GSM PA control loop bandwidth ??

[Wilson_yu_chen]

Hi all,

Recently I got question about control loop bandwidth of PA need you comment.
Does it varies with different control method (Voltage sensing, power sensing, and even current sensing) ??
For power feedback control type of PA, that control loop bandwidth may be around 300KHz which is different from RAMPDAC sample frequency. ( That's why switching spectrum only test |offset frequency| larger/equal than 400KHz. Because there seems to be no possibility on kill the spur within that loop bandwidth, isn't it ?)

Also, how is the difference for open loop bandwidth and close loop bandwidth?
Can open loop case taken as unity gain loop bandwidth= 0.35/ rise time?

Thanks

 

[springf2000]

would you please provide more background matrial about the control loop bandwidth, for example is it the usage in the whole system or in the PA design
procedure?

 

[Wilson_yu_chen]

Here is the document my referenced.
Any body can give me comment on last postage ?
Thanks

wilson

 

[springf2000]

i have study the document of the LTC1758-1/-2, in fact this is a simple over drive kind circuit of the PA, the loop bandwidth is a measurement of response time! for example when the power amplifier output power is over the limited rate, then this chip shall shut down the PA, then the PA output power is zero, if the loop bandwidth is large(that means response quick), then the chip shall open the PA, then close, then open....., that mean the loop is oscillated!
so the loop bandwith is very important, this circuit is similair to the AGC or ALC circuit, the method of analysis is same as the AGC orALC circuit, you should analyse the dynamic feature of this kind of circuit when y decide to use this circuit!
i do not know whether it useful for you!
thanks!