# Resolution of a bit in ADC value based on SAM method

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#### chandu.kurapati

##### Full Member level 3
Hi,

I'm working with a 10 bit ADC based on successive approximation method,
max & min input voltages are 5v & 0v respectively.

can any one explain about resolution of each bit & how to calculate it..

#### KlausST

##### Super Moderator
Staff member
Hi,

There are many different ADC solutions. Each has it´s own definition... you can find in the datasheet.

****
For many ADCs the folowing is true:

Resolution (V) = V_REF / 2^n.

Where n = the number of bits.

****

Klaus

#### chandu.kurapati

##### Full Member level 3
Hi,

I read controller data sheet & got how to program number of bits & where to collect
digital value.

But in that datasheet didn't mention any reference voltage(V_Ref), is that V_Ref is equal to
input voltage (Vin) in successive approximation (or) is it different from input voltage.

Vin mentioned as 3.3v - 5v in datasheet.

#### KlausST

##### Super Moderator
Staff member
Hi,

Maybe VRef is eqaul to VCC, maybe not. Usually you can choose which VRef you use.

Give us the datasheet and we can show you where to find the informations.

Klaus

#### chandu.kurapati

##### Full Member level 3
Hi,

https://www.infineon.com/dgdl/xc220...r.pdf?fileId=db3a304316f66ee801177897ffab372c

In that i observed VRef is equal to maximum digital result value is obtained if the analog
input voltage equal to the reference voltage, from that i concluded that max analog input
voltage is equal to reference voltage.

Is it correct, if it wrong please correct my sentence.....

#### KlausST

##### Super Moderator
Staff member
Hi,

datasheets says:
Analog supply voltage range from 3.3 V (minimum) to 5 V (nominal) for VDDPA
Don´t mix "supply voltage" with "analog signal input voltage"

Each digital value in the
available result range (from 0 to 2n-1) represents an input voltage range that is defined
by the reference voltage divided by 2^n...
result at 2n-1..

Reference selection:
Bit field REFSEL defines which reference input is used for the conversion (see
Section 16.2.12.2)
...
Please note that the smallest granularity 1 LSBn for n bit resolution refers to the selected
reference voltage. The granularity becomes very small if a low reference voltage is
applied, and as a consequence, the resulting TUE increases due to noise effects.
Therefore, it is recommended to avoid small reference voltages.

Reference Input Selection:
This bit field defines the reference source for this channel.
00B The standard reference input VAREF is selected.
01B The alternative reference input CH0 is selected.

My info:
While the allowed analog input voltage range is: 0V...AVDD. (not to destroy the chip)
The decodable analog input voltage range is: 0V...ARef. (for a digital output value of 0x000 to 0x3FF)
You may choose VRef from 0V to VDDPA. To keep errors low you should not use low voltage VRef.

Klaus

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