Acquisition of time-domain pulses is a common measurement in many applications, and often the pulse characteristics is determined relative to a fixed baseline (DC level). It is crucial that this baseline is measured with high accuracy in order to avoid false readings and/or performance degradation.
Factors such as component aging, temperature variations, and pattern noise all adversely affect the accuracy of the baseline measurement and often induce a baseline fluctuation/drift. Tracking and removing baseline variations is crucial as it otherwise can lead to missed pulses, erroneous detection of false pulses, and incorrect analysis of pulse characteristics.
The baseline variation consists of a slowly drifting DC-level, often in combination with a zigzag pattern – so-called pattern noise - caused by time-interleaved analog-to-digital converters (ADCs). Time-interleaving is a common technique used in many of today’s high-performance ADCs in order to achieve high sampling rates.
Figure 1. The baseline variation consists of a slowly drifting DC-level due to temperature variation (left) in combination with a zigzag pattern originating from the difference in DC-offset between individual time-interleaved ADC cores (right).
Both these contributing sources need to be considered for removing the baseline fluctuations and thereby increase the sensitivity of the system. Tracking and correction should be done in real-time so that an already corrected data stream is transferred to the host PC. It is also important that the correction is done with high accuracy, especially in systems where many records will subsequently be averaged in order to improve the signal-to-noise ratio (SNR).
The Digital Baseline Stabilizer (DBS) technology from Teledyne SP Devices is built-in to all our firmware packages for time-domain applications. It removes baseline variations in real-time with high accuracy and operates in the background without any need for calibration signals or measurement disruptions. DBS stabilizes the baseline by removing unwanted variations and adjust its level to a user-defined target value. This helps capture even the smallest pulses, increase the dynamic range and improve the accuracy of the pulse analysis.
Figure 2. Since DBS is always active, it will automatically and continuously monitor baseline variations and correct for any time-invariant behavior.
In addition to correcting for baseline drift DBS also corrects offset errors between individual ADC cores in time-interleaved ADCs. The errors are visible in the digitized waveform and typically show up as a zigzag pattern, hence the name pattern noise. These errors can be a significant noise source and can therefore severely distort the baseline if left uncorrected.
Figure 3. Left image: the noise level (black) caused by pattern noise is significantly reduced when using DBS (blue). Right image: when zooming in, the zigzag pattern due to the four interleaved ADC cores becomes apparent.
The combination of high sampling rate and high resolution have led to advances in many different application areas. However, with increased sensitivity, the negative effect of analog imperfections becomes more evident and can limit the overall system performance. Baseline variation is no exception and DBS is therefore used by many of our customers in a wide range of applications. Here are some examples:
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