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Abstract

A single chip superhetrodyne AM receiver including a local oscillator which sweeps through a frequency range at a rate higher than a modulation frequency of the incoming RF signal. The local oscillator frequency is mixed with the incoming RF signal. An IF filter passes a selected frequency band from the mixer to a demodulator. The demodulator is tuned to demodulate any signal within a band of frequencies determined by the sweeping of the local oscillator. This increases the signal to noise ratio of the receiver since it allows for variations in the transmitter output frequency. The frequency responses of the various filters are tied to the reference frequency and allows the user to set the tuning and alignment of the receiver. To compensate for process variations in the implementation of the IC, bias currents setting the operating conditions for various amplifiers and other components in the system are adjusted based on frequency control signals in a PLL circuit in the local oscillator.

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First Claim