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.

Downstream : Solutuions for Post processing PCB Designs

Aldec

Featured Video
Editorial
Peggy AycinenaWhat Would Joe Do?
by Peggy Aycinena
Real Intent: Leveraging on Investments
More Editorial  
Jobs
Senior R&D Engineer...Timing Closure Specialist for EDA Careers at San Jose or Anywhere, CA
FPGA Engineer for Teradyne Inc at San Jose, CA
Senior Front-End RTL Design AE for EDA Careers at San Jose, CA
Technical Support Engineer EU/Germany/UK for EDA Careers at N/A, United Kingdom
Analog Hardware Engineer for Teradyne Inc at San Jose, CA
Upcoming Events
CODES+ISSS 2017, Oct 15-20, 2017, Lotte Hotel, Seoul, South Korea at Lotte Hotel Seoul Korea (North) - Oct 15 - 20, 2017
DVCon 2017 Europe, Oct 16 - 17, 2017, Munich, Germany at Holiday Inn Munich City Centre Munich Germany - Oct 16 - 17, 2017
11th International Symposium on Networks-on-Chip (NOCS 2017) at Seoul Korea (South) - Oct 19 - 20, 2017



Internet Business Systems © 2017 Internet Business Systems, Inc.
25 North 14th Steet, Suite 710, San Jose, CA 95112
+1 (408) 882-6554 — 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 PolicyAdvertise