RF Mixer Basics & Selection
A RF Mixer is a non linear component that is used to up-convert or down-convert the frequency of an input signal. RF Mixers mix the frequency of an input signal (RF) with that of a Local Oscillator (LO) to produce two new signals at the sum RF + LO and difference RF – LO of the original frequencies.
RF Mixers are primarily used in receivers to down-convert a high RF frequency to a lower frequency which is typically easier to process. For example a 2.4 GHz signal input to a receiver can be down-converted to 10 MHz to further process. Similarly it is used in transmitters when up-conversion to a particular higher frequency is required.
RF Mixer Selection
When selecting a RF Mixer it is important to know the parameters that you need to specify. Below are a list of the key parameters to look out for when selecting a RF Mixer:
Frequency: There are three frequencies that are of importance when selecting a mixer – RF Frequency – This is the high frequency which is usually received by the receiver or transmitted out from a transmitter. LO Frequency – This is the frequency of the local oscillator (LO), it is used to up-convert the Intermedia Frequency (IF + LO) or to down-convert the RF frequency (RF - LO). The Intermediate Frequency (IF) is the low frequency required for processing the signal in the receive chain.
Conversion Loss/Gain: This is the loss or gain in the amplitude of the signal after frequency conversion.
Isolation: This is an important parameter, RF/LO Isolation – is the measure of signal leakage from the local oscillator to the RF path and the LO/IF Isolation is the signal leakage from the LO to the IF path. The higher the isolation the better the mixer performance.