Re: how to run transient simulation with time varying resist
v_c said:
My model can be used as floating or grounded resistor -- just take a look at the subcircuit and please try it. Why are you bringing in a diff pair? This has nothing to do with the question asked. I do understand the difference between and grounded and floating resistor and if you just try out the file below you will see that I have used it as a grounded resistor. But there is nothing that prevents you from using it as a non-grounded resistor.
Try out the following circuit, save it as a *.cir file and simulate in PSpice.
Once you try experimenting with this you will see how this works.
If you don't believe it, just search on the web and on the Cadence web site
and you will see references to stuff like this -- I did not invent this, I am just using it.
Code:
* sample circuit
Vs 1 0 30V ; this is just a 30V dc source
Rs 1 2 5 ; 5 ohm series resistance
Xr 2 0 3 var_res ; this is our variable resistance
Vc 3 0 10 ; this is the control voltage = 10V this makes
; the variable resistance a constant 10 ohms
* subcircuit definition
.subckt var_res plus minus control
Gpm plus minus value={v(plus,minus)/v(control)}
Rcontrol control 0 10k
.ends var_res
.op
.end
This is the difference between a grounded and a floating resistor :
A grounded resistor is a single terminal device. One end of it is always (note the always) connected to ground. If this model is used in a bigger circuit, it can be connected in a bigger circuit in only one node. The other node * cannot * be used.
A floating resistor is a two-terminal device. When you use a resistor in a circuit, ie, when you design a circuit using the resistor, you should be able to connect it across any two nodes in a circuit. The two nodes can be any nodes - high impedance nodes, low impedance nodes , supply nodes etc.
Now, is this difference of using the resistor model in a bigger circuit clear?
When you model a resistor, the intent is to be able to use it in a bigger circuit, simulating the model standalone is * NOT * the purpose of the model.
Now, where are the places you would be using a resistor - take your pick - I just chose two specific examples - load resistor in a differential pair (one end is connected to VDD, other end to output of the diff pair),. The second example i chose to illustrate my point was a feedback resistor in an opamp, where one terminal is connected to input and second terminal is connected to output of an opamp. Both these examples require you to have a floating two-terminal resistor, not a one-terminal grounded resistor.
Now, what are the two nodes of the resistor in your model which i can use to connect to other nodes in a bigger cirucit ? A model's utility is to be able to use it in a bigger circuit, otherwise it is useless. I always see only a grounded one-terminal, not a generic two-terminal resistor in this model.
You replies never specify cleary what are the two nodes of the resistor in your model? Specify that point, then we can discuss this further, otherwise we seem to going around in circles.
Bharath