Input Modes
generic names
- ground (reference)
- AC-coupled (selectable independently for each channel
- DC-coupled (selectable independently for each channel
- inverted
- differential (no ground reference)
- high gain
- fast rise time
- dual trace
- A/B altenate
- A/B chopped
- A + B
- A - B
- high-z input
- 50 Ω input
- wide band
- digital inputs
- multi-channel
- audio only
Common Input Selections
almost always three input selection
- ground (reference)
- AC-coupled (selectable independently for each channel
- DC-coupled (selectable independently for each channel
looking at wave form consisting of 30V DC on top of a 1V sawtooth wave
select ground reference to vertically position 0V at bottom of screen
selecting AC position will show the entire waveform if vertical voltage scale is
set high enough
1V sawtooth will be hard to measure
select AC and adjust scale to better see and measure amplitude of sawtooth wave
input selections are set per channel
some scopes have an Inverted selection which puts the low voltage at the top of
the screen, generally available with scopes having math functions
Single Channel Modes
high gain front end may not be compatible with system looking for high frequency
Wide Band refers to highest frequency dispalyed that displays at least 70.7%
of correct amplitude value of a sine wave
Fast Rise Time is important for digital measurements, fast in reference to the rise
and fall time of digital pulse being measured
most scopes designed to have minimum loading on circuit being viewed
some scopes have High-Z input
input values
- normal input looks like 1MΩ resistor in parallel with 10 pF
-
high-z input looks like several tens of megohms while capacitance is generally at
least 5 pF
Dual Channel Inputs
just about all models have a two-channel (dual-trace) input
with chopped input each input is alternately sampled and displayed one increment
at a time
generally as long as waveforms are very much lower than sampling frequency the switch
is relatively invisible
Dual Channel with Arithmetic
waveforms can be combined 4 ways with each channel referenced to ground
A+B
A-B
B-A
-A-B
in differential mode inputs reference each other instead of ground
introducing ground connection may show noise and other extraneous signals
Special Modes
dual channel scopes may not be adequate for viewing digital signals
some scopes have logic signals only inputs