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Method and apparatus for a low voltage high current bi-directional termination voltage regulator
| Details |
Inventors: Covaro, Mark;
Assignee: Cisco Technology, Inc. (San Jose, CA)
Primary Examiner: Wong; Peter S.
Assistant Examiner: Patel; Rajnikant B.
Attorney, Agent or Firm: Ritter Van Pelt and Yi, LLP
A low voltage high current bi-directional termination voltage regulator for use in a bus termination circuit in a repeater stack is disclosed that includes an operational amplifier, a bipolar transistor current source circuit, and a bipolar transistor current sink circuit. The operational amplifier is configured to source current to a first node when the output voltage at a second node is pulled below a nominal termination voltage and configured to sink current from the first node when the output voltage at the second node is pulled above the nominal termination voltage, the second node being connected to a termination load. The bipolar transistor current source circuit is configured to source current to the second node when the operational amplifier sources current to the first node so that the output voltage at the second node is pulled up as a result of the current sourced by the bipolar transistor current source circuit through the second node to the termination load. The bipolar transistor current sink circuit is configured to sink current from the second node when the operational amplifier sinks current from the first node so that the output voltage at the second node is pulled down as a result of the current sinked by the bipolar transistor current source circuit through the second node from the termination load. Thus, the output voltage at the second node is maintained at the nominal termination voltage. |
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DETAILED DESCRIPTION Accordingly, the present invention provides a low voltage high current bi-directional termination voltage regulator.
In one embodiment, the bi-directional termination voltage regulator is used to source and sink a large amount of current for a termination circuit that terminates a stack bus for a Class II Fast Ethernet repeater stack.
The termination circuit is connected to the bus at the repeaters in the repeater stack that happen to be plugged into the top and bottom ends of the stack.
The termination circuit prevents reflections of signals on the bus that would otherwise occur and degrade the performance of the bus.
The voltage regulator sources and sinks approximately 1 Amp of current from data lines which make up a stack bus for a stack bus termination circuit that terminates the stack bus to approximately 2.
5V at an impedence of approximately 68.
OMEGA.
.
The termination voltage regulator is powered by a low voltage power supply at approximately 4V that provides power over the repeater stack connection cable.
Power is provided to the top and bottom repeaters regardless of whether or not they happen to be powered on.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium.
Several inventive embodiments of the present invention are described below.
In one embodiment, a low voltage high current bi-directional termination voltage regulator for use in a bus termination circuit in a repeater stack includes an operational amplifier, a bipolar transistor current source circuit, and a bipolar transistor current sink circuit.
The operational amplifier is configured to source current to a first node when the output voltage at a second node is pulled below a nominal termination voltage and configured to sink current from the first node when the output voltage at the second node is pulled above the nominal termination voltage, the second node being connected to a termination load
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Multiplexer-related 
