Chi-Hang Chan

A 10-bit 100-MS/s Reference-Free SAR ADC in 90 nm CMOS

A 1.2 V 10-bit 100 MS/s Successive Approximation (SA) ADC is presented. The scheme achieves high-speed and low-power operation thanks to the reference-free technique that avoids the static power dissipation of an on-chip reference generator. Moreover, the use of a common-mode based charge recovery switching method reduces the switching energy and improves the conversion linearity. A variable self-timed loop optimizes the reset time of the preamplifier to improve the conversion speed. Measurement results on a 90 nm CMOS prototype operated at 1.2 V supply show 3 mW total power consumption with a peak SNDR of 56.6 dB and a FOM of 77 fJ/conv-step.

An 8-b 400-MS/s 2-b-Per-Cycle SAR ADC With Resistive DAC

An 8-b 400-MS/s 2-b-per-cycle (2 b/C) successive approximation register (SAR) analog-to-digital converter (ADC) is fabricated in 65-nm CMOS. With the implementation of a low-power and small-area resistive DAC and associated highly integrated circuit implementation, the proposed SAR ADC achieves rapid conversion rate, low power, and compact area, leading to SNDR of 44.5 dB and SFDR of 54.0 dB, at 400 MS/s with 1.9-MHz input. The measured FOM is 73 fJ/conversion-step at 400 MS/s from 1.2-V supply and 42 fJ/conversion-step at 250 MS/s from a 1-V supply. The active area with the digital calibration is 0.028 mm2.

Split-SAR ADCs: Improved Linearity With Power and Speed Optimization

This paper presents the linearity analysis of a successive approximation registers (SAR) analog-to-digital converters (ADC) with split DAC structure based on two switching methods: conventional charge-redistribution and Vcm-based switching. The static linearity performance, namely the integral nonlinearity and differential nonlinearity, as well as the parasitic effects of the split DAC, are analyzed hereunder. In addition, a code-randomized calibration technique is proposed to correct the conversion nonlinearity in the conventional SAR ADC, which is verified by behavioral simulations, as well as measured results. Performances of both switching methods are demonstrated in 90 nm CMOS. Measurement results of power, speed, and linearity clearly show the benefits of using Vcm-based switching.

A 0.024mm 2 8b 400MS/s SAR ADC with 2b/cycle and resistive DAC in 65nm CMOS

The successive-approximation (SA) algorithm is traditionally used for low-bandwidth applications because it requires n clock cycles or more to obtain n-bit resolution. However, the use of modern nanometer CMOS technologies and special design solutions overcome the speed limit, enabling conversion rates in the hundreds of MHz with very low power consumptions [1]. This design uses the successive-approximation method to obtain 8b up to 400MS/s with very low power using a 1.2V supply. Key features of the architecture are a resistive DAC and a 2b-per-cycle conversion with interpolated sampling front-ends and shift registers. A cross-coupled bootstrapping network is also implemented to alleviate the signal-dependent clock feed-through. The very compact layout leads to a silicon area of 0.024 mm2.

A 3.8mW 8b 1GS/s 2b/cycle interleaving SAR ADC with compact DAC structure

An 8b 1GS/s ADC is presented that interleaves two 2b/cycle SARs. To enhance speed and save power, the prototype utilizes segmentation switching and custom-designed DAC array with high density in a low parasitic layout structure. It operates at 1GS/s from 1V supply without interleaving calibration and consumes 3.8mW of power, exhibiting a FoM of 24fJ/conversion step. The ADC occupies an active area of 0.013mm2 in 65nm CMOS including on-chip offset calibration.

A 50-fJ 10-b 160-MS/s Pipelined-SAR ADC Decoupled Flip-Around MDAC and Self-Embedded Offset Cancellation

This paper presents a time-interleaved pipelined-SAR ADC with on-chip offset cancellation technique. The design reuses the SAR ADC to perform offset cancellation, thus saving calibration costs. The inter-stage gain of 8 is implemented in a 6-bit capacitive DAC with a flip-around operation. A capacitive attenuation used in both the first and second DACs significantly reduces the power dissipation and optimizes conversion speed. The detailed circuit implementation of the subthreshold op-amp is discussed, and the possible limits caused by nonidealities are analyzed for a proper correction in the design. These include the inter-stage-gain error and various channel mismatches of offset, gain, and timing. Measurements of a 65-nm CMOS prototype operating at 160 MS/s and 1.1-V supply show an SNDR of 55.4 dB and 2.72 mW total power consumption.

A 35 fJ 10b 160 MS/s pipelined-SAR ADC with decoupled flip-around MDAC and self-embedded offset cancellation

A Time-Interleaved (TI) pipelined-SAR ADC with on-chip offset cancellation technique is presented. The design reuses the SAR ADC to perform offset cancellation, which significantly saves calibration area, power and time. A 6 bit capacitive DAC is built as a flip-around MDAC for low inter-stage gain implementation. The capacitive attenuation solutions in both 1st and 2nd DACs minimize the power dissipation and optimize conversion speed. Measurements of a 65nm CMOS prototype operating at 160MS/s and 1.1V supply show 2.72mW total power consumption. The SNDR is 55.4dB and the FoM as low as 35fJ/conv.-step.

A 4.8-bit ENOB 5-bit 500MS/s binary-search ADC with minimized number of comparators

This paper presents a topology to improve the system linearity and reduce the complexity of high-speed binary-search ADCs. The proposed topology, when compared with previous binary-search ADC architectures, further reduces the number of comparators from 2N-1 to N for N-bit precision, the comparator structure is simplified, and it can avoid both the signal dependent offsets and the kickback noise. The proposed binary-search ADC has been implemented in 65nm CMOS process and it consumes 1.63mW at an operation frequency of 500MS/s. The measurement results demonstrate that the binary-search ADC achieves 30.7dB SNDR (4.8-bit ENOB).

A 34fJ 10b 500 MS/s partial-interleaving pipelined SAR ADC

A 10b 500MS/s ADC is presented that shares a full-speed SAR at front-end and interleaves the pipelined residue amplification with shared opamp and 2nd-stage SAR ADCs, which achieves high speed, low power and compact area. The prototype ADC in 65nm CMOS achieves a mean SNDR of 55.4dB with 8.2mW power dissipation at 1.2V. The active die area including the offset calibrations is 0.046mm2.

An 11b 60MS/s 2.1mW two-step time-interleaved SAR-ADC with reused S&H

An 11b 60MS/s 2-channel two-step SAR ADC in 65nm CMOS is presented. The scheme shares the op-amp between channels for the residual generation and takes advantage of time interleaving for reusing the input S&H of the first stage. A reduction of the gain in the residual generator and sub-threshold operation enables the use of a power-effective, singlestage op-amp with 69dB-gain. The ADC achieves peak SNDR of 57.6dB while consuming 2.1mW from 1-V analog and 0.85-V digital supply, resulting in an FoM of 57fJ/step.