Specifications

The tight coupling through the transformer windings into the signal Hi and Low
leads, forces the common mode noise at the input amplifier side of those windings
to 0 volts. This achieves the 110 dB to 10 MHz desired, keeping the high frequency
common mode noise out of the amplifier, thus preventing the amplifier from
rectifying this into an offset error.
This effectively does the same thing that shielded, twisted pair cable does, only
better. It is especially effective if the shield connection to the VT1419A ground
can’t be a very low impedance due to large dc and/or low frequency common mode
voltages.
The tri-filar transformers don’t limit the differential (normal mode) signal
bandwidth. Thus, removing the requirement for “slowly varying signal voltages.”
The nature of the tri-filar transformer or, more accurately, common-mode inductor,
is that it provides a fairly high impedance to common mode signals and a quite low
impedance to differential mode signals. The ratio of common-mode impedance to
differential-mode impedance for the transformer used is ~ 3500:1. Thus, there is
NO differential mode bandwidth penalty incurred by using the tri-filar transformers.
Wiring and Noise Reduction Methods
376 Appendix D
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