[USRP-users] USRP ADC input voltage limit

Marcus Müller marcus.mueller at ettus.com
Mon Apr 6 16:33:04 EDT 2015


Dear Zhao,

the ADC is part of the USRP motherboard. Which one are you using? For
the N2x0, I think the max voltage was 1.2V (reference voltage of the
ADC); for all boards but the Basic and LF boards, you should make sure
your signal input power does not exceed -15dBm.

LFRX is just a 50Ohm-matched differential voltage follower, so the
maximum acceptable voltage for the ADC would also be the maximum
acceptable voltage at the SMA port.

> Another question is about the unit of the ADC output. Is it V (volt)?
> Or, is there a reference
It's digital bits; nothing more, nothing less. It's measured voltage
related to the reference voltage of the respective ADC, but it's not
calibrated, and though our devices tend to be very linear over wide
operational ranges, it's impossible to give exact numbers, due to
frequency-dependent behavior and component variance of each individual
device, as there is a lot of analog signal processing on the RF-capable
boards; if you want to match digital value to input voltage, you will
have to calibrate; in your baseband signal case, that might be rather
simple, if you have a oscilloscope and some kind of signal generator.

Best regards,
Marcus


On 04/06/2015 08:32 PM, Zhao Tian via USRP-users wrote:
> Hi,
>
> I am trying to use USRP+LFRX to sample the output of a photodiode. I
> guess there must be a voltage limit for the ADC input but I could not
> find it with Google. I don't want to damage the hardware.
>
> Any suggestions about the USRP ADC input voltage limit, or where I can
> find it.
>
> Another question is about the unit of the ADC output. Is it V (volt)?
> Or, is there a reference?
>
> Thank you so much!
>
> Best,
> Zhao
>
>
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
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