[time-nuts] Fury Interface Board: How about TI OPA277?

[kevin-usenet at horizon.com]

Vos is 1 uV/C guaranteed, 0.15 V/C typical.  (And you can get a
high-spec part with the latter guaranteed.)  Can take 24 V supply,
and pull to within 1.5V of the rails over the full temperature range,
so can produce +/-10V.

Also pretty cheap.

Even at 0.1 ppm/V, that would be a worst-case 1e-13/C tempco, which is
comparable to the best double-oven oscillators, and it'll usually be
much less than that.


Of course, the tempco of the resistors in the circuit is also an issue.
I haven't done a full sensitivity analysis, but do know that thin-film
resistors usually track very well, so as long as you can keep them
isothermal, it'll work well.

One trick I use to get better tracking is to build ratios out of multiples
of a single resistor value.


As I said in my other mail:
- I really fail to see how the LT1085 power supply circuits work at all.
  An LT1085 is an adjustable three-terminal regulator with a reference
  voltage (where it tries to keep Vout - Adj) of 1.25V.  U4 will keep
  the Vcc net 1.25V above Gnd, and U5 will do just plain strange things.
  Having Vin lower than Vout will turn on internal diodes and short
  them together.

- Wouldn't it make more sense to configure U1A and U1B as simple
  non-inverting amplifiers, that will present a high-impedance load to
  EFC_input, thereby avoiding the need for all the J8-J10 and J21-J23
  jumpers?  You need a 3.3V reference for the U1A circuit rather than
  1.5V, but that's easy enough to make out of a TL431.