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Design of a fully tunable gaas mesfet OTA-C integrator suitable for high-precision continuous-time filtering

Visocchi, Pasqualino Michele; (1997) Design of a fully tunable gaas mesfet OTA-C integrator suitable for high-precision continuous-time filtering. Doctoral thesis (Ph.D.), University College London (United Kingdom). Green open access

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Abstract

The Operational Transconductance Amplifier-C (OTA-C) integrator has become the favoured building block for the implementation of integrated Continuous Time (CT) filters by many researchers around the world. The use of an OTA-C integrator for the realisation of an integrated CT filter does however, require full tunability, since the integrator time constants are dependent on absolute fabricated component values which are subject to process tolerances. In addition, the OTA may be used as a linear tunable resistor providing filter Q control. Integrated CT filters using OTA-C integrators have been implemented in Si CMOS, bipolar and GaAs MESFET technologies, with demonstrated operating frequencies ranging from 10s of KHz to 2GHz. This thesis describes a novel circuit for the realisation of an OTA-C integrator to be used for the implementation of a bandpass CT filter. The new OTA-C integrator, which has been fabricated in 0.5[mu]m GaAs MESFET technology, features independently tunable intrinsic output conductance, and transconductance. Thus additional OTAs configured as extrinsic linear resistors to provide Q-control are not required. A novel method of transconductance tuning is described which offers the widest tuning range reported in this technology, without varying any DC conditions and which preserves a good level of linearity. In addition, a single geometry device is used throughout the design, operating, with the exception of two triode region devices, under common bias conditions, well into the saturated region with no reliance on early saturation effects for gain enhancement. Using this approach a fully tunable 2nd order bandpass filter featuring independent control of centre frequency, Fo and Q has been fabricated using only two OTA-C integrators. The bandpass filter transfer function has been demonstrated with an accuracy of 1.5[percent] both in amplitude and group delay operating at a filter complexity (FoQ) of 1.5GHz.

Type: Thesis (Doctoral)
Qualification: Ph.D.
Title: Design of a fully tunable gaas mesfet OTA-C integrator suitable for high-precision continuous-time filtering
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: (UMI)AAI10017764; Applied sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10100138
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