CX28331 datasheet(42/68 Pages) CONEXANT

42 / 68 page

2.0 Functional Description

CX28331/CX28332/CX28333

2.3 Receiver

Single/Dual/Triple E3/DS3/STS-1 Line Interface Unit

2-10

Conexant

100985A

2.3 Receiver

This section describes the detailed operation of the various blocks in the CX2833i

receiver.

2.3.1 Receive Sensitivity

The receiver recovers data from the coaxial cable that is attenuated due to the

frequency-dependent characteristics of the cable. In addition, the receiver

compensates for the flat loss (across all frequencies) in the various electrical

components and the variation in transmitted signal power.

The CX2833i device is able to recover data that has been attenuated by a

maximum of 900 feet of coax having characteristics and attenuation consistent

with ANSI T1.102-1993, Annex C, Figure C.2. This approximates the

characteristics of AT&T type 734/728 cable; almost the same attenuation

characteristic is achieved by one-half the length of AT&T type 735 cable.

2.3.2 AGC/VGA Block

The Variable Gain Amplifier (VGA) receives the AMI input signal from the

coaxial cable. The VGA supplies flat gain (independent of frequency) to make up

for various flat losses in the transmission channel and for loss at one-half the

symbol rate that cannot be made up by the equalizer. The VGA gain is controlled

by a feedback loop which senses the amplitude of the equalizer output, acting to

servo this amplitude for optimal slicing.

2.3.3 Receive Equalizer

The receive equalizer receives the differential signal from a VGA and acts to

boost the high frequency content of the signal to reduce inter-symbol interference

(ISI) to the point that correct decisions can be made by the slicer with a minimum

of jitter in the recovered data.

The REQH pin is provided to allow lower amounts of equalization (shorter

equivalent cable lengths) for cases where a square-shaped pulse (that does not

meet the DS3/STS-1 standards) is transmitted to the receiver. A square-shaped

input has a much larger high-frequency content and could have overshoots at the

EQ output high enough to cause bit errors. Setting REQH = 0 will lower the gain

and reduce the amount of overshoot.

CX28331 Datasheet(PDF) 42 Page - Synaptics Incorporated.