Analog Device AD6654 in SPI Mode with Differential Inputs

what is your smode and mode pin connected to? Is it your FGPA? Pull up or pull down resistors?

what pins are you using for the spi signals?

you can post your VHDL and i will look at i to see if it will work.

can you pull out the psendo random numbers on each channel from your SPI using the PN pin?

do you have sdo pulled high with a pull up resistor?

there could be alot of possibilities why your chip is not working.

it says you should have slower than a 3 n sec rise/fall time on your serial clock. your FPGA can be faster than that if you have it programmed to the max speed and max current drive.

the OVR signal should not be going off. it looks to me that this signal is for overflow on the input. so if your input amplitude is too high, this pin will go off. it should not go off for normal operating conditions.

I will look at the NCO stuff and tell you what i find. i have and problems with other chips with an internal PLL and it becoming unstable. I had to add a new loop filter to make the chip work. i will let you know what i find.

are you using the PLL?

based on page 35 of data sheet http://www.analog.com/static/imported-files/data_sheets/AD6654.pdf and if your carrier frequency is 20MHz and your freq clock is 60MHz (no pll), you would do 60/20= 3.0 so mod(3.0)=0

your frequency word your sending is 362AAAABh or 362AAAABh/2^32 .211 of Fclk or 12.6953MHz so your mixed signal should be at 7.3MHz (20-12.7).

if you are trying to mix your 20MHz down to dc then you would need a 40MHz clock. so maybe your tune word should be 40/60*2^32 or send a AB AA AA AB for Address: 0x70, 0x71, 0x72, 0x73. i could be wrong with the last clock frequency. if so you would want to mix with 20Mhz so you would have 20/60*2^32 or 55 55 55 55.

what do you think? have you played around with the NCO freq much to see what the differences are? it might be good to go back to the eval board and master the chip before you try to spin your own.

Did you get it working?

Do you need any help?

Or was your question more of a rhetorical question?