2.2.11 Sampling Rate in Analog System Builder

For analog‑to‑digital converters (ADCs) that perform one sample per conversion, the throughput rate is also referred to as the sampling rate. This is the case for Fusion devices. The sampling rate, or sampling frequency, is the rate at which the ADC acquires an analog input and converts it into digital data. It is expressed in samples per second (S/s) or in Hertz (Hz).

The sampling rate is typically the inverse of the ADC conversion time. For example, an ADC that requires 10µs to acquire and convert an analog signal can generate approximately 100 000 samples per second. When only a single channel is sampled, the sampling rate of that channel is equal to the total system sampling rate.

When the sampling sequence contains multiple channels, or when a channel is sampled multiple times relative to other channels, the sampling‑rate calculation becomes more complex.

The following figure shows a silicon view of the analog signal path.

Figure 2-30. Analog Signal Path Timing Components (Silicon View)
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The silicon‑level analog signal path includes the following timing components:
  • Tprescaler_settling: Applicable only to the Voltage Monitor when the prescaler circuit is used.
  • Tstrobe: Applicable only to Current, Temperature, and Differential Voltage peripherals.
  • Tsample: Time required for the sample‑and‑hold circuit to sample the analog input voltage into the input capacitor.
  • Tconversion: ADC conversion time.
  • Tturnaround: Time required for an ADC client to process data and issue the next start‑conversion request. In Fusion devices, this function is handled by the Analog Sample Sequence Controller (ASSC).
Figure 2-31. Simplified Analog Signal Path Used by ASB
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To simplify the user‑interface experience, ASB presents a condensed view of the signal path. In this view, the prescaler settling time, strobe time, and sample time are combined into a single Tacquisition_hold value. This is the acquisition and hold time specified during peripheral configuration. ASB enforces legal ranges for this value based on silicon requirements.

The following sections describe how ASB computes sampling rates. ASB allows you to specify a minimum sampling time and a minimum sampling rate. Based on these inputs, ASB reports the total system sampling rate as well as the actual sampling rate for each channel.