1. Locate zero current in the output reference domain
A bidirectional measurement must represent sensed differences of both polarities. With a single output supply, that requires a defined output position from which a positive or negative sensed difference can move. TI's INA240 reference discussion explains this output-bias role. The reference establishes the zero-differential-input coordinate instead of simply adding another supply name to the description.
TI describes placing the output center within the permitted reference context. A centered arrangement can allocate output range to both directions; a noncentral choice can accompany an asymmetric current requirement. The important selection question is therefore which output position represents zero and how the wanted current directions relate to it. This is different from asking which bus voltage appears at the sense inputs.
That distinction also separates the reference question from the shunt connection. Current and voltage-sense terminals define the measurement boundary at the resistive element. The output reference defines how the amplifier represents the resulting differential input downstream. A well-defined sensing boundary does not supply the output coordinate. Keeping these two responsibilities separate makes a bidirectional requirement understandable without selecting a shunt value or transferring the input common-mode limit into an output-bias statement.
2. Separate supply-derived and externally defined centers
A midpoint needs a reference quantity. TI distinguishes an output center related to the INA240 supply from one established by an external reference. Although both can be described informally as centered outputs, they do not have the same relationship to supply movement. The quantity from which the center is derived remains part of its meaning.
For the supply-derived case, TI describes a ratiometric offset: the zero-input output position follows the supply relationship. An externally defined center instead relates the output bias to that external source. These alternatives answer different system questions even when an abbreviated requirement describes each only as a midpoint. The reference's origin should remain attached to the chosen output interpretation.
This does not imply that one relationship automatically cancels every error downstream. The receiving measurement has its own reference context. Before describing a system as ratiometric, identify which quantity determines the amplifier's zero-current output and which quantity the receiver uses to interpret it. The manufacturer provides distinct output-centering arrangements; those arrangements do not establish a universal cancellation result or make every center interchangeable merely because each leaves room for current of both signs.
3. Keep reference source impedance in the output-bias requirement
A nominal reference voltage does not completely describe the reference source. TI states a low-impedance reference context for the INA240 reference interface and discusses a resistor-divider alternative separately. This adds a drive relationship to the output-bias requirement. A voltage description and the source presenting that voltage are connected, but they are not the same property.
The distinction becomes concrete when a reference is described only by its intended level. Two sources associated with that level can present different impedances to the interface. TI's discussion of internal impedance shifts in the divider arrangement explains why a detached voltage label does not establish an identical output-reference behavior. The source relationship has to remain visible alongside the chosen center.
Compare a directly defined reference and a divider-derived reference according to their documented use, rather than treating the divider as a transparent label change. This identifies why the reference-source question deserves its own decision before the output is interpreted. It does not prescribe physical reference connections, select resistor values or design a buffer. The purpose is to retain the interface characteristic needed to understand what the stated output-bias voltage actually represents.
4. Distinguish single-ended and differential output interpretation
The amplifier output can be interpreted against ground or relative to a reference quantity. These readouts preserve different information about movement of the output center. TI's divider discussion specifically distinguishes differential use with respect to that divider voltage from a single-ended interpretation. The measurement coordinate is therefore part of the requirement, rather than a detail implied by the output's nominal level.
An output statement alone describes where the signal is presented. A differential interpretation additionally identifies the second quantity against which it is evaluated. If the reference moves, that relationship is relevant to the meaning of the observed result. This is an output-domain question, distinct from the amplifier's rejection of disturbances common to its sense inputs.
Complete the comparison by naming the zero-current center, the source defining it and the receiver's readout reference. Those three items connect the output-bias decision without merging it with gain selection or ADC conversion suitability. A bidirectional label does not supply any of them automatically. The resulting requirement explains how both current directions are represented, while leaving any achieved measurement accuracy or receiving-converter acceptance to the actual system evidence.
Sources and further reading
TI INA240 SBOS662C, revised December 2021, physical pages 13-15: output reference and bidirectional-measurement prose only. No reference wiring, shunt sizing, gain selection, numeric error or ADC acceptance is provided.