| 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.
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