0.1µF
0.1µF
0.1µF
13Ω
PLLOUT
PLLIN
REFP
VCM
REFN
1kΩ
1:2 Transformer
Tip
txLINEP
txLINEN
47nF
200Ω
0.1µF
13Ω
Ring
Neg
Pos
47nF
Compromise
Hybrid
txDATP
txDATN
Neg
Pos
txCLK
375Ω
375Ω
rxSYNC
rxLOOP
rxGAIN1
rxGAIN0
rxD13 - rxD0
rxHYBP
rxHYBN
DSP
AFE1203E
100pF
14
Input anti-alias
filter fC 2MHz
AGND
DGND
AGND
AGND
AGND
AGND
rxLINEN
rxLINEP
375Ω
100pF
375Ω
PLL
AVDD
DVDD
AVDD AVDD AVDD
5V Analog
5V to 3.3V Digital
0.1µF
0.1µF 0.1µF 0.1µF
10µF
0.1µF
+
1 - 10µF
100µF
5Ω - 10Ω Resistor for Isolation
FIGURE 2. Basic Connection Diagram.
rxHYBAND rxLINE INPUT ANTI-ALIASING FILTERS
rxHYB AND rxLINE INPUT BIAS VOLTAGE
The –3dB frequency of the input anti-aliasing filter for the
rxLINE and rxHYB differential inputs should be approxi-
mately 2MHz for operation at 2.3Mbps. Suggested values
for the filter are 375Ω for each of the two input resistors and
100pF for the capacitor. Together the two 375Ω resistors
and the 100pF capacitor result in –3dB frequency of just
over 2MHz. The 375Ω input resistors will result in a mini-
mal voltage divider loss with the input impedance of the
AFE1203.
The transmitter output on the txLINE pins and the rxLINE
inputs are centered at midscale, 2.5V.
Inside the AFE1203, the rxHYB and rxLINE signals are
subtracted as described in the paragraph on echo cancella-
tion above. This means that the rxHYB inputs need to be
centered at 2.5V just as the rxLINE signal is centered at
2.5V. The external compromise hybrid must be designed so
that the signal into the rxHYB inputs remains centered at
2.5V.
This circuit applies at rates of 1Mbps to 2Mbps. For slower
rates, the anti-aliasing filters will give best performance with
their –3dB frequency approximately equal to the bit rate. For
example, a –3dB frequency of 500kHz should be used for a
single pair bit rate of 500kbps.
®
7
AFE1203