Circuit Description—
7D14
settings
of 1
V, the signal is applied to the junction of R103
and
R104 through relay K103S1; the output is taken from
the
junction
of R104-R105 through relay K103S2. For the
S10
setting
of 10 V
(1 MΩ
only}, the signal is applied to
the
junction
of R101-R102 through relay K101S1; the out
put
is taken
from
the
junction of R104-R105 through
relay
K103S2.
R101 re-establishes the 1 MΩ input
impedance
when S10 is set
to the
10 V position.
Trigger
Source Amplifier
The
Trigger
Source
Amplifier amplifies
oscilloscope
trigger pickoff
signals from the Interface Connector in the
TRIG
SOURCE position of the INPUT SENS switch, and
applies
the
signal
to
the Input Amplifier through
C222-C223.
Since
the output of the Trigger Source Ampli
fier
is applied to the plus input of the Input Amplifier, the
trigger pickoff
—
Trig
In
signal is amplified by this stage.
This
maintains the
same phase
relationship to the Clock
output
as a signal applied to the CH A INPUT connector.
Resistor R212 establishes
the
input resistance for this
stage.
Also, R212,
in conjunction with R871, provides a
load for
the
oscilloscope trigger pickoff
circuitry. The input
signal
is coupled through
C212-R214 to the base of Q216.
C212
blocks
the DC component of the trigger pickoff sig
nal;
otherwise, the DC level of the signal will be affected by
the
vertical unit position control(s).
Input
Amplifier
The
Input Amplifier stage consists of Q130A-B, Q132,
and
Q232.
This
stage is a wide-bandwidth
operational
amplifier that converts
the
single-ended input signal
to a
differential (push-pull) signal
to drive the Bandwidth Selec
tion
stage. The minus input of the operational amplifier is
the gate
of Q130A, and the plus input
is the gate of Q130B.
The
minus input
is the summing point for input signals
(from
the CH A
INPUT
connector), the triggering LEVEL
(or
Preset) control
current, and negative-feedback signals.
CR1
14-CR115-CR116-CR1
17
form a diode clamp network
to
protect the input components from damage due to
excessive
input voltages. These diodes will
conduct only if
the voltage
at
the
summing point exceeds about ±1.2 volts.
Negative
feedback
from the output of the Input Ampli
fier
through
C132-R113, and through
L
1
34-C
1 19-R 119-R 1 17-R 11 3
to the minus input
compensates
the high-frequency
response of this stage.
C132 provides high-frequency compensation.
The
sum
of the currents into the minus input summing
point
sets the Trigger
Amplifier output DC level as deter
mined
by PRESET-VAR switch S20. When the PRESET
button
is
in, the voltage level at the junction of
R121-R126-R127-R128
is determined by R125,
Preset.
R125
adjusts the current into the
summing point through
R128-R117-R1
13
to balance the Trigger Amplifier outputs
for
a zero-volt difference. When
the VAR button is in, the
voltage
set by R22 (LEVEL)
is connected to the junction
of
R121-R126-R127-R128
through R121
to provide front
panel adjustment of the triggering point.
Bandwidth Selection
The Bandwidth
Selection stage consists of five-
megahertz (MHz) amplifier Q136-Q236, 525-MHz amplifier
Q141-Q241,
and associated components. The BW switch,
S8,
selects
the bandwidth
by providing an emitter ground
return
for one
of
the two bandpass amplifiers. Diode
clamps,
CR135-CR136 and CR235-CR236,
protect the
transistors
from damage due to excessive input voltage.
The bandwidth
of transistor-pair Q136-Q236
is limited
to
about five
MHz by
inductors
L134-L135-L138 and
L234-L235-L238.
When the
BW switch 5 MHz button is in,
emitter
resistors R135 and R235 are
returned to ground
through R138
to
enable Q136-Q236. When the 525 MHz
button
is
in, the ground return for Q136-Q236
is discon
nected; + 15
volts
through R137 to R135-R235
ensures
cutoff
of
Q136-Q236.
The
bandwidth
of transistor-pair Q141-Q241 exceeds
525
MHz. When the 525 MHz button is in, emitter resistors
R140-R240
are returned to ground through R238 to enable
Q141-Q241.
When the
5 MHz button is in, this ground
return
is
disconnected; +15 volts through R237 to
R
140-R240 ensures cutoff of Q141-Q241.
Trigger
Amplifier
The Trigger
Amplifier
stage
consists of emitter
coupled
pair
Q147-Q247,
and associated
components. This stage
provides amplification for the
differential signal
from the
Bandwidth
Selection
stage to drive the Trigger Generator.
Trigger
Generator
The
Trigger Generator consists of
Q152, Q252, Q154,
Q254,
and
associated components. This stage shapes the
output signal from
the Trigger Amplifier to provide a trig
ger pulse with a fast leading edge
to
the
Slope Switching
stage.
Q152
and
Q252 are emitter-coupled current switches.
Emitter-followers Q154 and
Q254 feed
the output signals
back
to
the
opposite
inputs. The differential
signal at the
collectors
of Q154 and
Q254 is applied to
the Feedback
Amplifier stage.
@i
3-5
Summary of Contents for 7D14
Page 4: ...7D14 ...
Page 11: ...Operating Instructions 7D14 Fig 2 1 7D14 front panel controls and connectors 2 2 ...
Page 33: ... 3 13 Fig 3 11 Logic diagram for Zero Cancel Logic stage Circuit Description 7D14 ...
Page 38: ...3 18 Fig 3 16 Time Base and Control circuit detailed block diagram Circuit Description 7D14 ...
Page 44: ...NOTES ...
Page 46: ...NJ Fig 4 1 Electrode configuration for semiconductors in this instrument I ...
Page 68: ...NOTES ...
Page 96: ... 7DI 4 DIGITAL COUNTER UNIT ...
Page 98: ...GRS 0371 BLOCK DIAGRAM ...
Page 99: ......
Page 103: ...0 0 I 200 mV 500 µs 0 001 200 mV 500 µs 0 001 MHz 00 mV E 00 µs 0 001 MHz ...
Page 106: ...1 ...
Page 110: ...A2 Logic Circuit Board Assembly jQ798i 798 jc743 CR744t uni R724 R742 JL744S FrR796 ...
Page 113: ......
Page 114: ...P 0 A2 LOGIC BOARD ...
Page 121: ... A B D t F H J NPR Tj ZWX V A AC M AEA HUM qAZ DEF HJ N P R S T J V V7X y ABM APAI AA 7DI4 ...
Page 129: ......
Page 130: ...4 7D14 DIGITAL COUNTER ...