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Simulators >> Circuit Simulators >> DC sweep failed for Initial block
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Message started by ywguo on Dec 4^th, 2010, 4:46am

Title: DC sweep failed for Initial block
Post by ywguo on Dec 4^th, 2010, 4:46am

Hi Guys,

I am wondering what a spectre simulator do for a "initial_step" block. For eg., I have an initial_step block as below. It is used to measure a PTAT voltage. An integer variable named dat is a digitized number for the input voltage, which is the PTAT voltage. Then I run a dc analysis in ADE-L, sweeping temperature from -40 to 125C. However, the dat is always equal to the number corresponding to -40C. In results browser, I check the dcOp-dc result, it varies if I change the number in Setup --> Temperature.... What's the difference between dcOp-dc and dc-dc for the Initial_step block?

Code:

analog begin

@ ( initial_step ) begin
halfref = vref / 2;
unconverted = V(vin);
dat = 0;
for (i = (`NUM_ADC_BITS-1); i >= 0 ; i = i - 1) begin
if (unconverted > halfref) begin
dat = dat + pow(2,i);
unconverted = unconverted - halfref;
end else begin
dat = dat;
end
unconverted = unconverted * 2;
end
end

Best Regards,
Yawei

Title: Re: DC sweep failed for Initial block
Post by Geoffrey_Coram on Dec 6^th, 2010, 11:57am

I believe the Verilog-AMS LRM specifies what happens with initial_step, and that it's only the first point of a dc sweep.

Perhaps what you want is if(analysis("static")) ?