TW/fmal/Lin Zhuhui/2007-9-14 丄乃2501 The latch thief 220 starts the startup procedure of the audio amplifier circuit 200. The bias voltage 252 provides a small bias voltage (e.g., 0.1 V) that causes the second comparison L to transition after charging of the bypass capacitor Cb 114, such as a low voltage representing 〇 representing a voltage of i. When the VCb is discharged to a certain extent 'e.g., ^__αι', the second comparison signal is switched from the original low voltage to the high voltage to reset the latch 22'. The switching signal of latch 22 thus controls switch 230 to intercept the discharge path of bypass capacitor Cb 114. After the discharge path of the bypass capacitor Cb 114 is cut off, it is recharged (if VDD), and when the field Cb ^--αΐ, the second comparison signal is switched from the high voltage to the low voltage, so that the latch 220 is deactivated. . The audio amplifier circuit 2 further includes a delay and latch 260 coupled to the second comparator 250 to receive the second comparison signal, and output immediately when the second comparison signal changes from a low voltage to a high voltage. The second comparison signal is used to immediately turn off the first comparator 21, and when the second comparison signal is switched from a high voltage to a low voltage, the second comparison signal is delayed to be output, and the first comparator 21 is turned on by delay φ. Hey. Delaying the turn-on of the first comparator 210 ensures that the VDD is normal and the audio amplifier 2 再 operates the first comparator 210 after a period of normal operation to avoid erroneous discharge of the bypass capacitor Cb 114 due to instability at startup. Figure 3 is a diagram showing a bypass voltage control method 300 for an audio amplification circuit in accordance with an embodiment of the present invention. The audio amplifier circuit includes an operational amplifier having a positive input coupled to a first reference voltage and a negative wheel input; a feedback resistor coupled between the output of the operational amplifier and the input An input resistor coupled to the negative input terminal for receiving amplification

Client's Docket No.: TT's Docket No: 〇975-A41241-TW/fmal/林璟辉/2007-9-14 10 1352501 • '::: and a bypass capacitor coupled to the positive input to stabilize the first - Reference power [Bypass amplifier circuit bypass method (4) method includes the following steps: Step 3H), the power of the audio amplifier is reduced by the -component voltage resistor to determine - the second reference power and a third reference power. And, in step 320, discharging the bypass capacitor to a third reference voltage when the second reference current is reduced to the electrical waste of the bypass capacitor. The bypass voltage control method of the above audio amplifying circuit 3, wherein when a second reference voltage is lowered to the voltage of the bypass capacitor, the operational amplifier is turned off and the feedback resistor is short-circuited. When the bypass capacitor is discharged to the third reference voltage, the startup process of the audio amplifier circuit is started.

In this way, by controlling the reference voltage, it is possible to prevent the transistor from entering the saturation mode when the VDD changes instantaneously, thereby avoiding the treble. The invention is illustrated and described herein by way of example only, and is not intended to Many different modifications and structural changes are made within the scope and scope of equalization. The scope of patent protection is subject to the scope of the patent application and its equivalent. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a conventional audio amplifier circuit 10A. Figure 2 is an audio amplification circuit 2A according to an embodiment of the present invention. Figure 3 is a diagram showing a bypass voltage control method 300 for an audio amplification circuit in accordance with an embodiment of the present invention.

Client’s Docket No.: TT’s Docket NG:0975-A41241.TW/final/Lin Zhuhui/2007-9-14 Howling 5〇1

[Description of main component symbols]: 100~ audio amplifier circuit, 110·η2-114~capacitor, 120-126~ resistor, 130~ operational amplifier, 140 load. 200~ audio amplifier circuit, ~ comparator, 220~ latch, 23〇~ switch, 241_249~ resistor, ~ comparator, 252~ offset voltage, 260~ latch and delay. 3〇〇 ~ method, 310-320~ steps.

Client’s Docket No.: TT’s Docket No:0975-A41241-TW/final/林璟辉/2007-9-14

Claims (1)

1352501 Case No. 096136533 Revised on January 24, 100, this application patent scope: 蚧年)月曰曰曰本1. An audio amplifier circuit comprises: an operational amplifier having a positive input coupled to a first reference voltage And a negative input terminal; a feedback resistor coupled between the output end of the operational amplifier and the negative input terminal; an input resistor coupled to the negative input terminal, receiving one of the audio to be amplified; a capacitor coupled to the positive input terminal to stabilize the first reference voltage; a first comparator comparing a second reference voltage with a voltage of the bypass capacitor to output a first comparison signal; a latch according to the Setting a first comparison signal to generate a switching signal; a first switch selectively coupling the bypass capacitor to the ground according to the switching signal; and • a second comparator comparing the third reference voltage with the The voltage of the bypass capacitor outputs a second comparison signal for resetting the latch and starting the startup process of the audio amplification circuit. 2. The audio amplifying circuit of claim 1, wherein when the second reference voltage is lowered to a voltage of the bypass capacitor, the switch signal controls the first switch to couple the bypass capacitor to the ground and control A second switch shorts the feedback resistor and turns off the operational amplifier. 3. The audio amplifying circuit of claim 2, wherein the 0975-A41241-TW/finall 13 1352501 switch and the bypass capacitor or the first switch and the ground are further coupled to a discharge resistor To control the discharge rate of the bypass capacitor. 4. The audio amplifier circuit of claim 1, further comprising: a second comparator that compares a third reference voltage with the voltage of the bypass capacitor and outputs a second comparison signal; and a delay and latch The second comparator is coupled to receive the second comparison signal, and when the second comparison signal changes from a low voltage to a high voltage, the second comparison signal is immediately output to immediately turn off the first comparator. The second comparison signal delays outputting the second comparison signal when the high voltage is turned to a low voltage to delay turning on the first comparator. 5. The audio amplifying circuit of claim 1, wherein the first and second reference voltages are determined by a voltage dividing resistor coupled to one of the power sources of the audio amplifying circuit. 6. The audio amplifying circuit of claim 5, wherein the ratio of the voltage dividing resistor is further set such that the first reference voltage is one half of the power source. 7. The audio amplifying circuit of claim 4, wherein the third reference voltage is determined by a component voltage resistor coupled to one of the power sources of the audio amplifying circuit. 8. The audio amplifying circuit of claim 7, wherein the ratio of the voltage dividing resistor is set such that the third reference voltage is one half of the power source. A bypass voltage control method for an audio amplifier circuit, wherein the audio amplifier circuit comprises an operational amplifier having a positive input coupled to a first reference voltage and a negative input terminal; a feedback resistor coupled to the operation An input end of the amplifier is coupled to the negative input end; an input resistor coupled to the negative 0975-A41241-TW/fmall 1352501 input terminal for receiving an audio to be amplified; and a bypass capacitor coupled to the positive The input terminal stabilizes the first reference voltage; and comprises the steps of: coupling a power supply of the audio amplifier by a voltage resistor to determine a second reference voltage and a third reference voltage; and when the second reference voltage is lowered When the voltage of the bypass capacitor is discharged, the bypass capacitor is discharged to a third reference voltage. 10. The bypass voltage control method of the audio amplifying circuit of claim 9, wherein the method further comprises: • when a second reference voltage is lowered to the voltage of the bypass capacitor, turning off the operational amplifier and causing the feedback The short circuit of the resistor; when the bypass capacitor is discharged to the third reference voltage, the starting procedure of the audio amplifying circuit is started. 0975-A41241-TW/fmall 15