HP 3478A Technical Manual page 100

3478A 3478A
Figure 7-F-3. Figure 7-F-3. Simplified Schematic Simplified Schematic Of The DC/Ohm
Input Amplifier Input Amplifier
switches. switches. The The following following paragraphs
ohms current is generated and how the ohms circuitry ohms current is generated and how the ohms circuitry
operates. operates. Refer to Refer to Schematic I Schematic I and
explanation. explanation.
7-F-20. 7-F-20. Current Current Generation. Generation. The
current is generated is as follows: current is generated is as follows:
a. a. The Voltage Splitt The Voltage Splitter's (U201) ou er's (U201) output is + 12V (or 8.
for the 30M ohm Range only) which is applied for the 30M ohm Range only) which is applied to to
Of The DC/Ohms s
paragraphs explain h explain how ow the
and Figure 7-F-4 Figure 7-F-4 for the for the
The explanation explanation on on how
tput is + 12V (or 8.4V
the positive the positive terminal of
put, which is applied to the positive terminal of the Out- put, which is applied to the positive terminal of the Out-
put FET Control Amp U203, is divided down to + 8V, put FET Control Amp U203, is divided down to + 8V,
irrespective of range, by feedback resistors RR3 and irrespective of range, by feedback resistors RR3 and
RR4 in conjunction with R206. RR4 in conjunction with R206.
b. b. The output of t The output of the Buffer is + 1
30M ohm Range only) which is applied to one side of 30M ohm Range only) which is applied to one side of
either Range Resistor RRS, RR6, RR7, or RR8 either Range Resistor RRS, RR6, RR7, or RR8
(dependent on the selected rang (dependent on
Range Resistors is applied to the Output FET Control Range Resistors is applied to the Output FET Control
Amp. Amp.
c. c. Since the Since the Output FE
operational amplifier with its non-inverting terminal at operational amplifier with its non-inverting terminal at
the
how
4V
Figure 7-F-4. Ohms Circuitry Figure 7-F-4.
7-F-6 7-F-6
terminal of Buffer U202. Buffer U202. The reference out
he Buffer is + 12V (or + 8.4 2V (or + 8.4V for the
the selected range). e). The other side of the
Output FET Control T Control Amp is a
Ohms Circuitry Configuration
TM 11-6625-3071-14 TM 11-6625-3071-14
The reference out- -
V for the
The other side of the
Amp is a high gain high gain
Configuration