Micropower Generation

1
Realisation of Autonomous Micropower Artefacts
Imperial College
2
Physical Implementation of Artefact Functionality

• Artefact size and power consumption are related
  to
• functionality (data processing requirements)
• communication (one or two way, data rate)
• reconfigurability
• performance specifications

implanted
wearable
mobile
fixed
fixed server
3
Artefact Interconnections

• BlueTooth 2.4GHz
• 100m (up to 1000m), 1 Mb/s,
• 100mW average in 1s sniff mode
• Unlicensed Band 315/413 MHz
• AM
• 100m, typ. 4kHz bandwidth
• 8 mW TX, 1.5mW RX
• FM
• 250m, 9.6kHz bandwidth
• 24mW TX, 25mW RX
• Low Power BlueTooth
• 10m range, 500 MHz carrier, low bit rate
• Possible to achieve 1mW
• Ultra-low Power Wireless Link
• Could we achieve operation at 0.1 mW or less ?

implanted
wearable
mobile
fixed
fixed server
4
Ultra-Low Power Wireless Link

• Consider specifications for low-power link, e.g
  433MHz carrier, 20 kb/s data rate, simple FSK
  modulation scheme, allows us to derive the
  following graph

NF of 20dB allows us to transmit 100m (10-20m
indoors) with just -12.5dBm of power, i.e. less
than 0.06mW!
Transmit Power versus Receiver Noise Figure
5
Circuit Implementation of Micropower Functionality

• If artefacts (level 1 and 2) are to be
  self-powered, ultra-low power consumption is
  necessary. This implies
• low voltage, low current operation
• intelligent power saving operation
• low-power wireless link to higher level artefacts
• Submicron CMOS is the most appropriate process
  technology to meet these goals.

6
Analog versus Digital Processing

• Analog is more efficient than digital in terms of
  both area and power consumption if the required
  output signal to noise ratio (SNR) is around 60
  dB or less.
• This level of accuracy is adequate for most
  sensor applications

7
An Example Micropower Filters...
Power consumption 200nW/pole Tuning range
100Hz-10kHz Dynamic Range 60dBs
...A state-of-the-art example of sub-threshold
MOSFET design
8
Micropower GenerationEnergy sources and
conversion mechanisms
Energy source
Conversion to electricity
Kinetic
e.g. body movement
Magnetic (induction) Piezoelectric Electrostatic
Thermal
e.g. DT between body and surroundings
Thermoelectric (TC) Thermo-electro-mech
Electro- magnetic
Low freq (lt MHz) RF (MHz to GHz) Optical
(IR/visible)
Induction loop Antenna Photodetector
Ultrasonic
Piezoelectric
9
Micropower GenerationRecent Examples
1. Kinetic / piezo (Glynne-Jones et al,
Univ. Southampton)
3. Thermal / thermoelectric (Strasser et al,
Munich Univ. Technol. Infineon)

• Resonant, with fo 100 Hz
• cm-scale
• Pout 3 mW

2. Kinetic / magnetic (Ching et al,
Chinese Univ. Hong Kong)

• BiCMOS no moving parts
• 6 x 6 mm2 area
• Pout lt 0.1 mW

• fo 60 - 100 Hz
• 1 cm3 vol
• Pout 700 mW

10
Micropower GenerationElectrostatic Generator

• Resonant devices have scaling problem
• Pout ? Mw3z2 ? low-frequency devices with
  small displacement are inadequate
• IC Approach Non-linear devices can do better,
  e.g.
• Mass moves only when applied acceleration
  exceeds electrostatic closure force
• Parametric Oscillating Generator

11
Electrostatic Parametric Oscillating
GeneratorPreliminary Design

• Preliminary calculations indicate energy per
  cycle of 1 mJ for micromachined device
• (with a 7 x 7 x 1 mm Au mass)

12
Micropower GenerationMajor Issues

• Any small (lt 1 cm3) kinetic generator is likely
  to be limited to mW average power levels

? low duty-cycle operation only

• Much higher power levels possible if we can
  include infrastructure for (wireless)

power delivery

• Trade-off between power budgets for
  communications and feature extraction in

type 12 artefacts needs careful consideration
Power budget
comms
Incr. Feature extraction
13
Task 3.5 Implementation of Artefact Functionality

• Investigate trade-offs in the hardware
  implementation of wireless micropower artefacts
  (levels 1 and 2)
• Wireless communication strategy (trade-offs is
  power consumption vs. data rate, transmission
  range etc).
• Hardware partitioning between analog and digital.
• Micropower transistor-level circuit
  implementations of artefact functionality.

14
Task 3.6 Micropower Supply/Generation

• Identification of most appropriate micropower
  solutions for chosen scenarios

will depend on
Sensor and processor requirements when
active Duty cycles for measurement and data
transmission Communication range and
bandwidth Size limitations Environment
... need to consider specific cases

• Detailed design of selected micropower generators