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Old 30th August 2013, 05:53 PM   #1
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Default Kind of current mirror.

After i finished reading this thread:
Current Mirror Discussion
This is one of awesome thread in our forum. Manythings i can learn.

Well, here are 2 of best current mirror which i found from this thread. They're simple but have very good performance.
So, in ''Glen current mirror'' (left). R1, R2 are degen resistors of transistor. Ib (Q1) + Ib (Q2) + I (R3) = Ie (Q3).
Please, reply me: How much current through R3 is enough?

In Hawksford cascoded symmetrical Vas, what's the kind is better? I have seen Wilson current mirror in Mongrel circuits, Symasym...

Last edited by Walkalone; 30th August 2013 at 05:56 PM.
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Old 30th August 2013, 05:55 PM   #2
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Sorry, i'm forget the pic.
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File Type: gif Current Mirror 01.GIF (9.7 KB, 252 views)
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Old 31st August 2013, 03:43 AM   #3
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Anyone can help me?
In left, is Hfe of Q3 have influenced the result? Q3 need Vce > supply rail, if current through them too high, hard to find a accordant transistor (high Hfe and high Vce).
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Old 31st August 2013, 09:39 AM   #4
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It depends what the value of R3 is. Q1 and Q2 need to be balanced matched pair and require a nominal 0.6v to start with.
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Old 31st August 2013, 12:17 PM   #5
AndrewT is offline AndrewT  Scotland
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adjust R3 until Iin exactly equals Iout

Measure Iin & Iout at the "top" end using precision matched resistors of a value that gets adequate resolution at the currents you are using.
eg. if feeding an LTP, the LTP degen resistors could be 100r and passing 1.5mA each. A 199.9mVdc DMM would read 150.xmVdc across the degen resistors. You can get current match approaching 0.1% if careful.
Then replace the Vr for a fixed value of R3.
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Old 12th September 2013, 09:43 AM   #6
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I' tested with a current mirror like here.
But i can't balancing current at 2 side of diff Vas to exactly. It's different a bit.

With improved Wilson current mirror, the current of two side seem very equal, to part per thousand of a Volt.

What's the best of CM for diff Vas?! Vas's used Hawksford cascode.
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Old 12th September 2013, 09:47 AM   #7
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Add a pic.

Resistors i'm used like pic, 100R x 2 for degen and 470R for base/compensator.
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File Type: jpg Glen's current mirror_001r.jpg (14.4 KB, 110 views)
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