Paper presentation Ultra-Portable Devices Paper: Xiaoyu Zhang, et - PowerPoint PPT Presentation

Paper presentation – Ultra-Portable Devices Paper: Xiaoyu Zhang, et al. An Energy-Efficient ASIC for Wireless Body Sensor Networks in Medical Applications IEEE transactions on biomedical circuits and systems, vol 4, no. 1, pp. 11-18, Feb. 2010. Presented by: Reza Meraji 2010-05-31 Paper Presentation - Ultra Portable Devices 1

Outline • Introduction of wireless body sensor network (WBSN) • Work on demand solution for power efficiency – Sensing and stimulating nodes – Work and standby modes – Introducing a secondary channel – Active and passive standby nodes • ASIC architecture • Circuit implementation • Measurement results • Summary 2010-05-31 Paper Presentation - Ultra Portable Devices 2

System diagram of typical WBSN applications 2010-05-31 Paper Presentation - Ultra Portable Devices 3

Typical WBSN slave sensor nodes • Sensing node: – Biomedical information acquisition, signal processing, data storage, wireless transmission (sometimes direct transmission without any processing) – Functions of sensing node are usually periodically performed • Stimulating node: – Medical treatment, drug delivery, nerve stimulating, etc. – Functions of stimulating node can be either periodical or event driven 2010-05-31 Paper Presentation - Ultra Portable Devices 4

Proposed standby modes for WBSN • Active standby mode (for sensing and stimulating nodes) : – Only an ultra low power (ULP) timer with a low-frequency clock generator are active – It periodically powers up the sensor node • Passive standby mode (for the stimulating nodes) : – The whole sensor node is power silent – A secondary passive RF circuit works as the supervisor circuit – The passive RF receiver can harvest energy from the RF signals transmitted by the master node – The passive standby node consumes zero power ideally 2010-05-31 Paper Presentation - Ultra Portable Devices 5

Typical scenario of WBSN operation • 1) The sensing nodes wake up and sense the biomedical signals periodically. • 2) Once the sensing nodes detect any abnormality, an emergency event is reported to the master node immediately. • 3) The master node makes the decision accordingly, and wakes up the corresponding stimulating node if needed • 4) The stimulating node performs medical treatment as demanded by the master node. 2010-05-31 Paper Presentation - Ultra Portable Devices 6

(a) States (b) work state (c) MCU power of slave nodes 2010-05-31 Paper Presentation - Ultra Portable Devices 7

Work and standby: energy efficiency • Periodical toggling between work and standby modes: – Suitable approach for the sensing nodes since these nodes should sense/process/transmit data periodically – Not energy efficient for the event-driven stimulating nodes Low duty cycle: minimizing energy, maximizing response delay or missing the stimulating requests High duty cycle: maximizing energy, minimizing response delay 2010-05-31 Paper Presentation - Ultra Portable Devices 8

Work-on-demand solution with a secondary channel • Primary channel: – Bidirectional communication channel to exchange information • Secondary channel: – Communication channel is one-way – Master node has a transmitter and slave nodes only have a passive receiver for this channel 2010-05-31 Paper Presentation - Ultra Portable Devices 9

Features of the secondary channel • 1) the passive receiver in the slave node does not consume any current from its own battery; instead, the receiver has an energy harvesting block to convert the received RF signals to a dc power supply. • 2) the passive receiver in the slave nodes is always ready to receive any emergency commands from the master node • 3) the transmitter in the master node transmits not only useful information but also energy to the slave nodes. 2010-05-31 Paper Presentation - Ultra Portable Devices 10

Differences between primary and secondary channels 2010-05-31 Paper Presentation - Ultra Portable Devices 11

Typical scenario of WBSN: sensing and stimulating nodes 2010-05-31 Paper Presentation - Ultra Portable Devices 12

Function blocks of a slave sensor node 2010-05-31 Paper Presentation - Ultra Portable Devices 13

Control flow of slave nodes 2010-05-31 Paper Presentation - Ultra Portable Devices 14

Power management • Sensor node ASIC is powered by a 3-V battery power supply • Two linear regolators are integrated to convert 3-V power supply into the other voltage levels • Digital core is powered by a 1.8-V supply generated by the regolator • Analog blocks are powered by a 2.5-V supply from the other regolator 2010-05-31 Paper Presentation - Ultra Portable Devices 15

Power modes in standby state 2010-05-31 Paper Presentation - Ultra Portable Devices 16

Circuit implementation: A. Digital core functional blocks 2010-05-31 Paper Presentation - Ultra Portable Devices 17

Circuit implementation: B. Power management unit, Schematic of the LDO M1-M8: error amplifier M9-M12: unit gain buffer R1, R2: feedback network 2010-05-31 Paper Presentation - Ultra Portable Devices 18

Circuit implementation: C. Block diagram of the passive RF receiver 2010-05-31 Paper Presentation - Ultra Portable Devices 19

Passive RF schematic: (a) Energy recovery for the dc supply and (b) clock data recovery (CDR) 2010-05-31 Paper Presentation - Ultra Portable Devices 20

Circuit implementation: D. Low power clock generation: (a) 24-MHz clock generation Used for the digital core Capacitor C0 and C1 are charged and discharghed by turns By merging VC0 and VC1 a saw-tooth wave is generated at node N0 and compared with a reference voltage A second comparator U1 Resets the oscillator if the Frequency is too high Simulated power consumption: 625 µW in 0.18 µ CMOS 2010-05-31 Paper Presentation - Ultra Portable Devices 21

Circuit implementation: D. Low power clock generation: (b) 20-kHz clock generation Used for th ULP timer to tune the osc. freq. Simulated power consumption: 4 µW in 0.18 µ CMOS 2010-05-31 Paper Presentation - Ultra Portable Devices 22

ASIC on the testing board and die photo 0.18µm standard CMOS technology Die area: 2.0mm x 1.5 mm 2010-05-31 Paper Presentation - Ultra Portable Devices 23

WBSN prototype setup 2010-05-31 Paper Presentation - Ultra Portable Devices 24

Waveforms of the WBSN sensor node: (a) 500 ms/div. (b) 250 µs/div. 2010-05-31 Paper Presentation - Ultra Portable Devices 25

Passive RF receiver performance 2010-05-31 Paper Presentation - Ultra Portable Devices 26

SENSOR NODE POWER WITH THE ASIC, UNDER DIFFERENT STATES AND MODES 2010-05-31 Paper Presentation - Ultra Portable Devices 27

Summary • The standby power issue and the response latency in the WBSN have been inspected in this work • an energy-efficient protocol with work-on-demand has been proposed for WBSN • Compared to the conventional structure, the proposed WBSN slave sensor node has a passive secondary wireless receiver 2010-05-31 Paper Presentation - Ultra Portable Devices 28