Asynchronous logic application in a power management unit for ultra low power wireless sensor nodes

Asynchronous subthreshold CMOS event detector for wireless BAN sensor nodes

“…1, the system is designed to operate in four possible power states. Herein, the control of the power-state transitions is distributed over several state-machines consisting of clock less and clocked circuits communicating by means of handshakes and synchronous signalling [2]. As addi tionally shown in Fig.…”

“…The AFSM in the PMU belongs to the class of the asynchronous speed-independent circuits [3]. The primary reason to choose the asynchronous circuits to control the described PMU-operation is the lack of any clock-signal which in that case would lead to an increased energy dissipation caused by a permanently active bandgap circuit during the inactive phase of the circuit [2]. The realized event detector circuit model reflects the communication handshake protocol established between the circuit envi ronment and the event detector itself [2].…”

“…The primary reason to choose the asynchronous circuits to control the described PMU-operation is the lack of any clock-signal which in that case would lead to an increased energy dissipation caused by a permanently active bandgap circuit during the inactive phase of the circuit [2]. The realized event detector circuit model reflects the communication handshake protocol established between the circuit envi ronment and the event detector itself [2]. Furthermore, the circuit performs an automatic initialization based on assumptions on the slow environment during powering-up the circuit and on faster environment during activationphase of the handshake communication when operating the circuit after the described initialization-phase.…”

“…Many of these devices need the most of the available energy in standby mode. The work presented in [1] shows a state of the art wireless sensor node which includes an event detector, presented in [2], as part of the PMU. Amongst other scenarios, a target application of such sensor nodes lies in body area networks (BAN) characterized by low duty cycles per day and long standbytimes with lifetimes of the system approaching one year or more, when supplied by a battery.…”

“…Therefore, the leakage energy dissipated in the power-down mode of the system dominates the overall energy consumption. As described in [2] and [1], the PMU is based on an asynchronous wake-up event detector in order to reduce the leakage energy of the system. In spite of energy efficient design of the conventional system, the implementation by subthreshold logic cells significantly increases the lifetime of the system.…”