some questions about RF system design

[ehsan_r34]

VGA Dynamic Range

Hi Dear all;

I have some questions about RF system design. It is very important.
Please help...

1- What is the Input Dynamic Range of a "VGA"(Variable gain amplifier)?
for example AD8367

2- In a Log Amp Detector if we give a signal larger than it need to saturate the log amp, what happen? Dose the log amp stay in saturation?

 

[ehsan_r34]

Re: VGA Dynamic Range

Please help if you know
:?:

 

[karesz]

VGA Dynamic Range

Datasheet tells us:
Input signal is in 200 Ohm system version maximum 700mVpp, output signal typical 3.5Vpp(in 200Ohm system).
Than, if you have high amplification, you must calculate backwards from output 3.5Vpp, at i.e. 40dB amplifying: input can have a signal of maximal 3500mVpp divided by 100=35mVpp...
2,
You sayd itself: if the signal is larger as saturating limit for a device_it will go in saturation!!
What it means exactly_depends on your device!
Most, in saturating controlled, devices have a longer "dead time" (after them saturating signal is off) to "operate normal", or the output signal changes polarity,(if bipolar is) or takes values on, their are absolute illegal...
K

 

[biff44]

Re: VGA Dynamic Range

Depends on what you mean by a log amp. Do you mean an RF log amp with an RF output port? If so, by overdriving the input the output will be a clipped signwave.

 

[ehsan_r34]

Re: VGA Dynamic Range

Thank you karesz

I mean, if the RF signal we need to saturate the log amp was (for example) -10dbm and we give a signal larger tham -10dbm what happen for log amp?
If log amp works normally in saturation,dose the delay of log amp change?