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AD8158

Rev. B | Page 16 of 36

THEORY OF OPERATION

The AD8158 is a buffered, asynchronous, three-port transceiver

that allows 2:1 multiplexing and 1:2 demultiplexing among its

ports. The 1:2 demux path supports bicast operation, allowing

the AD8158 to operate as a port replicator as well as a redundancy

switch. The AD8158 offers loopback on each lane, allowing

the part to be configured as a twelve-lane equalizer or redriver

with FFE.

MUX

TXC

RXA

RXB

DEMUX

RXC

TXA

TXB

Figure 35. Mux/Demux Paths, Port A to Port C

The part offers extensively programmable transmit output levels

and preemphasis settings as well as squelch or full disable. The

receivers integrate a programmable, multizero transfer function

for aggressive equalization and a programmable loss-of-signal

feature. The AD8158 provides a balanced, high speed switch

core that maintains low lane-to-lane skew while preserving

edge rates.

The I/O on-chip termination resistors are tied to user-settable

supplies for increased flexibility. The AD8158 supports a wide

primary supply range; VCC can be set from 1.8 V to 3.3 V. These

features, together with programmable transmitter output levels,

allow for a wide range of dc- and ac-coupled I/O configurations.

The AD8158 supports several control and configuration modes,

shown in Table 5. The pin control mode offers access to a subset

of the total feature list but allows for a much simplified control

scheme. Table 6 compares the features in all control modes.

The primary advantage of using the serial control interface is

that it allows finer resolution in setting receive equalization,

transmitter preemphasis, loss-of-signal (LOS) behavior, and

output levels.

By default, the AD8158 starts in the pin control mode. Strobing

the RESETb pin sets all on-chip registers to their default values

and uses pins to configure switch connectivity, PE, and EQ

levels. In mixed mode, switch connectivity is still controlled

through the SEL[3:0], LB_[A:C], and BICAST pins. The user

can override PE and EQ settings in mixed mode. In serial

mode, all functions are accessed through registers and the

control pin inputs are ignored, except RESETb.

The AD8158 register set is controlled through a 2-wire I2C

interface. The AD8158 acts only as an I2C slave device. The 7-bit

slave address for the AD8158 I2C interface contains the static

value b1010 for the upper four bits. The lower three bits are

controlled by the input pins, I2C_A[2:0].

Table 5. Control Interface Mode Register

Address

Default

Bit

Bit Name

Functionality Description

0x0F

0x00

Control

interface mode

7:2

Reserved

Set to 0.

1:0

Mode[1:0]

00: toggle pin control. Asynchronous control through toggle pins only.

10: mixed control. Switch configuration via toggle pins, register-based

control through the I2C serial interface.

11: serial control. Register-based control through the I2C serial interface.

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