Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2000-11-22
2002-02-12
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S552000, C327S553000, C327S336000
Reexamination Certificate
active
06346851
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to electronic systems and in particular it relates to low-pass filters.
BACKGROUND OF THE INVENTION
The prior art simple low-pass filter shown in
FIG. 1
includes transistors
20
,
22
, and
24
; current source
26
; capacitor C
1
; input node
30
; and output node
32
. The limited high frequency attenuation of the prior art low-pass filter shown in
FIG. 1
is due to signal feed forward through the gate-to-drain capacitance (C
3
) of transistor
24
. The maximum attenuation is C
3
/C
1
. Since transistors
22
and
24
are not totally off, the feed forward capacitance is usually much higher than C
3
. Unlike a true R-C filter, which has no zero, the simple configuration shown in
FIG. 1
has a zero at a certain frequency.
SUMMARY OF THE INVENTION
Generally, and in one form of the invention, the low-pass filter circuit includes: a first compound transistor device coupled between an input node and an output node; a first transistor coupled to the input node, a gate of the first transistor is coupled to a drain of the first transistor; a second compound transistor device coupled between a gate of the first compound transistor device and the gate of the first transistor; a second transistor coupled to the first transistor and having a gate coupled to a gate of the second compound transistor device, the gate of the second transistor is coupled to a drain of the second transistor; a current source coupled to the drain of the second transistor; a first capacitor coupled to the output node; and a second capacitor coupled to the gate of the first compound transistor device.
REFERENCES:
patent: 5465400 (1995-11-01), Norimatsu
patent: 5764095 (1998-06-01), Carobolante
patent: 5999043 (1999-12-01), Zhang et al.
Hellums James R.
Muza John M.
Zhang Zhengwei
Brady III Wade James
Le Dinh T.
Stewart Alan K.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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