CHAPTER 5

Chopping: a technique for noise and offset reduction


Prev TOC Next

5.3. Chopping seen as a modulation technique

Another method for noise and offset reduction is the chopping technique. Chopping is a modulation technique which shifts the spectra of low frequency stationary processes at multiples of chopper frequency out of the band of interest. To understand this, consider a stationary random process x(t) of autocorrelation function Rxx(t) and power spectral density Sxx(f) which is applied to a band limited amplifier A(f) as illustrated in fig.5.4. The modulation signal (chopper signal) m(t) is periodic with a period T and can be expanded in Fourier series:

(5.8)

The Fourier transform of this signal is a sequence of Dirac pulses decaying with the order of the harmonic and having contributions only at odd multiples of the chopping frequency 1/T.

(5.9)

The power spectral density of the output process y(t)=[Ax(t)]m(t) can be found from the following convolution:

 

Fig.5.4: Chopper modulation

(5.10)

This gives contributions only at the odd multiples of the chopping frequency 1/T:

(5.11)

Therefore, the output power spectral density is a repeated replica of the input power spectral density at the odd multiples of the chopper frequency rapidly decreasing with the order of the harmonic. That is why foldover effects are not present in the case of chopping. This is the main difference between chopping and sampling methods.

Aldec

Featured Video
Editorial
Peggy AycinenaWhat Would Joe Do?
by Peggy Aycinena
Simon Davidmann: A re-energized Imperas Tutorial at DAC
Peggy AycinenaIP Showcase
by Peggy Aycinena
ARM: A Gnawing Sense of Unease
More Editorial  
Jobs
LVS for PDK Design Engineer SILICON VALLEY for EDA Careers at San Jose, CA
LVS PEX DESIGN ENGINEERS SILICON VALLEY for EDA Careers at San Jose, CA
Senior Front-End RTL Design AE for EDA Careers at San Jose, CA
DDR 3-4-5 Developer with VIP for EDA Careers at San Jose, CA
Upcoming Events
11th International Conference on Verification and Evaluation of Computer and Communication Systems at 1455 DeMaisonneuve W. EV05.139 Montreal Quebec Canada - Aug 24 - 25, 2017
DVCon India 2017, Sept 14 - 15, 2017 at The Leela Palace Bengalore India - Sep 14 - 15, 2017
SMTA International 2017 at Rosemont IL - Sep 17 - 21, 2017
S2C: FPGA Base prototyping- Download white paper



Internet Business Systems © 2017 Internet Business Systems, Inc.
595 Millich Dr., Suite 216, Campbell, CA 95008
+1 (408)-337-6870 — Contact Us, or visit our other sites:
AECCafe - Architectural Design and Engineering TechJobsCafe - Technical Jobs and Resumes GISCafe - Geographical Information Services  MCADCafe - Mechanical Design and Engineering ShareCG - Share Computer Graphic (CG) Animation, 3D Art and 3D Models
  Privacy Policy