A General Approach to Twin-T Design and Its Application to Hybrid Integrated Linear Active Networks

Abstract

In this paper we approach twin‐T design with a view to controlling the sensitivity of the transmission zero with respect to component variations, according to criteria that are of particular interest in the design of hybrid integrated linear active networks. We give design examples and derive conditions that relate null depth and component characteristics with expected zero displacement in the s‐plane.

Active filters and hybrid technology

“…However Bruton a has pointed out that the voltage transfer function of a filter is not '4 '5 Zin altered by scaling all the components by some function of s. In particular it is possible to multiply all the impedances by K/s. In this way all the inductors of impedance sL become resistors of value KL and the capacitors of impedance 1/sC now have a value of K/s C. This latter impedance can be realised by using Antoniou's ' 9 General Impedance Converter (GIC) shown in Figure 17. The GIC can, by proper choice of components, be made to have a very high Q factor over a relatively wide frequency range and can be tuned to a specific impedance value by resistor adjustment alone and may use equal valued capacitors.…”

Low-sensitivity SAB band-pass active-RC filter using impedance tapering

“…From (6) it follows that the coefficient a 1 sensitivity to the gain is inversely proportional to q , i.e. to the pole Q factor of the passive network which is limited to less than 0.5 [7]. The value of q can be maximized by appropriately impedance-wise scaling individual sections of an RC network from one another.…”

“…The class-4 filter circuit has an RC-ladder network in the positive feedback loop (see [4]). The design presented in [1] is based on "impedance tapering".…”

“…The filter circuit is class-3 referred to as a "single-amplifier biquad" (SAB), and has an RC bridged-T network in the negative feedback loop as shown in [4]. It is shown here that by the use of impedance tapering, in which Lsections of the RC network are successively impedance scaled upwards, from the driving source to the negative amplifier input, the sensitivity of the filter characteristics to component tolerances can be significantly decreased, in comparison to standard designs.…”

Low active-sensitivity allpole active-RC filters using impedance tapering

“…It is well known that in order to minimize the sensitivity of filter characteristics to tolerances of the gain elements, the gainsensitivity-product (GSP) of the filter should be minimized [3], [4], [5]. In the LP case it is defined by:…”