Abstract
This work addresses the problem of optimal operational transconductance amplifier (OTA) macromodel creation in terms of its application in active FBAR filters. Existing macromodels of active elements are reviewed from their structure and application point of view. A nonlinear macromodel of OTA was developed on the basis of single-pole three-stage macromodel, which takes into account the necessary effects of real devices: the finite input and output impedances, the frequency dependence of transconductance coefficient and its nonlinearity behavior, noise characteristics. The features of presented solution include versatility of application in most of nowadays CAD systems, the ability to estimate with sufficient accuracy the frequency response of the filter and its performance, dynamic range, harmonic and noise analysis. Simple structure allows the speed-up of calculation and direct digital optimization techniques can be adopted to optimize the characteristics of the filter. The verification of macromodel was demonstrated on the example of FBAR connected to gyrator circuit, which showed high precision imitation of transistor-level circuit. The analysis of transient response and harmonic balance proved the acceptance of power series approximation of operation range. The use of two diodes outside this range allowed for modeling in wide input voltages range. The developed macromodel can be successfully used for the synthesis of active FBAR filters.
Highlights
Active filters are widely distributed today and perform various frequency processing functions in IF devices, audio equipment and DSP [1]
Active filters based on operational transconductance amplifiers (OTA) elements are simpler in design, have built-in tuning features, and together with film bulk acoustic resonators (FBAR) frequency defining elements allows the realization of devices, which can meet modern requirements of operation frequency range, wideband and selectivity
The peculiarities of OTA application in high frequency FBAR active filters requires the development of a special macromodel, that takes into account all necessary, but excessive effects
Summary
Active filters are widely distributed today and perform various frequency processing functions in IF devices, audio equipment and DSP [1]. Active filters based on OTA elements are simpler in design, have built-in tuning features, and together with FBAR frequency defining elements allows the realization of devices, which can meet modern requirements of operation frequency range, wideband and selectivity. 5-order filter consists of up to 10 active elements each of them includes 10-15 transistors Simulation of such complex systems, including low-level OTA models, is inefficient in terms of complexity and calculation time. In case of transient analysis, calculation time may be reduced by 3 orders of magnitude with almost no loss in accuracy [3] This opens up the possibility of application of direct numerical optimization techniques for filter structures regarding their nonlinearity, noise effects and dynamic range. The purpose of this work is the development of the simplified macromodel, which imitate the properties of real amplifiers with sufficient accuracy
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