Alex Yue Alex.Yue@uwe.ac.uk
Senior Lecturer in Bioinstrumentation and Sensor Interfacing
Alex Yue Alex.Yue@uwe.ac.uk
Senior Lecturer in Bioinstrumentation and Sensor Interfacing
H. G. Krapp
E. M. Drakakis
The Tanh transfer function of the differential pair operating in weak inversion is employed to implement the non-linear pre-amplification for the comparator of the SAR ADC. This non-linear preamplifier achieves a low gain for large input signals therefore the comparator can operate at a full speed (overdrive-free), while the high gain it achieved for small input signals improves the accuracy of the comparator. By combining the non-linear preamplifier and CMOS inverters, the issue of the comparison point shift in CMOS inverter due to fabrication process can be neglected, providing an output code offset-free solution. Simulations for the most critical zero-crossing overdrive cases for a 12-bit SAR ADC demonstrated that by cascading four stage differential pairs, the gain difference between the input signals of (1/2)LSB and (1/4)V is 49 dB, while the output of the preamplifier for the input of (1/2)LSB is big enough to tackle the comparison point shift in the following comparison stage. Fabricated using the 0.35 μm AMS CMOS technology, the comparator occupied an area of 130×140 μm while consuming 6.2 μW of power under a 1.5 V single power supply which is suitable for low-power applications. Chip tests demonstrated that the fabricated chips achieved 12-bit resolution without offset when working at 100 KSPS. This pure analog comparator could lead to higher resolution or higher speed by cascading more stages of the non-linear pair or by applying more current in the last stage of the non-linear pair.
Journal Article Type | Article |
---|---|
Acceptance Date | Feb 6, 2013 |
Online Publication Date | Mar 13, 2013 |
Publication Date | May 1, 2013 |
Deposit Date | May 7, 2021 |
Journal | Microelectronics Journal |
Print ISSN | 0026-2692 |
Publisher | Elsevier |
Peer Reviewed | Peer Reviewed |
Volume | 44 |
Issue | 5 |
Pages | 414-420 |
DOI | https://doi.org/10.1016/j.mejo.2013.02.011 |
Public URL | https://uwe-repository.worktribe.com/output/5667465 |
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