HP 3562A Service Manual page 318

· ' T
D E SC R I PT I ONS
Summer/driver
U400 is an operational ampl ifier used to s u m together the sou rce s ig n a l and the u ser­
selected dc offset com ing from U301 . U401 is the cu rrent driver for U400 and f i nal ampl ifier
Tor the analog sou rce. K201 is used for p rotection of the source c i rcu its from outside signals
a n d for d iscon necting the sou rce from the front panel d u ri n g the time that it i s u sed for
c a l ibration. Duri ng ca l ibration K201 opens and K202 or K200 is selected (closed) for cal ibra­
t i o n . The c a l ibration signal is red to the i n put boards via the m other board f rom p i n 9
of the analog source board.
front End Interface
!
nformation for the dc offset, control d ata, and atte nuator output leve l comes onto the
: ) oard as serial data on p i n 30 (C NT LD). The CNTC L K 1;2 signal (p i n 28) sh ifts the serial
o it stream i nto the serial-to-pa ral lel s h ift reg isters U501 and U 502 and LDSRCL loads the
J ata i nto latches U500 and U 502 . U500 h o l d s d c offset i nformation for the DAC U301 .
U 502 holds i nformation on the atte n u ation of the sou rce signal and control i nformation
for: 1) selecti on of signal types (contro l s U452), 2) operation of the rel ays on the board ,
::md 3) d isconnecti ng the dc offset DAC output from U1 50 when a zero dc offset is sel ected.
de
Offset DAC
U 301 receives offset i nformation i n d igital format from U500 and converts i t to an analog
c u rrent si gna l . The cu rrent s ignal is changed to a voltage signal by U300. The output of
U 300 is con nected to the switch U1 51 . T h i s s i g n a l is oppos ite in polarity and half the f i n a l
a m p l itude o f t h e d c offset. T h e switch i s req u i red because the DAC o u t p u t s ignal i s not
exactly zero when zero offset is selected.
Offset Switch
The offset switch, U1 51 , either connects the dc offset signal to ampl ifier U1 50 or term inates
the l ine by connecting it to ground through R1 53. Control of the switc h i ng operation comes
f rom the d igital sou rce board through U502 as descri bed for the front end i nterface. One
and o n ly one of the 5vvitcheS i n U1 52 is c l osed at any given time.
Overload Protection
U600 is two comparators configu red to sense voltage on the sou rce output l i ne and signal
an ove rl oad condition (sou rce output fau l t) when the signal appeari ng on the output ex­
ceeds 1 2 Vpp.
Calibrator Introduction
T h e cal i brator is d r iven by either squ a re wave s ignals (64 k H z or 4 k H z) or pseu do ran­
d o m noise. These s i g n a l s are generated on the ana log sou rce board, s e lected accord i n g
t o t h e needs of the cu rrent i n stru ment p rocess, a n d reclocked t o ass u re sy n c h roni zatio n .
I
MO D E L 3562A