Relay switch including an energy detection circuit
A semiconductor relay switch having two data ports receiving incoming signals and a power supply terminal receiving a power supply voltage is responsive to a power supply voltage level and an energy level of the incoming signals to open and close its conduction paths. The relay switch is open when a valid power supply level is detected and when there is no supply power on the power supply terminal but a high energy level is detected in the incoming signals. The relay switch is closed to allow conduction between the two data ports only when there is no power supply voltage on the power supply terminal and an energy level below a predetermined threshold is detected in the incoming signals. In one embodiment, the semiconductor relay switch includes a main conduction switch circuit, an energy detect circuit and a control signal generator.
1. A method for operating a relay switch connected between a first data port and a second data port and receiving a power supply voltage signal, the method comprising:
measuring the voltage level of the power supply voltage signal;
measuring an energy level of incoming signals on either one of the first and second data ports;
opening the relay switch to isolate the first and second data ports when the voltage level of the power supply voltage signal is greater than a predetermined supply voltage threshold level;
opening the relay switch to isolate the first and second data ports when the voltage level of the power supply voltage signal is equal to or below the predetermined supply voltage threshold level and the energy level of the incoming signals on either one of the first and second data ports is greater than a predetermined energy threshold level; and
closing the relay switch to electrically connect the first and second data ports when the voltage level of the power supply voltage signal is equal to or below the predetermined supply voltage threshold level and the energy level of the incoming signals on either one of the first and second data ports is less than or equal to the predetermined energy threshold level.
2. The method of claim 1 , wherein the relay switch comprises a plurality of pairs of complementary conduction paths connecting the wires of the first data port to the wires of the second data port, the method further comprises:
shunting a first conduction path in each pair of complementary conduction paths to the power supply voltage signal when the relay switch is open; and
shunting a second conduction path in each pair of complementary conduction paths to a ground potential when the relay switch is open.
3. The method of claim 1 , wherein the first data port and the second data port each comprises a pair of wires carrying differential signals, measuring an energy level of incoming signals on either one of the first and second data ports comprises:
accumulating energy from first transitions of the incoming signals being carried on the pairs of wires of the first data port and the second data port; and
collecting charge at a charge storage device at a first time constant,
wherein the first time constant is selected to allow charge to accumulate at the charge storage device when the incoming signals have a high pulse density.
4. The method of claim 3 , wherein collecting charge at a charge storage device at a first time constant comprises:
accumulating charge onto and removing charge from the charge storage device at a rate determined by the first time constant, a net charge accumulated on the charge storage device being a function of the pulse density of the incoming signals.
5. The method of claim 1 , wherein the relay switch comprises a plurality of pairs of complementary conduction paths connecting the wires of the first data port to the wires of the second data port, the method further comprises:
generating one or more control signals in response to the voltage level of the power supply voltage signal and the energy level of the incoming signals, each control signal of the one or more control signals driving a conduction path in the plurality of pairs of complementary conduction paths; and
opening the relay switch and closing the relay switch in response to the one or more control signals.
6. The method of claim 5 , wherein generating one or more control signals comprises:
providing a plurality of pairs of complementary precursor control signals, each precursor control signal corresponding to a control signal in the one or more control signals;
generating at least one precursor control signal in a pair of complementary precursor control signals; and
driving a control signal corresponding to the other precursor control signal in the pair of complementary precursor control signals to a complementary state.
7. The method of claim 6 , wherein generating one or more control signals further comprises:
driving the control signals corresponding to the pair of complementary precursor control signals through feedback to boost the voltage values of the control signals.