VLSI Chip Design Project
Project Description and
Requirement Specification
Version 1.0
Project: A First-Order Sigma-Delta Modulator
with 3-bit Quantizer
Project number: 1
Project Group:
Project members
Project leader and designer 1(5)
Designer 2(5)
Designer 3(5)
Designer 4(5)
Designer 5(5)
Customer and Supervisor: Ali Fazli
Office: B-house 2D:433, Phone: 013-282794, Fax: 013-139282
Email: ali@isy.liu.se
A First-Order Sigma-Delta Modulator with 3-bit Quantizer
1 Background
This document describes the design requirement specification of a First-Order Sigma-Delta
modulator with a 3-bit quantizer (3-bit ADC). One of the bottlenecks in systems today is the
data converters (A/D and D/A) required to move between analog and digital domain. Instead
of using an ADC with a large number of bits, which is tough to design because of matching
requirements, an oversampled low resolution ADC together with noise-shaping can be used.
Sigma-Delta converters are commonly used today when the bandwidth of the input signal is
less than 1MHz. The main issue with Sigma-Delta ADCs is the need of oversampling. As one
can understand there is of cause a limit what we can do in terms of oversampling frequency.
Project Goal
The project goal is to design an integrated circuit (IC) in complementary metal-oxide
semiconductor (CMOS) technology. Students, participating in this project as project members
and project leaders, should learn the different steps of the IC design flow. That includes the
given system architecture analysis, simulation, layout implementation and verification. The
project students have an optional choice to manufacture the designed IC circuit on a chip. To
test the manufactured chips, another course (TSEK11) is available after the project.
Milestones and Deadline
1: Project selection
Week 3
2: Pre-study, project planning, and discussion with supervisor
Week 4
3: High-level modeling design and simulation result (report)
February 12
4: Gate/transistor level design and simulations result (report)
March 18
5: Layout, DRC, parasitic extraction, LVS, post-layout
simulations, modification and chip evaluations.
May 6
6: DEADLINE, Delivery of the completed chip.
May 13
7: DEADLINE, Final report, and oral presentation
May 20
The following parties are involved in this project:
1- Customer: Ali Fazli
2- Project supervisor: Ali Fazli
• Formulates the project requirements
• Provides technical support
• Reviews the project documents.
3- Project leader: One of the members in the design team.
• Responsible for organization of the team and the project planning.
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A First-Order Sigma-Delta Modulator with 3-bit Quantizer
• Divides the design and documentation work in an efficient way
• Organizes the team meetings as well as the meetings between the team and supervisor
• Keeps the supervisor informed about the progress of the project (at least one email or
meeting per week)
4- Project design members (including the project leader)
• Are equally responsible for project planning and design.
• Participate actively in all the meetings
• Support the team and the project leader
• Keep the team and project leader informed about the progress of their tasks.
Project Description
System Description
The complete system to be built should be a working first-order Sigma-Delta modulator. The
total system is shown in Figure 1. The main components to be designed are an integrator, a 3bit flash-ADC, and a 3-bit DAC. The switched-cap integrators require an Operational
amplifier (OP). A schematic of a suitable OP will be given to you in order to save some time.
The digital filter that is needed after the Sigma-Delta modulator can be done in Matlab when
doing chip measurements.
Z −1
1 − Z −1
Figure 1: First-order Sigma-Delta modulator architecture.
The target for this design will be to achieve about 55-60dB dynamic range over a 500kHz
bandwidth. The dynamic range (SNR=Signal-to-noise ratio) that can achieved with a firstorder Sigma-Delta modulator can be calculated as
SNR = 6.02 ⋅ N + 1.76 − 5.17 + 30 log(OSR )
Where N is the number of bits from the quantizer, and OSR is the oversampling ratio (the
ratio of input bandwidth and the nyquist frequency). Using a sampling frequency of 32MHz
(OSR = 32 MHz / (2 * 500 kHz) = 32) gives an SNR of about 60dB. This is equivalent with a
9.6-bit ADC. For a first-order sigma delta modulator an increase of the oversampling ratio by
a factor of two means an increase of the equivalent number of bits by 1.5.
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A First-Order Sigma-Delta Modulator with 3-bit Quantizer
Important Design Metrics
The circuit must be designed for a sampling frequency of at least 32MHz. This will be
translated to requirements on the integrators, 3-bit quantizer, and the 3-bit DAC. Important
things to consider are:
Timing, settling, and internal noise in the integrators
Precision in the ADC
The structure is also sensitive to settling- and matching-errors in the DAC
Furthermore, the power-consumption is of large interest and should be minimized.
3 Area and Performance Requirements
The table below summarizes the circuit performance requirements. Each requirement has its
number, formulated text, and the given degree of priority. Three degrees of priority are used:
high, medium, and low. High is a firm requirement with no possibility of relaxation, while
medium requirements can be relaxed somewhat after good motivation.
Requirement Requirement Text
Sampling frequency at least 32MHz
Integrate as many system components as possible on-chip
Schematic and layout must be verified by simulation
Layout matching
Simulated chip power consumption < 100mW at max. freq.
Chip core area < 0.27mm2
Total project pin count: 12
Design technology is AMS 4-Metal 0.35µm CMOS
The most important system nodes should have off-chip access pins
On-chip current densities < 1 mA/µm
All requirements fulfilled in “typical”, “slow”, and “fast” process Medium
corners and for temperatures between 25oC and 110oC
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A First-Order Sigma-Delta Modulator with 3-bit Quantizer
520 µm
520 µm
Design Area
Other Projects
Figure 2: Schematic picture of a 3mm2 chip with 40 generic pads four VDD and four VSS pads
(total 48 pads), which will be shared between a number of projects.
Available Resources
• Scientific publication database (available from LiU):
• IEL – IEEE/IEE Electronic Library, http://www.bibl.liu.se/english/databas/
• Circuit simulation and layout tools from Cadence, http://www.cadence.com/
4 References
• J.M. Rabaey, A. Chandrakasan, and B. Nikolic., “Digital Integrated Circuits”, 2nd ed.,
Prentice Hall, 2003, ISBN 0-13-120764-4.
• D.A. Johns and K. Martin, “Analog Integrated Circuit Design”, John Wiley & Sons, 1997.
• A 12-mW ADC delta-sigma modulator with 80 dB of dynamic range integrated in a singlechip Bluetooth transceiver; Grilo,J.;Galton,I.;Wang,K.;Montemayor,R.G.; Solid-State
Circuits, IEEE Journal of , Volume:37, Issue:3, March2002 Pages:271 – 278
• Delta-sigma data conversion in wireless transceivers Galton, I.; Microwave Theory and
Techniques, IEEE Transactions on , Volume: 50 , Issue: 1 , Jan. 2002 Pages:302 - 315
For more literature references consult with your supervisor.
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