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.

Teledyne Optech:

Trimble Catalyst

Featured Video
Jobs
Imagery Analyst for ARA at Albuquerque, NM -1229, NM
Database Specialist for MDA Information Systems LLC at Gaithersburg, MD
Sr. GIS Technical Analyst for Southern California Edison SCE Transmission and Distribution Organization at Rosemead, CA
Data Scientist for University of Utah at Salt Lake City, UT
Inside Sales for SolidCAM at Newtown, PA
Project Architect for LAMBERT Architecture and Interiors at Winston-Salem, NC
Upcoming Events
2017 GIS/CAMA Technologies Conference at Chattanooga Convention Center Chattanooga Tennessee - Mar 6 - 9, 2017
IGTF 2017 ASPRS Annual Meeting 2017 at Marriot Waterfront Baltimore Baltimore MD - Mar 11 - 17, 2017
MAPPS Federal Programs Conference at Sheraton Hall Silver Spring Maryland - Mar 13 - 15, 2017
WorldCover 2017 Conference at ESRIN Italy - Mar 14 - 16, 2017
Teledyne Optech
Teledyne:
xponential2017



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 EDACafe - Electronic Design Automation TechJobsCafe - Technical Jobs and Resumes  MCADCafe - Mechanical Design and Engineering ShareCG - Share Computer Graphic (CG) Animation, 3D Art and 3D Models
  Privacy Policy