4DSP Support Forum

Products => FMC Products => FMC150 => Topic started by: paulleons on July 23, 2014, 11:40 AM

Title: Offset Problem?
Post by: paulleons on July 23, 2014, 11:40 AM

Hello,


I am giving a sine wave from a function generator with peak-to peak of 1.8 V where min_voltage = -900mv and max voltage of 900mv. When I pass this signal to FMC 151, I expect ADC values to span almost the full range of ADC with shape of a proper sine wave.


But when I probe the signal in chipscope, I get a graph which is not a sine wave anymore. However, when a offset voltage of +1V is provided, then I get the shape of the sine wave. But the range of the received sine wave do not span the full range of the ADC. The values are only ranged from 2460 to 10111.


Please note that I probe the signal phy_out_data_0 in the reference firmware.  Could anyone please explain the reason for this?


Thank you.


Paul

Title: Re: Offset Problem?
Post by: g.feu on July 25, 2014, 06:13 AM

I have an issue with offsets on both ADC and DAC channels. please checks my post. You might find interesting information

http://www.4dsp.nl/forum/index.php?topic=3072

Title: Re: Offset Problem?
Post by: arnaudNL on July 28, 2014, 04:36 AM

Dear Paul,


It looks like you are representing twos complement samples as binary values. The signal will look fine until the sign bit is reached in a word point of view I think. And indeed we do see a big offset on your signal.


Arnaud

Title: Re: Offset Problem?
Post by: paulleons on July 28, 2014, 03:08 PM

Thank you for the reply.


This issue is fixed now and it's the problem of representation.


Paul

Title: Re: Offset Problem?
Post by: arnaudNL on July 29, 2014, 06:01 PM

Great to hear Paul!


You know where to find us if you need anything more!


Best Regards,
Arnaud

Title: Re: Offset Problem?
Post by: arnaudNL on July 29, 2014, 06:01 PM

This topic is being closed because the issue is considered as resolved by 4DSP. Feel free to create a new topic for any further inquiries.