Norton Amplifiers (was: Re: Wave Wraper revisted #1)

[ld]

John Simonton of PAIA over the years has used norton LM 3900's (cheap,easily
found) in many of his designs..as I recall the paia gnome among others..I suggest
going to paia.com and viewing/downloading the gnome and other schematics to peruse
for ideas of use of these devices.

Rene Schmitz wrote:

> >I do not too. It was also used by ARP for their filters. It seems to be
> >interesting for
> >low noise designs...
> >Is there anybody knowing how to use these "Norton amplifiers ?".
>
> Nortons are current differencing amplifiers, that is they have a current
> mirror instead of the differential amp of ordinary opamps.
> The input currents flow to the Vee terminal. So both inputs look like a
> diode to Vee. There is a high gain amplifier connected to the inverting input.
> A simple example of operation:
> Think of the inverting amplifier configuration, feedback resistor (R1) from
> out to inv-input and input resistor (R2) to inv-input. Lets say that the
> Norton is powered from +/- 15V. To make it work with a Norton, we have to
> bias the current mirror so that there is zero current difference for 0V
> input. So we have to use a resistor equal to R1||R2 from GND to the
> non-inv. input.
> Usually all these are rather large values, to avoid large currents into the
> mirror, which would affect the mirror-gain which we want to be unity.
> This biasing scheme is extremely useful in single supply circuits.
>
> Now, the interesting trick is that when sourcing current into the
> noninverting-input the inverting input starts to sink that current!
> In the ARP-filter there is a differential pair working on the current
> mirror inputs. This acts as a simple OTA structure. The rest of the
> amplifier acts as the buffer-integrator.
>
> For more on the subject of Nortons see Nationals AN-72.
>
> Hope this helps.
>
> René
>
>              ,   : (uzs159 at uni-bonn.de)
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