single supply unity gain amplifier

[texane]

Hi,

I am designing a circuit that measures the voltage of a DC load. This voltage
can be up to 12V, and I need to divide it by 4 so that an ADC can handle it. Also,
I want to minimize the current drawn for the measure.

To do so, I plan divide the voltage using a resistor divider with large values, and
feed the divided voltage to a single supply unity gain amplifier. I will power the
amplifier using a regulated 4V supply. I expect the amplifier to behave correctly
in [ 0V - 3V ], and up to a few KHz.

I am not used to choose amplifier ICs. Do you know an amplifier that  would fit ?
This is for a home project, and I would spend up to 3$ in the amplifier (qtity 5).

Any advice and help is welcome !

Cheers,

[poorchava]

The basic approach is ok, but there is one thing: a rail to rail opamp powered from 5V ang GND will NEVER to down to GND on the output, most will also have reduced performance near rail potentials. I would try to shift the voltage up by 0.1-0.2V or something and digitally subtract that later.

For a cheap r2r opamp MCP6051/2/4 seems ok. It also has high input impedances (datasheet states 10^12 Ohms). They have quite poor GBP of 385KHz, but that's fine in your application.

[texane]

Thanks you for the answer.

Do you know a circuit that would offset the measured voltage
(mostly DC) ? Otherwise, I think the best solution is to forget
about single supply ...

Thanks,