This method of measurement of noise in an ADC is fairly simple and can
even be easily implemented on a system level after the ADC is placed in
the final system on a PCB. As stated above, we would need to ground the
analog input terminals of the ADC and take a number of readings to plot
the histogram. We will now see, with the help of the sample histogram in
**Figure 3**, how to calculate the noise parameters of an ADC.

**Click on image to enlarge.**
**Figure 3: Grounded input histogram of an ADC**

**Figure 3 **depicts
a typical grounded input histogram of an ADC. We can define a number of
parameters in terms of counts of ADC output with the help of this
histogram. For example, the peak-to-peak noise of an ADC is the span of x
axis over which the grounded input histogram exists. For example, the
peak-to-peak noise for the ADC corresponding to

**Figure 3** is (1 –
(-3)) or 4 counts. Alternatively, it can be expressed in number of LSBs
of ADC output. In the aforementioned case, peak-to-peak noise would be
(log

_{2} 4) = 2 LSBs.

In the next installment of this series (

**ADC Guide Part 11**), we will continue talking about the noise performance, EnoB, and SINAD specifications of an ADC.

**Earlier articles** are listed below:
**About the authors**
**Sachin Gupta**
is working as Product Marketing Engineer 2 with Cypress Semiconductor.
He holds a Bachelor’s degree in Electronics and Communications from Guru
Gobind Singh Indraprastha University, Delhi. He has several years of
experience in mixed signal application development. He can be reached at
sgup@cypress.com.

**Akshay Phatak** is an Applications Engineer
with Cypress Semiconductor. He holds a Bachelor's degree in Electronics
and Telecommunications form College of Engineering, Pune (India). He
likes to work on mixed-signal embedded systems. He can be reached
at akay@cypress.com.