Hybrid ADC for Low-Power Applications

2021 ELE Engineering Design Project (FY03)

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Faculty Lab Coordinator

Fei Yuan

Topic Category

Microelectronics

Preamble

Analog-to-Digital Converters (ADCs) play an important role from biomedical sensors to cellular phones. Among various architectures of ADCs, successive approximation register (SAR) ADCs introduced in 1950s and debuted in CMOS in 1970s played a major role in advancing the state-of-the-art of ADCs since their inception. Although popular in telephony and instrumentation where data rate is typically low in the past, SAR ADCs have re-established themselves as the most promising ADC architecture inherently crafted for modern CMOS technologies with emerging applications in wireless sensors and biomedical instruments where power consumption is of a great importance. The power consumption of SAR ADCs rises sharply with their resolution, mainly due to the increased transconductance of the front-end transistors of comparators needed to sense and amplify a small voltage. The resolution of state-of-the-art voltage-mode SAR ADCs is limited to approximately 10 bits. One attractive technique emerged recently to increase the resolution of SAR ADCs without an overwhelming amount of power consumption is a hybrid architecture of SAR ADCs consisting of a coarse voltage-mode SAR ADC, a voltage-to-time converter (VTC) that maps the residual voltage of the coarse SAR ADC to a time and a time-to-digital converter (TDC) that digitizes the output time of the VTC. A distinct characteristic of this hybrid architecture is that the front-end voltage-mode SAR ADC allows it to accommodate a large input voltage with a high degree of linearity. The excellent linearity of the VTC, attributed to its small input voltage range, is also critical to the overall linearity of the ADC. The wide range of the choice of TDCs is an added bonus of this architecture.

Objective

Design a 10-bit hybrid SAR ADC.

Partial Specifications

1) Hybrid architecture consisting of a 6-bit voltage-mode SAR ADC, a VTC, and a 4-bit Vernier TDC.
2) Power consumption: a few micro watts.
3) Data rate: 10 kS/s.
4) INL (Integral nonlinearity): No more than 1 LSB.
5) ENOB (Effective number of bits): 10 bits.
6) Technology: TSMC 130 nm 1.2V CMOS.

Suggested Approach

1) Study the fundamental of ADCs and SAR ADCs.
2) Study the fundamental of time-based signal processing.
3) Develop the architecture of the system and the specifications of the building blocks of the system.
4) Carry out detailed circuit design of all building blocks and conduct extensive simulation to ensure that the performance of the building blocks meet design specifications.
5) Carry out silicon implementation of the building blocks and conduct post-layout simulation to ensure that the performance of the building blocks meet design specifications.
6) Carry out the post-layout simulation of the entire ADC to ensure that the performance of the building blocks meet the design specifications.

Group Responsibilities

The group members of the project will work as a team to undertake this challenging project. A full corporation is needed to ensure the progress and completion of the project.

Student A Responsibilities

The student is responsible for the design and implementation (schematic and layout) of the sample-and-hold (S/H) block of the SAR ADC. The performance of the S/H should be quantified using the spectrum of its output obtained using DFT analysis. The student is also responsible for the generation of the sampling clocks that powers both the S/H and SAR. The sampling clock is generated using a frequency synthesizer that locks to a reference frequency.

Student B Responsibilities

The student is responsible the design and implementation (schematic and layout) of a 6-bit SAR, a differential capacitive DAC including the switching network, and comparator. The performance of the SAR ADC should be quantified using the spectrum of its output obtained using DFT analysis.

Student C Responsibilities

The student is responsible the design and implementation (schematic and layout) of the VTCs. The performance of the VTCs should be quantified using the spectrum of its output obtained using DFT analysis. The student should also work with student-1 on the generation of the sampling clock.

Student D Responsibilities

The student is responsible the design and implementation (schematic and layout) of the 4-bit Vernier TDC. The performance of the TDC should be quantified using the spectrum of its output obtained using DFT analysis.

Course Co-requisites

ELE724 / ELE734 (at least two students should take ELE724)

To ALL EDP Students

Due to COVID-19 pandemic, in the event University is not open for in-class/in-lab activities during the Winter term, your EDP topic specifications, requirements, implementations, and assessment methods will be adjusted by your FLCs at their discretion.