Thesis presented in partial fulfillment of the requirements for the degree of Doctor
of Philosophy in the subject of Electrical and Computer Engineering by the Universidade Nova de Lisboa,Faculdade de Ciências e TecnologiaSignal amplification is required in almost every analog electronic system. However
noise is also present, thus imposing limits to the overall circuit performance, e.g., on
the sensitivity of the radio transceiver. This drawback has triggered a major research
on the field, which has been producing several solutions to achieve amplification with minimum added noise. During the Fifties, an interesting out of mainstream path was followed which was based on variable reactance instead of resistance based amplifiers.
The principle of these parametric circuits permits to achieve low noise amplifiers since
the controlled variations of pure reactance elements is intrinsically noiseless. The
amplification is based on a mixing effect which enables energy transfer from an AC
pump source to other related signal frequencies.
While the first implementations of these type of amplifiers were already available at that time, the discrete-time version only became visible more recently. This discrete-time version is a promising technique since it is well adapted to the mainstream nanoscale CMOS technology. The technique itself is based on the principle of changing the surface potential of the MOS device while maintaining the transistor gate in a floating state.
In order words, the voltage amplification is achieved by changing the capacitance value
while maintaining the total charge unchanged during an amplification phase.
Since a parametric amplifier is not intrinsically dependent on the transconductance of the MOS transistor, it does not directly suffer from the intrinsic transconductance MOS gain issues verified in nanoscale MOS technologies. As a consequence, open-loop and opamp free structures can further emerge with this additional contribution.
This thesis is dedicated to the analysis of parametric amplification with special emphasis on the MOS discrete-time implementation. The use of the latter is supported on the presentation of several circuits where the MOS Parametric Amplifier cell is well suited:
small gain amplifier, comparator, discrete-time mixer and filter, and ADC. Relatively to the latter, a high speed time-interleaved pipeline ADC prototype is implemented in a,standard 130 nm CMOS digital technology from United Microelectronics Corporation (UMC). The ADC is fully based on parametric MOS amplification which means that one could achieve a compact and MOS-only implementation. Furthermore, any high
speed opamp has not been used in the signal path, being all the amplification steps
implemented with open-loop parametric MOS amplifiers. To the author’s knowledge,
this is first reported pipeline ADC that extensively used the parametric amplification
concept.Fundação para a Ciência e Tecnologia through
the projects SPEED, LEADER and IMPAC
