HP 3478A Technical Manual page 102

3478A
verter. All ac ranging is done in the AC to DC Con-
verter.
7-F-27. The AC to DC Converter consists of three
amplifier stages and a True RMS Converter. The pur-
pose of the amplifier stages is to provide the same full
scale input voltage to the RMS Converter for all full scale
ac inputs, and to be a buffer between the converter and
the ac inputs. The True RMS Converter does the actual
ac to dc conversion. The following explains the cir- cuitry
operation.
7-F-28. Amplifier Stages. Refer to Figure 7-F-5 and
Schematic 2 for the following explanation.
amplifier with gains of X.00, X. 1, or XI (dependent on
the ac range and function selected).
deter- mined by resistors RAI, RA2, RA3, and RAII (all in
U102), as shown in Figure 7-F-5. Capacitor C302 and
resistor R305 are used for high frequency compensation
(for flat gains at high frequency). The gain determining
resistors are selected by MOSFETS
S6AC, and SIIAC (all in U102) which operate as
switches. The gains of the amplifier and FETs selected
for the ac functions are listed in Table 7-F-2.
inverting amplifier with gains of X.4 or X4 (dependent on
the ac
Figure 7-F-5. AC Gain Configurations
7-F-8
a. The first amplifier stage (U301A) is an inverting
b. The second amplifier stage (U301B) is an
TM 11-6625-3071-14
The gains are
SIAC through