3-16
CIRCUIT DESCRIPTIONS
In the Scope Meter the response of the H.F
attenuator sections is adjusted by means of three variable
capacitors C2209, C2207 and C2114. These variable
capacitors
are
used to compensate for parasitic
capacitors of the printed circuit board.
The 1 to 1.48 divider
(1
to 1.48 section) can
be adjusted with
variable
capacitor C2209.
The 1 to 14.8 divider
(1
to 1 .46 and 1
to 10 sections) can be adjusted with variable capacitor C2207.
The 1 to 148 divider
(1
to 1.48,
1 to 10
and
1 to 100 sections) can be adjusted with capacitor C221 4.
NOTE: These capacitors
do not
have
to be readjusted at every calibration, (see chapters, section
5.6.
1)
The capacitors are rough adjustments,
used to compensate for hardware differences.
The attenuator response is fine adjusted by means of the
LF. caiibration section (see next
page).
Impedance
converter
The output of the H.F. path Is connected with the Impedance converter, formed
by transtsiors V2207
and V2209 (see circuit diagram A2a, figure
10.5). The
bias voltage
of V2207 Is determined by R2216.
To prevent destruction of the gate of V2207 by high voltages or voltage
peaks, two clamps V2206 and
V2204 are provided. Summation of the H R and the L.R signal
parts Is obtained in transistor V2207.
which acts as the collector impedance of V2208.
LF. (Lew frequency) path
The L.F. part of the inptrt signal
enters the L.F. path, which consists of a L.F. attenuator section, a
L.F.
cal bration section
and a regulating feedback loop, which consists of a summator, Inverter, another
summator, and
an
emitter follower
(see figure 3.7).
L.F. attenuator
Fig 3.8 shows the L.F. attenuator section in detail:
OPPser
vouTAoe
The L.F. attenuator consists of
an inverting amplifier. N2201
,
which atter>uates the L.F. signal by
a
factor, depending on the settings
of switches D2201. These switches are controlled by signals named
Srib...Sr4b.
A
'high" signal switches
on
the
corresponding latched relays.
Table 3.3 Attenuator drive signals Sr1b...Sr4b.
Attenuator settings Srib Sr2b
Sr3b Attenuation
5 mV/dlv...100 rr>V/dfv high low low 1 -48 times
200 mV/djv...1 V/div high
high low 14.8 times
2V/div...10V/dlv low low
high 148 times
20 V/dlv...100 V/dIv
low high high 1 480 times
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