®

AFE1104

7

FIGURE 2. Basic Connection Diagram.

rxHYB AND rxLINE INPUT ANTI-ALIASING FILTERS

The –3dB frequency of the input anti-aliasing filter for the

rxLINE and rxHYB differential inputs should be about

1MHz. Suggested values for the filter are 750

Ω for each of

the two input resistors and 100pF for the capacitor. Together

the two 750

Ω resistors and the 100pF capacitor result in a

–3dB frequency of just over 1MHz. The 750

Ω input resis-

tors will result in a minimal voltage divider loss with the

input impedance of the AFE1104.

This circuit applies at both T1 and E1 rates. For slower rates,

the antialiasing 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.

rxHYB AND rxLINE INPUT BIAS VOLTAGE

The transmitter output on the txLINE pins is centered at

midscale, 2.5V. But, the rxLINE input signal is centered at

1.5V in the circuit shown in Figure 2 above.

Inside the AFE1104, 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 1.5V just as the rxLINE signal is centered at

compromise hybrid must be designed so that the signal into

the rxHYB inputs is centered at 1.5V.

PLL

OUT

REF

P

V

CM

REF

N

DV

DD

PV

DD

AV

DD

AFE1104

AV

DD

AV

DD

PLL

IN

txDAT

txCLK

rxSYNC

rxCLK

rxLOOP

rxGAIN1

rxGAIN0

rxD13 - rxD0

DAC+

TX_SYM_CLK

HOLD_

MCLK19_2

AD13 - AD0

SPAROW

AGND

PGND

DGND

AGND

AGND

AGND

txLINE

P

txLINE

N

rxHYB

P

rxHYB

N

rxLINE

N

rxLINE

P

1k

Ω

200

Ω

0.1µF

0.01µF

Neg

Neg

Pos

Pos

750

Ω

13

Ω

13

Ω

750

Ω

750

Ω

750

Ω

100pF

100pF

Compromise

Hybrid

0.01µF

5V Analog

0.1µF

0.1µF

10µF

0.1µF

0.1µF 0.1µF

1 - 10µF

+

5V to 3.3V Digital

5 - 10

Ω resistor for isolation

Input antialias

filter f

1:2 Transformer

Tip

Ring

0.1µF

0.1µF

0.1µF

2k

Ω

2k

Ω

REF

N

2k

Ω

2k

Ω

REF

N

0.1µF

0.1µF

0.1µF

0.1µF

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