Device, method and system for estimating the termination to a wired transmission-line based on determination of characteristic impedance
View Patent ↗A system and method for measuring a characteristic impedance of a transmission-line comprises transmitting energy to the line, and shortly after measuring the voltage/current involved and thus measuring the equivalent impedance. The measured characteristic impedance may then be used in order to determine the termination value required to minimize reflections. In another embodiment, the proper termination is set or measured by adjusting the termination value to achieve maximum power dissipation in the terminating device. The equivalent characteristic impedance measurement may be used to count the number of metallic conductors connected to a single connection point. This abstract is not intended to limit or construe the scope of the claims.
1. A device for estimating the termination to a wired transmission-line carrying a signal in a first frequency band, the device comprising:
a port for connecting to one end of the wired transmission-line,
an energy transmitter coupled to said port for transmitting energy to the wired transmission-line, the energy being in a second frequency band distinct and separate from the first frequency band, while the signal in the first frequency band is being carried simultaneously with the energy in the second frequency band by the wired transmission-line, and
an impedance measuring unit coupled to the one end of the transmission-line for instantaneously measuring the characteristic impedance Z of the transmission-line on the basis of the energy in the second frequency band, wherein the optimal termination value of the transmission-line is estimated based on the measured value Z.
2. The device according to claim 1 , further comprising a memory coupled to said impedance measuring unit for storing the measured impedance value.
3. The device according to claim 1 , wherein the estimated value is equal to the measured value Z.
4. The device according to claim 1 , further comprising means for connecting a termination having the estimated value to the wired transmission-line.
5. The device according to claim 1 , wherein the wired transmission-line comprises a wire pair at least partially hidden in the wall of a building and connected to an outlet having a front faceplate, and said port comprises a connector for connecting to a further connector on the front faceplate of the outlet.
6. The device according to claim 1 , further comprising a selector for operating said device either periodically, or upon application of an external signal, or upon a manual action, or upon powering up of the device.
7. The device according to claim 1 , wherein said impedance measuring unit is operative to measure the characteristic impedance on the transmission-line in the absence of any reflections on the transmission-line.
8. The device according to claim 1 , further comprising a pulse generator connected for applying to the transmission-line a measuring pulse having a period τ, and said impedance measuring unit is operative to measure the characteristic impedance Z of the transmission-line during the period τ.
9. The device according to claim 8 , wherein the period τ is shorter than the time between the start of the measuring pulse and appearance of any reflection of the measuring pulse at said impedance measuring unit.
10. The device according to claim 1 , wherein said impedance measuring unit comprises a pulse generator and a single resistor having a known resistance value permanently connected in series between said pulse generator and said port, said pulse generator producing a measuring pulse having a known voltage value to cause a current to flow through said resistor and the transmission-line, and further wherein said impedance measuring unit has an input connected to a point between said resistor and the transmission-line to detect the voltage at said point in response to the measuring pulse.
11. The device according to claim 1 , wherein the measured characteristic impedance is the lumped characteristic impedance of the transmission-line.
12. The device according to claim 1 , further comprising a filter coupled between said port and said energy transmitter, said filter being operative to substantially pass only the energy in the second frequency band.