2. Acknowledgement
This presentation has been summarized from
various books, papers, websites and presentations
related to the topic all over the world. I couldn’t
remember where these large pull of hints and work
come from. However, I’d like to thank all professors
and scientists who created such a good work on
this emerging field. Without those efforts in this
very emerging technology, these notes and slides
can’t be finished.
3. • Suppose you have an
idea/requirement/application….
• And you want to develop a Electronic System
that works for it..
4. Typical Considerations…
• Cost Constraints
• Design Time
• Component Supply
• Prior Experience
• Training
• Contact Arrangement ( User Constraints)
• Size/Volume/Weight Constraints
• Power Source
• Power Consumption Constraint
• Rapid prototyping
• In-service updatebility/product upgrade
5. The system will include
• Mechanical Parts
Package etc
• Electronics Parts
PCB
IC
Components
Wires
Connectors
6. Integrated Circuits
• Based on Application
Linear (Analog) – Digital - Mixed
• Based on Fabrication Technology
Monolithic - Hybrid
• Based on Device
BJT-CMOS
• Based on Device Count
SSI-MSI-LSI-VLSI-ULSI
7. When you are system developer….
You may use
• Standard Product ICs
Off – the-self electronic component that you
purchase and use
• Application Specific Integrated Circuits (ASICs)
Specifically designed by you for your application
requirements
13. ASIC Design Methodologies
• Full Custom
Consider circuit performance vs design time
Design + Fabrication + testing time
Technology Window
• Semi Custom
Updateability
Divide and conquer…..
Use readily available….
• Programmable
Reprogrammable/erasable
Field Programmable
Very fast…
14. Design Hierarchy
Top Down Design
• The initial work is quite abstract and
theoretical and there is no direct connections
to silicon until many steps have been
completed.
• Acceptable in modern digital system design
• Co-designing with H/W-S/W is critical
Bottom-Up Design
• Starts at the silicon or circuit level and builds
primitive units such as logic gates, adders and
registers as first step
19. Specification
• Specification of the size, speed, power and
functionality of the VLSI system.
• Decisions on the architecture, e.g., RISC/CISC, #
of ALU’s, pipeline structure, cache size, etc. Such
decisions can provide an accurate estimation of
the system performance, die size, power
consumption, etc.
Architectural Design
20. Functional/Behavioural Design
• Identify main functional units and their
interconnections. No details of implementation.
• Functional design is generally done with HDL
21. Register Transfer Level
+
+
0010
0001
0100
0011
• Components, data types
• Design the logic, e.g., Boolean expressions,
control flow, word width, register
allocation, etc.
• RTL is expressed in a HDL mostly
synthesized from behavioral description
22. Logic Level
• Discrete Level, Discrete Time
• Design the circuit including gates, transistors,
interconnections, etc. The outcome is called a
netlist.
• Homework
ISCAS Gate level
Netlist
26. Few more words…
• Circuit Partitioning – Partition a large circuit into
sub-circuits (called blocks). Factors like #blocks,
block sizes, interconnection between blocks, etc., are
considered.
• Floorplanning – Set up a plan for a good layout.
Place the modules (modules can be blocks,
functional units, etc.) at an early stage when details
like shape, area, I/O pin positions of the modules,
…, are not yet fixed.
• Placement – Exact placement of the modules
(modules can be gates, standard cells, etc.) when
details of the module design are known. The goal is
to minimize the delay, total area and interconnect
cost.
27. • Routing – Complete the interconnections between
modules. Factors like critical path, clock skew,
wire spacing, etc., are considered. Include global
routing and detailed routing.
• Compaction – Compress the layout from all
directions to minimize the total chip area.
• Verification – Check the correctness of the
layout. Include DRC (Design Rule Checking),
circuit extraction (generate a circuit from the
layout to compare with the original netlist),
performance verification (extract geometric
information to compute resistance, capacitance,
delay, etc.)
28. Cont….
• Logic Synthesizer
Translation from RTL specification to netlist
Adequate for the design that do not have
critical performance parameter
Provides room to make design improvement
Understanding of device architecture is
necessary
• Gate Level Simulation
To ensure correctness of synthesis
translation
Vendor supplied parameters are used to
simulate the actual target device parameters
29. Cont…
• Extraction
Actual resistance and capacitance figures modelled
for interconnections are extracted to simulate timing
performance
• Post Layout Simulation
Functionality taking care of timings
Time extraction imported
Both gate and interconnection delays are considered
• Back Annotation
To update the initial circuit data with information
that was obtained later in the design cycle
Passing the information related to the extra load that
may occur in practice
33. Why the processors are faster??
• A question from computer architecture…..
• https://slideplayer.com/slide/7567250/
34. ASIC Design Styles
• Full Custom IC Design
• Sea-of-Gates (Mask Programmable)
• Gate Arrays (Mask Programmable)
• Embedded Gate Arrays (Mask Programmable)
• Standard Cell Based IC Design
• PLD (PAL-PLA-CPLD)
• FPGA
• Platform/Structured ASIC
• Software Programmable Devices
• Commercial Off-the-Cell (COTS) Devices
35. Full Custom ASIC Design
• The Design flow ( we already learnt!)
Full-custom ICs are the most expensive
to manufacture and to design
Manufacturing lead time (not including design time!) is
typically 8 weeks
• When does it make sense?
there are no suitable existing cell libraries available
existing logic cells are not fast enough
logic cells are not small enough
logic cells consume too much power
ASIC is so specialized that some circuits must be
custom designed
• Trends: fewer and fewer full-custom ICs are being
designed (excluding mixed analog/digital ASICs)
36. Mask Programmable Gate Arrays
• Mapping of designs on to the gates in the array
• Gates are designed, characterized and
prefabricated
• Customized placement and interconnect
• Fabrication of only top-most interconnects
• Lead time is few days to two weeks
• Channelless Gate Array
• Channelled Gate Array
• Structured Gate Array
38. SoG
• Channelless gate array (sea-of-gates or SOG)
there are no predefined areas set aside
for routing between cells
we customize the contact layer that
defines the connections between metal1 and transistors
when use area of transistor for routing,
do not make any contacts to the device underneath
• Characteristics
only some (the top few) mask layers
are customized – the interconnect
manufacturing lead time is
between 2 days and 2 weeks
40. Channelled Gate Arrays….
• Channelled gate array
we leave space between the rows of transistors
for wiring
• Characteristics
only interconnect is customized
the interconnect uses predefined spaces
between rows
manufacturing lead time is between 2 days
and 2 weeks
42. Embedded Gate Array
combines features of CBIC and MGA
motivation: MGA has only fixed gate-array base cell;
difficult and inefficient implementation of memory
we set aside some IC area and dedicate it to a specific
function
(contain different cells, more suitable for building memory
cells, for example, or complete block, such as a
microcontroller)
• Characteristics
only some (the top few) mask layers
are customized – the interconnect
custom blocks can be embedded
manufacturing lead time is
between 2 days and 2 weeks
problem: embedded function is fixed
44. Standard Cell Based Design
• Cell-Based ASIC (CBIC) uses predesigned cells
(AND, OR gates, multiplexers, flip-flops, ...)
• Standard-cell areas are built of rows of standard
cells
• Standard-cell areas can be used in combination
with larger predesigned cells (microcontrollers, or
even microprocessors), known as megacells
48. Platform ASICs
• A pre-manufactured device, used to implement a
custom system on a chip (SoC)
• consists of a group of slices offering different gate
ranges, memory, I/O, PLLs and other intellectual
property such as high speed
Serializer/Deserializers (SerDes)
• A slice may be customized through few layers of
metal for a user application.
• Since only a few layers of metal are customized
for any given design, NRE costs are significantly
lower than a cell-based ASIC where a full mask
set is needed.
51. Programmable Logic Devices
• PLDs
standard ICs, available in standard configurations
sold in high volume to many different customers
PLDs may be configured or programmed to create
a part customized to specific application
• Characteristics
no customized mask layers or logic cells
fast design turnaround
a single large block of programmable interconnect
a matrix of logic macrocells that usually consists of
programmable array logic followed by a flip-flop or latch
52. PLDs…..
• Types of PLDs
PROM: uses metal fuse that can be blown permanently)
EPROM: used programmable MOS transistors whose
characteristics are altering by applying a high voltage
PAL – Programmable Array Logic
programmable AND logic array or AND plane,
and fixed OR plane
PLA – Programmable Logic Array
programmable AND plane
followed by programmable OR plane
CPLD
FPGA
• Depending on how the PLD is programmed
erasable PLD (EPLD)
mask-programmed PLD