discrete current mirrors

Zetex sells discrete matched pairs already configured as current mirrors. They're in the Digi-Key catalog.

Digikey sells MAT03 (as well as other matched transistors, as Tim mentioned).

The LM394 NPN matched pair is widely available.

I don't understand why you would need to find an npn pair matched to the pnp pair. The matching is only important between the two transistors that make up the mirror, because you are trying to ensure the same Ic versus Vbe relationship.

Mouser sells some very inexpensive matched pairs, both NPN and PNP - just search for "matched NPN", for instance. The ones I saw are not so good for the low-current source that we were discussing, because they have much higher collector leakage current than the MAT03.

Note that the design Win gave was for a dividing current mirror with an adjustable, large, ratio. It is not what you would want for a normal (1:1) current mirror.

Are you THAT OLD ?:-)

MAT03's are relatively modern parts from Analog Devices.

...Jim Thompson

By the way, what's wrong with using the OPA860, which seems to be the modern replacement for the OPA660? I don't know anything about OTAs, just wondering.

My guess is that the MAT is for "matched".

They're pretty decent, if you don't mind the price and single-sourced aspects:

I had not noticed these ones previously:

Is there any reason why you want to use discrete components? An op-amp will make a lot of the errors go away if you don't need to deal with high frequencies.

Best regards, Spehro Pefhany

Hi all,

there are much schematics around desribing how to design a current mirror on a integrated circuit. But how to to this in good quality in discrete parts? I want to built something like good old but obsolete OPA660.

in the Task "Low current source" Winfield published the following schematic: . 50nA current source without high-value resistors . . 9V --+--- 13k ---+--- 1.0M ---, . | | | . e e gnd . b --+-- b . c | c MAT03 . | | | . +-----' '----------O -->

. | 50nA . 1.8M . | . gnd

I can not find a dealer for MAT03 and 7$ per piece seems me a little high, isn't it. Do I need a npn-pair matched to the pnp-pair? would be the best solution, but where to find.

Any ideas?

Marte

Hmmm............. I can just about remember MATs. Micro alloy transistors. Very very old.

I suggest you use something more recent !

Graham

Very

I recall coming across them in a hobbyist article in one of the electronics mags

- probably back around 1969 IIRC.

That makes more sense - lol !

Graham