AD8148ACPZ-RL(Rev0) View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD8148ACPZ-RL
(Rev.:Rev0)

Triple Differential Driver for Wideband Video

Analog Devices 

AD8146/AD8147/AD8148

Sync pulse amplitudes applied to the AD8147 and AD8148

must be less than or equal to the positive supply voltage. In low

positive supply applications, such as those that use ±2.5 V supplies,

external limiting may be required because many logic families

produce amplitudes up to 5 V. Figure 32 illustrates how to use a

monolithic triple diode to limit a sync pulse with 5 V amplitude

to an amplitude of approximately 2 V.

INCOMING

SYNC PULSE

+5V

0V

LIMITED

301Ω

SYNC PULSE

+2V

123

HN2D02FUTW1T1 0V

654

Figure 32. Limiting Sync Pulse Amplitude in Low Positive Supply Applications

DRIVING TWO UTP CABLES WITH ONE DRIVER

Some applications require driving two UTP cables with a single

driver. Each individual driver of the AD8146/AD8147/AD8148

is capable of driving two doubly terminated cables, which places

a differential load of 100 Ω across the outputs of the driver.

Figure 33 illustrates how to drive two cables.

49.9Ω

AD8146/AD8147/AD8148

100Ω

UTP

49.9Ω

100Ω

VOCM

49.9Ω

100Ω

UTP

49.9Ω

100Ω

Figure 33. Driving Two UTP Cables With One Driver

Driver bandwidth is affected to a small degree when driving the

100 Ω load presented by the two cables, as compared with

driving a typical 200 Ω load. Figure 34 illustrates the AD8146/

AD8147/AD8148 bandwidths when driving a 100 Ω load.

15

12

AD8148

9

6

AD8147

3

AD8146

0

RL, dm = 100Ω

VOUT = 2V p-p

–3

1

10

100

1000

FREQUENCY (MHz)

Figure 34. Large Signal Frequency Response Driving 100 Ω Loads

USING THE AD8146 AS A RECEIVER

While the AD8146 excels as a differential driver, it can also be

used as a differential-to-differential receiver applied as an

input buffer that protects a more sophisticated device, such as a

differential crosspoint switch. See Figure 35 for an illustration of

this type of application.

Because the AD8146 VOCM input pins are uncommitted, any

incoming common-mode signal, such as encoded sync pulses,

can be reproduced at the AD8146 outputs by stripping it from

the received signal and applying it directly to the VOCM pin.

The two series 54.9 Ω resistors form a differential termination

resistor of 109.8 Ω, which when loaded with the 1 kΩ differential

input resistance of the AD8146, provides an overall termination

of approximately 100 Ω. The received common-mode voltages

are available at the center taps between the two resistors.

Rev. 0 | Page 18 of 24

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