Two New CMOS Synthetic Transformer Designs and their Application

The transformer is an important component of electrical engineering for many applications including those for integrated circuits. For integrated circuit applications, the use of a synthetic transformer has been recognised to be a viable option for a number of applications. This paper presents two new designs of electronically-controllable CMOS active transformers. The first preposition is based upon a capacitive T-network embedded between two active CMOS gyrators each of which has been obtained by a parallel back-to-back connection of one non-inverting and other inverting electronically-controllable CMOS transconductor. This circuit requires thirty-two MOSFETs, all operating in saturation region. The second design simulates an inductive T-network using two CMOS electronically-controllable floating inductors and one electronically-controllable CMOS grounded inductor thereby employing eighty MOSFETs. The first design offers the advantage of realising a step up as well as step down transformer by appropriate selections of the transconductances of two transconductors. The second design although uses a larger number of MOSFETs than the former but has the advantage of using three grounded capacitors which is a desirable from the view point of IC implementation. It may also be mentioned that using more MOSFETs does not increase layout area significantly since the capacitors require more layout area than all the MOSFETs put together. The workability of both the designs, along with their various performance characteristics and non-ideal analysis, has been well corroborated by computer simulations using SPICE software using 0.18 µm CMOS technology parameters. The application of the proposed circuits in the design of double tunned band pass filter has also been shown and its workability too has been validated by computer simulations using SPICE software.