The auxiliary device is assumed to turn ON at a specific input power level (breaking point), typically 6 dB backed-off from the maximum total power of the Doherty amplifier. Though, Class-C peaking amp has large AM-PM component. Phase alignment of the carrier and peaking channels may have great influence on the Doherty amplifier linearity. Thus, the optimal bias level of the peaking channel is a subject to investigate and it would depend on the amplifier design.
You can see example of influence of the peaking channel bias in page 40 of this useful presentation:
Christopher Burns, RFMD, High Power Doherty Design, Modeling & Measurement
https://www.keysight.com/upload/cmc_upload/All/7March2013Webcast.pdf
> Is it allowed to increase the peaking bias?
Yes. But an optimum value exist.
> If so up to what voltage? (without damaging amplifier)
In the extreme case, you can provide the same (class AB) bias for carrier and peaking devices, so that, both will work in parallel. It will work. It will provide the same maximum output power. But it will lose efficiency advantage of Doherty design at mid power.
> How does this affect the improving the linearity/gain?
See the presentation above.
Unfortunately, we can not provide you similar curves for A2T07D160W04SR3 reference design. Please note that datasheet provides gain and efficiency curves for single-carrier W-CDMA signal with PAR 9.9 with 0.01% Probability on CCDF. These are very different from the single tone curves in the presentation.
Have a great day,
Pavel
TIC
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