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I designed a circuit to read analog signal, in range of -10V to +10V with resolution of 1mV. I need to validate my design by testing it in different input voltages. So I soldered a voltage divider circuit using a potentiometer. But I think it is not a good way due to the fact that it affects actual voltage by drawing current. Other way is to use an op-amp as a voltage buffer to eliminate effect of voltage divider circuit. I want to know: how to make a circuit to provide different input voltages for ADC with negligible effect on ADC? Thanks in advance.

EDIT1: Link suggested by Roger Rowland is about validating procedure, but my question is about the circuit which provides different input voltages for ADC with negligible effect.

EDIT2: I measure the voltage test by Fluk8846A. When I connect it, voltage changes and oscillates 4mV peak to peak. How Can I remove the noise induced by Fluk?

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    \$\begingroup\$ Possible duplicate of Quick Test of an ADC \$\endgroup\$ – Roger Rowland Feb 18 '16 at 8:20
  • \$\begingroup\$ @RogerRowland how can I provide different input voltages accurately with negligible effect? \$\endgroup\$ – Pana Feb 18 '16 at 8:42
  • \$\begingroup\$ Google suggests many methods depending on what characteristics of your ADC you want to test. Do any of those links help? \$\endgroup\$ – Roger Rowland Feb 18 '16 at 8:46
  • \$\begingroup\$ I added EDIT to my question. Please note that my question is about the circuit which provides different input voltages with negligible effect on actual voltage, NOT testing procedure. \$\endgroup\$ – Pana Feb 18 '16 at 8:49
  • \$\begingroup\$ You should probably show the schematic of your ADC circuit - does it include sample and hold? Do you already buffer the input? Maybe you just want to know how to build a variable voltage reference? It's not really clear what you want to test - there are a number of ways an ADC can be characterised. \$\endgroup\$ – Roger Rowland Feb 18 '16 at 8:58
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As the ADC is not supposed to draw any current (or a very small amount), a voltage divider circuit using a potentiometer should work. Make sure your power supply is stable enough, and use relatively small resistor values - 10k max - to make sure the divider circuit current is large enough compared to any other possible currents (ADC input & voltmeter).

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I'd probably turn it around: provide some (slowly) varying voltage, and measure it with a know-good circuit (probably another ADC).

Note that you can test a lot (linearity, no missing values) with just a sawtooth input.

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  • \$\begingroup\$ Please note that my question is mainly about the circuit design which provides different input voltages for ADC, NOT validating procedure. \$\endgroup\$ – Pana Feb 18 '16 at 10:17
  • \$\begingroup\$ Your question is about providing a range of voltages. My suggestion does this. If your question is just " I want to know how I can build a variable voltage reference with negligible effect", why mention an ADC at all? \$\endgroup\$ – Wouter van Ooijen Feb 18 '16 at 10:25
  • \$\begingroup\$ Note that a good ADC and a (digital?) feedback loop might actually be the best way to generate a variable voltage reference... \$\endgroup\$ – Wouter van Ooijen Feb 18 '16 at 10:26
  • \$\begingroup\$ You are right. I edited my title. Please explain your suggestion of generating a variable voltage reference by digital feedback. \$\endgroup\$ – Pana Feb 18 '16 at 10:38
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    \$\begingroup\$ The principle is simple, I guess you are familiar with it? A high-low feedback would simply use a capcitor at the output, and switch between a small current into it or out of it depending on whether the capacitor voltage is below or above the desired voltage. Just like your room temperature control. \$\endgroup\$ – Wouter van Ooijen Feb 18 '16 at 11:00

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