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Honored Contributor I
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Cannot meet timing constraints for LVDS I/O at 800 Mbps on Cyclone V SX

Hi! 

I have been badly struggling for 8-10 days trying to meet the timing constraints for LVDS I/O at 640Mbps. I am trying to use SERDES for LVDS data (2 lane) from 16 bit ADC (AD9563) to the FPGA (5CSXFC6D6F31C6) at 640Mbps.  

There is always input setup and hold violations. I have tried what all I could do. I am assuming that the 16 bit ADC is sampled at 80MSPS and hence LVDS rate on each of the 2 lanes will be 640Mbps. Also the ADC_0_DCO clock out from the ADC is exactly at the centre of the data (data window is 1.5625ns). Thus can I assume that Tco of the external device which is the ADC is 1.5625/2 (= 0.78125 ns) ? 

 

My project is very simple. I am using ALTLVDS_RX with 640Mbps data rate, 320MHz inclock, serialization factor of 8. I learnt from some forum about constraining and got hold of some example on constraining DDR inputs and the same has been implemented in my design. The constraints are as below: 

 

set input_clock ADC_0_DCO; # Name of input clock 

set trco_max 0.781; # Maximum clock to output delay from rising edge (external device) 

set trco_min 0.781; # Minimum clock to output delay from rising edge (external device) 

set tfco_max 0.781; # Maximum clock to output delay from falling edge (external device) 

set tfco_min 0.781; # Minimum clock to output delay from falling edge (external device) 

set trce_dly_max 0.781; # Maximum board trace delay 

set trce_dly_min 0.781; # Minimum board trace delay 

set input_ports { Datain[0] }; # List of input ports 

# Input Delay Constraint 

set_input_delay -clock $input_clock -max [expr $trco_max + $trce_dly_max] [get_ports $input_ports]; 

set_input_delay -clock $input_clock -min [expr $trco_min + $trce_dly_min] [get_ports $input_ports]; 

set_input_delay -clock $input_clock -max [expr $tfco_max + $trce_dly_max] [get_ports $input_ports] -clock_fall -add_delay; 

set_input_delay -clock $input_clock -min [expr $tfco_min + $trce_dly_min] [get_ports $input_ports] -clock_fall -add_delay; 

 

I have attached the files for reference. 

 

Can pl some help and meet the timing... Thanks in advance 

 

best wishes,
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