The time it takes in an ADC (Analog-to-Digital Converter) for a sample of an Analog input to be converted to its equivalent Digital value.
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Calculator
Enter:
- Sample and Hold time
- Conversion time
Formula
Sampling Time = Conversion time + S/H time
Sampling Rate = 1/Sampling Time
Example Calculation
If the S/H time is 10 μs and the Conversion time is 55 μs, then the total sampling time is 65 μs.
The ADC Sampling Rate using the calculator is 15.4 kHz or 15.4 kSPS.
The value of the input impedance can negatively impact the sample and hold time. Most ADC vendors make recommendations on the maximum value of the input impedance. In the case of the Arduino for instance, Atmel recommends a max value of 10 kΩ. Anything higher will increase the settling time and result in an inaccurate reading of the voltage level.
The Basics of Analog-to-Digital Conversion
Analog-to-Digital Conversion is the process of converting an analog signal into a digital signal. In simple terms, it means converting a continuous analog voltage signal into discrete binary values.
This conversion is essential in modern technology, as most devices and systems operate on digital signals.
An analog signal is a continuous electrical signal that represents information, such as radio, optical or audio in its original form. On the other hand, a digital signal represents information in the binary form of 0’s and 1’s.
The process of analog-to-digital conversion involves sampling the analog signal at regular intervals and assigning numerical values to the sampled values. This tool provides the digital equivalent of an analog level.
Digitization helps preserve and manipulate the content of the signal more easily and accurately. For example it can be digitally filtered and processed in a Field Programmable Gate Array. It also enables the efficient transmission and storage of data, as digital signals are less susceptible to noise and degradation.
The quality and fidelity of the digital signal depend on factors such as the sampling rate and bit resolution associated with analog-to-digital conversion.
Sample and Hold
The sample-and-hold (S&H) circuit plays a crucial role in the operation of analog-to-digital converters (ADCs). Its main purpose is to accurately sample the input signal and hold the sampled value constant for a specific interval of time. The time associated with this process is a factor in the sampling time and rate.
When the ADC is ready to convert the analog signal to a digital representation, the sample-and-hold circuit works by briefly connecting a capacitor to the input signal.
This action allows the circuit to capture and hold the instantaneous voltage of the analog signal, which is equivalent to sampling the input signal. The capacitor then keeps this voltage constant throughout the conversion process, ensuring that the ADC accurately tracks the input signal.
The picture below shows the effect of S&H (in red) on an analog waveform.
The sample-and-hold circuit’s ability to sample and hold the input signal is essential for the accurate conversion of analog signals into a digital equivalent.