FREQUENCY CONVERTER

PURPOSE:To improve the linearity and to make the circuit integration easy, by using a variable resistance element having a good linearity as a common emitter resistor of a differential amplifier. CONSTITUTION:The conductivity of a base region is modulated by injecting a minority carrier to the base region of a bipolar transistor structure from the emitter, and the variable resistive element 14 whose resistance value is controlled with the amount of minority carrier injection from the emitter is constituted by using the base region whose conductivity is modulated. The variable resistive element 14 is the common emitter resistor of transistor differential amplifiers 6, 7 to the base input of which an input signal is applied, the resistance value is controlled by a local oscillating signal obtained from a local oscillator 21, and a signal 4 having a frequency being the sum or subtraction of the frequency of the input signal and the frequency of the local oscillator, is extracted selectively from the collector output terminal of the differential amplifiers 6, 7.