Apparatus for sensing an output current in a communications device
First Claim
1. An apparatus for sensing current, comprising:
- a main transistor;
a sense transistor;
a first comparator configured to compare a drain to source voltage of the main transistor and a drain to source voltage of the sense transistor; and
a second comparator configured to compare a gate to source voltage of the main transistor and a gate to source voltage of the sense transistor,wherein the first comparator is further configured to provide an output that causes the drain to source voltage of the sense transistor to replicate the drain to source voltage of the main transistor and the second comparator is further configured to provide an output that causes the gate to source voltage of the sense transistor to replicate the gate to source voltage of the main transistor.
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Abstract
Power over Ethernet (PoE) communication systems provide power and data communications over the same communications link, where a power source device (PSE) provides DC power (for example, 48 volts DC) to a powered device (PD). The DC power is transmitted simultaneously over the same communications medium with the high speed data from one node to the other node. The PSE typically includes a controller that controls the DC power provided to the PD at the second node of the communications link. The PSE controller measures the voltage, current, and temperature of the outgoing and incoming DC supply lines to characterize the power requirements of the PD. The PSE controller includes a resistorless switch to measure the current. The resistorless switch includes a sense transistor and a current mirror to allowing the PSE controller to calculate the current based upon a replica current.
81 Citations
18 Claims
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1. An apparatus for sensing current, comprising:
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a main transistor; a sense transistor; a first comparator configured to compare a drain to source voltage of the main transistor and a drain to source voltage of the sense transistor; and a second comparator configured to compare a gate to source voltage of the main transistor and a gate to source voltage of the sense transistor, wherein the first comparator is further configured to provide an output that causes the drain to source voltage of the sense transistor to replicate the drain to source voltage of the main transistor and the second comparator is further configured to provide an output that causes the gate to source voltage of the sense transistor to replicate the gate to source voltage of the main transistor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An apparatus for sensing current, comprising:
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a main transistor configured to provide a first current in response to a first drain to source bias and a first gate to source bias; a sense transistor configured to provide a second current in response to a second drain to source bias and a second gate to source bias; a first comparator configured to compare the first drain to source bias and the second drain to source bias; and a second comparator configured to compare the first gate to source bias and the second gate to source bias, wherein the first comparator and the second comparator are further configured to provide a first output and second output, respectively, the first output and the second output causing the second current to replicate the first current. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification