Patent ID: 8319553

Claim:
An apparatus, comprising: a first transconductance amplifier having a first voltage input, a second voltage input, a first current output, and a second current output, the first transconductance amplifier comprising: a resistor; a first transistor having a gate, a drain, and a source, the gate electrically connected to the first voltage input; a second transistor having a gate, a drain, and a source, the gate electrically connected to the second voltage input, wherein the first and second transistors are configured to generate a voltage across the resistor resulting in a current, wherein a difference in output currents between the first and second current outputs corresponds to the current; a first amplifier having a first input, a second input, and an output, the first and second inputs electrically connected to the drain and to the source of the first transistor, respectively; a third transistor having a gate, a drain, and a source, wherein the drain and the source of the third transistor are disposed in a signal path between the source of the first transistor and the first current output, and wherein the first amplifier is configured to control the voltage of the gate of the third transistor so as to control a difference in voltage between the drain and the source of the first transistor; a second amplifier having a first input, a second input, and an output, the first and second inputs electrically connected to the drain and to the source of the second transistor, respectively; and a fourth transistor having a gate, a drain, and a source, wherein the drain and the source of the fourth transistor are disposed between the source of the second transistor and the second current output, and wherein the second amplifier is configured to control the voltage of the gate of the fourth transistor so as to control a difference in voltage between the drain and the source of the second transistor.