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Author Topic: REQ: precision -100 to +100 mV source design  (Read 662 times)
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CortexM0Inside
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« on: November 27, 2014, 06:01:10 06:01 »

Hi all,

Can anybody suggest a circuit diagram for a precision -100 to +100 mV source for lab testing, it should be accurate to 0.1 mV.

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vern
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« Reply #1 on: November 27, 2014, 08:37:18 08:37 »

how much current do you need? Just as a voltage reference or as a power supply?
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pickit2
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« Reply #2 on: November 27, 2014, 10:36:32 10:36 »

https://archive.org/download/AlternatingCurrentMachines/Say-AlternatingCurrentMachines.pdf
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CortexM0Inside
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« Reply #3 on: November 27, 2014, 11:40:59 11:40 »

how much current do you need? Just as a voltage reference or as a power supply?

Just as a milivoltage reference.
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kreutz
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« Reply #4 on: November 27, 2014, 05:39:10 17:39 »

I suggest using a 10.000Vdc, 5.000Vdc or 2.5000Vdc precision reference IC and adding a Precision Voltage Divider to get your 100 mv reference (Not cheap).

kreutz
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PICker
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« Reply #5 on: November 27, 2014, 08:33:33 20:33 »

For a battery-powered and low-ripple reference the problem is to design the negative rail of the power supply (for obtaining the -100mV signal).
In my experience the two best alternatives are:
1) a virtual ground buffered at 1/2 Vcc (Vcc= +Vcc; GND = -Vcc; 1/2Vcc = NEW (virtual) GROUND. There are a lot of IC for doing this or you can do it yourself.
2) a negative rail generator (voltage pump or inductive) some MURATA IC can generate -5Vcc from +5Vcc with 50-100 mA max load and low ripple if associated with good inductors/capacitors.
If you can use a power supply the project is much simple (transformer) but the MAINS  noise (ripple) may be a serious problem in relationship with the precision of your application.
Cheers.
PA.



Posted on: November 27, 2014, 07:42:02 19:42 - Automerged

You could use also digital potentiometers for driving voltage references as in the following datasheet:
http://www.analog.com/static/imported-files/data_sheets/AD5263.pdf
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vern
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« Reply #6 on: November 27, 2014, 09:28:17 21:28 »

I'm still trying to understand what you need.
You need one source that is adjustable from -100 to +100mV? And the accuracy of 0.1mV as to what? To an input? to a digital value? or just 0.1mV resolution?
You want it to adjust analog or digital?
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kreutz
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« Reply #7 on: November 28, 2014, 01:22:04 01:22 »

I also hate when there are not accurate/complete specifications. I assume that they are trying to get a reference voltage adjustable between +100 mVdc and - 100 mVdc with a 0.1% tolerance. There is no temperature range specified, so I also assumed that in their lab environment the temperature is 25 degrees C +/_ 2.5 degrees.

Note:  Each block include the complete reference circuit and not just the IC (see the manufacturer's data sheet). The Precision voltage dividers (type Kelvin–Varley) could be 4 decades (+ 99.99 to - 99.99) or more. You should use two  0.01% resistors respectively connected between the outputs of the Voltage references and  the Precision Voltage divider (Kelvin–Varley divider) in order to limit the voltage output to the range you specified. The values could be easily calculated based on the Reference voltages and the Kelvin-Varley divider total resistance.

Didn't I tell you that this is not a cheap solution? Smiley
« Last Edit: November 28, 2014, 02:04:46 02:04 by kreutz » Logged
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