A Distributed RC Network Broadband FM Discriminator in Thin-Film Technique

The paper describes a frequency discriminator using two distributed RC null networks with different null frequencies, which can be realized in thin- or thick-film technology. The null networks with their null frequencies situated on either side of the carrier frequency use a common input. Their output signals are rectified and subtracted. The demodulated output signal is available either balanced or unbalanced. The analysis covers exponentially tapered and uniformly distributed networks, their difference in sensitivity, and harmonic disitortion due to nonlinearity of the response. The circuit can handle wide frequency deviations of up to /spl plusmn/ 20 percent and delivers an unbalanced output signal of approximately 0.46 volt rms using exponentially tapered networks and an input signal of 1 volt rms with /spl plusmn/ 10 percent frequency deviation. The harmonic distortion in this case is 3.3 percent. Calculated results are compared with measurements of an experimental 1O-MHz discriminator.