Filter apparatus including differential slave gm-C filter...

Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression

Reexamination Certificate

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Details

C327S552000

Reexamination Certificate

active

07459963

ABSTRACT:
In a filter apparatus including a master circuit for receiving a reference frequency signal having a reference frequency to generate a control voltage and a slave gm-C filter formed by at least one operational transconductance amplifier and at least one capacitor where the operational transconductance amplifier of the slave gm-C filter is controlled by the control voltage to tune a cut-off frequency or center frequency of the slave gm-C filter, the master circuit is constructed by first and second gm-C filters each formed by at least one operational transconductance amplifier and at least one capacitor and having different frequency characteristics from each other, the first and second gm-C filters being adapted to receive the reference frequency signal, first and second amplitude detectors having inputs connected to outputs of the first and second gm-C filters, respectively, and a differential amplifier having an input connected to outputs of the first and second amplitude detectors and being adapted to amplify a difference-voltage therebetween to generate the control voltage, so that the difference-voltage is brought close to zero.

REFERENCES:
patent: 5117205 (1992-05-01), Nauta
patent: 5731737 (1998-03-01), Cranford et al.
patent: 6791401 (2004-09-01), Miwa
patent: 4-165805 (1992-06-01), None
patent: 06140872 (1994-05-01), None
patent: 10-13188 (1998-01-01), None
Francois Krummenacher, et al., “A 4-MHz CMOS Continuous-Time Filter with On-Chip Automatic Tuning”, IEEE Journal of Solid-State Circuits, vol. 23, No. 3, Jun. 1988, pp. 750-758.
Katsuji Kimura, “An MOS Operational Transconductance Amplifier and an MOS Four-Quadrant Analog Multiplier Using the Quadritail Cell”, IEICE Trans. Fundamentals, vol. E75-A, No. 12, Dec. 1992, pp. 1774-1776.

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