Tektronix CSA7404B, User Manual

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Glossary
Glossary- 4
CSA7000B Series & TDS7000B Series Instruments User Manual
dB
Decibel: a method of expressing power or voltage ratios. The decibel scale is
logarithmic. It is often used to express the efficiency of power distribution
systems when the ratio consists of the energy put into the system divided by
the energy delivered (or in some cases, lost) by the system. One milliwatt of
optical power is usually the optical reference for 0 dBm. The formula for
decibels is:
dB
=
20 log
Ꮛ
Vi
Vl
Ꮠ
for optical, dB
=
10 log
Ꮛ
Po
Pi
Ꮠ
where V
i
is the voltage of the incident pulse, V
l
is the voltage reflected back
by the load, P
o
is the power out, P
i
is the power in, and log is the decimal-
based logarithmic function. See Optical Bandwidth on page 3--60.
dBm
A logarithmic measure of power referenced to 1 milliwatt (1 mW optical
power = 0.0 dBm):
dBm
=
10 log
Ꮛ
optical power
1 mW
Ꮠ
DC coupling
A mode that passes both AC and DC signal components to the circuit.
Available for both the trigger system and the vertical system.
Delay measurement
A measurement of the time between the middle reference crossings of two
different waveforms.
Delay time
The time between the trigger event and the acquisition of post trigger data.
Digitizing
The process of converting a continuous analog signal such as a waveform to a
set of discrete numbers representing the amplitude of the signal at specific
points in time. Digitizing is composed of two steps: sampling and quantizing.