Automatically tunable phase locked loop FM detection system
US4881042A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 25, 1988 |
| Grant date | Nov 14, 1989 |
| Priority date | — |
| Expiry date | Jan 25, 2008 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03B5/1243
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A FM detection system using a phase locked loop (PPL 20) and including: a wave shaping comparator (7) for accepting a signal V.sub.CO2 from a voltage controlled oscillator (4) which is 90.degree. out of phase with a control signal V.sub.CO1 from the voltage controlled oscillator (4), the comparator reshaping the signal to a square wave; an in-lock detector (8) for accepting the square wave and a frequency modulated input signal (VFM) to provide a sum frequency and a difference frequency; a low-pass filter (9) cutting off the sum frequency component, and filtering out the difference frequency signal when the PLL (20) is unlocked; a comparator (10) for comparing the output of the low-pass filter (9) with a reference voltage (V.sub.REF1), and providing a constant logic level when the PLL (20) is locked, or providing a clock pulse corresponding to the difference frequency when the PLL (20) is unlocked; a ripple counter (11) for counting the clock pulse and providing a binary signal output reflective of the count; a D/A converter (12) for accepting the binary output to provide an analogue current; and the oscillation frequency of the voltage controlled oscillator (4) being controlled in…
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