Hello guys, My device is 10CX220YF780E5G and the Quartus is QPP23.4. I implemented one channel LVDS receiver in my project. External PLL was checked. After full complilation, I found LVDS module was...
This issue happened just as I made one simple project for LVDS test and trying. Now we try internal PLL, instead of external PLL, the LVDS function looks fine.
As you mentioned to try clock input, as following images, we already try this to receiver external ADC output.
However, here i have another question about LVDS need you help. Which is of LVDS constrain. We know that LVDS needs input termination and with the value of "Differential", as above image. We applied this constrain for ADC output pairs. They run well.
So we have another type LVDS pairs input, which are not from external ADC chips. They come from comparator devices output. FPGA use differential I/O pairs to receiver them. When we apply same constrain as ADC output pairs, they can't run well. The comparator output run as pulse signal, we can use Signaltap to monitor its signal quality. It's very bad under this constrain.
But they can run well when On-Chip Termination for Transceiver Rx pin (with 100 ohms value)constrains were applied to them. My question is what's the different between them?