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Digital filter circuit and method for blocking a transmission line reflection signalRelated Patent Categories: Pulse Or Digital Communications, Systems Using Alternating Or Pulsating CurrentDigital filter circuit and method for blocking a transmission line reflection signal description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060140285, Digital filter circuit and method for blocking a transmission line reflection signal. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates in general to transmission line terminators, and more particularly, to a digital filter circuit and method for blocking transmission line reflection signals arising from an incomplete termination impedance being coupled to an end of the transmission line. [0002] In order to properly transmit data in a network, reflection signals on the transmission lines of the network need to be managed. Reflection signals are typically avoided by terminating a transmission line at both its input and output with the line's characteristic impedance. One disadvantage of using termination of both transmission line ends, however, is the amount of power that is consumed by the termination resistors. [0003] The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a blocking filter for a device receiving signals from a transmission line. The blocking filter includes a pulse generator for generating a masking pulse timed and of sufficient duration to block at the device a reflection signal within a received signal from the transmission line, wherein the reflection signal results from incomplete termination of the transmission line. The filter further includes logic for combining the masking pulse with the received signal, such that the reflection signal is blocked by the masking pulse at the blocking filter. [0004] In another aspect, a network is provided which includes a bus system having a transmission line which is incompletely terminated, wherein a reflection signal arises with transmission of a signal across the transmission line. The network further includes a device connected to the transmission line for receiving the signal. The device includes a blocking filter having a pulse generator for generating a masking pulse timed and of sufficient duration to block at the device the reflection signal, and logic for combining the masking pulse with the signal received from the transmission line, wherein the reflection signal is blocked by the masking pulse. [0005] In a further aspect, a method of filtering received signals from a transmission line is provided. The method includes: generating a masking pulse timed and of sufficient duration to block at a device connected to the transmission line a reflection signal within the received signal from the transmission line, the reflection signal resulting from incomplete termination of the transmission line; and combining the masking pulse with the received signal, wherein the reflection signal is blocked by the masking pulse. [0006] Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. [0007] The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: [0008] FIG. 1 is an example of a complex network topology within which transmission line reflection signal filtering can be employed, in accordance with an aspect of the present invention; [0009] FIG. 2 is a schematic of an approach for operating a transmission line with termination resistors at the input end and output end of the line; [0010] FIG. 3 is an alternate embodiment for operating a transmission line with the termination resistor at the output end of the line removed and only capacitive loading remaining; [0011] FIG. 4 graphically represents a signal at the input end of the transmission line of FIG. 3 for different values of input termination resistance as signal voltage falls from voltage V to ground; [0012] FIG. 5 graphically represents the signal at the output end of the transmission line of FIG. 3 for different values of input termination resistance as signal voltage falls from voltage V to ground; [0013] FIG. 6 depicts another embodiment of a transmission line operated with a termination resistance at the input end and capacitive loading at the output end, and having a capacitance at the input end modeling the capacitance of a common mode filter at the input of the line; [0014] FIG. 7 graphically depicts voltage input and voltage output signals for the transmission line depicted in FIG. 6, with a signal state change from voltage V to ground occurring; [0015] FIG. 8 is a high level, partial schematic of a receiver device with a blocking filter for handling a transmission line reflection signal, in accordance with an aspect of the present invention; [0016] FIG. 9 is a schematic of one embodiment of a blocking filter for the receiver of FIG. 8, in accordance with an aspect of the present invention; [0017] FIG. 10 graphically illustrates a received voltage signal (A), a desired output voltage signal (B) and a masking voltage signal (C) occurring within the blocking filter of FIG. 9, in accordance with an aspect of the present invention; [0018] FIG. 11 depicts another embodiment of a blocking filter showing one embodiment of the pulse generator of FIG. 9, in accordance with an aspect of the present invention; [0019] FIG. 12 graphically illustrates a received voltage signal (A), a desired voltage out signal (B), a masking signal (C), and a delayed reset signal (D) occurring within the blocking filter of FIG. 11, in accordance with an aspect of the present invention; [0020] FIG. 13 depicts another embodiment of a blocking filter, which allows part of the reflection signal to be outside of the masking signal while still blocking the reflection signal, in accordance with an aspect of the present invention; [0021] FIG. 14 graphically illustrates a received voltage signal (A), a desired voltage out signal (13), a masking signal (C), and an extended delayed reset signal (D) for the circuit of FIG. 13, in accordance with an aspect of the present invention; [0022] FIG. 15 depicts another embodiment of a blocking filter, which again allows part of the reflection signal to be outside of the masking signal, and which has fast reset of the delay circuit, in accordance with an aspect of the present invention; [0023] FIG. 16 graphically illustrates voltage signals using the circuit of FIG. 15, including a received voltage signal (A), a desired voltage out signal (B), a masking signal (C), a delayed reset signal (D), and an extended masking signal (E), in accordance with an aspect of the present invention; [0024] FIG. 17 is a schematic of one embodiment of a blocking filter for blocking both falling and rising edge reflection signals, in accordance with an aspect of the present invention; Continue reading about Digital filter circuit and method for blocking a transmission line reflection signal... 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