An LNB frequency down conversion integrated circuit in a chip including: a pre-amplifier, to receive output of a mid-stage high frequency, HF, amplifier of a front-end circuit and improve the noise factor of the chip, so that the noise of the whole LNB system will not worsen; to transform a single-ended signal sent from the mid-stage HF amplifier into a differential signal to improve the suppression function of common mode noise in the chip; wherein the said differential signal comprises a first signal with the phase of 0 degree and a second signal with the phase of 180 degree; a quadrature voltage-controlled oscillator, to output four LO signals with phase difference of 90 degrees between with each other, wherein the four LO signals are a first LO signal with the phase of 90 degree, a second LO signal with the phase of 0 degree, a third LO signal with the phase of 270 degree and a fourth LO signal with the phase of 180 degree, respectively; a quadrature frequency mixer, to receive the four LO signals sent from the said Quadrature voltage-controlled oscillator and the differential signal sent from the said pre-amplifier, wherein the quadrature mixer mixes the first LO signal with said first signal to produce a first IF signal with the phase of 90 degree, mixes the second LO signal with said first signal to produce a second IF signal with the phase of 0 degree, mixes the third LO signal with said second signal to produce a third IF signal with the phase of 270 degree, and mixes the fourth LO signal with said second signal to produce a fourth IF signal with the phase of 180 degree; an IQ intermediate frequency, IF, amplifier, to receive the four IF signals sent by the said quadrature frequency mixer, to improve the driving capability of the said quadrature frequency mixer and to prevent the signals from attenuation; a polyphase filter, to receive the output signals of the IQ intermediate frequency amplifier, and to filter the four IF signals, which eliminates mirror image signal; and then to add the first IF signal with the second IF signal, to add the third IF signal with the fourth IF signal, thus generating two signal outputs. a pre-amplifier, to receive output of a mid-stage high frequency, HF, amplifier of a front-end circuit and improve the noise factor of the chip, so that the noise of the whole LNB system will not worsen; to transform a single-ended signal sent from the mid-stage HF amplifier into a differential signal to improve the suppression function of common mode noise in the chip; wherein the said differential signal comprises a first signal with the phase of 0 degree and a second signal with the phase of 180 degree; a quadrature voltage-controlled oscillator, to output four LO signals with phase difference of 90 degrees between with each other, wherein the four LO signals are a first LO signal with the phase of 90 degree, a second LO signal with the phase of 0 degree, a third LO signal with the phase of 270 degree and a fourth LO signal with the phase of 180 degree, respectively; a quadrature frequency mixer, to receive the four LO signals sent from the said Quadrature voltage-controlled oscillator and the differential signal sent from the said pre-amplifier, wherein the quadrature mixer mixes the first LO signal with said first signal to produce a first IF signal with the phase of 90 degree, mixes the second LO signal with said first signal to produce a second IF signal with the phase of 0 degree, mixes the third LO signal with said second signal to produce a third IF signal with the phase of 270 degree, and mixes the fourth LO signal with said second signal to produce a fourth IF signal with the phase of 180 degree; an IQ intermediate frequency, IF, amplifier, to receive the four IF signals sent by the said quadrature frequency mixer, to improve the driving capability of the said quadrature frequency mixer and to prevent the signals from attenuation; a polyphase filter, to receive the output signals of the IQ intermediate frequency amplifier, and to filter the four IF signals, which eliminates mirror image signal; and then to add the first IF signal with the second IF signal, to add the third IF signal with the fourth IF signal, thus generating two signal outputs.