National Semiconductor Corporation

John Andrew Campbell

Jitendra Mohan

Gary A Brown

A stacked current mirror circuit includes four N-channel MOS transistors. One transistor serves as an input device for conducting via its drain, a majority of the reference current. Another transistor is connected as a mirroring device, with its drain coupled to a voltage source, its gate coupled to the gate of the input device, and its source coupled to the source of the input device at a first common node. These two transistors couple to form a first current mirror circuit which couples to the input of a second current mirror comprising the third and fourth transistors. The drain and gate of the third transistor couple to the first common node and the gate of the fourth transistor. The sources of both the third and fourth transistors couple to a second common node (e.g., ground), and the drain of the fourth transistor provides the output. As a result, current is mirrored from the input device transistor to the mirroring device transistor, and then forced through the third transistor. The current is then mirrored from the third transistor to the fourth transistor which forces the current to the output line.

Current mirror current source with current shunting circuit

A current mode driver capable of driving both 10 Base-T signalling and 100 Base-T signalling in a Local Area Network (LAN) includes two or four current sources. In a first embodiment, a differential signal generator drives four current sources. The generator outputs four signals, one of which is received by each current source. Using these signals, two of the current sources push or pull current across the load in one direction, while the other two current sources push or pull current across the load in the other direction, such that a full differential signal is generated across the load. In another embodiment, a signal generator drives two current sources which drive into the load one at a time. Two switches provide either high resistance or low resistance during half of a signal cycle such that current is pulled through the load in one direction, and prevented from flowing through the load in the other direction. When one current source turns on upon receipt of an input signal, one switch provides low resistance such that when the current source drives current into the load a voltage is generated across the load. At the same time, the other switch provides high resistance such that virtually no current is conducted. In this manner, only one current source pulls current across the load at a given time, while the other current source remains in a standby state.

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Davis, CA, United States of America

John Andrew Campbell