Diplex circuit forming bandstop filter

Details Diplex circuit forming bandstop filter Diplex circuit forming bandstop filter

2002-12-03

2004-05-18

Summons, Barbara (Department: 2817)

Wave transmission lines and networks

Plural channel systems

Having branched circuits

C333S176000, C333S167000, C725S128000

Reexamination Certificate

active

06737935

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to filter circuits of the type used in cable television (CATV) applications, and more specifically to bandstop filters.
A diplex circuit, or more simply a “diplexer,” is a device which separates or combines RF signals. It has been found expedient to utilize diplexers in connection with CATV equipment in a number of situations, some of which use two diplexers back-to-back. These include step attenuators, power bypass circuits, cable simulators and equalizer circuits. Many of the prior art CATV diplex circuits are used to act on signals traveling in so-called forward and return paths, e.g., relatively high frequency RF signals pass from a source of such signals to a television set at subscriber premises in the forward direction over one leg of the circuit while lower frequency (DC) signals pass from the premises in the return direction.
Bandstop or “notch” filters are commonly employed in the CATV industry to block transmission of signals in a specified frequency range. For example, certain channels may be designated as premium channels, requiring payment of a fee from the subscriber in order to receive the signals carrying information representing such channels. If the service is not ordered, i.e., the fee is not paid, an appropriate filter is installed in the cable line coming into the non-paying premises. This is but one of the more traditional uses of bandstop filters, i.e., as a so-called trap. A more recent example is the aforementioned use in the handling of forward and return path signals between a headend and subscriber facilities.
It is desirable that bandstop filters be as compact as possible commensurate with quality performance of their intended function. It is also desirable, of course, that the filters be as inexpensive as possible, again while maintaining high performance criteria. Passband insertion and return loss is of critical importance in such filters, particularly in the digital signal market, which is steadily growing in significance.
It is an object of the present invention to provide a bandstop filter of smaller size than prior art filters offering the same level of performance.
Another object is to provide a bandstop filter for CATV applications which requires a smaller number of components than prior art filters of comparable capabilities.
A further object is to provide a bandstop filter with improved passband insertion and return loss.
It is a principal object to provide a bandstop filter for the CATV industry which incorporates all of the above advantages, i.e., achieving economics of both size and cost while still realizing improved performance.
Other objects will in part be obvious and will in part appear hereinafter.
SUMMARY OF THE INVENTION
In accordance with the foregoing objectives, the bandstop filter of the invention two diplexers, back-to-back, in series. A single input line carries signals in a frequency range of , e.g., 0-3 GHz, to a node connected to each of a highpass and a lowpass filter, in parallel. Only signals having a frequency above a first, predetermined value pass through the highpass filter, and only signals having a frequency below a second, predetermined value pass through the lowpass filter. The first and second values are chosen so that a predetermined range of frequencies, i.e., the range or band of frequencies below the first and above the second value, is “stopped” from passing to the single output line. Thus, the RF signals are divided by the first diplexer between those at frequencies which pass the highpass and those which pass the lowpass filters. The outputs of the high and lowpass filters are connected at a second node to form a second diplexer having an output including only signals having frequency values which pass the high and lowpass filters. Frequencies between those passed by the high and lowpass filters do not appear at the output, thereby providing the bandstop. The diplexers are frequency selective, resulting in lower insertion loss due to frequency isolation of the two output ports.
By implementing this circuitry with surface mount technology the bandstop filter of the invention requires fewer components than conventional filters of the same type and level of performance. This means, of course, that the filter of the invention may be fabricated in smaller size and at lower cost than comparable prior art filters. In the preferred embodiment, the components are of the surface mount type with the components forming the highpass and lowpass filters mounted on opposite sides of a single printed circuit board. The circuit also exhibits improved passband insertion and return loss, which is a particularly important feature in the digital signal market.


REFERENCES:
patent: 2462491 (1949-02-01), Hallett
patent: 3579154 (1971-05-01), Deen
patent: 3806813 (1974-04-01), Eller
patent: 3956717 (1976-05-01), Fisher et al.
patent: 4100516 (1978-07-01), Hall
patent: 4701726 (1987-10-01), Holdsworth
patent: 4783639 (1988-11-01), Hudspeth et al.
patent: 4954790 (1990-09-01), Barber
patent: 4963966 (1990-10-01), Harney et al.
patent: 5150087 (1992-09-01), Yoshie et al.
patent: 5278525 (1994-01-01), Palinkas
patent: 5304967 (1994-04-01), Hayashi
patent: 5548255 (1996-08-01), Spielman
patent: 5745838 (1998-04-01), Tresness et al.
patent: 5793265 (1998-08-01), Spielman
patent: 5815052 (1998-09-01), Nakajima et al.
patent: 5821831 (1998-10-01), Marland
patent: 5881362 (1999-03-01), Eldering et al.
patent: 5898406 (1999-04-01), Matero
patent: 5906512 (1999-05-01), Reynolds
patent: 5999796 (1999-12-01), Tresness et al.
patent: 6031432 (2000-02-01), Schreuders
patent: 6177849 (2001-01-01), Barsellotti et al.
patent: 6191666 (2001-02-01), Sheen
patent: 6252474 (2001-06-01), Mizutani

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