# Measurement of output impedance (ro) of a modified wilson current mirror

How do I measure the small signal output impedance (ro) of a modified wilson current mirror?

example Q4:

• Are you looking for a sophisticated Test Engineer's approach? Do you have some acceptance criteria? or just idle curiosity? – Sunnyskyguy EE75 Apr 26 at 0:21
• At this point just doing some side research for a project – Roo Apr 26 at 0:23
• If you apply a square wave to DC at V1 with a current sense resistor of suitable value, what do you expect for $R_O = \frac{\Delta V}{\Delta I}=10^7?, 10^{10}?$? – Sunnyskyguy EE75 Apr 26 at 0:28
• I found at gain of 6.3G ohm at 1 Hz, however, it gradually decreases with frequency. I'm not sure why the resistance decreases as the frequency increases. – Roo Apr 26 at 0:53
• What do you expect Coss to be? 1pF? 100pF? – Sunnyskyguy EE75 Apr 26 at 0:58

## 1 Answer

$$\R_O = \frac{\Delta V}{\Delta I}\$$

In other words, vary the output voltage and measure the corresponding change in current.

If you're asking something more subtle than that, please clarify by editing your question.

• updated the question – Roo Apr 26 at 0:13
• Same answer. Apply an AC voltage and measure the AC current. You can make it as large or small as you like. You can even vary the frequency. – Dave Tweed Apr 26 at 0:16
• where is the ideal place to place the AC source? – Roo Apr 26 at 0:20
• In series with V1. – Dave Tweed Apr 26 at 0:36
• I found at resistance of 6.3G at 1 Hz – Roo Apr 26 at 0:54