US Patent 7893756 Precision current source

A device for providing a precision current includes a first operational amplifier and multiple path transistors. The first operational amplifier outputs a gate voltage based on reference voltage and input voltages. The path transistors have corresponding gates for receiving the gate voltage from the first operational amplifier. Each path transistor is connected to a first enable transistor configured to selectively connect the path transistor to a reference path and a second enable transistor configured to selectively connect the path transistor to an output path. The first and second enable transistors are separately enabled by first and second enable signals, respectively. At least one path transistor is connected to the reference path through a corresponding first enable transistor to provide the reference current, and least one other path transistor is connected to the output path through a corresponding second enable transistor to provide the precision current based on the reference current.