University circuit enables zero-power standby
The circuit is a low-threshold analog voltage comparator with output buffer that only requires picowatts to activate other circuitry. One of the lead researchers, Bernard Stark, told eeNews Europe that the circuit, which is the subject of a patent application, uses multiple devices and thresholds to allow high Vin maximum of 20V and voltage thresholds for detection down to below 0.5V. There are also power-saving techniques to almost eliminate static current through the device. Off-state output leakage is below 100 picoamps.
“The voltage detector chip uses over a thousand times less energy than existing detectors to create a turn-on signal, merely five picojoules of energy and only around half a volt. Many sensors can provide this without requiring a power supply, therefore making listening effectively free,” the University of Bristol said in a statement.
The voltage detector only requires a few picowatts to activate. In a wireless sensor node for the Internet of Things (IoT) the voltage detector could be powered by the initial signal coming from the primary sensor. This could then be used to turn on the rest of the node to capture sensor data, process and transmit it.
In equipment, such as a security alarms, activity monitors, and other Internet of Things devices, the energy to keep the device alive and listening, can far outweigh the energy used to react. In these cases, it is especially important to eliminate listening power in order to increase battery life and make a system that is less environmentally wasteful.
The ability to be continuously in listening mode and waiting for an event with zero power consumption can result is smaller batteries, or a battery life that is extended, in some cases by years, the researchers claim.
A sensor can be used to generate a small voltage of 500mV or 650mV and the voltage detector is then able to trigger an open-drain output, which activates a switch. The circuit uses only a few picoamps 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 voltage gradients higher than 10V/ms, the threshold increases. Detection hysteresis prevents output oscillations.
Next: Good for consumer applications
The circuit could also have application in more conventional consumer products such as televisions, microwaves, and voice-activated interfaces.
The research team point out that modern televisions consume 0.5W, or 6AA batteries per day in standby so that they can be “switched on” from a remote controller. In times past they consumed as much as 10W or 15W. There is also the apocryphal argument that in its lifetime a microwave consumes more energy powering its display than heating food, because for more than 99 percent of the time it sits in standby.
The University of Bristol team has demonstrated a TV that uses the UB20M voltage detector IC to eliminate this standby power. The quiescent current of the detector of 5.4 pA at 1 V, allows the detector to be powered up from infrared photodiodes that are illuminated by an infrared TV remote controller. The UB20M detector activates a power gating switch in the TV’s 12V supply, in order to cut off the TV’s standby power.
The university has two voltage detector ICs available as samples, the UB20M and the UB20L both implemented in 180nm HVCMOS by AMS AG.
The UB20M has a threshold of 0.6V and draws sub-10 pA. The UB20L switches at 0.46V, but draws up to 100pA. The university can provide samples and datasheets and an evaluation board. “We are now actively seeking commercial partners to use the voltage detector chip in their product, and would welcome companies to get in touch,” said Stark.
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