• Skip to main content
  • Skip to search
  • Skip to footer
Cadence Home
  • This search text may be transcribed, used, stored, or accessed by our third-party service providers per our Cookie Policy and Privacy Policy.

  1. Community Forums
  2. Digital Implementation
  3. Clock doubler SDC modelling

Stats

  • Locked Locked
  • Replies 0
  • Subscribers 91
  • Views 3002
  • Members are here 0
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Clock doubler SDC modelling

jeffreypr293
jeffreypr293 over 1 year ago

Hi all,

I'm trying to model the clock of a clock doubler. The doubler consists of a delay cell and an XOR gate, which generates a pulse on both the rising and falling edge of the input clock. I've created a simple module to evaluate this. In this case, DEL1 and XOR2 are standard library cells. There is a don_touch constraint on both library cells as well as on clk_d.

module top (
input wire clk,
output reg Q);

//Doubler
wire clk_d;
wire clk_2x;
DEL1 u_delay (.I(clk),.Z(clk_d));
XOR2 u_xor (.A1(clk),.A2(clk_d),.Z(clk_2x));

//FF for connecting the clock to some leaf:
always @(posedge clk_2x) Q<=~Q;

endmodule

My SDC looks like this:

create_clock [get_ports {clk}] -name clk_i -period 100
set_clock_latency -rise 0.1 [get_pins u_xor/Z]
set_clock_latency -fall 0.4 [get_pins u_xor/Z]
create_generated_clock -name clk_2x -edges {1 1 2 2 3} -source clk [get_pins u_xor/Z]

The generated clock is correctly generated but the pulse width is zero. I would be expecting that the pulse width is the difference between fall and rise latency but is not applied:

report_clocks:

report_clocks -generated:

clk_2x is disconnected from the FF after syn_generic. What can I do to model some minimum pulse width? Will innovus later on model this correctly with the delay of DEL1?

  • Cancel

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.

© 2025 Cadence Design Systems, Inc. All Rights Reserved.

  • Terms of Use
  • Privacy
  • Cookie Policy
  • US Trademarks
  • Do Not Sell or Share My Personal Information