Push–pull output: Difference between revisions

Revision as of 17:00, 11 June 2021

Revision as of 13:35, 4 July 2021

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A '''push–pull''' amplifier is a type of [[electronic circuit]] that uses a pair of active devices that alternately supply current to, or absorb current from, a connected load. This kind of amplifier can enhance both the load capacity and switching speed.

Push–pull outputs are present in [[Transistor-transistor logic|TTL]] and [[CMOS]] digital [[logic circuit]]s and in some types of [[electronic amplifier|amplifiers]], and are usually realized asby a complementary pair of [[transistor]]s, one dissipating or ''sinking'' current from the load to ground or a negative power supply, and the other supplying or ''sourcing'' current to the load from a positive power supply.

A push–pull amplifier is more efficient than a single-ended [[Power_amplifier_classes#Class_A|"class-A"]] amplifier. The output power that can be achieved is higher than the continuous dissipation rating of either transistor or tube used alone and increases the power available for a given supply voltage. Symmetrical construction of the two sides of the amplifier means that even-order harmonics are cancelled, which can reduce distortion.<ref>Joe Carr, ''RF Components and Circuits'', Newnes, page 84</ref> DC current is cancelled in the output, allowing a smaller output transformer to be used than in a single-ended amplifier. However, the push–pull amplifier requires a phase-splitting component that adds complexity and cost to the system; use of center-tapped [[transformer]]s for input and output is a common technique but adds weight and restricts performance. If the two parts of the amplifier do not have identical characteristics, distortion can be introduced as the two halves of the input waveform are amplified unequally. [[Crossover distortion]] can be created near the zero point of each cycle as one device is cut off and the other device enters its active region.