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I have a 0-5V Single ended analog signal coming into an A/D pin on my microcontroller.

The Micro pin can tolerate only 0-3.3V analog signal.

What can I do? Can I just add a simple voltage divider (one resistor in series and other to GND to divide the voltage when it is at 5V down to 3.3V)?

I am concerned. Isn't this going to add noise from my ground on to this Analog signal of mine and distort it?

UPDATED with a related question: I also noticed in some circuits some folks add 'Rail to Rail Output Operational Amplifiers (like LMV321 from TI) - how exactly does this help?

Fizz
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user1406716
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  • The simple voltage divider places a load on the source of the signal. It also can limit the bandwidth of the A/D converter if the resistor values are high and the distributed capacitance to the A/D input causes an R*C filter effect. The opamp is used for a number of reasons. There can be a gain change (equivalent to the divider) but with resistors that lessen the load on the source. The low impedance output of the opamp can nicely drive the A/D input impedance and the trace connection capacitance without limiting the bandwidth too much. The third big advantage of the (continued) – Michael Karas Oct 28 '13 at 07:47
  • (continued from above) opamp is that it can be used to also sum in an offset in the signal translation should that be needed for certain applications. – Michael Karas Oct 28 '13 at 07:49

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Putting resistive voltage dividers in front of ADC inputs is a rather common design technique. It's done even in highly sensitive instruments (there it will be a somewhat more complicated RC network, but the principle stays the same) so your uC project will be just fine.

But, of course, such questions were asked before: How to Convert 0 to 10V analog signal to 0 to 2.5V for ADC input?

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oakad
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  • Thanks. Related question, do you know why "in some circuits some folks add 'Rail to Rail Output Operational Amplifiers (like LMV321 from TI) - how exactly does this help?" (updated the original question too) – user1406716 Oct 28 '13 at 05:55