Introduction to Mixers
A microwave frequency mixer is a 3-port electronic circuit that combines two or more signals into one or two composite output signals, and are categorized as switching mixers or nonlinear mixers– although many mixers are configured with both. Using diodes, the mixer is passive and has a conversion loss. Using active devices, such as transistors, a conversion gain is possible. A variety of circuit topologies exist for mixers and can be as simple as one that uses a single diode or more complex for enhanced performance.
Switching mixers include single-balanced and double-balanced mixers, widely used and known for reliability, while nonlinear mixers offer the ability for higher frequencies output. A single-ended mixer is usually based on a single Schottky diode or transistor. A balanced mixer typically incorporates two or more Schottky diodes or a Schottky quad. A balanced mixer offers advantages in third-order intermodulation distortion performance compared to a single-ended mixer, because of the balanced configuration. The popular modern mixer designs are Schottky diodes, GaAs FETs, and CMOS transistors depending upon the application. FET and CMOS mixers are often used in higher volume applications.