constant power (APC) current driver design

and I suddenly realize that PID is not efficient as in power electronics, the type III bandwidth usually has bandwidth of 20khz, way too slow.

An emitter-coupled pair with current source on the emitters (an inductor, at high frequency) will steer current effectively, and 1A/150 MHz is not out of the question. You won't like the results if you insist on '0' in the range, that gets into hard base-drive requirements (but you could always leave the transistor turned ON and steal some current...).

Doesn't need to be bipolar, of course, a source-coupled pair of MOSFETs could do something similar.

I'm dubious that the output impedance will be high enough to be 'practically infinite', like a good DC current source.

it seems working on open loop only. the feedback is a big issue, at @150MHz need to do feedback to keep constant power output.

"constant power" and "current source" are contradictory. You can have one or the other but not both. Which do you want? Mark

did

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my misleading, this power is not V*I. current source could be constant power , this power is from the driven object like a laser diode, this power is from the light emission and detected by a photodiode.