Factors which will degrade multiplexer and system DC CMR
are:
•
•
•
•
Amplifier bias current and differential impedance mis-
match
Load impedance mismatch
Multiplexer impedance and leakage current mismatch
Load and source common-mode impedance
AC CMR roll off is determined by the amount of common-
mode capacitances (absolute and mismatch) from each signal
line to ground. Larger capacitances will limit CMR at higher
frequencies; thus, if good CMR is desired at higher frequen-
cies, the common-mode capacitances and unbalance of sig-
nal lines and multiplexer-to-amplifier wiring must be mini-
mized. Use twisted-shielded-pair signal lines wherever pos-
sible.
SWITCHING WAVEFORMS
Typical at +25°C, unless otherwise noted.
BREAK-BEFORE-MAKE DELAY (t
OPEN
)
V
A
Input
2V/Div
V
AM
4.0V
Address Drive V
A
(V
A
)
Output
50%
t
OPEN
50%
50Ω
+4.0V
A
2
A
1
A
0
En
MPC508A
(1)
In 1
In 2 Thru In 7
In 8
+5V
0V
1 On
V
OUT
Output
0.5V/Div
GND
Out
1kΩ
12.5pF
NOTE: (1) Similar connection for MPC509A.
100ns/Div
ENABLE DELAY (t
ON
(EN), t
OFF
(EN))
Enable Drive
V
AM
4.0V
50%
0V
Output
90%
90%
t
ON
(EN)
t
OFF
(EN)
V
A
MPC508A
(1)
In 1
A
2
A
1
In 2 Thru In 8
A
0
En
50Ω
GND
Out
1kΩ
+10V
Enable Drive
2V/Div
12.5pF
Output
2V/Div
NOTE: (1) Similar connection for MPC509A.
100ns/Div
MPC508A, MPC509A
SBFS019A
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7
BURR-BROWN [ BURR-BROWN CORPORATION ]
