every scope has four functional parts
- vertical circuits
- horizontal circuits
- sync
- display
Vertical Circuits Handle the Input Signal
vertical circuit must be at least partially designed as an analog circuit
want to put wave form on screen with minimum distortion
must be able to limit the voltage of the input signal
attenuate or amplify to be within limits of following circuits
from simple block diagram
input signal can be switched between
- DC - to see absolute level of the signal
- AC - capacitor blocks DC voltage, only AC component is seen
- Ground - position the trace on the screen without a signal
input amplifier follows with controls for
followed by analog amplifier to processor
the screen overlay, customary calibration in centimeters
input voltage usually stated in volts per centimeter (V/cm)
horizontal time scale is usually described time units per centimeter
from dual channel analog block diagram
two switches and input amplifiers
channel selection switch between input amplifier and processor
channel selections
- a single input channel
- both input channels simultaneously
- both input channels simultaneously and combined (sum or difference)
-
chopped - both input channels shown simultaneously but processed so they
are alternately sampled
from dual channel digital block diagram
two switches and input amplifiers
output to A/D converters
channel selection is done in later processing
The Horizontal Section Sweeps the Trace Across the Screen
start time is
t = 0
sweep rate - how fast the trace moves across the screen
lower sweep rates used for voltages that vary slowly
some scopes have additional mode
sweep circuit is disabled
one channel is connected to vertical axis
one channel is connected to horizontal axis
permits on-screen plot of one signal versus the other
The Sync Circuit Triggers the Sweep
trigger the sweep so each sweep starts as the input wave form
when trigger voltage is on ascending side of wave it is a trigger with positive
scope
when trigger voltage is on descending side of wave it is a trigger with negative
scope
Display Types
-
CRT
high voltage power supply needed
deep package, 12 inches or mre for 5 inch CRT
great deal of heat radiated
-
Self-contained Flat Panel
LCD or similar display
no HV needed, not much heat generated, package depth much smaller
size driven by front panel controls and display
-
No Display, No Power Supply two types
Some Scopes Can Store Your Waveform
each increment of the waveform is stored as a digital number
math functions are almost free
waveform storage is now the norm along with indirect features (calculations &
numerical measurements