Re: [volt-nuts] Matched resistors
Hello Randy, I am using the LTC1043 in 1/2 VIN or 1/3 VIN configuration. A matching of the caps is not necessary. In the 1/2 VIN or 1/3 VIN configuration a matching would give the advantage that the settling time of the cirquit is reduced. But in 2* VIN or inverting configuration a matching gives no advantage. So perhaps it is better to put a 1/2 VIN divider into a feedback loop. The most important point: you will need a low leakage buffer amplifier at the output. The caps should be low leakage foil capacitors. (polypropylene would be best). The ESR is negligible against the switch resistance of around 1000 Ohms And dielectric absorption would also affect only settling time. In 1/2 VIN configuration I am using cheap small mylar capacitors (WIMA MKS02) (isolation time constant is given only with >1250 sec (3000 sec typ)). Buffer amplifier is a LTC1050. The circuit is very stable over temperature (10 - 40 deg C). The absolute amplification error is usually some ppm lower than exact 2:1 value. (depends somewhat on the pinning which is used so I am not shure wether the pins are mixed up regarding the charge compensation) So I dont know wether the ±1 ppm is more a stability figure than a absolute value. Even polypropylene capacitors do not change the amplification error. With best regards Andreas Am 17.07.2014 17:26, schrieb 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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
I am not sure if Fluke had matched tempco spare parts, but you can look at some NOS resistors from Fluke on ebay. They may be a good start and some of the pricing isn't bad. Todd On Thursday, July 17, 2014, Randy Evans wrote: > 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.stellm...@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 > > ___ > > volt-nuts mailing list -- volt-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > > mailman/listinfo/volt-nuts > > and follow the instructions there. > > > ___ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
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 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 > ___ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/volt-nuts > and follow the instructions there. > ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
