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...http://www.google.de/patents/US5091921?utm_source=gb-gplus-sharePatent US5091921 - Direct conversion receiver with dithering local carrier frequency for detecting transmitted carrier frequency
