XRT5894 Datasheet, PDF (17/19 Pages) Exar Corporation – Four-Channel E1 Line Interface (3.3V or 5.0V)

This may be further simplified:
R_T
I
V_s
V_eq
Figure 10. Equivalent Circuit
Where:
R_T = RS_int + Rs_ext
R_eq
=
R_L
n²
Therefore:
I=
R_T
Vs
+ Req
V_eq = I R_eq
V_o = n V_eq
And:
Return Loss
=
20 log
R_T + R_eq
R_T-- R_eq
XRT5894
Table 5 contains the results of calculations made with these equations. The numbers show that output pulse amplitude
is within millivolts of the nominal values of 2.37V and 3.00V specified by ITU G.703 for 75W and 120W operation. Also,
the 1:2 ratio transformer provides an almost-perfect match for 75W operation, and return loss is well within the ETSI
specification for the 120W load.
Rev. 1.10
Load Resistance
R_L (W)
75
120
Pulse Amplitude
Vo (Volts Peak)
2.43
3.01
Output
Return Loss (dB)
31.3
13.8
Table 5. Calculated Transmitter Pulse Amplitude and Return Loss
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