The gain error resulting from resistive voltage drop in PCB signal leads is important only with high precision and/or at high resolutions (the Figure 12.3 example), or where large signal currents flow.
Where load impedance is constant and resistive, adjusting overall system gain can compensate for the error. In other circumstances, it may often be removed by the use of “Kelvin” or “voltage sensing” feedback.
In this modification to the case of Figure 12.3 a long resistive PCB trace is still used to drive the input of a high resolution ADC, with low input impedance.
In this case however, the voltage drop in the signal lead does not give rise to an error, as feedback is taken directly from the input pin of the ADC, and returned to the driving source.
This scheme allows full accuracy to be achieved in the signal presented to the ADC, despite any voltage drop across the signal trace.