A practical and effective general approach is presented for extending the useful operating frequencies and improving the performance of linear active networks realized using operational amplifiers (OA's). This is achieved by replacing each OA in the active network by a composite operational amplifier (CNOA) constructed using N OA's. The technique of generating the CNOA's for any given N is proposed. The realizations employing the CNOA are examined according to a stringent performance criterion satisfying such important properties as extended bandwidth, stability with one- and two-pole OA models, low sensitivity to the components and OA mismatch, and wide dynamic range. Several families of CNOA's, for N = 2, 3, and 4 , are shown to satisfy ,the suggested performance criterion. In this contribution, the CNOA's applications in inverting, noninverting, and differential finite-gain amplifiers are given and shown theoretically and experimentally to compare favorably with the state-of-the-art realizations using the same number of OA's. Applications of the CNOA in inverting integrator and active filter realizations are presented in a companion contribution [32].

Composite operational amplifiers: Generation and finite-gain applications

A practical method of designing active filters in which the transfer function is independent of both first- and second-order operational amplifier time constant effects is presented. Neither matched operational amplifiers nor a tuning procedure dependent on an active parameter is required. The active portion of these filters is universal and readily integrable since it is comprised of conventional operational amplifiers and resistors. The method can be used to design a filter with any realizable transfer function of any order. Several new filters obtained from this method are introduced and evaluated both theoretically and experimentally. These configurations contain popular passive structures and the new universal active circuits. The significant improvements in filter performance of these new filters is demonstrated in this evaluation.

http://class.ece.iastate.edu/vlsi2/docs/papers done/1981-08-tcas1-rg ab.pdf

Design of active filters independent of first-and second-order operational amplifier time constant effects

Most second-order RC active filters show a marked dependence on the gain-bandwidth product (GB) of operational amplifiers (OA's) when the \omega_0 to be realized is greater than 1 percent of GB and Q > 10 . Here designs are given that are virtually independent of OA's when \omega_0 GB and Q . Even for \omega_0=0.05 GB and Q=10 , the center frequency shift due to OA's is less than 0.1 percent. This desirable result is achieved by designing filter amplifiers which have zero first-order sensitivities with respect to the time constant \tau = 1/GB of the OA's used in the design. As a result, the filter transfer function has also zero first-order sensitivity with respect to \tau . General criteria for such designs are given. Experimental results show excellent agreement with theory.

/pdf/active-filters-with-zero-transfer-function-sensitivity-with-4tg5vft6k6.pdf

Active filters with zero transfer function sensitivity with respect to the time constants of operational amplifiers

In this paper new circuits for realizing actively compensated finite gain amplifiers (FGA's) using operational amplifiers (OA's) and resistors are given. In IC technology, as the characteristics of the OA's and the resistor ratios track closely with each other with temperature and other variations of ambient conditions, the compensation should hold under such varying conditions. An application is considered in active-RC filters. Experimental results confirm the theoretical predictions. These results show that one can expect a substantial improvement in the operating frequency range of the circuits that employ the new amplifiers over the conventional amplifiers or the existing ones using two OA's.

Design of actively compensated finite gain amplifiers for high-frequency applications

SUMMARY It is shown that the active compensated non-inverting voltage controlled voltage source (VCVS) structures employing two operational amplifiers (op-amps) may be classified into two major classes. Class 1, in which the phase compensation condition does not depend on the unity-gain bandwidth of the op-amps used, and class 2, in which the phase compensation condition depends on the unity-gain bandwidth of both op-amps. Detailed comparison tables which include the condition for phase compensation, the phase error, the magnitude error and the realizable bandwidth are given.

Classification and generation of active compensated non‐inverting VCVS building blocks

A general theory is developed for extended bandwidth operation of actively compensated finite gain amplifiers. Designs for three new circuits are given which implement the theory. These circuits employ only operational amplifiers and resistors and their gains depend only on their resistor ratios. Thus they are suitable for IC fabrication. Further in IC technology, the characteristics of the operational amplifiers as well as the resistor ratios track closely with each other with reference to temperature and aging. Thus the extended bandwidth operation of the amplifiers will be available over a wide temperature range as well as under varying aging conditions. Their characteristics can be tuned easily by trimming only two resistors. Applications of the new amplifiers have been considered in RC active filters as well as in inductance simulation schemes. Experimental results are given which closely agree with theoretical predictions. The results also indicate that substantial improvement in the usable bandwidth of the circuits employing the new amplifiers may be expected over those using the conventional design of finite gain amplifiers.

S. Natarajan

Papers

Design and some applications of extended bandwidth finite gain amplifiers