PURPOSE: To attain the amplifier so as to be operated from a low intermediate frequency and to improve the temperature characteristic and linearity of an electric field detection voltage by providing a double balance differential amplifier connected to an output of each n-stage of differential amplifiers and a circuit adding a load current of the amplifiers and detecting an input signal with a DC level of the adding current.

CONSTITUTION: An IF input signal VIN is amplified by differential amplifiers Q1 Q2 of the 1st stage, and the level is shifted by transistors (TRs) Q3, Q4. The operation of the 2nd and succeeding stages is similar. When the signal VIN is increased, the output V2 of the 1st stage is saturated at all. The output V2 is a full wave rectified waveform and the saturation level is decided by the product between emitter resistors R6, R7 and a current source I2 and the quantity of the input signal VIN. The level of the 2nd and 4th act similarly. In taking the gain of each stage as g1∼g4, the ratio of the sensitivity of the signal of the 1st and the 4-th to the signal of the 1st input terminal is taken as (g), then the dynamic range to the signal VIN is expected to be up to g1×g2×g3×g4×g. In deciding the current ratio of the current source comprising a TR being a load of each stage depending on the emitter resistor, the output current of TRs Q49, Q50 adding the load currents of each stage has an LCG characteristic to the signal VIN and the excellent linearity is obtained.