M.Sc Thesis

M.Sc StudentPollak Dan
SubjectSigma Delta Analog to Digital Converters for Video Signals
DepartmentDepartment of Electrical and Computer Engineering
Supervisors PROFESSOR EMERITUS Arie Arbel (Deceased)
DR. Aharon Unikovski (Deceased)


The design of Analog to Digital converters incorporating speed, resolution and cost has always been a difficult task to achieve. In this paper we present a Sigma-Delta A/D converter, which is one of the ways to achieve high resolution by using a low cost CMOS process. This design achieves 12Bit resolution at 5Msps (2.5MHz Nyquist band-width) employing a low power and low cost process (no trimming).

The Sigma-Delta principle was introduced and studied 30 years ago but only recently it began to be used for mixed-signal integrated circuits, due to its robustness and the ability to use fast digital processing techniques.

Low frequency designs were introduced but wide bandwidth converters still needed to overcome stability and power dissipation difficulties.

Since Sigma-Delta converters employ the oversampling method, the clock frequencies are very high and thus limited by technology. To overcome the operating frequency limitation, higher order modulators are used while lowering the oversampling rates. High order modulators make the design more complicated and potentially unstable.

As frequencies get higher much higher current is needed for the proper operation of the convereter. Power dissipation and current consumption is very critical in applications like video and RF baseband, since most of those applications are mobile and hence battery operated. Carful design is needed in order to keep the power consumption of those convereters to minimum.

This paper introduces a novel design aimed at achieving high sampling rates suitable for Video signals and RF baseband while employing very low power and a robust design.

The design introduced exploits the precision achieved by Sigma-Delta D/A to form a highly linear feedback signal needed for high performance multi-bit Sigma-Delta converters, without increasing current consumption.