1.3.11 Sampling Rate in Analog System Builder

For ADC’s that perform one sample per conversion, the throughput rate is also referred to as the sampling rate – this is the case for Fusion. Sampling Rate or frequency is the rate at which the ADC acquires or samples the analog input and converts it to digital data. It is specified as samples per second ( S/s ) or Hertz ( Hz ).

The sampling rate is typically the inverse of the ADC Conversion Time. For example, an ADC that takes 10 microseconds to acquire and convert an analog signal to a digital value will be able to generate about 100,000 samples per second. In the case where only a single channel is being sampled, the channel’s sampling rate is equal to the total system sampling rate.

However, in the case where the sampling sequence contains multiple channels and where a channel may be sampled multiple times in relation to another channel, the sampling rate computation becomes more involved.

The following diagram displays a silicon view of the analog signal path.

Figure 1-32. Silicon view of the analog signal path
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Tprescaler_settling: Applicable only in Voltage Monitor peripheral when prescaler circuit is used

Tstrobe: Applicable only in Current, Temperature, or Differential peripherals. For more information, refer to the Sequencing in Fusion section.

Tsample: Time for sample and hold circuit to sample the analog input voltage into the input capacitor

Tconversion: Conversion time of ADC

Tturnaround: How fast a client of the ADC can process data and give another start conversion signal. In this case this falls onto the ASSC IP.

To simplify the user interface experience, ASB utilizes a simpler view of the signal path, as displayed below:

Figure 1-33. Signal path view
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Notice that the prescaler, strobe, and sample time have been condensed into the Tacquisition_hold time. This is the value that is specified by you during configuration of the peripheral. Legal ranges are enforced by ASB based upon requirements of the silicon.

The following sections describe the sampling rate computation for ASB. ASB enables you to specify the minimum sampling time and minimum sampling rate. ASB then reports the total system sampling rate and the actual sampling rate of each channel.