Spice model CA3080 and/or LM3080
> I don't have a SPICE model, but I do want to use a '3080
> in a new design (can't use the later LM13600 dual because
> of low supply volts). Can anyone suggest good sources of
A. Any Intersil distributor. This was originally an RCA
design, which was then 2nd-sourced by NSC.
RCA was purchased by Harris. Intersil was also purchased
by Harris as was the GE semiconductor operation. After
many years passed, whatever was left of this conglomeration
was spun off by Harris a few years back to an investor
group, who called themselves - DRUMBEAT - Intersil.
Intersil has been very good about keeping old designs in
production, including the venerable CA3080. Three cheers!
What other part can operate reasonably at 2.5V and 50nA?
A search at this Intersil URL shows all the CA3080 models
in production, http://www.intersil.com/design/index.asp
They have a new April 2001 datasheet, showing off (fig. 30)
the device's low 0.023pF input-to-output capacitance! :-)
The CA3080 is a great chip, but it has one serious problem,
the Iabc current mirror. This is not a Wilson mirror, as it
should be (see AoE page 89), and it's therefore subject to
the Early effect, which results in a changing mirrored Iabc'
with any change in the input-pair common-mode voltage, which
damages the chip's accuracy. This is important, because Iabc'
programs the 3080's basic property, its transconductance,
g_m = qI/2kT Sadly they don't document this problem in the
datasheet performance curves. Nor did NSC in their datasheet,
Intersil has a discussion of the issue, along with dramatic
curve-tracer photos, on pages 16 and 17 of app note an6668,
The Early voltage can be estimated from fig 39D at about 25V,
and if the transistors are the same as in the '3080, this can
be used in creating a reasonable Spice model (the rest of the
info needed is in the datasheet).
NSC fixed this problem in their LM13700, which is still
available, see http://www.national.com/ds/LM/LM13700.pdf
This part can operate reasonably at 3V and 50nA. :-)
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