HP 8112A, Руководство по эксплуатации, программированию и обслуживанию

Страница: 205 / 406

Period, Delay and Width
Generation
Because CUR REF, FRQ IN and TIME IN are virtual earth inputs,
the external input currents can be produced by a voltage source and
series resistance. The control mode functions (PERC, DELC, WIDC)
are produced by feeding the conditioned control input voltage to the
TIME IN input of the relevant timing IC. The approximate value of
current drawn by the input current pins is shown below.
Table 1 0.3-5. Reference current input levels
Reference Current FRQ IN TIME IN
RATE mode approx
80
µA
2
mA -
0.2
mA
0.2
mA const
TIME mode approx
80
µA
2
mA -
0.2
mA
0.2
mA const
CTRL mode approx
80
µA
2
mA -
0.2
mA
2
mA -
0.2
mA
Outputs
The three outputs of the Timing ICs (OUT, OUT, ERROR OUT)
are all open-collector with a fixed current (HI
=
0 mA, LO
=
12 mA)
and a fixed transition time of 2.5 ns.
Error Output. The error output from the timing IC indicates that
a trigger signal has been received before the completion of the
previously triggered event .
Period, Delay and Width signals are generated by Timing ICs U200,
U240 and U220 respectively.
U200 OUT
f4--
PERIOD
U220 OUT
--.j
f4--
DELAY C DELAY MUST BE LESS THAN PERIOD )
--.j f4--
W I DTH ( W I DTH MUST BE LESS
THAN PERIOD )
U240 OUT
C DEL MODE J
___JLJl__J�
U2 4 0 OUT
� < DBL MODE )
DOUBLE
PULSE
--.j f4--
TRE
U3 0 1 D I FFERENT IAL
OUTPUT < DEL MODE )
< LEE & TRE MUST BE LESS THAN WIDTH )
Figure 1 0.3-2. Example of signal generation
Period Generator
The period generator operating in the RATE mode produces 503
duty cycle square wave output pulses at a repetition rate governed
by the analog current input (from the Period DAC or Control Input)
and the internal range data.
Servicing the Timing and 1 0.3-5
Slope Generators