Foster-Seeley discriminator
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The Foster-Seeley discriminator is a common type of FM detector circuit. It uses a tuned RF transformer to convert frequency changes into amplitude changes. A transformer, tuned to the frequency of the carrier, is connected to two rectifier diodes. The circuit resmbles a full-wave bridge rectifier. If the input equals the carrier frequency, the two halves of the tuned transformer circuit produce the same rectified voltage and the output is zero. As the frequency of the carrier changes, the balance between the two halves of the transformer secondary changes, and the result is a voltage proportional to the frequency deviation of the carrier.
Foster-Seeley discriminators are sensitive to both frequency and amplitude variations, unlike some detectors. Therefore a limiter amplifier stage must be used before the detector, to remove amplitude variations in the signal which would be detected as noise. The limiter acts at lower amplitudes acts as a Class-A amplifier and at higher amplitudes it acts like a Class-C amplifier which clips off the peaks.
Other types of FM detectors are
- Slope detector
- Ratio Detector
- Quadrature Detector
- Phase-locked loop detector.ms:Litar pembezalayan Foster-Seeley
