Step-servoed tone detector

Details Step-servoed tone detector Step-servoed tone detector

1975-07-18

1976-10-26

Heyman, John S.

Demodulators

Amplitude modulation demodulator

Having specific distortion, noise or other interference...

328119, 328133, 328155, 329126, 333 70R, H04B 1500, H03K 906

Patent

active

039886875

ABSTRACT:
An incoming signal (tone) and the feedback signal of a biquadratic filter are converted into square waves by zero crossing comparators. The phase state of the square waves is decoded and the decoded result is phase compared to determine if a 90.degree. phase shift exists between the incoming and feedback signals. If a 90.degree. phase shift does not exist, a counter is incremented or decremented, depending upon whether the phase comparison indicates that frequency of the incoming signal is greater, or less than the feedback signal. The output of the counter is decoded and utilized through a switching circuit to control the center frequency of the biquadratic filter (determined by the impedance of its feedback path). The switching circuit changes the impedance of the feedback path so that the center frequency is moved toward the frequency of the incoming signal. When the center frequency of the biquadratic filter is at the frequency of the incoming signal, the output of the frequency decoder provides a coded indication of the frequency of the incoming signal.

REFERENCES:
patent: 3436647 (1969-04-01), Gobeli et al.
patent: 3539829 (1970-11-01), Langendorf et al.
patent: 3555435 (1971-01-01), Vosteen
patent: 3628057 (1971-12-01), Mueller
patent: 3714588 (1973-01-01), Deboo et al.

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