Equivalent Number of Bits in Delta-Sigma Analog-to-Digital Converter in Automatic Control and Monitoring Systems

The dynamic error of delta-sigma ADC working in analog information input devices of control and monitoring systems (CMS) is investigated. The traditional structure of the analog information input unit in CMS contains a sensor of physical quantity, ADC, analog anti-alias filter, amplitude multiplexer and analog storage device. These functional units determine the static and dynamic errors of the analog-to-digital conversion process. At the same time the equivalent number of bits of delta-sigma ADC, which are widely used today in the devices of radio engineering, automation and communication, is determined by the total error of the above mentioned functional nodes, consistently converting the output signal of the sensor. It is shown that in order to reduce dynamic errors it is reasonable to leave only the sensor and delta-sigma ADC in the signal conversion chain, which in this case is introduced into the channel of each sensor. In this case, to assess the influence of the dynamic characteristics of the sensor it is proposed to approximate its signal spectrum as a function of the signal spectrum at the output of the anti-alias low-pass filter with Butterworth approximation. Analytical dependences for determining the errors of analog-to-digital conversion with delta-sigma ADC are obtained, allowing to solve direct and inverse problems of CMS input circuit design: to evaluate the chosen variant or to design CMS functional units with the required characteristics.