A transconductance amplifier circuit for generating a nonlinear current comprising: a first amplifier having input terminals (IN+, IN-) for receiving an input voltage, the first amplifier configured to output a first current to a load, the first current having a substantially linear relationship to the input voltage within a first range so as to have a substantially linear transconductance (gm) over the first range; a plurality of resistances (R1-R4) connected in series between the first amplifier and the load, wherein the first current generated by the first amplifier causes a voltage drop across each of the resistances; and wherein nodes between the resistances provide different voltage taps as the first current is conducted by the plurality of resistances, characterized by: a plurality of first drive circuits (A1-A4) having enable terminals coupled to the different voltage taps, wherein the first drive circuits are successively enabled as the voltages at the voltage taps are increased as the first current goes more positive; and first current sources (M1-M4), each of the first current sources being controlled to be on or off by a respective one of the first drive circuits, wherein, when a particular one of the first drive circuits is enabled, the enabled first drive circuit turns on its associated first current source to increase current to the load by a discrete amount. a first amplifier having input terminals (IN+, IN-) for receiving an input voltage, the first amplifier configured to output a first current to a load, the first current having a substantially linear relationship to the input voltage within a first range so as to have a substantially linear transconductance (gm) over the first range; a plurality of resistances (R1-R4) connected in series between the first amplifier and the load, wherein the first current generated by the first amplifier causes a voltage drop across each of the resistances; and wherein nodes between the resistances provide different voltage taps as the first current is conducted by the plurality of resistances, characterized by: a plurality of first drive circuits (A1-A4) having enable terminals coupled to the different voltage taps, wherein the first drive circuits are successively enabled as the voltages at the voltage taps are increased as the first current goes more positive; and first current sources (M1-M4), each of the first current sources being controlled to be on or off by a respective one of the first drive circuits, wherein, when a particular one of the first drive circuits is enabled, the enabled first drive circuit turns on its associated first current source to increase current to the load by a discrete amount. a plurality of first drive circuits (A1-A4) having enable terminals coupled to the different voltage taps, wherein the first drive circuits are successively enabled as the voltages at the voltage taps are increased as the first current goes more positive; and first current sources (M1-M4), each of the first current sources being controlled to be on or off by a respective one of the first drive circuits, wherein, when a particular one of the first drive circuits is enabled, the enabled first drive circuit turns on its associated first current source to increase current to the load by a discrete amount.