Implementation of Impedance Converters in BiCMOS-Technology

H. Tenhunen, Royal Institute of Technology, Sweden
M. Koort, Tallinn Technical University, Estonia
V. Kukk, Tallinn Technical University, Estonia

General impedance converters have been considered as one of the most efficient solutions for implementation of high-Q resonators. Recent studies have shown that very high quality active filters can be realized using LC-emulation techniques. In these filters, uniform GIC-arrays have been used reducing the number of active frequency dependant elements to one type only. However, these realizations are based on the use of discrete op-amps and therefore, the circuits are power consumable, sensistive to parasitics, usable only at low frequencies only (up to 100kHz, for Q<100).

Standard GIC structure proposed by Antoniou consists of two amplification units which can be united into one more complex block, for example, a differential amplifier with resistive feedback that implements voltage mirror. Using this mirror and external resistor and capacitor one can implement current integrator and voltage follower in one basic block for LC-emulations.

The conditions for very high quality (or medium quality and high frequency) GIC can be satisfied in integrated technology that enables to keep under control important relations between components. To study facilities of different solutions, experimental designs of GICs have been carried out. To compare converters' properties, a set of test circuits have been worked out, both for simulation and measurements.

In this paper, GICs implemented in BiCMOS 0.6 micron technology are considered. As real immitance converters must be tunable for selecting different working frequencies and for compensation of technological variations, voltage-tunable CMOS resistors and bidirectional CMOS switches are studied as well.