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Compared to an equivalent class-AB device, a class-D amplifier's lower losses permit the use of smaller heat sinks for the MOSFETs while also reducing the amount of input power required, allowing for a lower-capacity power supply design. Therefore, class-D amplifiers are typically smaller than an equivalent class-AB amplifier.
In practical design, the result of a tradeoff is the class AB design. Modern Class AB amplifiers commonly have peak efficiencies between 30 and 55% in audio systems and 50-70% in radio frequency systems with a theoretical maximum of 78.5%. Commercially available Class D switching amplifiers have reported efficiencies as high as 90%. Amplifiers ...
This configuration is commonly used in the output stages of class-B and class-AB amplifiers. The base circuit is modified to operate the transistor in class-B or AB mode. In class-A mode, sometimes an active current source is used instead of R E (Fig. 4) to improve linearity and/or efficiency. [1]
A radio-frequency power amplifier (RF power amplifier) is a type of electronic amplifier that converts a low-power radio-frequency (RF) signal into a higher-power signal. [1] Typically, RF power amplifiers are used in the final stage of a radio transmitter , their output driving the antenna .
In the example shown, the operational amplifier is used to reduce the distortion of a push-pull pair. Operational amplifiers are differential voltage amplifiers with very high gain (sometimes modeled as infinite gain). In an ideal model, the output of the op amp is held such that both inputs of the op amp must be at exactly the same voltage.
Block diagram of fully differential and single-ended two-stage amplifiers. The following figure shows the block diagram of a two-stage amplifier in fully differential and single ended modes. In a two-stage amplifier, input stage can be a Telescopic or FC amplifier. For the second stage, common source amplifier with active load is a common choice.
Linear amplifiers need to operate with class-A or class-AB biasing, which makes them relatively inefficient. While class C has far higher efficiency, a class-C amplifier is not linear, and is only suitable for the amplification of constant envelope signals. Such signals include FM, FSK, MFSK, and CW . [5] [6]
A class-B push–pull amplifier is more efficient than a class-A power amplifier because each output device amplifies only half the output waveform and is cut off during the opposite half. It can be shown that the theoretical full power efficiency (AC power in load compared to DC power consumed) of a push–pull stage is approximately 78.5%.