Basic properties of the operational transconductance amplifier (OTA) are discussed. Applications of the OTA in voltage-controlled amplifiers, filters, and impedances are presented. A versatile family of voltage-controlled filter sections suitable for systematic design requirements is described. The total number of components used in these circuits is small, and the design equations and voltage-control characteristics are attractive. Limitations as well as practical considerations of OTA-based filters using commercially available bipolar OTAs are discussed. Applications of OTAs in continuous-time monolithic filters are considered.

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Active filter design using operational transconductance amplifiers: A tutorial

Fully integrated, high-frequency continuous-time filters can be realized in MOS technology using a frequency-locking approach to stabilize the time constants. A simple, fully differential integrator, optimized for phase-error cancellation, forms the basic element; a complete filter consists of intercoupled integrators. The center frequency of the filter is locked to an external reference frequency by a phase-locked loop. A prototype sixth-order bandpass filter with a center frequency of 500 kHz dissipates 55 mW and occupies 4 mm/SUP 2/ in a 6-/spl mu/m CMOS technology.

High-frequency CMOS continuous-time filters

The state of the art of continuous-time filter design is reviewed Several techniques are discussed and compared in terms of performance and implementation feasibility in different fabrication technologies This review does not aim at historical completeness, but rather emphasizes techniques that have proven their worth in commercial applications Brief mention is also made of experimental work which, in the opinion of the author, shows promise for the future >

Integrated continuous-time filter design /spl minus/ an overview

An updated version of a 1985 tutorial paper on active filters using operational transconductance amplifiers (OTAs) is presented. The integrated circuit issues involved in active filters (using CMOS transconductance amplifiers) and the progress in this field in the last 15 years is addressed. CMOS transconductance amplifiers, nonlinearised and linearised, as well as frequency limitations and dynamic range considerations are reviewed. OTA-C filter architectures, current-mode filters, and other potential applications of transconductance amplifiers are discussed.

CMOS transconductance amplifiers, architectures and active filters: a tutorial

The desirable features of fully integrated, VLSI-compatible continuous-time filters are discussed. A recently proposed integrated continuous-time filter technique is reviewed, in which MOS transistors are used in place of resistors along with the nonlinearity cancellation and on-chip automatic tuning. The filters obtained using this technique are compared to switched-capacitor filters, digital filters, and continuous-time filters using different techniques. Representative experimental results are given, demonstrating the high performance that can be achieved.

Continuous-time MOSFET-C filters in VLSI

A single-chip gyrator filter for separating the components of the video signal in a TV receiver is described which is suitable for mass production in a standard bipolar process (f/SUB T//spl ap/400 MHz). The 11 mm/SUP 2/ filter chip operates at frequencies up to 10 MHz, requires no tuning or alignment and has Q-factors which are stable with temperature. The IC contains an automatic tuning system which tunes the five resonators of the filter by aligning an auxiliary gyrator resonator with the crystal oscillator present in the color decoder of a TV receiver. Problems of matching the frequencies of the individual gyrator resonators are discussed, showing how alignment accuracy of 0.5 percent can be obtained when resistivities and specific capacitances have production spreads of at least 10 percent. Various gyrator circuit configurations are given which minimize the circuit complexity and, hence, the chip area. Computer aided design techniques for the filter using geometrically scaled models and macromodeling are presented and it is shown how a complete simulation of the chip led to a significant improvement in bandstop performance. Finally, the measured responses are presented and the filter performance is discussed in the light of present-day requirements.

P.J. Rankin

Papers

Gyrator video filter IC with automatic tuning