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15.2 Glossary
AC/DC Control
Each channel can be set to either AC coupling or DC coupling. With DC coupling,
the voltage displayed onscreen is equal to the true voltage of the signal with
respect to ground. With AC coupling, any DC component of the signal is filtered
out, leaving only the variations in the signal for the AC component.
Aliasing
When the signal frequency gets higher than half the scope’s maximum sampling
rate and exceeds the limit, a distorted waveform appears. This distortion is called
aliasing.
Analog Bandwidth
All oscilloscopes have an upper limit to the range of frequencies at which they can
measure accurately. The analog bandwidth of an oscilloscope is defined as the
frequency at which a displayed sine wave has half the power of the input sine
wave (about 71% of the amplitude).
Block Mode
A sampling mode in which the computer prompts the oscilloscope to collect a
block of data into its internal memory before stopping the oscilloscope and
transferring the whole block into computer memory. This mode of operation is
effective when the input signal being sampled is high frequency.
Buffer Size/Cache Size
This term indicates the size of the oscilloscope’s buffer memory. The buffer
memory is used by the oscilloscope to temporarily store data. This helps to
compensate for the differences in data transfer rate from one device to another.
Sampling Rate
This term is used to define the number of samples per second captured by the
oscilloscope. The faster the sampling rate of the scope, the more frequently it
measures the signal voltage, and so the more detailed will be the trace that
appears on the scope screen.
Streaming Mode
This term indicates a sampling mode in which the oscilloscope samples data and
returns it to the computer in an unbroken stream. This mode of operation is
effective when the input signal being sampled is at low frequency.
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