# How to calculate ADC Sampling Rate

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#### soumen21

##### Member level 4
According to datasheet, the ADC clock frequency should be
between 50kHz and 200kHz to ensure 10-bit effective resolution. 50kHz ADC clock frequency is chosen. Then the sampling frequency becomes ~3800 SPS.
Vref = 5V, Vin =2.5V

How the sampling frequency is calculated ?

#### alexan_e

I assume that you are asking for AVR.
The datasheet explains it in the ADC section, In ADCSRA register the bits 2-0 control the division factor

Code:
•  Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits

These bits determine the division factor between the XTAL frequency and the input

0                    0                    0                             2

0                    0                    1                             2

0                    1                    0                             4

0                    1                    1                             8

1                    0                    0                            16

1                    0                    1                            32

1                    1                    0                            64

1                    1                    1                            128

Alex

#### soumen21

##### Member level 4
Hi Alex,
Thanks for your reply. Yes, it is for AVR. But I could calculate the approximate value as mentioned (~3800 SPS) in the application note using the divisor table. Can you please show me the calculation ?

#### alexan_e

you divide the clock with the division factor, for example 8000000/128=62500Hz
This frequency should be between 50000Hz and 200000Hz.
The normal conversion takes 13 cycles so the sample/sec is ADC frequency/13

Alex

erdem.simsek

### erdem.simsek

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