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Impedance measurements require the use of the ATAP pins, together with the TBIC and ABMs, to apply and read analog test stimulae. The measurement of an impedance between a pin and ground may be done using the set up shown in figure 1. Figure 1: Test set up for measuring an impedance between pin and ground. The measurement procedure may be summarised as follows for this case: - A known current I
_{T}is applied through AT1, by way of switches S5 and SB1, to the unknown impedance (Z_{D}) - The resulting voltage V
_{T}is measured at AT2, which is connected to Z_{D}through switches SB2 and S6 - The value of Z
_{D}may then be computed as Z_{D}= V_{T}/ I_{T}
Notice that the error margin in this procedure depends
on the relative values of the unknown impedance (Z - Z
_{V}>> Z_{S6}+ Z_{SB2}(to guarantee that the voltage drop in S6 and SB2 is negligible)
Z |