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Measurements >> Phase Noise and Jitter Measurements >> Modelling jitter in divider
https://designers-guide.org/forum/YaBB.pl?num=1320237344

Message started by manikandan on Nov 2^nd, 2011, 5:35am

Title: Modelling jitter in divider
Post by manikandan on Nov 2^nd, 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

Title: Re: Modelling jitter in divider
Post by rajkumar palwai on Nov 2^nd, 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.