| 摘要 |
A power amplifier stage for producing a rectangular signal across a load, which may be predominantly capacitive, by means of a "bridge" amplifier comprises a first pair of transistors which operate alternately as an emitter follower and a second pair of transistors which alternately closes the circuit of the load. The four transistors of the bridge amplifier are respectively driven by identical four current sources in order to minimize the impedance of the circuit of the load for direct current. The transistors of the second pair are alternately connected as diodes. To control the signal amplitude, a generator supplies a control voltage whose value corresponds to a fixed component equal to 2.VBE, plus a variable component corresponding to the desired amplitude of the signal. Such a power amplifier stage can be used for driving a piezo-electric transducer, particularly for a telephone bell.
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