1. Technical Field
The present invention relates generally to electronic filters used in the cable television industry, and relates more particularly to the construction and assembly of such filters.
2. Background Art
Typical electronic filter constructions in the cable television (CATV) industry involve a considerable number of parts, such as, for example, one or more circuit boards, connecting wires or leads, filter circuit components, isolation plates, blocks or chambers, input and output terminals, moisture barrier seals or plugs, connector housings, sub-housings or caps, o-rings, outer housing sleeves, and potting material. This elaborate array of parts constrains efforts to: minimize the size and weight of the filters; reduce material and labor costs associated with assembly of the filters; and simplify and automate the assembly process. Examples of such filter constructions are shown and described in: U.S. Pat. No. 5,278,525 to Palinkas; U.S. Pat. No. 4,901,043 to Palinkas; U.S. Pat. No. 4,701,726 to Holdsworth; U.S. Pat. No. 4,451,803 to Holdsworth et al; U.S. Pat. No. 3,579,156 to Parfitt; and U.S. Pat. No. 3,065,434 to Calderhead.
For such CATV filters as highpass and lowpass filters, diplex filters, windowed highpass filters, and step attenuator (or return path) filters, tunable filter circuits and shielding between filter components and circuits are not normally required. Thus, for these types of filters, an opportunity is presented to simplify filter components, construction and assembly. U.S. Pat. No. 5,745,838 to Tresness et al. discloses (FIGS. 8-10) a filter construction for a return path filter called a xe2x80x9cstep attenuator.xe2x80x9d This construction is also shown in FIG. 2 herein, as representing the prior art construction for this type of filter. While simplification was achieved in U.S. Pat. No. 5,745,838, the construction still required two major o-rings around the male and female terminal caps and an outer housing sleeve (See FIG. 2 herein); and, manual assembly of these parts was still required.
Many diplex, windowed highpass, and return path filters (See, e.g., embodiments shown in FIGS. 1-5 of U.S. Pat. No. 5,745,838), have dual (or xe2x80x9cparallelxe2x80x9d) circuit paths. For example, FIG. 1, herein, shows a simplified step attenuator circuit 10 containing a forward (or highpass) path 12 and a return (or lowpass) path 14. Cascaded or elongated circuit board arrangements such as shown in U.S. Pat. No. 5,770,983 to Zennamo, Jr. et al., U.S. Pat. No. 4,901,043 to Palinkas, U.S. Pat. No. 4,701,726 to Holdsworth, U.S. Pat. No. 4,451,803 to Holdsworth et al., U.S. Pat. No. 3,579,156 to Parfitt, and U.S. Pat. No. 3,065,434 to Calderhead, are not optimum platforms for such dual path filters. A more optimum platform would be to have two circuit boards disposed in a parallel arrangement.
U.S. Pat. No. 5,278,525 to Palinkas discloses parallel circuit boards for a CATV notch filter (or xe2x80x9ctrapxe2x80x9d), rather than for a dual path filter. The construction includes a considerable number of extra parts, such as an isolation shield, circuit board housings, tuning screw housings, o-rings, and an outer housing sleeve.
In most CATV applications, the filters are installed in an outdoor environment. Thus, it is important that the filter construction be moisture resistant. Efforts to make filters moisture resistant have included enclosing the filter in an outer housing sleeve and employing o-rings between the filter and the outer housing sleeve. See, e.g., U.S. Pat. No. 5,745,838 to Tresness et al., U.S. Pat. No. 5,278,525 to Palinkas, U.S. Pat. No. 4,701,726 to Holdsworth, and U.S. Pat. No. 4,451,803 to Holdsworth et al. Such an approach requires the additional parts and expense of o-rings and outer housing sleeves, and may require manual assembly of such parts.
A prime path for moisture penetration into the filter is through the terminal fittings or connectors. While efforts to prevent moisture penetration through filter connectors (such as disclosed in U.S. Pat. No. 5,278,525 to Palinkas) have been satisfactory, there remains a need to improve moisture resistance through these connector paths.
Another consideration in CATV filter construction is to establish a good and reliable electrical ground between the filter circuit or circuits and the filter housing. Electrical ground has been established by soldering or fitting isolation shields or blocks between the circuit boards and the filter housing, or by soldering wires or leads between the circuit board and housing. See, for example, U.S. Pat. No. 4,701,726 to Holdsworth. However, such methods usually require additional components or manual assembly steps.
It is therefore an object of the present invention to provide an electronic filter construction that avoids the limits and problems associated with the prior art.
It is another object of the present invention to provide an electronic filter construction that is more suitable for automated assembly than previous filter constructions.
It is a further object of the present invention to provide an electronic filter construction that requires less parts than previous filter constructions.
It is still another object of the present invention to reduce material and labor costs associated with the assembly of an electronic filter;
It is still a further object of the present invention to reduce the size and weight of an electronic filter;
It is yet another object of the present invention to provide an electronic filter construction that is optimum for dual (or parallel) path filter circuits;
It is yet a further object of the present invention to provide an electronic filter construction that establishes an effective and reliable ground connection between the filter""s circuitry and the filter housing; and
It is still yet another object of the present invention to provide an electronic filter construction that has improved moisture resistance.
These and other objects are attained in accordance with the present invention wherein there is provided a filter assembly, comprising (1) a first terminal cap, (2) a second terminal cap, (3) a first circuit board, and (4) a second circuit board. The first and second terminal caps are disposed along a longitudinal axis in opposing relation to each other. The terminal caps are physically and electrically coupled to each other.
Both circuit boards are physically coupled to the first terminal cap. The first circuit board includesxe2x80x94(i) front and rear surfaces, (ii) a first filter circuit located on either or both of the front and the rear surfaces, (iii) a ground contact electrically coupled to the first filter circuit and to said first terminal cap, and (iv) a first filter terminal coupled to the first circuit. The second circuit board includesxe2x80x94(i) front and rear surfaces, (ii) a second filter circuit located on either or both of the front and the rear surfaces, (iii) a ground contact electrically connected to the second filter circuit and to said first terminal cap, and (iv) a second filter terminal coupled to the second circuit. The first and second circuits are electrically coupled to each other, and each circuit is electrically coupled to the first terminal cap via the ground contacts such that the circuits have a common ground through the first terminal cap.
The first and second circuit boards are positioned substantially parallel to each other and to the longitudinal axis, between the terminal caps. The front surface of the first circuit board substantially faces the front surface of the second circuit board. The first and second terminals extend into and are operatively supported inside the first and second terminal caps, respectively.
In a modified embodiment, the filter assembly of the present invention may include only a single circuit board physically coupled to the first terminal cap. In such an embodiment, the single circuit board would includexe2x80x94(i) front and rear surfaces, (2) a filter circuit located on either or both of the front and rear surfaces, (iii) a ground contact electrically coupled to the filter circuit and to the first terminal cap, and (iv) first and second filter terminals electrically coupled to the filter circuit. The filter circuit is electrically coupled to the first terminal cap via the ground lead, such that the circuit is grounded through the first terminal cap. The single circuit board is positioned substantially parallel to the longitudinal axis, between the terminal caps. The first and second terminals extend into and are operatively supported inside the first and second terminal caps, respectively.
In an alternative embodiment, a filter assembly is provided, which comprisesxe2x80x94(1) first and second terminal caps, (2) a filter circuit, (3) first and second filter terminals, (4) first and second sealing members, and (5) an o-ring. The first and second terminal caps are arranged in opposing relation to each other. The first cap is directly connected to the second cap to form a filter housing which defines an interior volume. The first cap contains an external groove, and the connection between the first and second caps is substantially sealed by solder received in the groove. The caps contain first and second terminal passages, respectively, between the interior volume and the exterior of the filter assembly.
A filter circuit is mounted inside the filter housing. The filter terminals are electrically coupled to the filter circuit. The first and second terminals extend through and are operatively supported inside the first and second terminal passages, respectively. The first sealing member is secured in and substantially closes the first terminal passage. The first sealing member contains a hole through which the first terminal tightly fits. The second sealing member is secured in and substantially closes the second terminal passage. The second sealing member contains a hole through which the second terminal tightly fits. The o-ring is seated inside the second terminal passage, between the second sealing member and the second terminal cap.