VGA output power level !!!

[imar]

hi freinds,
1- i am trying to achieve a system level design for a rf receiver that has freq range between 100 MHz to 900 MHz.
i am confused on the what way that i should use to fixe the output level of the VGA before coming to the ADC.
what are approximtly the power level accepted by the ADC?
is it always around 15 dBm which corresponds to 1.2 V rms; or it could be lower and even reaches some negative values (less than -5 dBm) ?
i didn't fixe yet the kind of ADC , it would be 9 bits with fsamp of 100Msps.

2-an other question please: is there any helpful reference that explains VGA, especially, what is the max of IIP3 that could reache the VGA?
3-what is the max of IIP3 that could reache an amplifier for gain >20 dB?


i appreciate any help

thanks in advance

imar

 

[biff44]

pick a part number, read the data sheet to see the input voltage range, and leave a little headroom.

Some ideas here:
**broken link removed**

Rich

 

[radiohead]

Of course you can go down 20 dB. But then your input signal is 10 times smaller, and the three highest bits are in fact useless. So instead of a 12 dB ADC you now effectively will have a 9 bt ADC. That's why AGC is so important.

 

[imar]

What are parameters that fix the ADC full scale power ?
i found in different exmaples that the full scale has different values and can goes from -4 dBm to higher one as 13 dBm.

 

[FvM]

It's been said.

pick a part number, read the data sheet to see the input voltage range, and leave a little headroom.

 

[imar]

thanks for the information!
but, if it is possible, why should we take a headroom between the full scale and the output vga power?
so,for what purpose ?