VIDEO INTERMEDIATE FREQUENCY AMPLIFIER CIRCUIT

PROBLEM TO BE SOLVED: To provide the excellent detection output of a stable SN ratio at all times regardless of an input level. SOLUTION: Between the AGC amplifier G1 for RF.AGC of a tuner 2 and the AGC amplifier G3 for IF.AGC of a detection circuit part 5, a SAW filter 4 for inputting IF signals and obtaining required frequency band characteristics and a preamplifier 3A for compensating the insertion loss are arranged. An RF-AGC 5d supplies an RF.AGC control voltage to the AGC amplifier G1 and controls a gain and a Schmitt comparator 10 for comparing the RF.AGC control voltage with a prescribed reference voltage Vcc supplies a compared result to the preamplifier 3A and controls the changeover of the gain. For instance, changeover control is performed so as to lower the gain in the case that an input electric field level is high and to raise the gain in the case that it is low inversely. Thus intermediate frequency amplification is performed so as to prevent the degradation of an S/N with the danger of being caused at the time of a weak electric field and distortion with the danger of being generated at the time of strong electric field and optimum video detection output is obtained.