HP 3478A Technical Manual page 102

3478A 3478A
verter. All ac ranging verter. All ac ranging is done in
verter. verter.
7-F-27. 7-F-27. The AC The AC to DC to DC Converter
amplifier stages and a amplifier stages and a True RMS
pose of the amplifier stages is to provide the same full pose of the amplifier stages is to provide the same full
scale input voltage to the RMS Converter for all full scale scale input voltage to the RMS Converter for all full scale
ac inputs, and to be a buffer between the converter and ac inputs, and to be a buffer between the converter and
the ac inputs. The True RMS Conv the ac inputs. The True RMS Converter does the actu
ac to dc conversion. ac to dc conversion. The following explains t The following explains the cir- cuitry
operation. operation.
7-F-28. 7-F-28. Amplifier Amplifier Stages. Stages. Refer to
Schematic 2 for the following explanation. Schematic 2 for the following explanation.
is done in the AC t the AC to DC Con- o DC Con-
Converter consists of consists of three
True RMS Converter. Converter. The pur-
erter does the actual al
he cir- cuitry
Refer to Figure 7-F-5 Figure 7-F-5 and
Figure 7-F-5. Figure 7-F
a. a. The
amplifier with gains of X.00 amplifier with
the ac range the a c range and fun
three
deter- mined by resistors RAI, RA2, RA3, and RAII (all i deter- mined by resistors RAI, RA2, RA3, and RAII (all in n
The pur- U102), as shown in Figure 7-F-5. U102), as shown in
resistor R305 are used for high frequency compensation resistor R305 are used for high frequency compensation
(for flat gains at (for flat
resistors resistors are
S6AC, and SIIAC (all in U102) which operate as S6AC, and SIIAC (all in U102) which operate as
switches. The gains of switches.
for the ac functions are listed in Table 7-F-2. for the ac functions are listed in
b. b. The s
and
inverting amplifier with gains of X.4 or X4 (dependent on inverting amplifier with gains of X.4 or X4 (dependent on
the ac the ac
-5. AC Gain AC Gain Configurations Configurations
7-F-8 7-F-8
The first first amplif amplifier ier stage stage (U301
gains of X.00, X. , X. 1, or
and function select ction selected).
Figure 7-F-5. Capacitor C302 and
gains at high frequency high frequency). ). The gain determinin
are selected selected by by MOSFETS MOSFETS
The gains of the amplifier the amplifier and FETs selected
The seco econd a nd ampl mplifie ifier st r stage
TM 11-6625-3071-14 TM 11-6625-3071-14
(U301A) i A) is an s an inver inverting ting
1, or XI (dependent XI (dependent on on
ed). The gains are The gains are
Capacitor C302 and
The gain determining g
SIAC SIAC through through
and FETs selected
Table 7-F-2.
age (U3 (U301B 01B) is a ) is an n