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ADC Sampling Rate

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • The ADC sampling rate refers to the number of samples per second. It can also be called the sample rate.

  • According to Nyquist, the signals should be sampled with at least twice the bandwidth of the signal to prevent a loss of data.

  • Resolution refers to the number of quantization bits of the ADC.

ADC Sampling Rate

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As all analog systems are getting converted or have already transitioned into digital systems, analog-to-digital converters are inevitable in modern electronics. Analog-to-digital converters (or ADCs) take continuous analog signals and convert them into discrete digital output equivalents. ADC is based on the sampling process. In ADC, the sampling rate and resolution are key factors to be considered when making the selection. In this article, we will explore ADCs and their sampling rates.

Analog to Digital Converters (ADC) and Sampling

When processing the signal or waveform digitally, one must convert the continuous analog signal into a discrete digital equivalent. The continuous real-world analog signals are sampled for conversion into digital.

The sampling process is an inevitable part of analog-to-digital conversion. The sampling process can be considered analogous to taking a screenshot of the continuous analog signal at regular intervals. The analog signal values between two sampling instants will be lost.

Analog signals are present at every instant. However, the sampled signals are available only at the moment of sampling.

Sampling Theorem

Even when a real analog signal is converted into digital for fast processing, we cannot accommodate any loss of data, values, or information. Improper or unscientific sampling can lead to the kind of scenario where a lot of crucial data may get lost.

The sampling theorem formulated by Harry Nyquist gives criteria for sampling. According to Nyquist, signals should be sampled with at least twice the bandwidth of the signal to prevent loss of data. The sampling rate should be selected such that it matches the Nyquist criteria.

ADC Sampling Rate

The ADC sampling rate refers to the number of samples per second. It is also called the sample rate. The unit of sampling rate is samples per second or Hertz. However, we know that Hertz is the unit of frequency. Therefore, the sampling rate can be also referred to as sampling frequency.

ADC Sampling Rate = ADC Sampling Frequency

Aliasing and ADC Sampling Rate

When the ADC sampling rate is insufficiently large, a loss of data occurs. The minimum ADC sampling rate or frequency can be deduced from the Nyquist criteria. The distortions in the sampled signal are called aliasing. In order to get rid of the aliasing effect, the ADC sampling rate must be greater than the highest frequency that needs to be preserved. An increase in the ADC sampling rate indicates that it is possible to record the higher frequencies without aliasing.

Nyquist Rate-Best Practices

The Nyquist theorem theoretically sets the minimum limit for the ADC sampling rate. However, practically, the ADC sampling rate can be greater than the highest frequency to be preserved or sampled. For accurate digitalization, the ADC sampling rate is chosen to be at least 5 to 10 times the required bandwidth.

Characteristics for Selecting ADC

While choosing ADC, the following characteristics need to be considered.

  1. Bandwidth
  2. Number of channels required
  3. Temperature stability
  4. Power consumption
  5. RMS noise
  6. Sampling rate 
  7. Resolution  

ADC Sampling Rate and Resolution

The two most important characteristics to look for in the selection of ADC are sampling rate and resolution; from the cost to the architecture of the ADC, sampling rate and resolution play an important role.

Resolution

Resolution refers to the number of quantization bits of the ADC. It is the resolution of the ADC that provides the number of bits required to encode the value of the analog signal of interest. Higher ADC resolution means more bits and a better representation of the analog signal. If the application involves high-precision measurements at low frequency, it is ideal to choose a high-resolution ADC. Lower-resolution ADCs can lead to missing information, which can be retrieved using some digital signal processing techniques.

ADC Sampling Rate and High-Frequency Analog Signals

The sampling rate is the primary consideration in the selection of the converter when dealing with high-frequency analog signals. There we bring in the concept of the Nyquist rate. Whereas when the application involves low-frequency signals, as in optical power measurements, the resolution of the ADC is given more importance.

Whenever you need to design and place ADCs in electronic systems, make use of the high-quality design features from Cadence’s OrCAD software. Cadence’s PCB design and analysis software can help you analyze and simulate the performance of not only ADCs but any circuit in the system.

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