TUNER FOR IMPROVING AMPLIFICATION FACTOR AND NOISE FACTOR ON RECEIVING OF WEAK ELECTRIC FIELD SIGNAL

PURPOSE: A tuner for improving an amplification degree and a noise figure when receiving a weak electric field signal is provided to improve the amplification degree and the noise figure when receiving the weak electric field signal and improve a signal distortion characteristic and a cross modulation characteristic when receiving a strong electric field signal by controlling the amplification degree of an LNA(Low Noise Amplifier) and an FET(Field Effect Transistor) amplifying circuit according to the level of an IF(Intermediate Frequency) signal. CONSTITUTION: An AGC(Automatic Gain Controller) detector(190) converts an IF signal outputted from a mixing unit(160) into a DC voltage, and outputs the DC voltage. An internal bias circuit of an LNA(110) is connected to an output end of the AGC detector(190). An amplification degree of the LNA(110) is decided according to the DC voltage inputted from the AGC detector(190). The amplification degree of the LNA(110) is increased when a weak electric field signal is received, and is decreased when a strong electric field signal is received. One gate of an FET amplifying unit(140) is connected to the output end of the AGC detector(190). An amplification degree of the FET amplifying unit(140) is decided according to the DC voltage inputted from the AGC detector(190). The amplification degree of the FET amplifying unit(140) is increased when the weak electric field signal is received, and is decreased when the strong electric field signal is received. 본 발명은 약전계 신호 수신시 증폭도 및 잡음 지수 개선 튜너에 관한 것으로, 상세하게는 혼합부로부터 출력되는 IF 신호를 직접 AGC 디텍터를 통해 DC 전압으로 변환시키고, DC 전압을 직접 저잡음 증폭기의 바이어스 회로와 FET 증폭회로의 게이트로 인가하여 IF 신호의 레벨에 따라 이들의 증폭도를 제어함으로써 약전계 신호가 입력될 시 증폭도 및 잡음 지수를 개선하고, 강전계 신호가 입력될 시 신호 왜곡 및 혼변조 특성을 개선할 수 있다.