Direct conversion receiver including mixer down-converting incoming signal, and demodulator operating on downconverted signal

Abstract

A direct conversion receiver includes a local oscillator for generating a first local oscillator signal having a variable frequency. A 90° phase shifter operates for shifting a phase of the first local oscillator signal by 90° to convert the first local oscillator signal into a second local oscillator signal. A first mixer operates for mixing a received RF signal and the first local oscillator signal. A second mixer operates for mixing the received RF signal and the second local oscillator signal. A first low pass filter processes an output signal of the first mixer. The first low pass filter has a controllable cutoff frequency. A second low pass filter processes an output signal of the second mixer. The second low pass filter has a controllable cutoff frequency. A demodulator recovers an information signal represented by the received RF signal from output signals of the first and second low pass filters. A frequency error detector operates for detecting an error between a frequency of a carrier of the received RF signal and the frequency of the first local oscillator signal in response to the information signal recovered by the demodulator. An oscillator controller operates for controlling the frequency of the first local oscillator signal in response to the error detected by the frequency error detector. A filter controller operates for controlling the cutoff frequencies of the first and second low pass filters in response to the error detected by the frequency error detector.