TABLE OF CONTENTS The following two chapters are devoted to exploring the potential of the FGMOS transistor operating in weak inversion for the design of analog low-voltage micropower continuous-time filters. It is demonstrated that the use of FGMOS in weak inversion as an alternative to conventional MOS devices relaxes the constraints relating to voltage supply and frequency response. Moreover, the increased number of terminals in the device permits a simplification in the topologies required to realise a certain mathematical function. This brings with it a reduction in power consumption, as well as other advantages such as a lower noise floor.
The term weak inversion defines the operating mode in an MOS transistor in which the bulk surface charge is inverted in relation to the rest of it, but still it is mostly due to the charge in the depletion region. The corresponding inversion layer charge can nevertheless cause non-negligible conduction. Weak inversion mode is especially suited for the design of micropower circuits for several reasons. The term micropower defines a class of circuits with power consumption of just a few microwatts. In order to obtain these power levels the maximum current the circuit can handle has to be very small. The weak inversion region is very convenient when these requirements have to be met for the following reasons:
Assuming that the required power consumption sets a very small, fixed value for the current, the maximum operating frequency of a single transistor is determined by the gate oxide capacitances, C GB, C
