mm-Wave Cascode Power Amplfier Biasing

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George Sarris

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Hello everyone,
I am making a mm wave PA and i am trying to employ the cascode topology. My main concern is Power Added Efficiency which i want maximized. Is there any particular methodology that could help me bias the circuit for maximum efficiency? For example one thing is that the voltage swing across the common emitter device should be small in order not to steal swing from the output (and consequently Pout and PAE). One way to achieve this is by lowering the base voltage of the cascode device. This eventually will bring my CE device in saturation. Is this acceptable? As i am new to PA field, if you have some suggestions about biasing for power efficiency and any reference, please help me.
Regards,
George
 

Unless you are not going to put the cascode PA working in E Class or something similar (switch operation) your circuit would have less PAE than any other single transistor amplifier.
For maximum PAE is not enough providing the right bias to the amplifier, but also the amplifier must get proper load resistance, which cascode topology generally cannot provide especially at medium and high output power levels.
 

Thank you for your answer. You mean it cannot provide without a matching network? Also what is the difference exactly between different power levels? Thank you in advance.
George
 

If use as a power amplifier definitely the circuit needs an output matching network to get the optimum output load, not only to improve efficiency but also improving output power.
Generally cascode topology is used in small signal amplifiers to improve stability, gain, and bandwidth.
 

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