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In my current project I'll possibly need to deploy a CCVS (Current controlled voltage source). It is transconductance amplifier or converter and many manufacturers offers transconductance amplifier but in form of a VCCS (Voltage controlled current source). In practice I need CCVS with 0.5ohm (or 500mV/A). When using simulation like one in TINA it's easy: there you can choose ideal CCVS and everything works perfect: for let say 5mA of current it's "mirroring" 2.5mV.

Current mirroring using ideal CCVS

I was playing with different current mirror topologies (with 2 to 4 transistors) and the best what I got is predictable "transfer" of 100 ohm, that means for 1mA of the current (Ibias on the picture) 100mV (Vbias). Something that seems to make things more challenging is that emitter is connected to approx. -6V (-15V + 9.1V zener) but this is another story. First I need to get a precise 0.5ohm "mirroring". My question is how to calculate 0.5ohm current mirror (any topology) that I can use in place of ideal CCVS.

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  • \$\begingroup\$ Perhaps I'm not understanding, but how about a 1/2 ohm resistor to ground with an opamp buffer... you could use a differential/ instrument amplifier if it needed to float. \$\endgroup\$ – George Herold Nov 22 '14 at 14:07
  • \$\begingroup\$ Yes, you understood correctly :) It seems like no brainer now. For some reason I thought that current mirror is a most easier way to go. Now I hope it's just a question of economics if we talk about cost and PCB space. Decent current mirror will require matched transistors, instrumental opamp matched resistors. Maybe I'll go with some PGA (Programmable gain amplifier) that has built-in matched resistor array. \$\endgroup\$ – prasimix Nov 22 '14 at 14:45
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Some background: A device (or circuit) in which the Output Voltage is controlled by the Current i.e. V(I), is a trans-resistance (or trans-impedance).

A device (or circuit) in which the Output Current is controlled by the Voltage i.e. I(V), is a trans-conductance.

What you need is a TIA (TransImpedance Amplifier). Using current mirrors and the voltage on the gate will be very non-linear. To be fair, I am assuming you want something linear, if that is wrong then use transistors.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Yes, I need something linear with decent stability. I believe using opamp is way to go. Thanks. \$\endgroup\$ – prasimix Nov 22 '14 at 22:28

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