Anti-pop circuit

• US 8,446,216 B2
• Filed: 11/18/2011
• Issued: 05/21/2013
• Est. Priority Date: 06/19/2009
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Fan, Xin, Larsen, Christian, Crespi, Lorenzo
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHIEM D
• Application Number:
  US13/300,012
• Publication Number:
  US 20120062320A1
• Time in Patent Office: 550 Days
• Field of Search: 330/51, 330297-298, 330/294, 381/94.5
• US Class Current: 330/51
• CPC Class Codes: H03F 1/305 in case of switching on or off of a power supply
• CPC Class Codes: H03F 2200/144 the feedback circuit of the amplifier stage comprising a passive resistor and passive capacitor
• CPC Class Codes: H03F 2203/45526 the FBC comprising a resistor-capacitor combination and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45534 the FBC comprising multiple switches and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45674 the LC comprising one current mirror
• CPC Class Codes: H03F 3/3022 CMOS common source output SEPP amplifiers H03F3/3008 takes precedence
• CPC Class Codes: H03F 3/45183 Long tailed pairs H03F3/4521, H03F3/45237 take precedence

Abstract

Presently many audio chips suffer from pop issues, which is especially serious for single ended audio drivers. An audio pop is a disturbance in the output caused by a sudden transition of chip power, particularly when a chip is powered on or powered off. Furthermore, compensation networks included in the amplifiers on audio chips for stability offer a significant path for transmitting power disturbances to the output. Hence, circuitry is developed to suppress pops in the output stages of an amplifier.

Claims

1. A reduced pop amplifier comprising:

an amplifier stage;

an output stage comprising;

a core having an input coupled to the amplifier stage; and

a compensation network coupled between the input of the core and an output of the core, the compensation network comprising a capacitor, the compensation network disconnects the input of the core from the output of the core and shunts the capacitor to a low voltage when the amplifier stage is powered down and until after the amplifier stage is powered up, and the compensation network connects the input of the core to the output of the core after the amplifier stage is powered up and until before the amplifier stage is powered down.

2. The reduced pop amplifier of claim 1, wherein the low voltage is ground.

3. The reduced pop amplifier of claim 1, wherein the compensation network further comprises a resistor.

4. The reduced pop amplifier of claim 1, further comprising a switch, wherein the switch pulls the output of the core to the low voltage when the amplifier stage is powered down.

5. The reduced pop amplifier of claim 1, wherein the core is a second stage having a second input and a second output, the second stage further comprises a second compensation network coupled between the second output and the second input, the second compensation network having a second capacitor, a first switch and a second switch, the first switch breaks a connectivity between the second output and the second input when a control signal is low but maintains the connectivity between the second input and the second output when the control signal is high and the second switch shunts the second capacitor to the low voltage when the control signal is low.

6. The reduced pop amplifier of claim 1 further comprising:

a bias circuit between the amplifier stage and the output stage;

the core is a push-pull amplifier having a second input;

the output stage further comprises a second compensation network coupled between the output and the second input, the second compensation network having a second capacitor, a first switch and a second switch, the first switch breaks a connectivity between the output and the second input when a control signal is low but maintains the connectivity between the second input and the output when the control signal is high and the second switch shunts the second capacitor to a low voltage when the control signal is low.

7. The reduced pop amplifier of claim 6 further comprising a third switch, wherein the third switch pulls the output to the low voltage when the control signal is low.

8. The reduced pop amplifier of claim 6, further comprising a third switch, wherein the third switch pulls the input to a high voltage when the control signal is low.

9. The reduced pop amplifier of claim 6, wherein the core further comprises a p-type field effect transistor (FET) and an n-type FET.

10. The reduced pop amplifier of claim 1, wherein the control signal is low when the reduced pop amplifier is powered down and remains low until after the reduced pop amplifier is powered up and remains high until before the reduced pop amplifier is powered down.

11. A method for reducing pop in an amplifier circuit comprising:

receiving a control signal;

when the control signal is low, performing the steps of;

breaking a connection between an input and an output of an output stage in an amplifier circuit to prevent current from flowing between the output and the input;

shunting a capacitor coupled to the amplifier circuit to a low voltage after breaking the connection; and

connecting the output to the low voltage; and

wherein the control signal is low when the amplifier is powered down, remains low until after the amplifier is powered up and remains high until before the amplifier is subsequently powered down.

12. The method of claim 11 wherein breaking the connections between an input and an output of the output stage further comprises:

breaking a connection in a compensation network coupled to a second input and a second output to prevent current from flowing between the second output and the second input; and

shunting a second capacitor in the second compensation network to the low voltage.

13. The method of claim 12 further comprising pulling the second input to a high voltage.

14. The method of claim 12 wherein a signal provided to the input and the second input represents a single differential input.

20. The method of claim 11 wherein breaking the connections between an input and an output of the output stage further comprises breaking a connection in a compensation network coupled to a second input and a second output to prevent current from flowing between the second output and the second input.

15. A reduced pop amplifier comprising:

an amplifier stage;

an output stage comprising;

a core stage having an input coupled to the amplifier stage and an output;

a compensation network comprising a capacitor coupled to the input and the output;

a switch for pulling the output to a low voltage;

a second input to the core;

a second output to the core; and

a second compensation network comprising a capacitor coupled to the second input and the second output.

16. The reduced pop amplifier of claim 15 comprising a first switch, controlled by a control signal, configured to break a connection in the compensation network to prevent current from flowing between the output and the input.

17. The reduced pop amplifier of claim 15 wherein the output stage further comprises means for pulling the output to the low voltage.

18. The reduced pop amplifier of claim 15 further wherein the output stage further comprises means for shunting the second capacitor in the second compensation network to a low voltage.

19. The reduced pop amplifier of claim 15 further wherein the output stage further comprises means for breaking a connection in the second compensation network to prevent current from flowing between the second output and the second input.