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Delay before rf amplifier gives stabilized output gain

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veeraselvi

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Amplifier switch on time

Hi,

I am designing power supply sequencing for RF monolithic amplifier. I want to know the delay time of amplifier response. After switch on the power supply, how many nS that amplifier will take to give stabilized output gain?

What are all the parameter has taken into account to calculate ?


regards,
Veeraselvi.B
 

Amplifier switch on time

As most RF amolifiers are AC coupled, you may want to check primarly the coupling time constants. A transient simulation
or empirical measurement is most likely necessary to determine the exact recovery time.
 

Re: Amplifier switch on time

Saw a wireless lan job recently that was all screwed up because the were trying to transmit before the DC bias levels had settled out in the transmit amplifier. Sorry, I do not remember how many ns it took to settle. It is probably a function of how much bias line capacitance you have to charge up. Unfortunately, with today's modern modulation schemes, you need a vector signal analyzer to measure error vector magnitude at turn-on to see the effect.
 

Re: Amplifier switch on time

amplifier response time (<5ns) is much shorter than bias stable time. you should make your bias stable time to be nano seconds level first. but it is challenging.
 

Re: Amplifier switch on time

This was a problem for the first CDMA IS95 handset power amplifiers. The system designers tried to shut down the PA during frames through the bias circuit, but the settle time of the bias circuit was too slow. So, all the CDMA PA’s (or WCDMA) have the bias always on.
For very fast settle time measurements you can use a crystal detector which has a response in a range of 200 picoseconds. Usually the measurement is done between 10% and 90% of the output power.
 

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