SSM2141
REV.
–6–
MAINTAINING COMMON-MODE REJECTION
In order to achieve the full common-mode rejection capability
of the SSM2141, the source impedance must be carefully
controlled. Slight imbalances of the source resistance will result
in a degradation of DC CMR—even a 5 Ω imbalance will
degrade CMR by 20 dB. Also, the matching of the reactive
source impedance must be matched in order to preserve the
CMRR over frequency.
Figure 1. Precision Difference Amplifier. Rejects
Common-Mode Signal =
[E
1
+
E
2
]
2
by 100 dB
Figure 2. Precision Unity Gain Inverting Amplifier
Figure 3. Precision Summing Amplifier
Figure 4. Precision Summing Amplifier with Gain
Figure 5. Suitable Instrumentation Amplifier
Requirements can be Addressed by Using an
Input Stage Consisting of A
1
, A
2
, R
1
and R
2
