DS2186

022798 4/11

The shape of the “pre–emphasized” T1 waveform is

controlled

by

inputs

LEN0,

LEN1,

and

LEN2

(TCLKSEL=0). These control inputs allow the user to

select the appropriate output pulse shape to meet

DSX–1 or CSU templates over a wide variety of cable

types and lengths. Those cable types include ABAM,

PIC, and PULP.

The CEPT mode is enabled when TCLKSEL=1. Only

one output pulse shape is available in the CEPT mode;

inputs LEN0, LEN1 and LEN2 can be any state except

all zeros.

The line coupling transformer also contributes to the

pulse shape seen at the cross–connect point. Trans-

formers for both T1 and CEPT applications must be

1:1.35.

The wave shaping circuitry does not contribute signifi-

cantly to output jitter (less than 0.01 UIpp broadband).

Output jitter will be dominated by the jitter on TCLK or

LCLK. TCLK and LCLK need only be accurate in fre-

quency, not duty cycle.

LINE DRIVERS

The on–chip differential line drivers interface directly to

the output transformer. To optimize device perform-

ance, length of the TTIP and TRING traces should be

minimized and isolated from neighboring interconnect.

FAULT PROTECTION

The line drivers are fault–protected and will withstand a

shorted transformer secondary (or primary) without

damage. Inputs MTIP and MRING are normally tied to

TTIP and TRING to provide fault monitoring capability.

Output LF will transition low if 192 TCLK cycles occur

without a one occurring at MTIP or MRING. LF will tri–

state on the next one occurrence or two TCLK periods

later, whichever is greater.

The threshold of MTIP and MRING varies with the line

type selected at LEN0, LEN1 and LEN2. This insures

detection of the lowest level zero to one transition (–15

dB buildout) as it occurs on TTIP and TRING.

T1 LINE LENGTH SELECTION Table 2

LEN2

LEN1

LEN0

OPTION SELECTED

APPLICATION

0

0

0

Test mode

Do not use

0

0

1

–7.5 dB buildout

T1 CSU

0

1

0

–15 dB buildout

T1 CSU

0

1

1

0 dB buildout,

0 – 133 feet

T1 CSU, DSX–1 Cross connect

1

0

0

133 – 266 feet

DSX–1 Cross connect

1

0

1

266 – 399 feet

DSX–1 Cross connect

1

1

0

399 – 533 feet

DSX–1 Cross connect

1

1

1

533 – 655 feet

DSX–1 Cross connect

NOTE:

1. The LEN0, LEN1 and LEN2 inputs control T1 output waveshapes when TCLKSEL=0. The G.703 (CEPT) template

is selected when TCLKSEL=1 and LEN0, LEN1, and LEN2 are at any state except all zeros.