Dear Sirs,
our customer is using Pulse Transformer for DP83848 between the board#A and the board #B, but they would like to change this Pulse Transformer to Capacitor and also change a number of communication board from two to four.
Q1: Is this avaialble to connect with 4board by like the attachment?
Q2: How should they change the capacitance(Calculating the Minimum Recommended Capacitance) and against this change?
The minimum series capacitance can be calculated using the following equation for return loss,
Return Loss = -20 Log |(Zload – Zo)| / |(Zload + Zo)| (1)
Where:
Return Loss = 16 dB
Zo = 100 ohms
Zload = 100 + 1/jωC + 1/jωC ohms (from circuit in Figure 5).
Substituting the above values into Equation 1 and solving, results in:
ωC = 0.0622 (2)
At 2 MHz, the minimum series blocking capacitor value, C, would be 4.95 nF based on the return loss requirement.
The ANSI standard also specifies a limitation on the phase angle of the load (+/-3° maximum). For the phase calculation, a 100
ohm load at -3° phase angle produces a worst case capacitance.
2 * 1/ωC = 100 sin(-3°) = -5.233 (3)
Solving Equation 3 for C at 2 MHz gives 30.42 nF, which represents minimum capacitor value required to meet the phase
specification. The recommendation of 33 nF is the nearest standard value generally available, and proved acceptable based on
validation testing.
National
