Practical Magic

Typically, Doherty test fixtures are inflexible with regard to combiner positioning. The generic Doherty development fixture shown here can quickly provide the designer with the final circuit requirements for multiple devices. The dynamic Doherty combiner enables this flexibility by using the 50-Omega line as part of the output transformation. An easy-to-implement 50-Omega line and a shunt cap provides the transformation required from the Doherty inverter to the amplifier output. Final circuit configurations can revert to the traditional lambda/4 transform once the phase length "Oslash" is identified. Flexible Doherty development circuits will assist in minimizing the fixtures required for development efforts. This Doherty development process is easy and straightforward to implement, and results can be obtained quickly. Simulation methods and models will continue to be used to create the 50-Omega tuning structures and optimize the design of Doherty circuits. However, this practical design approach can be applied for each circuit that needs to be designed, and good results will be obtained.