Microcontroller Internal Reference

Hello All,

I am currently playing with an Atmel Attiny84 uC. I am reading the ADC and using the internal 1.1V reference. I have a few questions regarding the 1.1V reference.

1) Does 1.1 ref depend on the operating voltage? The uC can run from 1.8-5.5V. Is it typically a constant 1.1V reference across the entire operating voltage range or does it change slightly with the operating voltage?

2)What circuitry is used to generate that 1.1V reference internally? I did not see this in the manual .

I have attached the manual in case it helps.

hi,
1. The Int Vref is ~1.1V over the full Vs supply range to the MCU.

2. Its derived from an Internal 'Band Gap' device.

E

Thanks alot for the answer E!!!!

The data sheet says that the reference is not very accurate and can be anywhere from 1 to 1.2V (see page 177).

NorthGuy said:

The data sheet says that the reference is not very accurate and can be anywhere from 1 to 1.2V (see page 177).

Click to expand...

1.1V+/-10%=1.0 to 1.2

Most of micro-controller's ADC Reference voltage control the ADC result resolution actually step size

micropad said:

Most of micro-controller's ADC Reference voltage control the ADC result resolution actually step size

Click to expand...

I agree, if the internal Vref range 1.0v thru 1.2v, the ADC will resolve correctly to the bit step/count.
This is why I replied to the OP.

The Int Vref is ~1.1V over the full Vs supply range to the MCU.

Click to expand...

E

You can easily measure the internal reference. Just set the operating voltage as reference voltage and measure the internal reference with ADC.