Wake-up receiver uses 51 µW

Imec and the Holst Centre have developed an ultra-low-power 2.4 GHz/915 MHz receiver with good sensitivity. The receiver runs on a record low power consumption of 51 µW when on continuously. It occupies 0.36 mm² in 90 nm CMOS, and for 10 Kbps on-off keying reception it achieves -69 dBm and -80 dBm sensitivity at 2.4 GHz and 915 MHz.

The receiver can be used in one of two ways: as a wake-up receiver, or as an ultra-low-power component in a very asymmetric radio link.

When used as a wake-up receiver, it monitors the communication channel and wakes up the main receiver when it is needed. Today’s battery-operated wireless communication systems - such as Wi-Fi or Bluetooth - consume a lot of power, even at times when there is no data transmitted or received.

A first step to reduce the power budget of these radios is through duty cycling - activating the radio at regular intervals and deactivating it in between.

But this is a minor role. The radio will still be active when there is no data to receive or transmit. Adding a wake-up receiver such as this, allows keeping the main receiver inactive when it is not needed.

A second use is as an ultra-low-power receiver in an asymmetric radio link, where one side is a highly sensitive transceiver and the other side an ultra-low-power node. An example of use is in smart buildings, where construction elements could be tagged with cheap, low-power wireless sensors driven by energy harvesters.

Other uses are in long-range radio-frequency identification (RFID), wireless sensor nodes for logistics, smart buildings, motor vehicles, health care etc. In this scenario, the ultra-low-power receiver can be further duty cycled, bringing its power budget down to a level that can be handled with energy harvesters.

For truly autonomous sensor nodes, using energy scavenging, there is only around 50 µW power available for a receiver. Receivers with such low-power budgets, normally make use of an envelope detector. However, such a detector will attenuate low-level input signal and add excessive noise, making the wake-up receiver less sensitive.

Imec and Holst’s work has focused on achieving an improved sensitivity using an envelope detector. A first technique is to amplify the signal before the detector, improving the signal-to-noise ratio.

Next, a double sampling technique is applied to the downconverting envelope detector to suppress the offset and IF noise. This not only improves the sensitivity, but also flattens the output noise floor of the receiver.

By reducing the data rate and narrowing down the output bandwidth, the receiver sensitivity is improved. This is a major advantage for the wake-up receiver, since it doesn’t require a high data rate.

The new receiver chip was implemented in a 90 nm digital CMOS technology and occupies an area of 0.36 mm². Measurements on Si show a sensitivity of -75 dBm (SNR>12 dB) for the 915 MHz receiver at 100 kbps OOK modulation.

When scaling the data rate to 10 Kbps and filtering the out-of-band noise, the sensitivity is improved by 5 dB. For the 2.4 GHz receiver, the sensitivity is 64 dBm and -69 dBm for 100 Kbps and 10 Kbps data rate.

For more information contact: program manager Guido Dolmans guido.dolmans@imec-nl.nl; or business development manager Olivier Rousseaux, olivier.rousseaux@imec-nl.nl.