[volt-nuts] Matched resistors
smither at c-c-i.com
Mon Jul 21 16:28:53 EDT 2014
On 07/17/2014 10:26 AM, Randy Evans wrote:
> 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?
There are some other error sources that might need to be considered when using
I have not used the LTC1043, but note that on the data sheet there is a small
charge injection at each of the switch pins. In the multiply by 2 circuit shown
on the data sheet they are using 1 ufd caps. Typical charge injection (depends
on voltage level) is 8 pC. With the 1 ufd caps this is 8 uV. I assume there is
some offsetting effect - but this might be a significant contributor to the 5
ppm error that is mentioned.
There is also a 6 nA (typical) leakage mentioned. During the "hold" time (
about 1 msec) of the output 1 ufd cap this comes to 6 uV.
-------------- next part --------------
A non-text attachment was scrubbed...
Size: 148 bytes
Desc: not available
More information about the volt-nuts