AD8153 查看數據表（PDF） - Analog Devices

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AD8153

XStream™ 3.2 Gbps Single Buffered Mux/Demux Switch

Analog Devices 

AD8153

Data Sheet

INTERFACING TO THE AD8153

TERMINATION STRUCTURES

To determine the best strategy for connecting to the high speed

pins of the AD8153, the user must first be familiar with the on-

chip termination structures. The AD8153 contains two types of

these structures: one type for input ports and one type for output

ports (see Figure 37 and Figure 38).

VCC

VTTI

55Ω

55Ω

IPX

1173Ω

INX

AC Coupling

One way to simplify the input circuit and make it compatible

with a wide variety of driving devices is to use ac coupling. This

has the effect of isolating the dc common-mode levels of the

driver and the AD8153 input circuitry. AC coupling requires a

capacitor in series with each single-ended input signal, as shown

in Figure 39. This should be done in a manner that does not

interfere with the high speed signal integrity of the PCB.

VCC

VTTI

VCC

50Ω

50Ω

CP

IP

55Ω

55Ω

CN

IN 1173Ω

AD8153

VEE

VEE

DRIVER

Figure 37. Receiver Simplified Diagram

Figure 39. AC-Coupling Input Signal of AD8153

50Ω

50Ω

VIP

VIN

VCC

VTTO

OPX

ONX

IT

VEE

Figure 38. Transmitter Simplified Diagram

When ac coupling is used, the common-mode level at the input

of the device is equal to VTTI. The single-ended input signal

swings above and below VTTI equally. The user can then use

the specifications in Table 1 to determine the input signal swing

levels that satisfy the input range of the AD8153.

If dc coupling is required, determining the input common-

mode level is less straightforward because the configuration of

the driver must also be considered. In most cases, the user

would set VTTI on the AD8153 to the same level as the driver

output termination voltage. This prevents a continuous dc

current from flowing between the two supply nets. As a

practical matter, both devices can be terminated to the same

physical supply net.

For input ports, the termination structure consists of two 55 Ω

Consider the following example: a driver is dc-coupled to the

resistors connected to a termination supply and an 1173 Ω

input of the AD8153. The AD8153 input termination voltage

resistor connected across the differential inputs, the latter being

(VTTI) and the driver output termination voltage (VTTOD) are both

a result of the finite differential input impedance of the equalizer.

set to the same level; that is, VTTI = VTTOD = 3.3 V. If an 800 mV

For output ports, there are two 50 Ω resistors connected to the

termination supply. Note that the differential input resistance

for both structures is the same, 100 Ω.

INPUT COMPLIANCE

differential p-p swing is desired, the total output current of the

driver is 16 mA. At balance, the output current is divided evenly

between the two sides of the differential signal path, 8 mA to each

side. This 8 mA of current flows through the parallel combina-

tion of the 55 Ω input termination resistor on the AD8153 and

The range of allowable input voltages is determined by the

the 50 Ω output termination resistor on the driver, resulting in a

fundamental limitations of the active input circuitry. This range

common-mode level of

of signals is normally a function of the common-mode level of

the input signal, the signal swing, and the supply voltage. For a

given input signal swing, there is a range of common-mode

voltages that keeps the high and low voltage excursions within

acceptable limits. Similarly, for a given common-mode input

VTTI − 8 mA × (50 Ω || 55 Ω) = VTTI − 209 mV

The user can then determine the allowable range of values for VTTI

that meets the input compliance range based on an 800 mV p-p

differential swing.

voltage, there is a maximum acceptable input signal swing.

There is also a minimum signal swing that the active input

circuitry can resolve reliably. The specifications are found in

Table 1.

Rev. A | Page 20 of 24

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