Tektronix 2215, Instruction Manual

Page: 55 / 345

The DC Restoration c irc u it raises the o u tp u t level o f the
Z-Axis A m p lifie r to allow it to be coupled to the c rt
control grid. D irect coupling is not employed due to the
am plitude o f the voltage levels applied to the c rt elements.
A front-panel PROBE A DJU ST o u tp u t is provided fo r
use in adjusting probe compensation. The voltage at the
PROBE ADJU ST connector is a negative-going square wave
th a t has a peak-to-peak am plitude o f approxim ately 0.5 V
and a repetition rate o f approxim ately 1 kHz.
DETAILED CIRCUIT DESCRIPTION
VERTICAL ATTENUATORS
Both the Channel 1 and Channel 2 A tte n u a to r circuits,
shown in Diagram 1, are identical in operation. In the
fo llo w in g discussion, only the Channel 1 A tte n u a to r c irc u it
is described. The matching components in the Channel 2
A tte n u a to r c irc u it perform the same fu n ctio n .
The A tte n u a to r c irc u it (see Figure 3-2) provides control
o f in p u t coupling, vertical deflection factor, and variable
volts-per-division balance. In p u t signals fo r c rt vertical
deflection may be connected to either or both the CH 1 OR
X and the CH 2 OR Y in p u t connectors. In the X-Y Mode
o f operation, the signal applied to the CH 1 OR X con­
nector provides horizontal (X-Axis) de fle ctio n fo r the
display, and the signal applied to the CH 2 OR Y connector
provides the vertical (Y-Axis) deflection fo r the display.
Input Coupling
The signal applied to the CH 1 OR X in p u t connector
can be ac-coupled, dc-coupled, or in te rn a lly disconnected
from the in p u t o f the High-Z In p u t A tte n u a to r circ u it.
Signals applied to the CH 1 in p u t connector are routed
through resistor R101 to In p u t Coupling switch S I01.
When S101 is set fo r dc coupling, the CH 1 signal is applied
d ire ctly to the in p u t o f the High-Z A tte n u a to r stage. When
ac-coupled, the in p u t signal passes through R100 and
d e b lo c k in g
capacitor C l 02. The blocking capacitor
prevents the dc com ponent o f the in p u t signal fro m being
applied to the A tte n u a to r circu it. When S I01 is set to
GND, the direct signal path is opened and the in p u t o f the
attenuator is connected to ground. This provides a ground
reference w ith o u t the need to disconnect the applied signal
fro m the in p u t connector. The coupling capacitor is
allowed to precharge through R102, a high-resistance com ­
ponent, w hich is connected across In p u t Coupling switch
S101 in the GND position.
3-4