Patent ID: 7081781

Claim:
A differential charge pump, comprising: a current switch responsive to a pulse width difference between a differential up voltage and a differential down voltage to source and sink a current in a complementary fashion from a pair of differential output nodes, wherein the differential output nodes are voltage isolated from the current switch; a first transconductance amplifier configured to convert a voltage at a first one of the differential output nodes into a first current; a second transconductance amplifier configured to convert a voltage a second one of the differential output nodes into a second current that is complementary to the first current; a resistive load coupled between a first node and a second node, wherein the first transconductance amplifier is configured to couple the first current to the first node and the second transconductance amplifier is configured to couple the second current to the second node; a first differential pair of transistors biased by a first current source to conduct the current, the transistors in the first differential pair being responsive to the differential up voltage such that when the differential up voltage is pulsed the current is conducted by a first transistor in the first differential pair and when the differential up voltage is not pulsed the current is conducted by a remaining second transistor in the first differential pair; a second differential pair of transistors biased by a second current source to conduct the current such when the differential down voltage is pulsed the current is conducted by a first transistor in the second differential pair and when the differential up voltaqe is not pulsed the current is conducted by a remaining second transistor in the second differential pair; a first current source configured to source twice the current to a third node; and a second current source configured to source twice the current to a fourth node, wherein the first transistor in the first differential pair and the second transistor in the second differential pair couples to the third node through a first pair of resistors, and wherein the second transistor in the first differential pair and the first transistor in the second differential couples to the fourth node through a second pair of resistors, whereby the first and second pairs of resistors perform the voltage isolation of the current switch from the differential output nodes.