Wideband high impedance bridging module
View Patent ↗A bridge module provides connection between first and second conductors of a line under test and a test instrument adapted for use with the bridge module. The bridge module provides monitoring and measurement of DSL communication signals between the telephone company DSL terminal (DSLAM) and the subscriber home DSL equipment across a wide range of frequencies. The bridge module can be used at any point in the communications link and can be used while the link is active. The bridge module provides a clickless connection to the active DSL communications link to avoid interruption in DSL service.
1. A bridge module for providing connection between a test instrument and a line under test, the line under test having a first conductor and a second conductor, the bridge module comprising:
a first high impedance resistor in communication with the first conductor;
a second high impedance resistor in communication with the second conductor;
a first input switch in communication with said first conductor;
a second input switch in communication with said second conductor;
a first coupling capacitor in communication with said first high impedance resistor and said first input switch;
a second coupling capacitor in communication with said second high impedance resistor and said second input switch;
a receiver to amplify the signals received from said first and second capacitors;
wherein when said first and second switches are in an off state, a charging path is provided by said first and second high impedance resistors and said first and second capacitors to charge said first and second capacitors; and
wherein when said first and second switches are in an on state, a signal path is provided from said line under test to said test instrument by said first and second switches, said first and second capacitors and said receiver.
2. The bridge module as defined in claim 1 , further comprising a timer in communication with said first and second high impedance resistors and said first and second switches and wherein upon expiration of said timer said switches change from an off state to an on state.
3. The bridge module as defined in claim 2 , wherein said timer is provided by a resistor and a capacitor.
4. The bridge module as defined in claim 2 , wherein the timer is provided by a digital timer.
5. The bridge module as defined in claim 2 , further comprising a voltage detection comparator which receives a voltage between said first and second high impedance resistors.
6. The bridge module as defined in claim 5 , further comprising a bridge rectifier and wherein said voltage between said first and second high impedance resistors is provided to said bridge rectifier prior to said voltage detection comparator.
7. The bridge module as defined in claim 5 , wherein said voltage detection comparator is provided by an operational amplifier and a reference voltage is provided to said operational amplifier.
8. The bridge module as defined in claim 7 , wherein said reference voltage is approximately 1 volt.
9. The bridge module as defined in claim 2 , further comprising a timer comparator and wherein upon expiration of said timer a signal is provided from said timer comparator to change said switches from an off state to an on state.
10. The bridge module as defined in claim 9 , wherein a time constant is provided by said first high impedance resistor and said first coupling capacitor and wherein expiration of said timer does not occur until a time equivalent to at least four time constants has passed subsequent the provision of power to the bridge module.
11. The bridge module as defined in claim 1 , wherein said receiver is provided by a first receiver and a second receiver and wherein said first receiver receives signals from said first coupling capacitor and said second receive receives signals from said second coupling capacitor.
12. The bridge module as defined in claim 1 , wherein said receiver is provided by an operational amplifier.
13. The bridge module as defined in claim 1 , wherein said receiver provides a differential amplifier formed by a first amplifier and a second amplifier.
14. The bridge module as defined in claim 1 , wherein said receiver is a transimpedance amplifier.
15. The bridge module as defined in claim 1 , further comprising a controller (U 3 ) and an override switch (Q 1 ), wherein said controller provides an override signal from said test instrument to said first and second switches to turn said first and second switches on through said override switch.
16. The bridge module as defined in claim 1 , wherein power to the bridge module is provided by internal batteries.
17. The bridge module as defined in claim 1 , wherein power to the module is provided by the test instrument.
18. The bridge module as defined in claim 1 , further comprising an interconnect cable providing a connection between the bridge module and the test instrument.
19. The bridge module as defined in claim 18 , wherein said interconnect cable is provided by a 100 ohm cable.
20. The bridge module as defined in claim 1 , further comprising first and second leads for connection of said bridge module to said first and second conductors and wherein a length of said first and second leads is shorter than approximately ten percent of one-fourth of the wavelength of a signal to be applied to the first and second conductors.
21. A system for testing a line under test having a first conductor and a second conductor comprising:
an interconnect cable having a first end and a second end;
a test instrument for testing characteristics of the line under test, said test instrument including a connector for receiving said first end of said interconnect cable, wherein said test instrument provides a passive mode of operation;
a bridge module for providing connection between said test instrument and the line under test, the bridge module including:
a connector for receiving said second end of said interconnect cable;
a first high impedance resistor in communication with the first conductor;
a second high impedance resistor in communication with the second conductor;
a first input switch in communication with said first conductor;
a second input switch in communication with said second conductor;
a first coupling capacitor in communication with said first high impedance resistor and said first input switch; and
a second coupling capacitor in communication with said second high impedance resistor and said second input switch;
said system including a receiver for receiving signals from said first and second coupling capacitors and amplifying said signals;
wherein when said bridge module is in a passive mode and said first and second switches are in an off state, a charging path is provided by said first and second high impedance resistors and said first and second capacitors to charge said first and second capacitors; and
wherein when said bridge module is in a passive mode and said first and second switches are in an on state, a signal path is provided from said line under test to said test instrument by said first and second switches and said first and second capacitors.
22. The system of claim 21 , wherein said receiver is provided by said bridge module.
23. The system of claim 21 , wherein said receiver is provided by said test instrument.
24. The system of claim 21 , wherein said receiver is provided by a first receiver ad a second receiver and wherein said first receiver receives signals from said first coupling capacitor and said second receive receives signals from said second coupling capacitor.
25. The system of claim 21 , wherein said receiver is provided by an operational amplifier.
26. The system as defined in claim 21 , wherein power to the bridge module is provided by internal batteries.
27. The system as defined in claim 21 , wherein power to the module is provided by the test instrument.