Chapter 5: Sample Rate Flashcards
ADCs?
Analogue to Digital Converters
DACs
Digital to Analogue Converters
The importance of sample rates?
The sampling rate of an analogue signal is very important because it determines the maximum frequency that can be observed or generated.
Nyquist sampling theorem:
the sampling rate should be at least twice the highest frequency in the analogue signal; the Nyquist rate.
What is the the Nyquist sampling rate?
The sampling rate required to get a good representation of analogue data?
Graph: Sinusoidal curve sampled at its Nyquist rate
Graph: Sinusoidal curve sampled below its sample rate?
Graph: (Right) Sinusoidal curve sampled above its Nyquist rate
– only higher frequencies would fit the data.
What is aliasing?
If an analogue signal is sampled below the Nyquist rate, then there are different ways to reconstruct the waveform with lower frequency components, as shown in the figure above (bottom right). This effect is known as aliasing and is generally an undesirable effect.
Issues with Analogue frequencies above the Nyquist frequency?
Analogue frequencies above the Nyquist frequency will appear as lower frequencies in the digital domain.
In order to avoid this, it is important to filter the analogue signal before conversion using a low pass filter to remove these noise sources.
Issues with DAC outputs?
For digital to analogue conversion, the stepped nature of the output creates harmonics of the sampling frequency in the output. These must be filtered out if they will affect systems connected to the analogue output.
Graph showing Stepped nature of output from DAC?
Graph: High frequency components removed from analogue signal using low pass filter.
