[volt-nuts] Matched resistors

[Randy Evans]

Frank,

The high cost is my concern, although high performance demands high price
typically.  I am trying to double the voltage reference from either an
LM399 or LTZ1000, hence the need for precision matched resistors for a x2
non-inverting amplifier (using a LT1151 precision op amp).  An alternative
I am investigating is using the LTC1043 in a voltage doubling circuit as
shown in Linear Technology app note AN 42, page 6, Figure 16.  It states
that Vout = 2xVin +/- 5 ppm.  I am less concerned about the absolute
accuracy than I am about the long term stability.  I assume that a high
quality capacitor is required (low leakage, low ESR, low dielectric
absorbtion, etc.) but the circuit does not appear to be dependent on the
absolute value of the capacitors.  I'm not sure if the two 1uF caps  need
to be matched.  If they do then that would be a show stopper.

Does anyone have any experience using the LTC1043 in such a circuit?

Thanks,

Randy


On Wed, Jul 16, 2014 at 9:40 PM, Frank Stellmach <frank.stellmach at freenet.de
> wrote:

> Randy,
>
> resistor matched in T.C. are extremely expensive, as the manufacturer (or
> yourself) would have to select these from a batch of many samples.
>
> reistors with very small T.C. (<1ppm/K) would do the job also, but they
> also need to be stable over time, in shelf life opereation mode, i.e.
> P<10mW.
>
> That means, you need those hermetically sealed VHP202Z from Vishay, T.C.
> is typically < 1ppm/K and they are stable to < 2ppm over 5years. But they
> cost already 80€ each, depending on tolerance.
>
> I made a longterm observation of these and found these parameters
> confirmed.
>
> Frank
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