Nanowatt wake-up receiver for ultra-low power RF devices

Start date July 2012

Client University College Cork
Investigator

Dr David Nugent
david.nugent@elucidare.co.uk

Abstract

Researchers at University College Cork have developed a nanowatt wake-up receiver (WUR) for use in ultra low power devices such as implanted medical devices. Consuming barely a fifth of established WUR solutions, the UCC technology will improve the battery lifetime of associated microprocessors whilst enabling perpetual sensing applications through energy harvesting. A patent has been filed and UCC is seeking exploitation partners such as wireless transceiver and medical implant vendors.

Technology

The receiver architecture is based on an envelope detector, used for the OOK demodulation. A
charge pump (two-stage voltage doubler-multiplier) is used as an OOK signal envelope detector, and the demodulated signal fed to a data slicer, which raises the demodulated digital signal to voltage levels that can be used by later digital circuitry. The comparator threshold is adaptive, rather than constant, and is determined by the wake-up signal strength. This digital signal is then classified using passive circuitry to detect the “intended” wake up signal and to reject random toggling due to noise or nearby wireless communications. Classification is done by detecting the wake-up preamble if it is generated at the expected OOK data rate range.

The next part of the circuit is a Pulse-Width Modulation (PWM) decoder and SPI adapter. This part of the circuit first decodes the PWM encoded signal and generates SPI compatible signals for data transfer to the processor. The architecture is power efficient since most components constituting it are passive. The only active components are the data slicer (comparator) and the SPI adapter. Due to the simplicity of this circuit, the power consumption is kept very low.

The basic functionality is achieved by using an envelope detector as a simple and low power wireless receiver, and building simple active circuitry around it to raise the voltage levels, reject false wake up signals, and make the output SPI compatible.

Specifications

Power consumption: Operating at 434 MHz the measured power consumption is only 270nW. This is barely 20 percent of specialist ULP devices such as the Zarlink ZL70102 (2.45 GHz) and Texas Instruments CC1100E (868 MHz), and over 100 times less than consumer standards such as Bluetooth and Zigbee. An ASIC implementation will further reduce parasitic capacitances and thereby power consumption.

Availability: The UCC receiver operates in an always-on state. This is unlike contemporary schemes where the WUR itself is woken periodically by a separate strobe pulse. As tabulated below, these strobe pulses consume more current than the WUR itself, representing a major source of power consumption in implanted devices. An additional issue with strobing is that the frequency of the low-power RC oscillator used for the WOR functionality varies with temperature and supply voltage. To keep the frequency as accurate as possible, the RC circuit is calibrated periodically by the crystal oscillator. By comparison, the UCC technology operates in an always-on state, thereby eliminating the costs and current drain of the strobe pulses.

Frequency: The operating frequency is easily changed by a few discrete components. UCC researchers have tested from 27 MHz up to 2.45 GHz. Unlike conventional techniques employed in implanted medical devices, where a dedicated 2.45 GHz antenna is required for the wake-up circuit, the UCC implementation can share the RF data link antenna thereby cutting costs and space requirements.

Modulation scheme: On-off-key (OOK) modulation is employed since it avoids the need for a local oscillator and synthesizer in the receiver.

Coding scheme: The UCC design can support a variety of coding schemes including Manchester, Pulse Internal Encoding, and Pulse Width Modulation. PWM is preferred in order to have very low power clock/data extraction and conversion to an SPI compatible interface.

 

Vendor
Zarlink
Zarlink
TI
UCC
Device
ZL0101
ZL70102
CC1100E
Lab demo
Data released
Nov-2006
Jun-2010
Apr-2009
Sep-2011
Test mode
Measured
Specified
Specified
Measured
WUR frequency
2.45 GHz
2.45 GHz
868 MHz
434MHz
Modulation scheme
OOK
OOK
Not specified
OOK
Coding scheme
Manchester
Not specified
Not specified
Pulse width modulation
 
Wake-up pulse duration
240us
240us
Not specified
Always on
Strobe frequency
1.15 secs
Not specified
Not specified
Always on
Idle current drain
10nA
Not specified
Not specified
Always on
Active WUR current
715uA
Not specified
Not specified
Always on
Average WUR current
159nA
290nA
300nA
135nA
Strobe current
<400nA
<400nA
400nA
Always on
Total current
559nA
690nA
700nA
135nA
Min operating voltage
2.0V
2.0V
1.8V
2.0V
Power consumption
1,118nW
1,380nW
1,260nW
270nW
 
Data source

 

 

 

 

 

 

 

Documents available for download

Access to the following documents may require subscription to the relevant publication.

 

Marinkovic, S.J.; Popovici, E.M., "Ultra Low Power Signal Oriented Approach for Wireless Health Monitoring", Sensors 2012, 12(6), 7917-7937
Marinkovic, S.J.; Popovici, E.M., "Power efficient networking using a novel wake-up radio," Pervasive Computing Technologies for Healthcare (PervasiveHealth), 2011 5th International Conference on , vol., no., pp.139-143, 23-26 May 2011
Marinkovic, S.J.; Popovici, E.M.; , "Nano-Power Wireless Wake-Up Receiver With Serial Peripheral Interface," Selected Areas in Communications, IEEE Journal on , vol.29, no.8, pp.1641-1647, September 2011
Marinkovic, S.J.; Popovici, E.M.; Spagnol, C.; Faul, S.; Marnane, W.P.; , "Energy-Efficient Low Duty Cycle MAC Protocol for Wireless Body Area Networks," Information Technology in Biomedicine, IEEE Transactions on , vol.13, no.6, pp.915-925, Nov. 2009
"Low Power Wake-Up System and Method for Wireless Body Area Networks", WIPO Patent Application WO/2012/010676