Single-amplifier filter biquads and especially Sallen-Key filters are widely used to build higher-order filter cascades. This paper investigates high-frequency current amplifier non-idealities and their effects on all-pole Sallen-Key filter biquads. It is shown that a non-ideal current amplifier input causes parasitic zeros in the filter transfer function, and thus imposes fundamental limitations on the realisable pole frequency. Design equations are given, providing compensation for the amplifier's port impedances and its phase lag, by predistortion of the component values. It is also shown how design specifications for a current-amplifier can be derived from the filter specification, minimising the amplifier's power dissipation. Finally, a video-frequency lowpass filter is discussed. 1. INTRODUCTION Single-amplifier filter biquads are widely used for building discrete -component filters (e.g. in [1] and [2, Sec. XV]). Among these filters, the positive-feedback filters (normally call...

The classification of universal amplifiers presented in this paper places all operational amplifiers and current conveyors known from the literature into a common framework, together with abstract concepts such as the universal active element and the nullor. Our approach is new in that we base it on four-terminal theory, which results in a classification that is more extensive but not more complex than classifications derived using two-port theory. It turns out that our classification contains a new type of operational amplifier, which we call current-feedback operational transconductance amplifier (CFB OTA), and also a new class of voltage-inverting current conveyors. We then demonstrate that our classification is very closely related to integrated-amplifier design by showing how all operational amplifiers and current conveyors can be implemented in CMOS using only a few CMOS circuits. Since the basic ideas behind CMOS and bipolar circuits are very similar, this paper is not process specific and can be seen as an attempt to bridge the gap between amplifier theory and amplifier design that has become ever wider in the past few years.

In this paper, a tunable single-amplifier biquadratic lowpass filter is presented. It consists of one balanced low-gain current amplifier and a second-order MOSFET–C feedback network. The filter was integrated in a double-poly 0.6 µm CMOS process and operates from a 3.3 V power supply. The pole frequency is tunable from 15.2 to 17.2 MHz, the pole Q is 3, the spurious-free dynamic range is at least 60 dB, and the filter consumes only 2.4 mW per pole. Furthermore, the active area used per pole is only 0.06 mm 2. The filter is well suited for low-power video-frequency applications, and demonstrates that the MOSFET–C filter technique can be applied successfully to filters other than those based on integratorconnected topologies. 1.