High Accuracy Two-Step Flash ADC with Changeable Comparison Range Using Latch Based Comparator

High Accuracy Two-Step Flash ADC with Changeable Comparison Range Using Latch Based Comparator

Due to the technology development and decreasing supply voltages, undesirable effects on sensitive analog signals like noise, kickback are becoming more expressed. Mentioned issues are present in analog to digital converters (ADC) and design of high accuracy ADCs is becoming more complex. In this work, a circuit was proposed based on a latch comparator and comparison range shifter, which increased the accuracy of a two-step flash ADCs by excluding the chance of incorrect coarse conversion, when the input analog voltage is close to separating points of the comparison range of first stage of the ADC. The proposed circuit was constructed using an 16nm FinFET process, the simulations were done with HSpice simulator. The idea was to increase the accuracy of an already designed two-step flash ADC by adding the proposed circuit, which was done by shifting the comparison range during the coarse conversion, for the difference of input voltage and separating points not to be smaller than the offset of comparators used in ADC. It was established that the use of the proposed circuit increased the comparison time, as the sampled input analog voltage firstly should be compared with comparison range separating points, but on the other hand the ADC became more sensitive to its input change (up to 4mV offset) and was performing stable, excluding the chance of wrong coarse conversion. It has been shown that proposed architecture allows avoiding the use of low offset and high accuracy complex comparators in two-step flash ADCs, which greatly reduces the layout area.
Vazgen S. Gevorgyan
Synopsys Armenia Educational Department, Yerevan, Armenia; National Polytechnic University of Armenia, Yerevan, Armenia
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