Compensation of the Power Supply Noise in a Sigma Delta Converter
Original Publication Date: 1988-Aug-01
Included in the Prior Art Database: 2005-Feb-15
Sigma-delta analog-to-digial converters, such as coders, using CMOS switches come widely into use in modern telecommunication products. However, these converters are extremely sensitive to the noise of common power supply devices that affect their overall functioning. A better immunity of a sigma-delta coder against power supply noise and, particularly, longitudinal noise, may be achieved by returning a portion of the noise signal, which spoils the CMOS switches, with an opposite phase to the input of the coder. Therefore, that re-injection will compensate the effects of the power supply noise and increase the overall performance of the coder. As shown in the figure, the coder includes an operational amplifier (OA) 1 which receives the analog input signal to be coded and the feedback signal.