); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY [EMAIL PROTECTED] wrote: > 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. > > Flicker noise is probably a little high. > 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. > > > Can you guarantee this works every time? > 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. > > LT1085 regulators are probably too noisy even when configured correctly. The output voltage tempco is probably a little high also. OCXO requires a supply voltage with better than 0.01% stability for time intervals less than the discipling loop response time. > - 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. > > Not really practical if one needs to compensate for small voltage differences between the Fury EFC gnd and the OCXO EFC gnd, However with a suitable star ground and independent supplies for the Fury and the interface board this should not be an issue. There is little point in using a low drift opamp with a TL431 reference.
Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
