Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Patent
1983-09-23
1985-04-02
Ng, Jin F.
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
H03J 718
Patent
active
045092044
ABSTRACT:
Disclosed is a stop detector circuit for issuing a stop signal in an electronically tuned AM radio when the radio is center tuned on a radio signal that exceeds a predetermined level of signal strength. An intermediate frequency signal and an automatic gain control signal are used to determine when the stop signal is to be issued. Included in the stop detector circuit are a resonator driver (16), a resonator circuit (18), a resonator signal amplifier (20), a current switch (22), a threshold adjustment and filter (24), and a threshold detector (26). The resonator driver generates a resonator signal having a series of current pulses at the same frequency as the intermediate frequency signal. The resonator circuit converts the resonator signal current to a voltage, the AC component of which is at a minimum when the radio is not center tuned and at a maximum when the radio is center tuned. The resonator signal amplifier amplifies the resonator signal voltage. This is necessary because the resonator signal current is kept small in order to minimize tweet interference caused by feedback. The current switch generates a station strength signal in response to the resonator signal voltage and the current of the automatic gain control signal. The current of the station strength signal equals a large fraction of the current of the automatic gain control signal when the radio is center tuned. The threshold adjustment and filter provides means for filtering current pulses from the station strength signal converting the station strength signal to a DC voltage and for adjusting this voltage. When the voltage of the station strength signal exceeds a predetermined value, the threshold detector issues the stop signal. The predetermined value is exceeded only when the radio is center tuned and the automatic gain control signal is sufficiently high.
REFERENCES:
patent: 3714580 (1973-01-01), Close
patent: 4262363 (1981-04-01), Wiechmann et al.
National Semiconductor Corporation
Ng Jin F.
Pollock Michael J.
Winters Paul J.
Woodward Gail W.
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