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LTC6957-3 Evaluation Board Output Impedance Matching

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Product Number: DC1766A

Hello all,

Regarding the output impedance matching that is done over the EVM:

Taken from the EVM manual (page 2):

NOTE: The CMOS outputs of the DC1766A are AC-coupled and attenuated through two 100Ω resistors as shown in the DC1766A schematic diagram to present a 50Ω source impedance appropriate to connect to a 50Ω input impedance instrument.

If the output impedance of the LTC6957-3 in between 30 - 40ohm, so why didn't they take it when calculating the 50ohm matching?

The actual impedance is (Rs + R[series]) || R[parallel] = (35+100) || (100) = 57ohm, when R[series] should actually be 65ohm... (35+65) || 100 = 50ohm

Am I right?

Thanks!

Nir



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[edited by: NirAlon at 8:54 AM (GMT -4) on 11 Sep 2022]