Amplifiers – With semiconductor amplifying device – Including differential amplifier
Patent
1993-01-25
1994-06-28
Mottola, Steven
Amplifiers
With semiconductor amplifying device
Including differential amplifier
330303, H03F 345
Patent
active
053250702
ABSTRACT:
An active filter circuit (10) that has a cut off frequency being substantially independent of absolute and temperature variations due to on chip resistors (R.sub.1, R.sub.2 and R.sub.3) has been provided. The active filter includes a transconductance gain amplifier (16) having first and second currents (I.sub.B and I.sub.E) the ratio of which are controlled such that the absolute and temperature effects of any on chip resistors of the active filter circuit are removed. The ratio of the first and second currents of the transconductance gain amplifier are controlled by a circuit that generates third and fourth currents (I.sub.b and I.sub.e) which are a function of a bandgap voltage. The circuit then utilizes the third and fourth currents and provides, to the transconductance gain amplifier, a current that is substantially equal to the ratio of square of the third current to the fourth current, and a current substantially equal to the fourth current.
REFERENCES:
patent: 4339729 (1982-07-01), Jason
patent: 4498053 (1985-02-01), Katakura
patent: 4853647 (1989-08-01), Low
patent: 4926138 (1990-05-01), Castello
Bingham Michael D.
Botsch Sr. Bradley J.
Motorola Inc.
Mottola Steven
Nguyen Tiep
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