Analysis and improvement of post-threshold mode of adaptive cyclic ADC operation

Abstract

ABSTRACT The paper presents the results of studies on the behavior of adaptive cyclic analog-to-digital converters (ADCs) for greater number of cycles (iterations) of the sample conversion. A distinguishing feature of the adaptive cyclic ADCs is iterative calculation of output codes of converted samples using a simple digital processing unit (DPU) according to dedicated conversion algorithm. Previous research showed that application of DPU extends radically the possibility of analytical and simulation analysis of cyclic ADCs functioning and allows to improve the effective resolution of the ADCs in comparison with similar conventional sub-ranging cyclic ADCs forming the output codes using logic elements. Moreover, DPU and possibility of optimization of the adaptiv e cyclic ADCs create a number of new effects important for applications, unachievable in known cyclic ADCs. One of them is restoration of monotonic growth of the adaptive cyclic ADC resolution in the “post-threshold” cycles of conversion, where resolution of conventional cyclic ADCs is fixed without possibility of improvement by increasing number of cycles. In the paper, there is proposed and analyzed a new conversion algorithm for the adaptive cyclic ADCs that combines the most desired features of the algorithms developed earlier, i.e. provides the greatest possible rate of increase of effective number of bits (ENOB) of ADC in the initial “pre-threshold” phase of conversion, and enables fu rther increase of ENOB in the “post-threshold” phase. Keywords: analog-to-digital conversion, sub-ranging ADC, adap tive cyclic ADC, threshold effect, ENOB, optimization