Table 3-1: Attenuation Factors Vs. Logic Levels - Tektronix 2212 Service Manual

2212 Service Manual
Vertical System
Table 3-1 shows the relation between the logic level on the control lines and the
attenuation factor.
Table 3-1: Attenuation Factors vs. Logic Levels
V/DIV Attenuation x2 Pre-Amp Control Llne No.
Setting
Ratio Amplifier Setting 7 6 5 4 3 2 1 0
2mV* x1 ON
2mV
x000001
X
SmV x1 OFF
2mV x001001x
10mV x1 OFF SmV x011001x
20mV x1 OFF 10mV
X
1 0 1 0 0 1
X
SOmV x10 OFF 2mV
X
0 0 1 1 0 1
X
0.1 V x10 OFF 5mV
X
0 1 1 1 0 1
X
0.2V x10 OFF 10 mV
X
1 0 1 1 0 1
X
0.5 V x100 OFF
2mV
X
O O 1 0 1 1
X
1V
x100 OFF 5mV
X
O 1 1 0 1 1
X
2V
x100 OFF 10mV
X
1 0 1 0 1 1
X
5V x1000
OFF 2mV
X
O O 1 1 1 1
X
GND
X X X X X X X X X
0
X
INVERT
X X X
1
X X X X X X X
AC GOU.
X X X X X X X X X X
0
DC GOU.
X X X X X X X X X X
1
*
Reduced Bandwidth to 10 MHz
The output of the attenuator is connected to the vertical input buffer Q100. The
buffer circuit provides a very high impedance to the attenuator circuit resulting
in accurate attenuation factors.
The output impedance of the buffer circuit is relatively low, which is necessary
to drive the pre-amplifier circuit.
The input buffer is protected for high amplitude input signals by a high value
resistor and protection diodes. The resistor
(475 kn)
limits the current in over-
load situations through the protection diode
CR101
or the FET Q100.
The output signal of the input buffer is connected to either the 2 m V amplifier
or the pre-amplifier circuit.
Pre-amplifier circuit U101 converts the single side input voltage to a differential
output current. This circuit provides logic controlled gain switching
(see Table 3-1). The overall gain can be controlled by a de voltage ranged
between
+2.5
V and
-2.5
V and applied to the VAR input. The gain ratio
between these two levels is at least
2.5:1.
The VAR input is used to calibrate the
vertical sensitivity. The output current of the pre-amplifier is connected to the
summing point of the delay line driver.
3-9