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discriminator

A discriminator is a demodulator for frequency modulated signals. Since in frequency modulation the information content lies in the frequency change, the frequency-modulated signal must first be converted into an amplitude-modulated one before it is subsequently converted into the low-frequency modulation frequency in a demodulator.

From the circuit technology, discriminators always work with a conversion of the frequency modulated signals into another modulation form, in order to be able to demodulate them then amplitude or pulse width wise. One of the best known circuit principles is the phase discriminator.

Structure of the phase discriminator

Structure of the phase discriminator

In this circuit, according to the principle, two rectified modulation voltages are added with two opposite modulation voltages. The added modulation voltages are rectified and subtracted from each other. With unmodulated carrier frequency, the rectified modulation voltages add/subtract to zero. With modulation-induced frequency deviation, one of the two voltages becomes larger than the other and the voltage difference corresponds to the modulation frequency. The greater the modulation-induced frequency deviation, the higher the demodulated modulation voltage will be.

In addition to the phase discriminator mentioned above, there is also the pulse width discriminator and the counting discriminator. Discriminators are used wherever signals are frequency modulated and the modulation signal must be separated from the carrier signal. For example, in FM broadcasting or in the audio signal of classic analog television, in measuring receivers, spectrum analyzers and other measuring and communications equipment.

Informations:
Englisch: discriminator
Updated at: 02.10.2010
#Words: 231
Links: demodulator, frequency (f), frequency modulation (FM), information, content
Translations: DE
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