Factors which will degrade multiplexer and system DC CMR
are:
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.
•
Amplifier bias current and differential impedance mis-
match
•
•
•
Load impedance mismatch
Multiplexer impedance and leakage current mismatch
Load and source common-mode impedance
SWITCHING WAVEFORMS
Typical at +25°C, unless otherwise noted.
BREAK-BEFORE-MAKE DELAY (tOPEN
)
VA Input
2V/Div
MPC508A(1)
In 1
+5V
4.0V
VAM
A2
Address Drive
(VA)
VA
A1 In 2 Thru In 7
A0
1 On
0V
In 8
50Ω
Output
0.5V/Div
Output
VOUT
Out
1kΩ
En
GND
50%
50%
+4.0V
12.5pF
tOPEN
100ns/Div
NOTE: (1) Similar connection for MPC509A.
ENABLE DELAY (tON (EN), tOFF (EN))
Enable Drive
Enable Drive
2V/Div
MPC508A(1)
VAM 4.0V
+10V
In 1
A2
50%
A1
A0
0V
In 2 Thru In 8
Output
90%
90%
Out
1kΩ
En
50Ω
GND
VA
12.5pF
Output
2V/Div
t
ON(EN)
tOFF(EN)
NOTE: (1) Similar connection for MPC509A.
100ns/Div
MPC508A, MPC509A
7
SBFS019A
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