AFE1302

10

SBWS014

SYSTEM

This analog front-end will give the best performance only

when included in an optimized system. This section de-

scribes external components that will work best with the

AFE1302. See Figure 5 for the basic connection diagram.

TRANSMIT

The key noise specification for an ADSL analog front-end

is the noise that is added to the RX channel. It is essential

to reduce the transmit noise that reaches the receiver for

proper system operation. An on-chip fourth-order low-pass

transmit filter has been included on the AFE1302 to reduce

transmit noise in the receive bandwidth. However, external

filtering, as shown in the reference design in Figure 6, is

required on the transmitter output to optimize the receive

path noise mask. The reference design circuit not only

implements extra filtering for the transmit noise, but also

includes the drivers necessary to achieve the G.992.2

specified +13dBm output power on the line, thus achieving

a minimum component solution.

ADSL DSP

AFE

External

Circuit

Telephone Line

DV

VREF1

VRNRX

VRPRX

VRNTX

VRPTX

CMO

CMI

AV

TXP

TXN

GP0

GP1

GC0

GC1

RXP

RXN

3.3V to 5V Digital

AFE1302

TX[0:3]

RX[0:3]

CLWD

CLKNIB

CLKM

5V Analog

CTRLIN

RX

TX

DSP

Computer

CPE

0.8:1

UTP Line

Receive

Amp

High-Pass/

AA Filter

Hybrid

CO

HP POTS

Filter

LC Passive

TX Filter/Line Driver

G

G

AFE1302

FIGURE 5. Basic Connection Diagram.

FIGURE 6. CPE Block Diagram (contact factory for detatiled reference design).