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

摘要

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.

主权项

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.