SHA1134_15 Datasheet, PDF (4/4 Pages) Analog Devices – GENERAL PURPOSE SAMPLE AND HOLD AMPLIFIER

OPERATION WITH AN AID AND MULTIPLEXER
The subsystem of Figure 3 may also be connected to a multi-
plexer like Analog Devices' model MPX-8A as shown below:
THROUGHPUT RATE
The rate at which the systems of Figures 3 and 6 can perform
conversions will, of course, depend on the conversion time of
the AID converter used. The table below lists the minimum
CHANNEL
1 INPUT
i
I
I
I
I
I
I
I
I
CHANNEL "NPUT
MPX'A
OUTPUT
SHA1134
INPUT
OUTPUT
MOOE
CONTROL
A!O
CONVERTER
INPUT
STATUS STATUS
OIGITAL
OUTPUT
]
system throughput rates achievable with several of Analog
Devices' 12-bit successive approximation AID converters.
AID
CONVERTER
MINIMUM SYSTEM
THROUGHPUT RATE
ADC12QZ
22.1kHz
CONVERT
COMMANO
INPUT
Figure 6. AID, SHA, and MPX Connections
ADC12QM
ADC12QU
ADCll02
33.1kHz
49.6kHz
74.0kHz
The leading edge of the convert command pulse sets the
ADCl1O3-003
115.6kHz
STATUS output to logic "0" thereby switching the SHAI134
POWER SUPPLY AND GROUNDING CONNECTIONS
to "hold"; the corresponding change to logic "1" of the
The proper power supply and grounding connections are shown
STATUS output increments the binary counter and changes
the multiplexer address. Since the SHA1134's aperture time is
small with respect to the multiplexer switching time, it will
have switched to the hold mode before the MPX-8A actually
changes channels. The multiplexer switching transients will
settle out long before the SHA returns to "sample" at the end
of conversion. The timing sequence described above is illustra-
O_{ted in Figure 7.}
--^{B CONVERT}
---^-,^{1l Sn n COMMAND}
n r _{6A;Eug;;!'NPUT}
O _{MUL TIPLEXER}
CHANNEL
f ^{LE MULTIPLEXER}
OUTPUT!
TE ^{SHA INPUT}
n
I I CHI' +8V ^CH2,-IOV
CH 3, +3V
I
CH4, OV
:v.
bel()win Figure 8.
ct15V
+15 COM -15
+5V
COM
+5
TO DIGITAL
LOGIC
10l1F
35V '+
10l1F
.+35V
ANALOG GND
2
0 -15V
3
+15V
8
DIG GND
Figure 8. Power Supply and Grounding Connections
SHA ,,34 MODE
The :t15V power supplies must be externally bypassed as shown.
SHA OUTPUT!
AID INPUT
",:!. -IOV
CHANNEL BEING
DIGITIZED
t _{- -} ^ow..
CHANNEL I
CHANNEL 2
CHANNEL 3
The capacitors should be tantalum types and should be installed
as close to the, module pins as possible. The analog and digital
ground lines should be run separately to their respective power
supply commons to prevent coupling of digital switching noise
to the sensitive analog circuit section.
.
L,..!.).
~0
M"MU"
8
Figure 7. AID, SHA, and MPX Timing
This method of sequencing the multiplexer may be altered to
permit random addressing or addressing in a preset pattern. The
timing of multiplexer address changes may also be altered but
consideration should be given to the effects of feed through in
<!
(j"J
the SHA1134. Feedthrough is the coupling of analog input sig-
nals to the output terminal while the SHA is in "hold". For
::>
z
the SHAII34, a 20V pop input signal will typically produce a
ImV signal at the output. If large multiplexer switching trans-
Z0wf-
ients occur while the AID conversion is in progress, errors can
be introduced.
Cccl.
8
-4-
- ~~ ~