The concept of the asynchronous Sigma-Delta analog-to-digital converter (ASD-ADC) based on the charge pump integrator is discussed in the paper. A twolevel conversion scheme is utilized. The first level is accomplished by amplitude-to-pulse-width mapping in the asynchronous Sigma-Delta modulator. The other level consists in the time-to-digital conversion. The ASD-ADC belongs to a class of mean value converters since the digital outputs correspond to the mean values of the input signal in time windows of varying width. The configurations of the charge pump modulator either with bipolar, or with unipolar controlled current sources are presented. The design of the charge-pump-based modulator model using classical solutions of bipolar technology is exemplified. The input/ output simulation results of the designed asynchronous Sigma-Delta modulator (ASDM) are reported. Next, the design of the time-to-digital converter, the analysis of the quantization error, and two concepts of the converter digital output interface are presented. The comparison of the minimum transmission bit rate of the serial output port(s) for both concepts is carried out. Finally, the procedure of evaluation of the ASD-ADC key design parameters for speech signal supporting a possible original input signal recovery is exemplified.
This paper presents a systematization and a comparison of the binary successive approximation (SA) variants. Three different variants are distinguished and all of them are applied in the analog-to-digital conversion. Regardless of an analog-to-digital converter circuit solution, the adoption of the specific SA variant imposes a particular character of the conversion process and related parameters. One of them is the ability to direct conversion of non-removeable physical quantities such as time intervals. Referencing to this aspect a general systematization of the variants and a name for each of them is proposed. In addition, the article raises the issues related to the complexity of implementation and energy consumption for each of the discussed binary SA variants.
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