Zero Power Standby Now Possible for IoT Sensors
The new UB20M voltage detector IC developed by the Electrical Energy Management Group of the University of Bristol enables zero-power sensing and listening. It allows circuit designers to eliminate standby power, to develop circuits that perform continuous monitoring without using battery power, and to implement wireless wake-up with zero receive power. The device is a sensor-driven circuit that requires no power supply, instead it uses power from a sensor signal to wake up. Suitable sensors are wireless antennas, infrared diodes, piezoelectric accelerometers, and other voltage-generating sensors.
The UB20M has a threshold of 0.6V and draws sub-10pA. The UB20L switches at 0.46V, but draws up to 100pA. The university can provide samples and datasheets and an evaluation board.
â€œThe ultra-low power UB20M voltage detector provides sensing that is continuous and free. This is because it is able to respond to minute quantities of power from unpowered sensors. No battery or other power is needed for the device to stay alive and listening, and battery maintenance is therefore reduced or not needed. We are now actively seeking commercial partners to use the voltage detector chip in their product, and would welcome companies to get in touch.â€ said Dr. Bernard Stark.
According to Dr. Stark, there are a number of areas, where it would be beneficial to reduce the listening power to zero, including: Mains-powered equipment, where savings for consumers and the environment are made; Battery-driven sensors and monitoring systems, where the long-term reliability and battery life are increased, and size decreased; Remotely-powered sensors, as these can be made smaller, by reducing battery capacity. It also reduces the power needed to remotely control these devices; The sensitivity of the voltage detector chip also allows the elimination of mechanical switches; It can also be used to generate sensing data only when useful data is available, which saves processing power.
The UB20M detector is patent pending (UK Patent Application No. 1607304.1). It was developed in the SPHERE IRC (Sensor Platform for HEalthcare in a Residential Environment) and funded by the Engineering and Physical Sciences Research Council (EPSRC), with grant EP/K031910/1.
A sensor circuit is used to generate a small voltage, 650 mV is sufficient, and the voltage detector is then able to trigger an open-drain output, which activates a switch. This allows the powering up of sub-systems. The voltage detector meets five criteria which allow it to be sensor-driven: Its input is rugged and survives 20V without using traditional protection circuits that would clamp the signal, and thereby affect the data or power in the signal. The threshold is low at 0.65V, to provide sufficient sensitivity (there are also lower threshold variants). The sensor uses only a few pA from the sensor, thereby permitting the use of conventional sensors, rather than more powerful and bulky energy harvesters. The detector is suitable for input signals with input voltage gradients from 0 to 10V/ms; at gradients higher than 10V/ms, the threshold increases. Detection hysteresis prevents output oscillations.
An IR receiver circuit that uses no power during listening has been demonstrated, using the UB20M voltage detector. This could be applied to TVs or any IR remote control or triggering mechanism. The extremely low quiescent current of the detector of 5.4pA (at 1V), allows the detector to be powered up from photodiodes that are illuminated by an infrared TV remote controller.
The UB20M voltage detector makes continuous sensing possible without use of a power source. Its power requirements are a few picowatts, and therefore conventional voltage-generating sensors, such as photodiodes, piezoelectric accelerometers, acoustic sensors, and RF receiving antennas can power the device up. In this way, the sensor is continuously monitored, using power from its own output signal, without drawing power from batteries or the mains. There is a small leakage current of below 100pA through the open-drain output. The extremely low quiescent current of the detector ensures that the loading of sensors is minimal, which leaves the sensor output intact for other tasks, such as analog sensing or energy harvesting.