m28333-3x Mindspeed Technologies, m28333-3x Datasheet - Page 34

• Manufacturer Part Number: m28333-3x
• Description: Single/dual/triple E3/ds3/sts-1 Line Interface Unit
• Manufacturer: Mindspeed Technologies

2.0 Functional Description
2.3 Receiver
2.3.1 Receive Sensitivity
2.3.2 AGC/VGA Block
2.3.3 Receive Equalizer
2-10
2.3 Receiver
This section describes the detailed operation of the various blocks in the M2833i
receiver.
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.
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.
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.
The receive equalizer receives the differential signal from a VGA and boosts the
high frequency content of the signal to reduce intersymbol 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 when set high (REQH = 1) boosts the amount of equalization in
the receive side of the LIU. DS3/STS-1 pulses require a greater amount of
equalization then standard E3 pulses. REQH is therefore normally set high
(REQH = 1) for standard DS3/STS-1 pulses.
For cases where a square-shaped DS3/STS-1 pulse (that does not meet the
DS3/STS-1 standards) is transmitted to the receiver REQH can be set low (REQH
= 0).
In E3 mode, the REQH pin should always be set low (REQH = 0) to prevent
over-equalization.
The M2833i device is able to recover data that has been attenuated by a
Mindspeed Technologies
Single/Dual/Triple E3/DS3/STS-1 Line Interface Unit
™
M28331/M28332/M28333 (–3x)
28333-DSH-003-A