Low Power Communication Circuits for WSN Nate Pletcher, Prof. Jan Rabaey, (B. Otis, Y.H. Chee, S. Gambini, D. Guermandi) Berkeley Wireless Research Center
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)
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
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
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
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
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
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
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 noise @ 1MHz offset 0.5V 100µW 1.9GHz 8%(150MHz) ~200kHz (10 bits eff.) -115dBc/Hz Presented at ESSCIRC 2005 N. Pletcher
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
Alternative: Σ ADC V dd =.65 Pd~20µW@100KS/S DR=75dB 3 rd Order -20-40 SPECTRE-Data 6400 Points Vin=50mV SQNDR=82dB X: 1.5e+004 Y: -32.96 Scalable power/speed (5 tuning bits) Single Stage Gm-Ro OTA Tapeout: May 1st Power Spectral Density -60-80 -100-120 -140 S. Gambini -160 10 3 10 4 10 5 10 6 10 7 Frequency(Hz)
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
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
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