Frequency converter and radio receiver using same

Abstract

A frequency converter includes: a signal synthesizer element for inputting first and second input signals to synthesize these signals and for outputting a synthesized signal, from which noises even times as large as the frequency of the second input signal are removed; an amplitude limitation amplifier element, composed of a differential amplifier circuit, for amplifying the synthesized signal outputted from the signal synthesizer element to output an amplified signal having a constant amplitude; and a filter for inputting the amplified signal outputted from the amplitude limitation amplifier element, to remove an unnecessary signal component to produce an output a baseband signal including only a desired signal component. In addition, a radio receiver using the frequency converter of such a construction is designed to input the output of a local oscillator to a variable attenuator or a variable gain amplifier, to input the output of the variable attenuator or the variable gain amplifier as the first input signal to the frequency converter so as to perform the gain control. Thus, not only is self-mixing, a common problem in direct conversion receivers, prevented, but also, because a smaller local oscillation driving signal is required, power consumption is significantly reduced.