What are Double Balanced Mixers?
Double Balanced Mixers are mixers that will suppress both the RF and LO input signals. The input signals are generally not wanted at the output and normally they would be removed by filtering which is inconvenient and bring additional cost. They provide high LO-RF, LO-IF and reasonable RF-IF isolations. Compared to unbalanced mixers, double balanced mixers can reduce the level of intermodulation products by up to 75%.
RF Mixers are nonlinear components that are used to up-convert or down-convert the frequency of a signal. They mix the frequency of the original signal (RF) with that of a Local Oscillator (LO) to produce two new signals at the sum RF + LO (up-converting) and difference RF – LO (down-converting) of the input frequencies.
Important Parameters for Double Balanced Mixers:
- Frequency: There are three frequencies that are of importance when selecting double balanced mixers:
- RF Frequency – This is the frequency of the original signal.
- LO Frequency – This is the frequency of the local oscillator (LO), it is used to up-convert or down-convert the RF frequency. the Intermedia Frequency (IF + LO) or to down-convert the RF frequency (RF - LO).
- Intermediate Frequency (IF) – This is the frequency obtained at the output, which is either the sum RF + LO (up-converting) and difference RF – LO (down-converting) of the input frequencies.
- 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 resistance of signal leakage from the local oscillator to the RF path and the LO/IF isolation is the measure of resistance of signal leakage from the LO to the IF path. The higher the isolation, the better the mixer performance.
- LO Drive Power: This is the signal power of the Local Oscillator.
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