Voltage reference source with a low supply voltage range and active feedback for pll

摘要

A current reference circuit includes a first, current mirror transistor having a gate coupled to a first feedback node, a source coupled to a first supply terminal and a drain forming a first reference node. A second, current mirror transistor has a gate coupled to the first feedback node, a source coupled to the first supply terminal and a drain forming a second reference node. A third transistor has a gate coupled to a second feedback node, a source coupled to a second supply terminal and a drain coupled to the first reference node. A fourth transistor has a gate coupled to the second feedback node, a source coupled to the second supply terminal and a drain coupled to the second reference node. A first operational amplifier has a first input coupled to the first reference node, a second input coupled to a bias node and an output forming the first feedback node. A second operational amplifier has a first input coupled to the second reference node, a second input coupled to the bias node and an output forming the second feedback node. The operational amplifiers are active elements which allow the current reference circuit to operate at a very low voltage and have a very low sensitivity to changes in the supply voltage.