Fluke 93 - Page 57

CIRCUIT DESCRIPTIONS
3-23
The oiitput signal*
SGNOUT, {output 1
B)
fs fed to the ADC.
The voltage range of
SGNOUT )s
1
,5V,
..3.5V, The
Intermediate level
of SGNOUTis derived
irom the VREF
voltage level, which is
made
by
the
ADC.
TRACK-
TRACK TRACK
A-AS(C
(defiyM
TRACK-)
TRACK
i
^
HOLD
1
TRACK
SSNOin'
OT A-ASIC
CLMADC
dalayed
.
>
:
oditf
1
HCUD
TRACK 1
TBATK
1 -An«
1
ADC lakes sample
'
Track
& Hoid timing
Externat
Trigger Amplifier
This amplifier
section prcxsesses the
incoming external trigger signal
so that it can be used in
the
trigger section.
The Input of this section
is TTL compatible
.
Trigger Selector
In this section tne channel
A, channel B or external trigger
input signal is selected
to ad as trigger
source. The trigger slope
is also selected in this
block.
Hysteresis
The hysteresis
section converts the trigger signal
into a pulse shaped
signal. Because of the
hysteresis,
the circuit will not trigger
on noisy signals. The LEVEL signal
(input
20)
that determines
the trigger level>
Is a DC voltage between
+0.5V and +2.0V. The LEVEL signal
Is a DC voltage,
generated in the Digital
ASIC. Resistor R2309 and
capacitors C2312 andC2313 form
alowpass filter,
to convert a pulse width
modulated signal into the DC
voltage.
Detta^T
circuit
The Delta-T
circuit measures
the lime between a trigger pulse
and the moment the input
signal is
sampled. Figure 3.14 shows
the timing diagram with relaton
to the signal HLDF (Input 1
0),
START
(internal), STOPN
(output
9),
and TOUT (output
15).
1$} ir<3
clocX
CtOCA
START: Internal (in
the A-ASIC) start
signal for the
Delta-T
measurement.
TOUT: a voltage
proportional to the
measured
value (time) of
Delta T.
Figure 3.14 Timing
diagram Delta-T
circuH
Control logic
The control logic
section contains
a
serial-ln
parallel-out shift register.
This section gets
Its data from
the microprocessor
(D1
201,
circuit
diagram A1. figure
10.2) viafrie CDAT (serial
data), CCLK (sertd
clock),
and DTAE (data-latch) lines.
The control logic section
controls ail functional blocks within ttie
A-ASIC,