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Issues in Modelling an INV output having 10mVp-p as its VSS (Read 2143 times)

kumar.g

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Posts: 51
Frankfurt, Germany

Issues in Modelling an INV output having 10mVp-p as its VSS
Jul 05^th, 2010, 2:28am

Hallo All,

I am designing a current starved INV which has an output high(VDD) and low (VSS). VDD = 1.8V, VSS = 200m+ 10mVp-p, 1GHZ. I wrote the following piece of code but it gives me an error saying "contribution statement encountered inside an analog event"

Assume Td_p,Td_n = 1p

@(cross(V(Vin)-(V(V_swing)/2),+1)) begin
V(V_ph) = V(Vss);
end
@(cross(V(Vin)-(V(V_swing)/2),-1)) begin
V(V_ph) = V(Vdd);
end
V(Vout) <+ transition(V(V_ph),0,Td_p,Td_n);
end

But the code works if I change V_ph as a real variable. But I dont see the 1Ghz 10mVp-p sinusoid on 200m(dc) VSS. Instead it is a constant 200m low and 1.8 V high. Can someone help me with this.

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Marq Kole

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Hmmm. That's
weird...

Posts: 122
Eindhoven, The Netherlands

Re: Issues in Modelling an INV output having 10mVp-p as its VSS
Reply #1 - Jul 5^th, 2010, 4:30am

As the error says, the problem is with the contribution statement inside an event: that's not allowed. Instead, you should assign to a variable inside the event and contribute the variable value outside the event. In your case you can do without the contribution and use the variable value directly in the transition function:

Code:

@(cross(V(Vin)-(V(V_swing)/2),+1)) begin
  V_ph_value = V(Vss);
end
@(cross(V(Vin)-(V(V_swing)/2),-1)) begin
  V_ph_value  =  V(Vdd);
end
V(Vout) <+ transition(V_ph_value, 0, Td_p, Td_n);

Cheers,
Marq

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boe Community Fellow Offline Posts: 615	Re: Issues in Modelling an INV output having 10mVp-p as its VSS Reply #2 - Jul 5^th, 2010, 11:08am kumar, Note that Code: V(Vout) <+ ... places a voltage source between node 0 (global simulator ground: 0 V) and node Vout. If you want the source between VSS and Vout, you have to use Code: V(Vout, VSS) <+ ... BOE
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