HP 3478A Technical Manual page 109

3478A 3478A
Figure 7-F-15. Figure 7-F-15. Determining the Determining the DAC Setting
S-4 current and the S-I current is 1/1000 the S-4 current. S-4 current and the S-I current is 1/1000 the S-4 current.
The S + 2 and S + I currents use the same circuitry con- The S + 2 and S + I currents use the same circuitry con-
figuration as the S+4 current (see Figure 7-F-11 figuration as the S+4 current (see
case, resistor values chosen are such that the S + 2 case, resistor values chosen are such that the S + 2
current is 1/100 the value of S+4 current and S+ 1 is current is 1/100 the value of S+4 current and S+ 1 is
1/1000 the value of S+4. 1/1000 the value of S+4.
DAC Setting
Figure 7-F-11). ). In In this this
Figure 7-F-16. Figure 7-F- 16. A/D Hybrid
7-F-49. A/D 7-F-49. A/D Converter and Converter and Reference Circuitry
A/D Converter Circuitry consists of the A/D Hybrid A/D Converter Circuitry consists of the A/D Hybrid
(U403), A/D Integrator (U401 and associated circuitry), (U403), A/D Integrator (U401 and associated circuitry),
A/D Controller (U462), and a DAC (U465 and associated A/D Controller (U462), and a DAC (U465 and associated
circuitry). Since the Voltage circuitry). Since the Voltage Reference Cir- cuitry
U405, U404, U402, and associated cir- cuitry) uses part U405, U404, U402, and associated cir- cuitry) uses part
of the A/D Hybrid (for stability pur- poses) and since it is of the A/D Hybrid (for stability pur- poses) and since it is
also used by the A/D Converter, it is considered part of also used by the A/D Converter, it is considered part of
the conv the converter circuit erter circuitry.
following explanation on the A/D Converter Circuitry following explanation on the A/D Converter Circuitry
(except for the DAC, see paragraph 7-F-46 and 7-F47 (except for the DAC, see paragraph 7-F-46 and 7-F47
for its explanation). for its explanation).
a. a. A A /D H /D Hyb ybri rid (U
Figure 7-F-16, Figure 7-F-16, operates as follows: operates as follows:
1.The A/D Hybrid has, internal to it, various 1.The A/D Hybrid has, internal to it, various
latches, decode latches, decoders, and rs, and a clock generat
receive control information from the A/D Controller, then receive control information from the A/D Controller, then
decode the information and pass the new information to decode the information and pass the new information to
the the latches. latches.
information to the various switches in the hybrid during information to the various switches in the hybrid during
each clock pulse. The clock pulses are generat each clock pulse.
clock clock
A/D Hybrid (U403) (U403)
7-F-15 7-F-15
TM 11-6625-3071-14 TM 11-6625-3071-14
Reference Circuitry. . The
Reference Cir- cuitry (U461,
ry. Refer to Refer to Schematic 3 for Schematic 3 for the
d (U40 403) 3). . The A/D Hybrid, shown in The A/D Hybrid, shown in
a clock generator. or. The decoders
The The latches latches then then transfer transfer the
The clock pulses are generated by t
The
(U461,
the
The decoders
the new new
ed by the he