Common-Mode Rejection (MPC507A Only)
The matching properties of the load, multiplexer and source
affect the common-mode rejection (CMR) capability of a
differentially multiplexed system. CMR is the ability of the
multiplexer and input amplifier to reject signals that are
common to both inputs, and to pass on only the signal
difference to the output. For the MPC507A, protection is
provided for common-mode signals of
±20V
above the
power supply voltages with no damage to the analog switches.
The CMR of the MPC507A and Burr-Brown's INA110
instrumentation amplifier (G = 100) is 110dB at DC to 10Hz
with a 6dB/octave roll-off to 70dB at 1000Hz. This measure-
ment of CMR is shown in the Typical Performance Curves
and is made with a Burr-Brown INA110 instrumentation
amplifier connected for gains of 500, 100, and 10.
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 frequencies, the common-mode capacitances and
unbalance of signal lines and multiplexer to amplifier wiring
must be minimized. Use twisted-shielded pair signal lines
wherever possible.
SWITCHING WAVEFORMS
Typical at +25°C, unless otherwise noted.
BREAK-BEFORE-MAKE DELAY (t
OPEN
)
V
AM
4.0V
Address Drive V
A
(V
A
)
Output
50%
t
OPEN
50%
50Ω
+4.0V
MPC506A
1
A
3
A
2
A
1
A
0
En
In 1
In 2 Thru In 15
In 16
+5V
V
A
Input
2V/Div
0V
1 On
V
OUT
GND
Out
1kΩ
12.5pF
16 On
Output
0.5V/Div
NOTE: (1) Similar connection for MPC507A.
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
MPC506A
1
A
3
A
2
A
1
A
0
En
50Ω
In 1 Thru
In 16 Off
NOTE: (1) Similar connection for MPC507A.
100ns/Div
Output
2V/Div
In 1
In 2 Thru In 16
+10V
GND
Out
1kΩ
1 On
12.5pF
MPC506A, MPC507A
SBFS018A
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