A mixer is a circuit in which the output signal frequency is equal to the sum, difference, or other combination of the two input signal frequencies. Mixers typically consist of nonlinear components and frequency selection circuits.
The mixer is located after the low-noise amplifier (LNA) and directly processes the RF signal amplified by LNA. To achieve the mixing function, the mixer also needs to receive the local oscillator (LO) signal from the voltage controlled oscillator, and its circuit works completely in the RF frequency band.