5640R DAC output architecture

[Vojtech_D.]

Hi, Does IF-RIO (PCI 5640R) have a preamplifier after the DAC? The DAC has 14 bit resolution. If I generate a signal with a very low amplitude, does the board use just lower bits of the DAC or does it use all 14 bits and scales the output by the preamplifier/attenuator to reach the required gain? If so, what are the limits of this preamplifier?


Message Edited by Vojtech D. on 06-09-2008 01:54 PM

[Ken_Tobler · Accepted solution]

Hi,

the 5640R has only one fixed input range of max 8.5 dBm
So if you feed in a very small signal only the lower bits will change

Best regards
Ken

[Vojtech_D.]

Hi,

I meanwhile got a response form NI:

The AD9857  (DAC with quadrature upconverter) supports a digital gain factor between 0 and 2, so you can change the output power without modifying I&Q values. But since it's applied before DAC conversion, it doesn't affect the overall available full scale range.

So at the end the answer is: adjusting power means adjusting I&Q values or this Output Scale Factor.