Output Coupling Capacitor Free Audio Power Amplifier Dynamically Configured for Speakers and Headphones with Excellent Click and Pop Performance

Abstract

First and second channel bridge amplifiers are dynamically configured to drive either speakers or headphones. The first channel bridge amplifier includes a first amplifier driving one end of a first speaker through a mechanical switch in a headphone-jack, and a second amplifier driving another end of the first speaker. The second channel bridge amplifier includes third and fourth amplifiers driving respective ends of a second speaker. An amplifier control circuit dynamically detects the insertion or removal of a plug in the jack and configures the amplifiers accordingly. When a plug is inserted into the jack, the mechanical switch disconnects the first speaker from the first amplifier, and the fourth amplifier is tri-stated disconnect the second speaker. The first and third amplifiers are configured to drive the first and second channels of the headphones, while the third amplifier drives the headphone common point (shield ring) as a virtual ground connection. The virtual ground connection permits the bridge amplifiers to drive either speakers or headphones without the use of output coupling capacitors. To suppress click and pop, the amplifier control circuit maintains certain amplifiers (depending on headphone or speaker mode) tri-stated until the input coupling capacitors have fully charged and an input signal is detected. In the headphone mode, the driving amplifiers are current limited, the output signal level is automatically attenuated, and the second amplifier is controlled to prevent a ground loop short circuit condition. When a ground short is detected, the second amplifier is tri-stated by the amplifier control circuit.

1 . A method for dynamically configuring an amplifier with a jack, comprising:
 automatically setting a first mode when the jack is empty;   automatically setting a second mode when a plug is inserted in the jack;   when in the first mode, differentially driving a first load coupled between a first output of a first amplifier and a second output of a second amplifier and differentially driving a second load coupled between a third output of a third amplifier and a fourth output of a fourth amplifier; and   when in the second mode, driving a series coupled third and fourth load between the first and third outputs generating a ground potential at the second output that is coupled through the jack to a common point between the third and fourth loads.   
     
     
         2 . An apparatus for monitoring a jack for a plug insertion, the jack having a first terminal driven by a signal and a second terminal that is separably coupled to the first terminal, the second terminal of the jack is decoupled from the first terminal when a plug is inserted into the jack, comprising:
 a first circuit that couples a supply voltage to the second terminal when the plug is in the jack;   a compare circuit that generates a compare signal responsive to a comparison of the signal to a potential of the second terminal;   an enable circuit that generates an enable signal when the signal is determined to be different from the supply voltage by a predetermined amount; and   a memory circuit that stores the compare signal when enabled by the enable signal such that the memory circuit produces an output signal indicating the disposition of the plug in the jack.   
     
     
         3 . An apparatus as in  claim 2 , wherein the first circuit includes a transistor that is biased to provide a path between the power supply voltage and the second terminal. 
     
     
         4 . An apparatus as in  claim 2 , wherein the enable circuit further comprises:
 a first reference voltage circuit that generates a first reference voltage that is different from the power supply voltage by a predetermined amount; and   a first comparator circuit that compares the signal to the first reference voltage to generate an enable signal, the enable signal indicating that the signal different from the power supply voltage by at least the predetermined amount.   
     
     
         5 . An apparatus as in  claim 2 , wherein the compare circuit produces a first output when the potential of the signal is the same as the potential of the second terminal, and the compare circuit produces a second output when the potential of the signal is different from the potential of the second terminal. 
     
     
         6 . A method of monitoring a jack for a plug insertion, the jack having a first terminal driven by a signal and a second terminal that is separably coupled to the first terminal, the second terminal of the jack is decoupled from the first terminal when a plug is inserted into the jack, comprising:
 coupling the second terminal to a power supply voltage when the jack is inserted;   generating a compare signal responsive to a comparison of the signal to a potential of the second terminal; and   storing the compare signal in a memory when the signal is different from the power supply voltage by a predetermined amount.   
     
     
         7 . An apparatus for monitoring a jack for a plug insertion, the jack having a first terminal driven by a signal and a second terminal that is separably coupled to the first terminal, the second terminal of a jack is decoupled from the first terminal when a plug is inserted into the jack, comprising:
 means for coupling the second terminal to a power supply voltage when the jack is inserted;   means for generating a compare signal responsive to a comparison of the signal by a potential of the second terminal; and   means for storing the compare signal in a memory when the signal is different from the power supply voltage by a predetermined amount.