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Cross function

Charanraj Mohan

Hey,

I am doing a simple DC sweep & using the cross function in the calculator, i am finding the x-axis in my sweep range for a particular y-axis value. I am also aware that cross function used here gives the user the choice for rising edge or falling edge.

My queries-

1. Is it possible to implement the same using veriloga code?

2. Actually I am changing the value of gate input of the circuit & doing the sweep to find the particular Value in x-axis & calibrate something. If I change the Value of gate in 2 decimals, for example 2.57 (say), I have no problem. But when I use a 3rd integer for example   2.575 (say), the cross function gives me a wrong result. If I calibrate for 2.58, it works. But I am unable to calibrate in between 2.57 & 2.58. Seems cross function is rounding the integer. Is it possible to have facility for the user to set this limit in veriloga code??

3. When I use 10mV step in my DC sweep, i get x (say)

   When I use 5mV step , i get x/2.

   When I use 2.5mV, i get x/4. Why is this changing ? What is the default step of limit of cross function in CADENCE IC6 calculator?? If we write this code in veriloga, can we have a provision to set this too ??

Thanks in advance

Parents
  • Thanks Andrew.
    I understand, for
    1. I think no cross function in veriloga in DC sweep
    2. I am using the expression (vg -cross(VDC(“/out”) 2.4 1 “either” nil nil) to find a result. Say, i am sweeping my DC from 0 to VDD in step size of 10mV. I am converting signal /out to scalar first & then finding the x-axis (DC sweep) value exactly when my y-axis (or output) is 2.4 using cross function & then subtracting it from vg. There is no problem when vg is 2.4 or 2.45 or 2.46. I am pretty sure that the result when vg is 2.455 should be in between the results of vg=2.45 & vg=2.46. But it gives me very less results. For example, if I get in mV range for vg=2.45 & vg=2.46, i get microvolt results in vg=2.455. Then I have to tune the step size of DC sweep to make it fall in between these results.

    For example, the above expression gives me --> 2.35mV if vg=2.45 V & 2.4mV if vg=2.46 V when I sweep DC in 10mV step size, i need to tune the step size for vg=2.455 & finally, I see the result for vg=2.455 settles in between 2.35mV & 2.4mV when step size is 12.3345mV (say).

    To put it very short--> why do we need to tune the step size for cross function when the input has 3 decimals ??

    3. Seems that there is a relation between step size of DC sweep & cross function. For every half of step size the result using cross function expression also gets halved.
Reply
  • Thanks Andrew.
    I understand, for
    1. I think no cross function in veriloga in DC sweep
    2. I am using the expression (vg -cross(VDC(“/out”) 2.4 1 “either” nil nil) to find a result. Say, i am sweeping my DC from 0 to VDD in step size of 10mV. I am converting signal /out to scalar first & then finding the x-axis (DC sweep) value exactly when my y-axis (or output) is 2.4 using cross function & then subtracting it from vg. There is no problem when vg is 2.4 or 2.45 or 2.46. I am pretty sure that the result when vg is 2.455 should be in between the results of vg=2.45 & vg=2.46. But it gives me very less results. For example, if I get in mV range for vg=2.45 & vg=2.46, i get microvolt results in vg=2.455. Then I have to tune the step size of DC sweep to make it fall in between these results.

    For example, the above expression gives me --> 2.35mV if vg=2.45 V & 2.4mV if vg=2.46 V when I sweep DC in 10mV step size, i need to tune the step size for vg=2.455 & finally, I see the result for vg=2.455 settles in between 2.35mV & 2.4mV when step size is 12.3345mV (say).

    To put it very short--> why do we need to tune the step size for cross function when the input has 3 decimals ??

    3. Seems that there is a relation between step size of DC sweep & cross function. For every half of step size the result using cross function expression also gets halved.
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