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AR# 37882

Virtex-6 System Monitor - Explanation of AC impedance matching in Figure 26 of UG370

Description

In the Virtex-6 System Monitor User Guide UG370, Figure 26, Voltage Attenuation Example, why is the 4k Ohm resistor in series with the Vauxn?

Solution

In the paragraph preceding the Figure it explains:
"To ensure that noise coupled onto the analog inputs is common to both inputs (reduce differential noise), the impedance on each input should be matched."

The AC impedance looking back from the differential inputs needs are matched in this example.
The AC impedance as seen from the Vauxp is the 20k Ohm resistor in parallel with the 5k Ohm, which is equal to 4k Ohm.
The AC impedance as seen from the Vauxn is the 4k Ohm resistor which is matched to the Vauxp.
AR# 37882
Date Created 09/07/2010
Last Updated 12/15/2012
Status Active
Type General Article
Devices
  • Virtex-6 HXT
  • Virtex-6 LX
  • Virtex-6 LXT
  • Virtex-6 SXT