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2.10 Device Level Energy Issues 97
factor and long life-time battery. Indeed, targeting below 1 mW would then
enable support from energy harvesting systems enabling energy autonomous
RF communications. In addition to this improvement, lighter communication
protocols should also be envisioned as the frequent synchronization requirement
makes frequent activation of the RF link mandatory, thereby overhead
in the power consumption.
It must also be considered that recent advances in the area of CMOS technology
beyond 90 nm, even 65 nm nodes, leads to new paradigms in the field of
RF communication. Applications which require RF connectivity are growing
as fast as the Internet of Things, and it is now economically viable to propose
this connectivity solution as a feature of a wider solution. It is already the case
for the micro-controller which can now easily embed a ZigBee or Bluetooth
RF link, and this will expand to meet other large volume applications sensors.
Progressively, portable RF architectures are making it easy to add the RF
feature to existing devices. This will lead to RF heavily exploiting digital
blocks and limiting analogue ones, like passive/inductor silicon consuming
elements, as these are rarely easy to port from one technology to another.
Nevertheless, the same performance will be required so receiver architectures
will have to efficiently digitalize the signal in the receiver or transmitter
chain [129]. In this direction, Band-Pass Sampling solutions are promising
as the signal is quantized at a much lower frequency than the Nyquist one,
related to deep under-sampling ratio [130]. Consumption is therefore greatly
reduced compared to more traditional early-stage sampling processes, where
the sampling frequency is much lower.
Continuous-Time quantization has also been regarded as a solution for
high-integration and easy portability. It is an early-stage quantization as
well, but without sampling [131]. Therefore, there is no added consumption
due to the clock, only a signal level which is considered. These two
solutions are clear evolutions to pave the way to further digital and portable RF
solutions.
Cable-powered devices are not expected to be a viable option for IoT
devices as they are difficult and costly to deploy. Battery replacements in
devices are either impractical or very costly in many IoT deployment scenarios.
As a consequence, for large scale and autonomous IoT, alternative energy
sourcing using ambient energy should be considered.