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From: acannell on 15 May 2007 19:36
Is there a clever way to make a current amplifier which acts like a
NPN transistor except that it has 0 Vbe? That is, with a "base"
resistor of 10k and an input voltage of 100mV, 10uA gets amplified
into 1mA at the "collector"? Preferably a method that does not use an
IC's (opamps, etc..)

From: D from BC on 15 May 2007 20:21
On 15 May 2007 16:36:18 -0700, "acannell(a)wwc.com" <acannell(a)wwc.com>
wrote:

>Is there a clever way to make a current amplifier which acts like a
>NPN transistor except that it has 0 Vbe? That is, with a "base"
>resistor of 10k and an input voltage of 100mV, 10uA gets amplified
>into 1mA at the "collector"? Preferably a method that does not use an
>IC's (opamps, etc..)

The OPA861 comes to mind but it's an 8 pin IC..
Clipped from datasheet...
"
The OTA or voltage-controlled current source can be
viewed as an ideal transistor. Like a transistor, it has
three terminals�a high impedance input (base), a
low-impedance input/output (emitter), and the current
output (collector). The OPA861, however, is self-biased and bipolar.
"
D from BC
From: John Popelish on 15 May 2007 20:25
acannell(a)wwc.com wrote:
> Is there a clever way to make a current amplifier which acts like a
> NPN transistor except that it has 0 Vbe? That is, with a "base"
> resistor of 10k and an input voltage of 100mV, 10uA gets amplified
> into 1mA at the "collector"? Preferably a method that does not use an
> IC's (opamps, etc..)

A cascade of an NPN and PNP emitter followers have
approximately zero offset voltage.

Integrates amplifiers made of two complementary emitter
followers in cascade make very fast, fairly low offset
voltage current amplifiers.
I know you asked for a non integrated solution, but you
might be able to get some ideas how this is done from this
data sheet.
http://cache.national.com/ds/LM/LMH6321.pdf
From: Eeyore on 15 May 2007 20:33


"acannell(a)wwc.com" wrote:

> Is there a clever way to make a current amplifier which acts like a
> NPN transistor except that it has 0 Vbe? That is, with a "base"
> resistor of 10k and an input voltage of 100mV, 10uA gets amplified
> into 1mA at the "collector"? Preferably a method that does not use an
> IC's (opamps, etc..)

With an op-amp, yes.

Graham


From: John Larkin on 15 May 2007 20:42
On 15 May 2007 16:36:18 -0700, "acannell(a)wwc.com" <acannell(a)wwc.com>
wrote:

>Is there a clever way to make a current amplifier which acts like a
>NPN transistor except that it has 0 Vbe? That is, with a "base"
>resistor of 10k and an input voltage of 100mV, 10uA gets amplified
>into 1mA at the "collector"? Preferably a method that does not use an
>IC's (opamps, etc..)


Something roughly like...

+5
|
|
10k |
| |
| c
+----------b npn
| e
| |
e 50r
----+-----b pnp |
| c gnd
10k |
| |
gnd gnd


John

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