Compressive Sensing system for recording of ECoG signals in-vivo

6. Analog Path Design6.1. Design DiscussionThe multipath neural acquisition system for a channel that is shown in Fig.3.4.1 has beenchosen as the implementation to be developed. It is included again below as reference duringthe design discussion. Having a look of the complete design it is clear that the complexity ofimplementing all of the blocks overcomes the scope of a final master thesis, and so, in order tointroduce design improvements, the design has had to be limited to some blocks, putting off thetotal implementation for future steps in the CS field.As it is commented in the Chapter 1 and 2, the main constraints of the system are: a) area, dueto the act that the chip to be placed over individuals brain has to be as smaller as possible, andso less invasive; and b) power consumption, because of the fact that a large battery cannot beincluded in the system, and overall safety issues, because low power consumption means lowheat dissipation and so the chip will be permitted as bioapplication. By the other hand, thesystem is not conditioned by time constraints, so any extra effort is employed in order to make ahigh-speed design. That is since real neural signals have a low bandwidth, and so there is noreason into exploit high-speed features which will be not used.By considering the main blocks of the system, and the design problems with which each of themis related, it is stated that the LNA, the ADC and the multiplexer boil over the time limitations,and so, previous designs are considered. By the other hand, a good design of howimplementing the mixing and integration blocks have not been already done in the state of theart, and so, it has been considered as the best feasible design to be completed under thescenario of this project. The main goal for being considered in the improvement is area savingin order to achieve an architecture in which the miniaturization of the integration capacitances,which regarding the literature are too large components of the integrator circuitry, could be carryout. Along the next points the different blocks of the multipath analog approach are analyzed indetails.A discussion about the amplification and conversion operations has been included in AppendixE. In order to address the mixer-integrator design, the same parameters which have beenconsidered during the Matlab and Simulink models are taken for the circuitry design inCadence. They are referred in Table 5.1. The same synthetic input signal that has been usedfor Matlab-Simulink simulations has been introduced into Cadence model. Similarly, the randommatrices which have been considered are those based on the new random generator presentedin Chapter 4 and the one which can be generated by randint in Matlab.54