Direct conversion receiver with dithering local carrier frequenc

Details Direct conversion receiver with dithering local carrier frequenc Direct conversion receiver with dithering local carrier frequenc

1990-04-20

1992-02-25

Chin, Stephen

Pulse or digital communications

Repeaters

Testing

375 97, 329302, H04L 2714

Patent

active

050919210

ABSTRACT:
An FSK receiver includes first and second channel paths to which the received FSK signals are applied. Each channel path includes a mixer circuit, a low-pass filter connected to the mixer circuit, and a limiting amplifier connected to the low-pass filter. A voltage-controlled oscillator generates a local carrier and a phase shifter applies its output to the mixer circuits with a 90.degree. phase difference therebetween. A frequency detector is coupled to one of the limiting amplifiers for generating a signal representative of the deviation frequency minus the offset frequency of the received FSK signal. An average circuit detects an average value of the signal from the frequency detector. A comparator circuit detects whether the frequency representative signal lies in or outside of the neighborhood of the average value. A ramp voltage of constant amplitude is periodically generated if the signal is detected as lying outside of the neighborhood and maintained at an instantaneous value if the signal is detected as lying in the neighborhood. The voltage-controlled oscillator is responsive to the ramp generator to control the frequency of the local carrier in search of the transmitted carrier frequency.

REFERENCES:
patent: 4193033 (1980-03-01), Voorman
patent: 4322851 (1982-03-01), Vance
patent: 4475219 (1984-10-01), Puckette
patent: 4517519 (1985-05-01), Mukaiyama
patent: 4521892 (1985-06-01), Vance et al.
patent: 4571738 (1986-02-01), Vance
patent: 4672636 (1987-06-01), Marshall et al.
patent: 4716579 (1987-12-01), Masterton
patent: 4752742 (1988-06-01), Akaiwa

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