Low Power Communication Circuits for WSN

Transcription

1 Low Power Communication Circuits for WSN Nate Pletcher, Prof. Jan Rabaey, (B. Otis, Y.H. Chee, S. Gambini, D. Guermandi) Berkeley Wireless Research Center

2 Towards A Micropower Integrated Node power management RF/antenna digital processing, baseband sensors power supply Strategies: Focus on global power consumption Maximize level of integration Aggressive use of new technologies (RF-MEMS, scaled CMOS, etc)

3 Taking Advantage of CMOS Scaling Greatest transconductance efficiency in subthreshold, but sacrifice f t 90nm: f t > 100GHz (!) Utilize deeply scaled CMOS with plenty of f t

4 RF MEMS: A new opportunity electrodes Si air AlN Agilent FBAR resonator used in Tx filters and duplexers (Ruby, et al. ISSCC 2001) Film Bulk Acoustic wave Resonator (FBAR) with AlN piezoelectric layer: High frequency resonance (~GHz) High quality factor 100µm Benefits: Small form factor Passive RF frequency reference (replace xtal) Enables simplified transmit and receive architecture B. Otis

5 MEMS-based Transceiver 1mm No External Components (inductors, crystals, capacitors) 0.13µm CMOS 2mm Full digital SPI control of analog/rf blocks Presented at ISSCC 2005 B. Otis, Y.H. Chee

6 Combination of submicron CMOS and micromechanical resonators yields compelling performance and 1mm 3 transceiver form factor B. Otis, Y.H. Chee Transceiver Performance Technology 0.13µm CMOS Die area (1x2)mm 2 P rx P tx (OOK) 380µA (1V) 1.05mW P out,tx 480µW Data rate 10kbps 500µm Future stringent requirements on wireless sensor cost and size require thin-film fabrication of all components

7 Injection-Locked Transmitter Problem Low Transmitter Efficiency Radiated power < 1mW in wireless sensor networks Power consumption of the pre-pa stages are significant, resulting in low transmitter efficiency Solution Injection Locked Transmitter Use a power oscillator instead of a power amplifier Self-drive reduces driver power Reference oscillator locks the power oscillator to an accurate carrier frequency Y. H. Chee

8 Spectrum Measurements Unlocked output spectrum Locked output spectrum 20µs RF Output Baseband Data 1.9GHz center frequency 0dBm output power at 32% global efficiency 50kpbs datarate Presented at CICC 2005 On-off keying signal at 50 kbps Y. H. Chee

9 100µW Digitally Tuned Oscillator 0.13µm CMOS, (2x2)mm 2 area Bondwire oscillator performance summary Supply voltage Power consumption Nominal frequency Tuning Range Resolution Phase 1MHz offset 0.5V 100µW 1.9GHz 8%(150MHz) ~200kHz (10 bits eff.) -115dBc/Hz Presented at ESSCIRC 2005 N. Pletcher

10 Micropower Mixed-Signal Successive Approximation ADC, 90nm CMOS Preliminary results: V dd = 0.5V Resolves 6bits@1.5MS/s Power dissipation ~ 10µW 8µW digital, 2µW analog Simulated: 4µW,1MS/S (Measurement in progress) S. Gambini

11 Alternative: Σ ADC V dd =.65 Pd~20µW@100KS/S DR=75dB 3 rd Order SPECTRE-Data 6400 Points Vin=50mV SQNDR=82dB X: 1.5e+004 Y: Scalable power/speed (5 tuning bits) Single Stage Gm-Ro OTA Tapeout: May 1st Power Spectral Density S. Gambini Frequency(Hz)

12 Short(er) Range Wireless New concept of wireless sensor network Dense network with hundreds of nodes Distance between nodes 5 cm Node size < 1x1 cm 2 Bit rate 20 kbps Inductor-based communication On-board inductors to maximize coupling Coupling factor k 1e-4 1e-5 8.1mm D. Guermandi

13 Pulse-Based Communication Information transmitted over short pulses The receiver can be duty-cycled to reduce power consumption as a function of the BR Local time base required on the receiver D. Guermandi

14 Goals Moving Forward Continue pushing the state-of-the-art in low power circuits Reducing circuit power helps to enable energy scavenging Take advantage of characteristics specific to WSN applications Explore alternatives to radiative communication for short distances