NWA Library, on Network Analysis
SummaryThe design of wideband amplifiers with ultimate performance requires a radical change of approach. The cumulation of all minor imperfections of individual devices often causes a dramatically reduction of the overall performance. These imperfections (parasitics) are to be taken into account from the very beginning; so definitely not marginally as it is commonly done.
This thesis introduces innovative methods and tools to facilitate the application of higher-order feedback, over several amplifying stages, in the presence of deleterious parasitics. Much attention is paid on (1) formal descriptions of transfer, feedback and noise, (2) characterization methods of devices and sub-circuits and (3) design methods for compensation networks in feedback loops.
Formal description of transfer, feedback and noiseThe formal descriptions provide unambiguous definitions of (a) multi-port y-, z- and s-parameters, (b) superposition parameters of feedback loops, such as loopgain and aperture, (c) noise spectra and (d) noise parameters. Signal representations, in terms of voltages, currents or waves, are discussed simultaneously.
The concept of virtual circuits is formalized for transfer as well as noise to simplify parameter extraction of device models. Algorithms have been described for analyzing transfer and noise properties of arbitrary linear networks. We illustrate, for instance, how to calculate the thermal noise levels in multi-port networks from transfer measurements.
Characterization of transferCharacterization enables the quantification of parasitic effects in terms of (a) multiport transfer parameters, (b) equivalent circuit models, and (c) poles and zeros. This thesis describes methods for measuring these device parameters between well-defined reference planes. A structured method is discussed for tracing relevant parasitics using these measurements (circuit stripping).
Algorithms have been developed for (a) extracting poles and zeros from transfer functions, and (b) reconstructing equivalent circuit models from full one- or two-port measurements.
These algorithms demonstrate that adequate (linear) modeling of transistors does not necessarily result in exotic and complicated transistor models. This approach has, for instance, resulted in a new (small-signal) bipolar transistor model, that is more appropriate to wideband analysis and synthesis than the well-known hybrid-PI model.
Characterization of noiseThe development of a new instrument, a lightwave synthetic noise generator, has facilitated the application of new methods of noise characterization. Our source generates white noise using lightwave principles, and has many advantages with respect to conventional 50 Ohm noise sources. The noise bandwidth of this source can be varied simply, exceeding 10 GHz in bandwidth (hundreds of GHz are feasible).
Novel instruments, principles and algorithms have been developed for (a) calibration of noise sources, (b) noise measurement of electrical and optical receivers, and (c) measurement of transistor noise parameters. The feasibility of our measurement methods is demonstrated in practice.
Feedback designParasitic effects degrade the dominant behavior of feedback loops. Characterization supplies the parameters for analyzing this degradation, e.g. in a circuit simulator. Adequate compensation networks can minimize this degradation. There is, however, in general no all-embracing answer to the question of how to design these compensation networks, particularly not in combination with harmful parasitics.
This thesis study resulted in robust algorithms for predicting the frequency response of these compensation networks, in terms of poles and zeros. These algorithms are suitable for implementation in (future) circuit simulators. Realistic examples up to 3 GHz demonstrate the effectiveness of our approach.
An integrated approachAll of these methods and tools have contributed to a closer integration of the fields of analog electronics and microwave techniques. The need for an integrated approach to characterization and design finds its origin in the fact that well-known suppression methods of parasitic effects become ineffective in the case of wide bandwidths. It required an in-depth return to the basics to combine various methods.
We have carried out an in-depth study of wideband lightwave receivers, resulting in various low-noise receivers using discrete 'low-cost' components. Overall feedback loops spanning two and even three amplifier stages, have been realized with bandwidths exceeding 1 GHz. The applicability of the methods proposed in this thesis have hereby been proven in practice.
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