Datasheet

DS26521 Single T1/E1/J1 Transceiver
67 of 258
8.11 Line Interface Units (LIUs)
The DS26521 combines an LIU transmit and receive front-end with its framers. The LIU contains three sections:
the transmitter, which waveshapes and drives the network line; the receiver, which handles clock and data
recovery; and the jitter attenuator. The DS26521 LIU can switch between T1 or E1 networks without changing any
external components on either the transmit or receive side.
Figure 8-17 shows a recommended circuit for software-
selected termination with protection. In this configuration, the device can connect to 100Ω T1 twisted pair, 110Ω J1
twisted pair, 75Ω or 120Ω E1 twisted pair without additional component changes. The signals between the framer
and LIU are not accessible by the user, thus the framer and LIU cannot be separated. The transmitters have fast
high-impedance capability and can be individually powered down.
The DS26521’s transmit waveforms meet the corresponding G.703 and T1.102 specifications. Internal software-
selectable transmit termination is provided for 100Ω T1 twisted pair, 110Ω J1 twisted pair, 120Ω E1 twisted pair,
and 75Ω E1 coaxial applications. The receiver can connect to 100Ω T1 twisted pair, 110Ω J1 twisted pair, 120Ω E1
twisted pair, and 75Ω E1 coaxial. The receive LIU can function with a receive signal attenuation of up to 36dB for
T1 mode and 43dB for E1 mode. The receiver sensitivity is programmable from 12dB to 43dB of cable loss. Also, a
monitor gain setting can be enabled to provide 14dB, 20dB, 26dB, and 32dB of resistive gain.