This circuit shifts bipolar -5V to + 5V analog input to a unipolar +2.5V to +12.5V voltage range, the counterpart to the inverting DC Level Shifter. The circuit uses only +15V power supply for the LM3900, preserving the 10Vpp input range centered about mid-range at 7.5V, as set by a Vos adjustment potentiometer.
This type of circuit is part of new thinking about analog signal processing using the LM3900 with positive-only power supply voltages, instead of circuits using traditional +\-15V power supplies. This system architecture introduces the concept of a programmable and arbitrary Vertical Zero Reference (VZR): the voltage programmed to represent 0 volts equivalently, for subsequent signal processing stages. Other voltages can be compared, added, or subtracted to the VZR internally, allowing the equivalent of bipolar signal representation in a single voltage supply system. More particularly, a VZR can be used as the switch-point in which currents change directions, a form of representation greatly enabled by the LM3900 due to its current-differencing mode of operation.
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