Hello Randy,
some information you will get on eevblog. (its much easier to post
(larger) pictures there).
Namely within the LTZ1000, LM399 and T.C. Measurements threads:
http://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/
http://www.eevblog.com/forum/projects/lm399-based-10-v-reference/
http://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/
http://www.eevblog.com/forum/projects/oshw-24bit-adc-measurement-system-for-voltage-references/
http://www.eevblog.com/forum/projects/building-a-7-decade-voltage-calibrator/
http://www.eevblog.com/forum/projects/ppmgeek!-5-5-digit-dvm-volt-ref-cal-%28for-arduino-or-any-uc-w-spi%29/msg296127/#msg296127
With best regards
Andreas
Am 19.07.2014 16:33, schrieb Randy Evans:
Andreas,
Thanks for the information. Do you have the drift chart, etc. posted
anywhere? that would be very interesting reading.
Thanks,
Randy
On Fri, Jul 18, 2014 at 10:11 PM, Andreas Jahn <andreas_-_j...@t-online.de>
wrote:
Hello Randy,
I think the only difference is in oscillator section (and thus power
consumption)
and of cause the TSSOP-package.
The LTC1043 is easily available from stock e.g. from digikey.
The LTC6943 is more difficult to get.
Within the Keithley 2002 LTC1043 is used.
http://www.eevblog.com/forum/testgear/keithley-2002-8-5-
digit-dmm-review-and-teardown/
http://dev.xdevs.com/projects/kei2002/repository/entry/
photos/K1/small/K2002_1-2251.jpg
I have added a drift chart with longterm drift data.
Note: the drift is for the whole measurement arrangement.
It consists of 3 7V references (2 LTZ1000A and 1 LM399)
measured via a LTC1043 divider with a 24 bit LTC2400 ADC with
temperature compensated voltage reference AD586LQ.
So most of the drift is related to the AD586LQ reference.
(X-axis is in days, Y-axis in ppm)
I get around 2 ppm drift for the LTZ1000A over 1 year
which I guess is mostly humidity related
from the ADC printed cirquit board + AD586 reference drift
and usually below 0.25 ppm standard deviation over 1000 hours. (42 days).
All at unstabilized room temperature.
I guess with resistors you will need ovenized temperature stabilisation to
achieve this.
with best regards
Andreas
Am 19.07.2014 05:57, schrieb Randy Evans:
Andreas,
That is good information, I appreciate it. I have contacted LT
application
support but they have yet to get back to me on my questions except they
did
recommend to use the LTC6943 instead of the LTC1043. Later generation I
guess.
I think i am going to try both the LTC6943 and the LT5400 resistor array
and characterize them. The LT5400 matching ratio looks pretty good over
temp (0.2ppm/C) but the absolute resistor change over temp is -10 to +25
ppm/C, a little larger than I would like for the circuit I am using.
Randy
On Thu, Jul 17, 2014 at 10:37 PM, Andreas Jahn <
andreas_-_j...@t-online.de>
wrote:
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
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