[SOLVED] How to measure ac resistance at the output of current mirror

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I am designinging current mirror with 0.1% mirror accuracy with Vout variations from 0.45V to 1.95V using cadence IC5.14 spectre simulator

I got some basic fundamental doubts

1) What is the difference between DC resistance and ac resistance

2) How can I measure AC resistance at the output

Thanks in advance
 


1)
R(dc) = V/I
R(ac) = dV/dI

2)
Method 1:
Inject a small current at the mirror outputs, and compute R(ac) as above.
Method 2:
Measure Iout at Vout_min and Vout_max and compute R(ac) using the above equation.
Method 3:
Inject a 1V AC current into the mirror outputs and measure in ac analysis the magnitude of voltage change at the outputs.
 
Hi checkmate,

1) R(dc) = V/I its OK
R(ac) = dV/dI its for small signal around operating point not ac resitance(sorry if my guess is wrong, I am not sure)
output voltage has to change 0.45 to 1.95V I want to check how 'Rout' is varied when Vout changes as above at particular frequency
 

AC resistance is small signal resistance, or to be more exact, small signal impedance.
If you want to find rout across your range, then you sweep vout and use either method 1 or 3.

Method 2 gives you a quick and dirty method to estimate rout with only 2 simulations, provided you can ensure that the output remains in saturation throughout the vout range. Furthermore, method 2 is probably the better method to characterize the actual silicon to correlate with simulations.
 
why can't I use ac voltage source at the output instead of ac current?

---------- Post added at 19:23 ---------- Previous post was at 19:09 ----------

The main confusion in mind is
1) For calculating DC Resistance Rdc=V/I ; I am connecting DC voltage source and measuring current
2) For AC Resistance why the amount method not giving correct results
 


rout=dv/di
For di-1A, rout=dv.
Hence, it's more convenient to inject an ac current rather than an ac voltage.
1) DC resistance is generally not meaningful for us when it comes to current sources.
2) What do you mean by "not giving correct results"? Can you be more specific?
 

Sorry mistaken I got results
rout=dv/di instead of 'di' i used 'I' in the calulation

Thanks for the postings.

---------- Post added at 19:40 ---------- Previous post was at 19:34 ----------

IN mind 1more doubt araised regarding AC resistance

In lab suppose we need to finout AC resistance at some port, how we can do?
apply ac(this can be large signal) voltage and measure ac current at the same port and calulate impedence?
or is there any other method?
 

As mentioned before, working with small ac signals is not an easy task for actual silicon. Using method 2 is more practical.
 
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