AD9546SLASHPCBZ datasheet(78/205 Pages) AD

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AD9546

Data Sheet

Rev. 0 | Page 78 of 205

REFERENCE RECEIVERS

REFERENCE RECEIVERS OVERVIEW

The four dedicated reference clock input pins (REFA, REFAA,

REFB, and REFBB) support up to four reference clock signals.

Two of the four pins designate the A reference input path, and

the other two pins designate the B reference input path. Both

the A and B reference inputs are configurable as either one

differential input or as two single-ended inputs. Each A and B

reference input path has a dedicated REFx input mode bit

(where x is A or B) for selecting single-ended or differential

modes in Bit 0 of Register 0x0300 for REFA and

mode, and Logic 1 selects differential mode. To accommodate

input signals with slow rising and falling edges, both the

differential and single-ended input receivers employ hysteresis.

Hysteresis also ensures that a disconnected or floating input

does not cause the receiver to oscillate.

The input receivers of the auxiliary references (accessible via

appropriately configured Mx control pins) are not configurable.

Instead, they have dc-coupled, single-ended, 1.8 V CMOS

receivers.

SINGLE-ENDED MODE

When configured for single-ended operation, the input receivers

accommodate either ac- or dc-coupled input signals via

Bits[7:4] of Register 0x0300 and Register 0x0304 per Table 47.

Bits[7:4] are only effective when single-ended mode is in effect

per Bit 0 of Register 0x0300 and/or Register 0x0304.

The ac-coupled mode has an internal bias termination equivalent

to a 0.6 V dc source with a 23.5 kΩ series resistance. The

dc-coupled modes have a 47 kΩ resistor connected to ground.

The internal pull-up mode has a 47 kΩ resistor connected to

1.2 V.

Single-Ended DC-Coupled Interface (1.2 V or 1.8 V CMOS)

Refer to Figure 32 for connecting a 1.2 V or 1.8 V CMOS driver to

a reference input. Be sure to select the corresponding dc-coupled

1.2 V or 1.8 V CMOS mode per Table 47.

Single-Ended DC-Coupled Internal Pull-Up Resistor

Refer to Figure 34 for connecting an open-collector or open-drain

driver to a reference input. Be sure to select the internal pull-up

mode per Table 47, which provides an internal pull-up resistor

(~47 kΩ) to 1.2 V.

Single-Ended AC-Coupled Interface

Refer to Figure 33 to ac couple a driver to a reference input. Be

sure to select the ac-coupled interface mode per Table 47,

which provides the appropriate internal bias network.

Table 47. Single-Ended Mode Bit Field Settings

Bits[7:4]1

Reference

Description

0x0300

XX00

REFA

AC-coupled 1.2 V interface (default)

XX01

REFA

DC-coupled 1.2 V CMOS

XX10

REFA

DC-coupled 1.8 V CMOS

XX11

REFA

Internal pull-up resistor (disable pull-down resistor)

00XX

REFAA

AC-coupled 1.2 V interface (default)

01XX

REFAA

DC-coupled 1.2 V CMOS

10XX

REFAA

DC-coupled 1.8 V CMOS

11XX

REFAA

Internal pull-up resistor (disable pull-down resistor)

0x0304

XX00

REFB

AC-coupled 1.2 V interface (default)

XX01

REFB

DC-coupled 1.2 V CMOS

XX10

REFB

DC-coupled 1.8 V CMOS

XX11

REFB

Internal pull-up resistor (disable pull-down resistor)

00XX

REFBB

AC-coupled 1.2 V interface (default)

01XX

REFBB

DC-coupled 1.2 V CMOS

10XX

REFBB

DC-coupled 1.8 V CMOS

11XX

REFBB

Internal pull-up resistor (disable pull-down resistor)

X means don’t care.

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