### Welcome to EDAboard.com

#### Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Status
Not open for further replies.

#### amilaachala

##### Newbie level 6
hi guys,

I want to know about 'minimum external voltage references' that can be given to ADC.suppose i give external voltage references as " 0 V and 3.3 V " then a step size would be ( 3.3/1023 ) V rit????

thanks ........

#### Tahmid

Step Count = (VREF / (Total No. of Steps)) * ADC result

Step size = VREF/(Max count)
So, the step size would be (3.3/1024)

Be careful, total no. of steps is 1024, not 1023.

The minimum external voltage reference you can use is 3.0V (if VDD ≧ 3.0V) or 1.8V (if VDD < 3.0V).

Hope this helps.
Tahmid.

Last edited:
amilaachala

### amilaachala

Points: 2

#### amilaachala

##### Newbie level 6
are you sure??? i mean to find a step size

step size = (Vmax - Vmin) / 1024

that will give you the voltage difference between 2 steps Right?????????

#### wp100

Hi,

Tahmid is correct.

step size = ( vmax 3v3 - vmin 0v) / 1024 = 3v3 / 1024 = 0.003226 v per single step

Also see the chips datasheet, section electrical charactristics, for the operating voltages of the ADC of your particular type of chip F or LF

#### amilaachala

##### Newbie level 6
Hi,

Tahmid is correct.

step size = ( vmax 3v3 - vmin 0v) / 1024 = 3v3 / 1024 = 0.003226 v per single step

Also see the chips datasheet, section electrical charactristics, for the operating voltages of the ADC of your particular type of chip F or LF

If you look closely you will see that Tahmid has muliplied the equation you posted with an additional Vin.

#### Tahmid

The extra VIN was an error that I have fixed.

amilaachala

Points: 2