Microwatt integrated radio transceiver circuits for aggressively duty-cycled wireless networks

Low-power mobile smart devices may gain energy autonomy by deploying energy harvesters, such as photovoltaic cells, in place of environmentally hazardous and costly batteries. However, compact energy harvesters may generate only microwatts of power in scarce environments. The same microwatt power budget is encountered if the operation time target of a smart device relying on a coin battery is extended up to more than 10 years. This dissertation demonstrates microwatt integrated radio transceiver circuits that meet the above power budget. The presented circuits utilize the same simple principal power-saving strategy: they rely on aggressive duty-cycling, that is, they remain active only for short periods of time. First, this dissertation presents a microwatt impulse radio transmitter front-end (TFE) for local-area networks with a range in the order of tens of meters. Secondly, this dissertation presents a temperature compensation method and an in-field calibration procedure for microwatt NB-IoT modems. Low-power wide-area networks, such as NB-IoT, have a range in the order of several kilometers. The impulse radio TFE is fabricated in a 65-nm CMOS process. The TFE is measured to produce 1.8-pJ pulses at a 7.5-GHz carrier frequency while consuming 69 pJ per pulse and while draining 380 nW of quiescent power. Consequently, the TFE consumes 3.8 µW at a pulse repetition rate of 50 kHz, corresponding to a data rate of 100 kbit/s presuming on-off keying modulation. The TFE can be powered by low-drive linear regulators, which, however, have to provide an accurate supply voltage level. The temperature compensation method deploys the existing phase-locked loop of an NB-IoT modem, therefore requiring little extra hardware resources. The performance of this kind of a temperature-compensated phase-locked loop (TCPLL) is evaluated through a discrete prototype. The TCPLL prototype achieves a 50-ppb (3σ) accuracy from a ±50000-ppb crystal reference when calibrated using the in-field calibration procedure. The achieved accuracy level is sufficient for ensuring swift network acquisition and a small number of data transmission repetitions even under low network coverage, which can allow energy savings of more than 40 %. The compensation logic of the TCPLL prototype is simulated to consume 290 nW of power in a 65-nm CMOS process.