The XTR111 offers low offset voltage error at the input, which normally does not require cancellation. If the signal source cannot deliver 0V in a single-supply circuit, add a resistor from the SET pin to a positive reference voltage or the regulator output to shift the zero level for the input (V_IN) to a positive voltage. Therefore, the signal source can drive this value within a positive voltage range. The example in Figure 6-8 shows a 100mV (102.04mV) offset generated to the signal input. The larger this offset, however, the more influence of drift and inaccuracy is seen in the output signal. The voltage at SET must not be larger than 12V for linear operation.

Figure 6-8 Input Voltage Level Shift for a 0mA Output Current

Transconductance (the input voltage to output current ratio) is set by R_SET. The desired resistor value can be found by choosing a combination of two resistors.