In analog integrated-circuit design, one common type of signal is an analog sampled-data signal. This signal exists with continuously varying amplitudes, just like a regular analog signal, but it is only defined at specific points in time. Essentially, instead of having a smooth, uninterrupted waveform, the signal is sampled at discrete intervals. However, unlike digital signals, which have quantized amplitude levels, an analog sampled-data signal retains its continuous range of amplitudes. This makes it a bridge between purely analog and purely digital signals, often seen in signal processing applications.
A key characteristic of an analog sampled-data signal is that it is often sampled and held — meaning that once a sample is taken, its value is maintained until the next sample is captured. This is crucial in circuits like sample-and-hold circuits used in analog-to-digital converters (ADCs) and switched-capacitor filters. Such signals play an important role in modern electronics, where analog signals need to be processed in discrete steps without immediately converting them to digital form. This technique enables efficient signal manipulation while preserving the accuracy of the original analog waveform.
The image below illustrates how an analog signal is sampled and held:
✔️ The gray curve represents the original analog signal, which is continuous.
✔️ The black crosses mark the sampled points, where the signal is measured at specific time intervals.
✔️ The black stepped waveform shows the sampled-and-held signal, where each sample value is held constant until the next sample is taken.
✔️ The annotation highlights the sampled-and-held analog value, demonstrating how the signal retains the last sampled value.
This concept is fundamental in ADC circuits, where an analog signal must be converted into a discrete digital representation.
