| 摘要 |
An audio preamplifier ( 10 ) based on an operational transconductance amplifier, in combination with a class D audio output amplifier ( 12 ) is disclosed. The input signal is coupled to the preamplifier ( 10 ) through a capacitor ( 14 ) in series with a resistor ( 17 ) that sets the transconductance of the preamplifier. The preamplifier ( 10 ) includes a differential operational amplifier ( 20 ) that drives output MOS transistors ( 22 a, 22 b), which are biased by current sources ( 24 a, 26 a; 24 b, 26 b). Feedback from the drain nodes of the output MOS transistors ( 22 a, 22 b) to the inputs of the differential operational amplifier ( 20 ), along with the series capacitor ( 14 ) and resistor ( 17 ) input coupling, ensures minimum offset voltage and current at the output of the preamplifier ( 10 ). Common mode feedback control amplifiers ( 25, 29 ) ensure proper bias of the components into the saturation region.
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