| 摘要 |
PROBLEM TO BE SOLVED: To enhance the sound quality at a high frequency component of a speaker that can reproduce a sound from a low to a high frequency by generating a bias voltage or current, that increases/decreases in response to increase/ decrease in frequency of an input signal by a bias generating circuit for receiving the input signal and increasing an input bias current of an output stage amplifier, in response to an output of the bias generating circuit when the frequency of the input signal increases. SOLUTION: An input terminal receives an input audio signal from a pre- stage amplifier such as a preamplifier. An output terminal 12 is connected to an output capacitor 4 and then to a piezoelectric speaker 5. The other terminal of the piezoelectric speaker 5 is connected to a ground line GND, and the piezoelectric speaker 5 is push-pull-driven by an output amplifier 8. In a differential amplifier circuit 6, a common emitter of npn differential transistor(TR) Q1, Q2 is connected to a TR Q6 of a current source 6a, the TR Q6 is connected to ground, and the TRs Q1, Q2 have current mirror pnp TRs Q3, Q4 respectively as collector loads and the emitters of the Q3, Q4 are connected to a power line VCC.
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