Field Programmable Gate Array with Integrated Microstructures

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Field Programmable Gate Array with Integrated
Microstructures

• Jason F. Cantin and Fred R. Beyette Jr.
• Photonic Systems Development Laboratory
• University of Cincinnati
• 10/31/2000

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Micro-Electro-Mechanical Systems (MEMS)

• The equipment used to make integrated circuits
  can also be used to make other things
• Various types of sensors
• Tiny emitters and Lasers
• Mechanical devices (micro-machines)
• Even chemical devices!
• We need not restrict ourselves to electricity

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MEMS are very useful when combined with circuits

• For example, optoelectronics
• Enhance the performance of optics with integrated
  control
• Improve I/O bandwidth and latency between
  electronic systems

Optics
Logic
Memory
Pads
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Lots of stuff can be fabricated with logic on a
silicon chip

• Optical detectors and temperature sensors made
  from reverse-biased diodes
• Optical emitters made from suspended polysilicon
  filaments (micro-heaters)
• Pressure sensors and strain-guages leveraged from
  parallel-plate capacitors
• And many more

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Some Applications

• Highly-integrated data acquisition systems
• Light-weight and low-power
• Space exploration
• Image processing systems
• Single-chip cameras
• Components for Optical Memories
• Prosthesis
• Artificial retinas have been successfully
  demonstrated in human patients

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Problem Motivation

• Wed like to do research with multi-technology
  designs, but
• Chips are hard to develop
• Expensive ()
• Long lead time
• CAD tools are unavailable or too expensive
• Typically the experimental optics are placed on a
  separate chip

Wires
Logic
Optics
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Digital designs can be prototyped using Field
Programmable Gate Arrays

• Uncommitted logic that is programmable
• A string of bits is loaded onto the chip to
  configure it
• Software defined hardware
• Dense enough to implement entire digital systems
• Processors, I/O controllers, etc.

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Designing with FPGAs

• Fast and cheap because the FPGA does the job of a
  custom chip
• Designs are specified in a high-level language,
  and a compiler generates low-level configuration
  data
• FPGAs are available in all shapes, sizes, and
  colors

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Simple FPGA
I/O Blocks
Routing channel (Wires that can be Connected to
blocks)
Logic Block (Function can be defined by user)
Die
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Our Idea
I/O Blocks
Routing channel
Same structure with sensors and emitters inserted
Logic Block
Reconfigurable Sensor
Reconfigurable Emitter
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Our first chip
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Our first chip
Logic Block
2.2 mm
Detector
Sensor Block
Wires
Clock Driver
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Crowbar

• Full-custom design
• 5,000 CMOS transistors
• 2 metal layers, 1 poly
• 1.5-micron channel lengths
• 8 logic-blocks
• Look-up tables for logic functions
• 4 sensor-blocks
• Each with a photodiode

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Crowbar Logic-Block Characteristics

• 32 Possible 3-input logic functions
• Inputs selected from the 4 nearest neighbors, and
  past outputs
• One flip-flop with reset
• Maximum Delay of 19.3nS

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Crowbar Logic-Block Structure
INPUTS (NS, NEWS, NEWS)
Configuration in
3-input lookup table
Scan chain in
FF
User Reset
Scan chain out
OUTPUT
Configuration Out
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Crowbar Logic-Block Layout
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Crowbar Logic-Block Layout
Look-up table
Multiplexers
Flip-Flop
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Crowbar Sensor-Block Characteristics

• N-well photodiode
• Receiver circuit with 8 selectable thresholds
• One flip-flop with reset
• Detector and Receiver
• 1Mhz maximum frequency

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Photodiode
Photons

• PN Junction between well and substrate
• Illumination creates electron-hole pairs in
  semiconductor
• In the depletion region, this enhances the drift
  current

5 volts
I-photo
P
N
N-type well
P-type Silicon Substrate
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Optical Receiver Schematic
VDD
IN0
IN1
IN2
I_OPT
VREF
IREF
VDD
Programmable Voltage Reference
Photodiode Amplifier
Comparator
Light goes here
OUT_H
OUT_L
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Crowbar Sensor-Block Structure
Configuration in
Config. Optical
Receiver Detector
(3 bits ? 8 possible thresholds)
Scan chain in
N, E, W, S, Clocks
FF
User Reset
Scan chain out
OUTPUT
Configuration Out
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Crowbar Sensor-Block Layout
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Crowbar Sensor-Block Layout
Receiver
Photodiode
Flip-flop
Multiplexer
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Added Bonus

• The Crowbar chip can be programmed optically
• Entire pages of configuration data received at
  once

Spatial Light Modulator
Configuration Data
Crowbar chip
Board
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Project Status

• Began 2/25/2000
• Prototype design sent to MOSIS on 5/30/2000
• First-silicon received on a 8/30/2000
• High-level language and compiler under
  development
• In my copious spare time

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Future Work

• Larger implementation in advanced manufacturing
  process
• Incorporating other types of sensors and emitters
  (not just optical)
• VHDL Support

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Thanks. ?