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Description
Summary
The device must have reduced final dimensions to be integrated on a single microchip, which, after having amplified and processed the information of external sensors, must be able to transmit it at distances of the order of meters, possibly using an integrated antenna. The miniaturization of the system to use more sensors, perfectly compatible with low-consumption electronics, can meet the needs of medical applications such as the remote control of biological parameters or the construction of robotic equipment (exoskeletons). The proposed mechanism will be developed in a prototype phase to discrete components in order to validate an initial feasibility study, and will then be integrated microchip in a final stage.
We have been able to mount in a preliminary data acquisition chain an amplifier for instrumentation, which we use to interface and read out the bio signals, a voltage controlled oscillator (VCO) to digitize the information and a wireless transmitter.
The transmission tests were carried out exploiting a specific digital modulation, namely Synchronized On/Off Keying (S-OOK) digital modulation. Moreover, for these tests the carrier was used nominally at 3.5 GHz. The S-OOK modulation is devoted to “translate” bit transmission requests into transmission trigger events for the following UWB transmitter. Standard OOK maps each 1 into an impulse trigger, and each 0 into a “space” that is a no impulse trigger, or just a delay. S-OOK adds a synchronizing impulse “S” before the data bit “D”, thus allowing the receiver to know whenever a data bit is being effectively transmitted and hence not requiring to recover any timing information regarding the data stream. Despite using a synchronizing impulse, this solution allows to design a fully asynchronous event-based receiver, more robust with respect to undesired delays due to the transmission channel. Here we have used an external S-OOK modulator together with the on-chip transmitter. Indeed, this S-OOK modulation was easily implemented in one prototype ASIC. In more detail, any digital series of 0s and 1s, i.e. the modulation sequence of bits, enables or disables the RF transmitter. Hence, the effective transmitted bits were formed by a series of RF bursts centered at a carrier frequency of 3.5 GHz.
The proposed approach using standard CMOS process suggests the use of this technology for monolithic implementations of generic sensors along with microelectronic readout circuits. In addition, the prototype that we have described allows an Ultra-Wide-Band, low-power digital modulation. The range of transmission via the integrated antenna is of the order of 1 m and the total power consumption was measured as low as a few hundreds of μW. Future improvements of the microelectronic design are oriented to include an additional on-chip remote powering system, using state-of-the-art deep submicron architectures. In this way the chip will be able to work without any in-system battery and this also fits medical applications.
