NPN BIPOLAR CIRCUIT TOPOLOGY FOR A TUNABLE TRANSCONDUCTANCE CELL AND POSITIVE CURRENT SOURCE

摘要

An active filter circuit component includes an all NPN bipolar tunable Gm cell (14) and positive current source (PCS) (12) for supplying common mode current. The tunable Gm cell includes a fixed Gm cell (26) having transconductance Gf, a current divider (28) and a recombination circuit (35) that together effectively multiply Gf by a tuning factor α, where -1 ≤ α ≤ 1, without effecting the cell's common mode current Icm. The PCS includes a pair of unity gain inverting amplifiers (18, 20) that are connected in antiparallel across a pair of matched resistors (R1, R2). Alternately, the resistors can be connected across the inverting and non-inverting sides of a differential amplifier (190). A constant voltage is applied across the resistors to supply Icm, while maintaining a common mode resistance of R/2 and a differential mode resistance approaching infinity.