A circuit configured to track a change in current mismatch between a first current source and a reference current source under varying temperatures, the circuit comprising: the first current source (14), wherein the first current source comprises a first transistor having a first transconductance which varies with temperature, wherein the first current source is driven by a first bias voltage; and a trim circuit coupled to the first current source to supply an output current to the first current source for calibrating the first current source, the trim circuit comprising: a bias circuit configured to generate a bias current that varies with temperature, wherein the bias circuit comprises a differential transistor pair having a second transconductance which varies with temperature, wherein the variation of the second transconductance with temperature is proportional to the variation of the first transconductance with temperature, and wherein the bias current is a difference between the drain currents of the differential transistor pair and is proportional to the second transconductance of the differential transistor pair, wherein the bias circuit further comprises a current generator generating current proportional to a bandgap voltage, and two substantially identical resistors causing a voltage drop proportional to the current, wherein the differential transistor pair is coupled to the current generator and the two resistors, and wherein gate voltages of the differential transistor pair differ by twice the voltage drop; and a calibration digital to analog converter, CAL DAC configured to set the output current of the trim circuit, wherein a second bias voltage of the CAL DAC is independent of the first bias voltage and is derived from the bias current such that the output current of the trim circuit varies with temperature so as to track the change in current mismatch between the first current source and the reference current source under varying temperatures. the first current source (14), wherein the first current source comprises a first transistor having a first transconductance which varies with temperature, wherein the first current source is driven by a first bias voltage; and a trim circuit coupled to the first current source to supply an output current to the first current source for calibrating the first current source, the trim circuit comprising: a bias circuit configured to generate a bias current that varies with temperature, wherein the bias circuit comprises a differential transistor pair having a second transconductance which varies with temperature, wherein the variation of the second transconductance with temperature is proportional to the variation of the first transconductance with temperature, and wherein the bias current is a difference between the drain currents of the differential transistor pair and is proportional to the second transconductance of the differential transistor pair, wherein the bias circuit further comprises a current generator generating current proportional to a bandgap voltage, and two substantially identical resistors causing a voltage drop proportional to the current, wherein the differential transistor pair is coupled to the current generator and the two resistors, and wherein gate voltages of the differential transistor pair differ by twice the voltage drop; and a calibration digital to analog converter, CAL DAC configured to set the output current of the trim circuit, wherein a second bias voltage of the CAL DAC is independent of the first bias voltage and is derived from the bias current such that the output current of the trim circuit varies with temperature so as to track the change in current mismatch between the first current source and the reference current source under varying temperatures. a bias circuit configured to generate a bias current that varies with temperature, wherein the bias circuit comprises a differential transistor pair having a second transconductance which varies with temperature, wherein the variation of the second transconductance with temperature is proportional to the variation of the first transconductance with temperature, and wherein the bias current is a difference between the drain currents of the differential transistor pair and is proportional to the second transconductance of the differential transistor pair, wherein the bias circuit further comprises a current generator generating current proportional to a bandgap voltage, and two substantially identical resistors causing a voltage drop proportional to the current, wherein the differential transistor pair is coupled to the current generator and the two resistors, and wherein gate voltages of the differential transistor pair differ by twice the voltage drop; and a calibration digital to analog converter, CAL DAC configured to set the output current of the trim circuit, wherein a second bias voltage of the CAL DAC is independent of the first bias voltage and is derived from the bias current such that the output current of the trim circuit varies with temperature so as to track the change in current mismatch between the first current source and the reference current source under varying temperatures.