Measuring Crosstalk Between Simultaneously Sampled ADC Channels

Simultaneous sampling establishes a timing relationship between channels, but it does not guarantee unlimited isolation. A large signal on one input can create a smaller unwanted component on another. Measure that interaction with controlled input impedances and a characterized fixture before assigning the effect to the ADC itself.

Define the aggressor and victim conditions

The TI ADS8588S data sheet specifies channel crosstalk with defined stimulus conditions and provides frequency-dependent characterization. The test conditions matter when comparing a board measurement with the component specification.

Choose one driven channel and identify the channels being observed. Record input range, sample rate, reference configuration, filtering, and the signal applied to the driven channel.

Control quiet-channel impedance

Terminate or bias the observed channels in a way that represents the application and remains within their valid input conditions. An open input is a different experiment from a low-impedance sensor connection.

Measure the quiet-channel baseline before enabling the aggressor. Preserve that record so an existing interference tone is not mistaken for newly created channel coupling.

Sweep the driven signal

Apply a known tone at several amplitudes and frequencies within the supported operating range. Search for the corresponding component in the victim channel, accounting for aliasing and the digital filter response.

State the reference used for the reported ratio. Crosstalk expressed relative to the actual aggressor amplitude is different from a residual stated relative to ADC full scale.

Challenge the measurement fixture

Move or replace cables, change source routing, and compare channel assignments while retaining equivalent electrical conditions. Coupling between test leads or signal-generator outputs can create a residual before the signals reach the PCB.

For example, swap the aggressor between a physically adjacent channel and a distant channel. A pattern that follows one cable arrangement suggests a different investigation from a pattern that consistently follows one board channel pair.

Repeat with the product’s actual drivers connected. Shared references, supplies, and return paths can contribute to the complete channel interaction even when the converter’s intrinsic isolation is adequate.

Keep overload testing distinct from the normal-range sweep and remain within absolute input limits. A saturated upstream amplifier or protection path can create effects that do not represent ordinary small-signal crosstalk.

Save the channel matrix, source levels, victim termination, fixture checks, and residual spectra. The final result should identify the operating conditions under which one channel can disturb another and whether the observed floor belongs to the board or the measurement arrangement. Simultaneous conversion alone does not answer that isolation question.