Saturation (electronics)

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The fully conductive state of semiconductor elements such as bipolar transistors is referred to as saturation (also called saturation mode ) . Before a semiconductor comes into saturation, it first goes into what is known as compression . Compression means that the gain of an amplifier decreases as the input power increases.


An increase in the control voltage or the control current does not cause any significant change in the output signal.

If the transistor is in saturation, the collector-emitter voltage is lower than its base-emitter voltage . The saturation voltage depends on the overload, the forward gain and the inverse gain of the BJT and can drop to a few tens of mV.

A transistor is deliberately operated in saturation when it is used as a switch.

Effects on a circuit

Static signals

Static signals are signals whose frequency is low and therefore has no influence on the circuit.

In measurement technology, the saturation or compression of an amplifier is important. If an amplifier is driven into compression or even saturation by an input level that is too high, the input signal measured is far too small. In order to still be able to measure the signal correctly, a correspondingly large attenuator must simply be connected in front of the input of the amplifier. The correct input power is then the measured signal plus the attenuation of the upstream attenuator. With many measuring devices, this damping can be adjusted so that the correct result is automatically displayed.

Dynamic signals

When transmitting signals, the saturation mode is a major disadvantage.

At high frequencies, i.e. with fast switching processes, the collector current cannot follow quickly enough, since the transistor first has to be cleared of the charge carrier flooding. This process takes time, which falsifies the output signal. If the frequencies are too high, this can result in the signal not being transmitted in the first place.

See also

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