[sdiy] SN76477 project / LF398 sample and hold ?'s

[Tom May]

"Derek Holzer" <republikasleazka at hotmail.com> writes:

> for the list, i've got a question:
> anyone have a simple schematic for a sample-and-hold circuit using an LF398 
> IC?

I've built S+H circuits with this chip with trimmable hold step
cancellation.  They work, but I wouldn't do it again, primarily
because there's some interesting stuff in Electronotes regarding
putting a resistor between the input buffer and the sample cap in a
discrete S+H so that the slew rate of the cap is limited, i.e., the
difference between output samples is limited.  This effect isn't
really possible to achieve with an LF398.  My circuit does something
similar by using a pot between the chip and the cap, but it has a
glitch during the sample aperture when the full input voltage is
applied to the output.  Since the aperture is only a few uS it's not
that big a deal, but still . . . using a chip didn't really buy me
anything.

fTom.