Pulse shaping is obtained by means of a Digital to Analog

Converter followed by a Continuous Smoothing Filter in or-

der to limit RF energy and crosstalk while minimizing Inter-

Symbol Interference (ISI)

Figure 2 shows the pulse shape

at the Lo output while a template for the typical power

spectrum transmitted to the line with random data is shown

in

Figure 3

Each line-driver output Lo0 – Lo3 is designed to drive a

transformer through a capacitor and termination resistor A

11 transformer terminated in 100X results in signal ampli-

tude of typically 13 Vpk on the line Over-voltage protection

must be included in each interface circuit

LINE RECEIVE SECTIONS

The input of each receive section Li0 – Li3 consists of a

continuous anti-alias filter followed by a switched-capacitor

low-pass filter designed to limit the noise bandwidth with

minimum intersymbol interference To correct pulse attenu-

ation and distortion caused by the transmission line an AGC

circuit and first-order equalizer adapt to the received pulse

shape thus restoring a ‘‘flat’’ channel response with maxi-

mum received eye opening over a wide spread of cable

attenuation characteristics

From the equalized output a DPLL (Digital Phase-Locked

Loop) recovers a low-jitter clock for optimum sampling of

the received symbols The MCLK input provides the refer-

ence clock for the DPLL at 4096 MHz

Following detection of the recovered symbols the received

and presented to the digital system interface circuit

When a transmission line is de-activated a Line-Signal De-

tect Circuit is enabled to detect the presence of incoming

bursts if the far-end starts to activate the loop

TLH11924 – 4

FIGURE 2 Typical AMI Waveform at Lo

TLH11924 – 5

6