Hi,

I have a CN0335 ADC Board which is a +/- 10V isolated system with the AD7091ADC, i'm very new with terminology and working with ADC's so i'm a bit confused with what is happening.

i have the CN0335 board connected to a FPGA which is reading the data via SPI. when I read the the data sheet for the CN3035 it says that even low the ADC is 12 bits a 16 bit word is outputted to be compatible with processor serial ports. As i am using a FPGA and only interested in the first 12 bits I only clock SCLK for 12 faling edges then bring CS_N back high.

The problem that i am having is if i represent the data as signed decimal on the FPGA logic anayse rand i increase the input signal to the adc from 0V DC to +10V DC i can see the the value start at 0 and increase to 2047 which is about 5.5V and then the number goes - 2047 and starts counting down as i raise the input voltage to 10 V

i have changed the representation to standard decimal and from 0V to 10V the data outputted is from 0 to around 40000 which seems plausible. however if i change the polarity so i have a -0V to -10V at -OV the data being outputted is 4000 and works is its way down to 0 as the voltage reaches -10V.

therefore the problem is an output of 1000 decimal could mean a positive number around 2-3 volts or a negative number around 6-7 V.

i hope this makes sense. any help would truley be appreciated

liam

Hi, Liam.

Did you get the chance to get some scope shots of the digital lines from your evaluation?

Regards,

Karen