Transient ADC Artifact

The sample-to-sample variation in the precise sampling instant, caused by clock phase noise in the ADC. This timing uncertainty translates directly to amplitude error, particularly on the steep slopes of a transient's rising edge.

• Effect: Adds non-linear noise proportional to signal slew rate
• Signature: Broadband noise floor elevation during rapid amplitude changes
• Mitigation: Ultra-low jitter clock sources and post-processing de-jitter algorithms

The irreducible difference between the true analog transient voltage and its nearest digital representation, determined by the ADC's bit depth. This error manifests as a noise floor that can mask subtle, low-amplitude fingerprint features.

• Uniform Distribution: Error is bounded by ±0.5 LSB for an ideal ADC
• Effective Bits (ENOB): Real-world resolution is always lower than the stated bit depth due to noise
• Dithering: Intentional noise injection to decorrelate quantization error from the signal

The cumulative deviation of the ADC's actual transfer function from an ideal straight line. INL introduces harmonic distortion and gain errors that alter the transient envelope shape, creating a systematic artifact that must be calibrated out.

• Measurement: Expressed in LSBs; high-performance ADCs achieve < 0.5 LSB INL
• Signature: Low-order harmonic distortion of the transient envelope
• Calibration: Look-up table correction or polynomial compensation

The local deviation in step width between adjacent digital codes. A DNL of -1 LSB indicates a missing code, where a specific digital output is never produced, creating a dead zone in the transient capture.

• Impact: Introduces localized distortion and information loss at specific amplitude levels
• Relationship: High DNL contributes directly to poor INL performance
• Detection: Histogram testing with a statistically rich input signal

When the transient's multi-frequency spectral components interact with ADC non-linearities, they generate sum and difference frequency products not present in the original signal. These spurious tones can be mistaken for transmitter artifacts.

• Second-order (IM2): f1 ± f2 products
• Third-order (IM3): 2f1 ± f2 and 2f2 ± f1 products — most problematic as they fall in-band
• Specification: Measured in dBc relative to the carrier amplitude

The broadband transient spectral splatter generated by the transmitter's rapid switching often exceeds the Nyquist bandwidth of the capture ADC. This out-of-band energy folds back into the digitized spectrum, corrupting the in-band fingerprint features.

• Anti-aliasing Filter: Must have sufficient stop-band attenuation at the Nyquist frequency
• Oversampling: Capturing at a rate significantly higher than the signal bandwidth relaxes filter requirements
• Signature: High-frequency transient components appearing at mirrored, lower frequencies

The sample-to-sample variation in the exact moment the ADC samples the input signal. This timing uncertainty causes a voltage error proportional to the signal's slew rate. During a fast turn-on transient, where the envelope changes rapidly, aperture jitter translates directly into amplitude noise, obscuring the fine structure of the ramp-up signature. It is a fundamental limit in high-speed transient capture.

The cumulative deviation of the ADC's actual transfer function from an ideal straight line. INL introduces harmonic distortion and gain errors that vary across the input range. For a transient envelope, this means the measured amplitude profile is warped, distorting the overshoot characterization and settling time analysis. Calibration is required to de-embed this static non-linearity from the dynamic transmitter fingerprint.

The variation in the analog step size between adjacent digital codes. Ideally, one least significant bit (LSB) is exactly one step. High DNL causes missing codes or non-monotonic behavior. In transient capture, this creates localized distortion in the amplitude ramp profile, particularly in low-amplitude regions near the noise floor during burst onset detection, potentially masking the initial rise of the signal.

The fundamental, irreducible error caused by mapping a continuous analog value to a finite set of discrete digital levels. This adds a noise floor of ±0.5 LSB. For low-energy transient spectral splatter or the subtle damped oscillation profile of a ringing artifact, quantization noise can bury the signal. Increasing the ADC's effective number of bits (ENOB) is the primary mitigation.

The ratio of the RMS signal amplitude to the amplitude of the largest spurious spectral component. ADC non-linearities create spurs that can be mistaken for real transmitter artifacts like transient carrier feedthrough or PLL reference spurs. A high SFDR is essential to ensure that the measured transient spectral centroid and other frequency-domain features originate from the device under test, not the digitizer.

The analog front-end bandwidth of the ADC must be sufficient to pass the fastest components of the transient, such as the leading edge jitter or a sharp phase discontinuity. Insufficient bandwidth acts as a low-pass filter, artificially slowing the measured burst leading edge slope and smoothing out critical identifying features. The ADC's own slew rate must exceed that of the transient signal to avoid introducing its own distortion.