Contents

**Introduction**

ADC (Analog-to-Digital Converter) bandwidth and sampling rate are two important parameters that are closely related but serve different purposes in the context of signal acquisition and processing.

In this post, we explore the differences between ADC bandwidth and sampling rate:

## ADC Bandwidth

Bandwidth in the context of an ADC refers to the range of analog frequencies that the ADC can accurately capture and convert into digital values.

- It is determined by the analog front-end of the ADC. There is most often a capacitive impedance associated with ADC inputs, so there is an unavoidable low-pass effect. As the input frequency increases the signal (and noise) will attenuate. The “analog input bandwidth” is also known as the “full power bandwidth”. It is the frequency at which the digitized signal is 3 dB down in power from what it was at low frequency.

The specification sheet for the AD9461 [1] shows the Analog BW is 615 MHz while the sampling rate for this ADC is only 130 MSPS.

- ADC bandwidth is typically specified in hertz (Hz) and represents the maximum frequency at which the ADC can accurately capture an analog signal.
- The bandwidth limits the range of frequencies that can be digitized without significant distortion or attenuation. Signals with frequencies beyond the ADC’s bandwidth may not be accurately represented in the digitized output.
- ADC bandwidth is essential for applications where it is necessary to preserve the full spectral content of the analog signal, such as in wideband communications, radar, and high-frequency measurements.

## ADC Sampling Rate (Sampling Frequency)

Sampling rate, also known as the sampling frequency, represents the number of samples (data points) the ADC takes per unit of time, usually expressed in samples per second (S/s) or hertz (Hz).

- Sampling rate determines how frequently the ADC captures and converts analog data into discrete digital values.

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- The Nyquist-Shannon sampling theorem states that the sampling rate must be at least twice the highest frequency component present in the analog signal to avoid aliasing and accurately reconstruct the signal.

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- The sampling rate limits the highest frequency that can be accurately represented in the digitized signal. Frequencies above the Nyquist limit are subject to aliasing and may not be correctly reconstructed.

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- In many cases, ADCs oversample the input signal to improve signal-to-noise ratio (SNR) and dynamic range, even though they may not have a bandwidth equal to the sampling rate. Oversampling involves taking multiple samples at a higher rate than the Nyquist rate and digitally filtering the result.

**NOTES**

ADC bandwidth is not the same as Nyquist bandwidth.

An analog input bandwidth of 1000 MHz (for example) tells you about the input signal attenuation with frequency. It does not necessarily mean that the ADC can convert a signal from 0 Hz to 1000 MHz.

The ADC bandwidth is typically higher than the Sampling rate of the ADC.

The Nyquist bandwidth is one-half of the sampling frequency. For a sampling rate of 500 MSPS, the Nyquist bandwidth will be 250 MHz. This is the theoretical maximum bandwidth that can be converted without aliasing.

In summary, ADC bandwidth refers to the analog frequency range that an ADC can accurately capture, while ADC sampling rate (sampling frequency) determines how frequently the ADC samples and converts analog data into digital values.

**References**

[1] AD9461 Datasheet

**Related Calculators and Posts**

- Signal-to-Noise Ratio
- ADC Noise Figure
- ADC Digital Output for a specified Analog input voltage
- ADC Signal to noise from number of bits
- ADC Oversampling Calculator