CMOS Bandpass Filters Using Immitance Converters

P. Ööpik, V. Kukk,

Tallinn Technical University

High selective bandpass filters can be realized using LC-emulation techniques and general immitance converters for implementation both inductances and capacitances. This techniques enables the use of copies of only one converter for all integrator blocks. LC-simulation reduces sensitivity and variation of element values to minimum.

Several practical problems arise when only active components of filters are ICs: sensitivity to parasitics, difficulties to change frequency corrections, keeping exact relationships between dimensioning resistors etc. So, amplifiers should be integrated into higher level blocks:
1) GIC as an integrator,
2) integrated two GICs for resonator,
3) GIC-array for n-th order filter etc.
Any of these cases has advantages and disadvantages. Additional problems come from technological restrictions.

In this paper, implementation of GICs in CMOS-technology is considered. The technology used enables producing of very accurate capacitors and resistors that is prerquisite for the type of filters considered. However, technological restrictions to particular values may be too restrictive, therefore both continuous-time and SC-implementations have been considered. Special attention is payed to built-in corrections to get maximum from the amplification characteristics which are usually predetermined by technology.

GIC-based circuits have such characteristics which need very accurate measurements. Therefore, special additional circuits were designed in addition to basic structures. Simple resonator, coupled rsonators, and higher order filter are considered.