how to improve Gain stability for multi-stage PA

Hello,
for multistage PA,each stage will have a Gain flatness and stability over temperature, then the total stability will be an add-up of each stage,which will be
poor. How to improve the Gain flatness and stability?

Thanks
Liu

the gain flatness with frequency is based on the frequency response of the each stage and the matching network

over temperature u need to make a temp compensation circuit to tune the gains of the amps

khouly

Actually the Gain flatness shouldn't be a problem in a multistage PA because there are more possibilities to adjust the Gain vs Frequency (input, output and interstage match).

For good stability the interstage matching topology plays an important role, as well the bias filtering of each stage.
Not to the last, the gain distribution per stage could be important getting a stable amplifier.

Ground inductance (bondwire or whatever the routing to the true,clean ground) plays an important role in stability. If you add this parasitic inductance to your pure ground in your simulation you will see the effect on stability. Mutliple bondwire is typically used to reduce this effect

Any good references?
Thanks

I assume that for You "stability" means "long time variations" and not "self oscillation".

Basically two way may be covered.

1) ad hoc DC supply.
Since the FET gm=f(Id, Temp), the power supply should change Id in order to compensate the change of gm vs temperature.

2) pay attention to thermal effects of the PA box.
Thermal resistance should be reduced as low as possible on all directions (same Rth also for PA upside down ).
The PA box should be thermostated.

An exellent thermal design is the 50% of the RF PA design !