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Modelling jitter  in divider (Read 2712 times)
manikandan
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Modelling jitter  in divider
Nov 02nd, 2011, 5:35am
 
hi,
this is a divider verilog a code from designers guide

module divider (out, in);

output out; voltage out;      // output
input in; voltage in;            // input (edge triggered)
parameter real vh=+1;            // output voltage in high state
parameter real vl=-1;            // output voltage in low state
parameter real vth=(vh+vl)/2;      // threshold voltage at input
parameter integer ratio=10 from [10:inf);      // divide ratio
parameter integer dir=1 from [-1:1] exclude 0;
                       // dir=1 for positive edge trigger
                       // dir=-1 for negative edge trigger
parameter real tt=1n from (0:inf);      // transition time of output signal
parameter real td=1n from (0:inf);      // average delay from input to output
parameter real jitter=0 from [0:td/5);      // edge-to-edge jitter
parameter real ttol=1p from (0:td/5);      // time tolerance, recommend ttol << jitter
integer count, n, seed;
real dt;

analog begin
   @(initial_step) seed = -311;
   @(cross(V(in) - vth, dir, ttol)) begin
     count = count + 1; // count input transitions
     if (count >= ratio)
         count = 0;
     n = (2*count >= ratio);
     dt = jitter*$rdist_normal(seed,0,1); // add jitter
   end
   V(out) <+ transition(n ? vh : vl, td+dt, tt);
end
endmodule

What should be the values of jitter and ttot to visualize the effect of jitter? What analysis should i be running in spectreRF to understand jitter?for example, say input is 10MHz and output is 1 MHz.

regards
mani
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rajkumar palwai
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Re: Modelling jitter  in divider
Reply #1 - Nov 2nd, 2011, 10:24pm
 
i dont know how to run a verilogA to find jitter. But if u want to find jitter of a ciruit in spectreRF, then u need to run PSS + PNOISE analysis.

Basically, there are two types of circuits: 1) autonomous ckts , eg:oscillators and 2) Driver ckts, eg:dividers. U need to run the pss+pnoise slightly different for these 2 types. There are lots of examples in internet on how to run pnoise analysis on dividers. Or else download the spectreRF manual.
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