Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2002-11-21
2004-07-06
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S175000
Reexamination Certificate
active
06759927
ABSTRACT:
BACKGROUND OF THE INVENTION
Various types of electrical signal filters are used in the CATV industry for controlling, on a frequency basis, the propagation of signals through a cable line. One example of such a filter is known as a notch filter. It is important that such notch filters offer a high level of attenuation, as well as precise and easy tuning capabilities, while maintaining a small size and economical construction.
A high level of attenuation can be realized by using a plurality of interconnected filter circuits on one or more circuit boards within the notch filter assembly. However, in this situation, it is critical that the multiple filter circuits (i.e., filter sections) be magnetically isolated from one another to avoid interference, such as cross-talk or magnetic coupling, between the filter circuits within the filter housing.
Using isolation shields to prevent unwanted cross-talk between filter circuits within a filter is known. One example of a filter having multiple filter circuits and including isolation shielding is disclosed in U.S. Pat. No. 4,451,803, the entirety of which is incorporated herein by reference. The '803 patent discloses a split tuning notch filter for removing a selected frequency or band of frequencies from a CATV signal. With reference to
FIG. 8
, a split tuning filter includes a common circuit board
100
having first
102
and second
103
filter sections formed thereon by discrete electronic components such as inductors, capacitors and the like (not shown).
Isolation shields
104
,
105
are arranged at a midpoint along circuit board
100
to provide magnetic isolation between first filter section
102
and second filter section
103
. Each shield includes a radially extending disc section
106
and a longitudinally extending flange section
107
. A slot
108
is formed in each shield, to allow the remaining, unslotted portion of disc
106
to slide into a corresponding slot
101
formed in circuit board
100
.
One of the shields is positioned in a slot formed on one side of the circuit board, and the other shield is positioned in a slot formed on an opposed side of the circuit board, as shown in FIG.
8
. As explained in the '803 patent, this type of arrangement prevents any “line of sight” communication between components in the first and second filter sections. Once the shields
104
,
105
are positioned on opposite sides of circuit board
100
and soldered in place. The circuit board is inserted into housing
109
, and the shields are then soldered into the housing
109
. The open end of the housing
109
is then closed by assembling the filter cap
110
. This subassembly is then often inserted into a tube sleeve housing (not shown) to form the final filter structure.
Another example of a filter having multiple isolated filter sections is disclosed in U.S. Pat. No. 5,150,087. Like the '803 patent, the '087 patent uses a pair of manually laterally inserted, axially opposed isolation shields to separate multiple filter sections. However, unlike the single circuit board used in the '803 patent, the '087 patent uses a plurality of isolated independent circuit boards interconnected by a wire through the pair of shields. Nonetheless, in order to achieve the proper isolation and grounding, two shields are required to prevent line of sight between the two circuit boards. But even a single circuit board having multiple filter circuits (e.g., '803 patent) typically requires at least two axially opposed isolation shields to accommodate a conductor or conductive trace (interconnecting multiple filter sections) while otherwise magnetically isolating the filter sections and preventing a line of sight therebetween. If the conductive trace is printed on the circuit board, it is also necessary for the slot
108
in each shield to include a clearance to prevent contact with the conductive trace.
While filters, such as the ones disclosed in the '803 and '087 patents, can successfully provide magnetic isolation between the first and second filter sections, there are several drawbacks associated with the use of such shield pairings. For example, although the discrete electrical components can be assembled on a circuit board using automated Z-axis manufacturing techniques and then wave soldered onto the circuit board en mass in a single economical and efficient manufacturing step, subsequent assembly steps, i.e., shield assembly and soldering steps, require substantial, precise manual labor.
More specifically, the shields must be manually attached to the circuit board by laterally positioning and fixturing the two shields into the corresponding slots in the circuit board. The shields must then be soldered to the circuit board before insertion into the housing. After insertion into the filter housing, the shields must again be soldered to the filter housing in order to properly ground the shields and the circuit board. The amount of manual assembly and soldering required in such a manufacturing process drives up the production cost and, in turn, increases the final cost to customers.
Thus, an electronic filter assembly, including a single circuit board separated into distinct and isolated filter sections using isolation shields, that can be economically produced using an automated manufacturing process, involving few, if any, manual assembly steps is desired. An electronic signal filter having a single circuit board including multiple filter circuits separated by isolation shields that can be automatically assembled onto the circuit board using Z-axis robotics-type automated assembly is also desired. Further, a substantially automated method of manufacturing such filters is desired, and it is especially desired that the automation steps be efficiently performed in a Z-axis direction with respect to an X-Y plane in which the circuit board resides.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the drawbacks of the prior art. More particularly, it is an object of the present invention to provide an electronic signal filter having a single circuit board including multiple filter circuits separated by isolation shields that can be automatically, and economically, assembled onto the circuit board using Z-axis robotics-type automated assembly performed in a Z-axis direction with respect to an X-Y plane in which the circuit board resides.
According to a first embodiment of the present invention, an electronic signal filter is provided including a cylindrical housing adapted to be electrically grounded, and having a first end, an opposed second end and an inner peripheral surface defining an interior compartment. The electronic signal filter also includes a single circuit board positioned within the interior compartment of the cylindrical housing, the single circuit board having a first surface, an opposed second surface, a first filter section proximate the first end of the cylindrical housing and a second filter section proximate the second end of the cylindrical housing. The circuit board is positioned such that it effectively divides the interior compartment into a first compartment defined by the first surface of the circuit board and a first portion of the inner peripheral surface of the cylindrical housing, and a second compartment defined by the second surface of the circuit board and a second portion of the inner peripheral surface of the cylindrical housing. As explained below in further detail, it is preferred that the circuit board is positioned at a location below the centerline of the filter housing.
A first shield member is also provided, extending from the first surface of the circuit board toward the first inner peripheral surface of the cylindrical housing. The electronic signal filter further includes a second shield member radially opposing the first shield member extending from the second surface of the single circuit board toward the second inner peripheral surface of the cylindrical housing, the second shield member being electrically connected the first shield
Clark Gary
Lamb Michael
Maguire Joseph N.
Zennamo, Jr. Joseph A.
Burr & Brown
Eagle Comtronics, Inc.
Pascal Robert
Takaoka Dean
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