Abstract: An amplifier circuit with improved turn-on and turn-off transient operation includes an amplifier and a controller for controlling the mode of operation of the amplifier during initial and subsequent circuit turn-on and turn-off. The amplifier is biased by a positive power supply voltage and has a differential input which is driven by a reference voltage and a single-ended input signal. Where the output is single-ended, a single amplifier provides a single-ended output signal. Where the output is differential, the amplifier includes cascaded, differential input, single-ended output amplifiers which together provide a differential output signal. One of each of the differential inputs is driven by the reference voltage which, following circuit turn-on, charges to a value of half of the positive power supply voltage.
Abstract: 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.V.sub.BE, 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.