# How to design a circuit which provides a range of voltages to test an ADC? [closed]

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?

• Possible duplicate of Quick Test of an ADC Feb 18, 2016 at 8:20
• @RogerRowland how can I provide different input voltages accurately with negligible effect?
– Pana
Feb 18, 2016 at 8:42
• Google suggests many methods depending on what characteristics of your ADC you want to test. Do any of those links help? Feb 18, 2016 at 8:46
• 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.
– Pana
Feb 18, 2016 at 8:49
• 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. Feb 18, 2016 at 8:58

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).

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.

• Please note that my question is mainly about the circuit design which provides different input voltages for ADC, NOT validating procedure.
– Pana
Feb 18, 2016 at 10:17
• 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? Feb 18, 2016 at 10:25
• Note that a good ADC and a (digital?) feedback loop might actually be the best way to generate a variable voltage reference... Feb 18, 2016 at 10:26
• You are right. I edited my title. Please explain your suggestion of generating a variable voltage reference by digital feedback.
– Pana
Feb 18, 2016 at 10:38
• 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. Feb 18, 2016 at 11:00