Many Microcontrollers (MCUs) incorporate onboard analog-to-digital converters (ADCs), usually with many multiplexed input channels. However, these ADCs are typically unipolar, able to handle only signals that are between the positive and negative reference voltages (+VREF to - VREF) with -VREF usually 0 V. To accommodate negative voltages, then, these ADCs need some form of signal conditioning. The typical approach uses an op-amp dc level shifter that raises the signal by one half of +VREF so the entire analog signal excursion lies within the positive domain where the ADC can handle it. But there are two drawbacks to this approach. One is that shifting the signal cuts the positive headroom in half.
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