Single-Balanced Mixers suppress any RF or noise energy that may be present with the LO (common mode or noise rejection). In addition, single-balanced mixer circuit are particularly easy to bias and monitor the diode currents.
A one-diode, or unbalanced mixer, is often used in economical receiver front ends, where tunable or fixed bandpass filters can easily separate the LO, RF and IF energy coupled to and from the diode. Early wideband receivers utilized two diodes in a single-balanced mixer circuit with a 90° hybrid to couple RF and LO power to a pair of diodes. This technique allowed overlapping LO and RF bandwidths without filters, but the isolation was dependent on how well the diodes were impedance matched. Broadband 180° hybrid balanced mixers eliminated this problem.
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