Highly linear operational transconductance amplifier with low transconductance

In an amplifier circuit, a method of providing first and second current output signals substantially proportional to a difference between first and second input voltages, comprising the steps of:

• providing a virtual ground node for sinking a virtual ground current;
• selectively diverting said virtual ground current through first and second circuit paths in response to first and second input voltages;
• dropping a voltage in said first and second circuit paths substantially proportional to first and second currents therethrough;
• mirroring said first and second currents flowing in said first and second circuit paths to third and fourth circuit paths, respectively;
• establishing a voltage on first and second nodes of the amplifier circuit in response to currents mirrored to said third and fourth, circuit paths respectively;
• and
• providing the first and second current output signals through said first and second nodes.

An operational transconductance amplifier, comprising:

• a virtual ground circuit, for providing a virtual ground node and for sinking a current from said virtual ground node to a first power supply voltage terminal;
• a first transistor having a first current electrode, a control electrode for receiving a first input voltage, and a second current electrode coupled to said node;
• a second transistor having a first current electrode, a control electrode for receiving a second input voltage, and a second current electrode coupled to said node;
• a third transistor having a first current electrode for providing a first current signal, a control electrode for receiving a transconductance signal, and a second current electrode coupled to said first current electrode of said first transistor;
• and
• a fourth transistor having a first current electrode for providing a second current signal, a control electrode for receiving said transconductance signal, and a second current electrode coupled to said first current electrode of said second transistor.