AD9260AS datasheet(38/45 Pages) AD

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AD9260

Rev. C | Page 37 of 44

Table 18. Evaluation Board Reference Pin Configuration

Reference

Voltage

Connect Jumper

Input Voltage

(p-p FS)

2.5 V

JP7

4.0 V

1.0 V

JP6

1.6 V

External

JP5, JP9, and JP10

4.0 V

The external reference circuitry is illustrated in Figure 77. By

connecting or disconnecting JP10, the external reference can be

configured for either 1.0 V or 2.5 V. By connecting JP10, the

external reference will be configured to provide a 2.5 V

reference and by disconnecting JP10 reference, it will be

configured for 2.5 V. By leaving JP10 open, the external

reference will be configured to provide a 1.0 V reference.

Flexible DC or AC Coupled External Clock Inputs

As illustrated in Figure 78, the AD9260 Evaluation Board is

designed to allow the user the flexibility of selecting how to

connect the external clock source. It is also equipped with a

playpen area for experimenting with optional clock drivers or

crystals.

Selecting DC or AC Coupled External Clock:

DC Coupled: To directly drive the clock externally via the

CLKIN connector, connect JP11 and disconnect JP12. Note:

50 Ω terminated by R27.

AC Coupled: To ac couple the external clock and level shift it to

midsupply, connect JP12 and disconnect JP11. Note: 50 Ω

terminated by R27.

Flexible Input Signal Configuration Circuitry

The AD9260 Evaluation Board’s Input Signal Configuration

Block is illustrated in Figure 79. It is comprised of an input

signal summing amplifier (U7), a variable input signal

common-mode generator (U10), and a pair of amplifiers (U8

and U9) that configure the input into a differential signal and

drive it, through a pair of isolation resistors, into the input pins

of AD9260. The user can either input a signal or dual signal into

the evaluation board via the two SMA connectors (J6 and J7)

labeled IN-1 or IN-2.

The user should refer to the Driving the Input section of the

data sheet for a detailed explanation of how the inputs are to be

driven and what amplifier requirements are recommended.

Selecting Single or Dual Signal Input

The input amplifier (U7) can either be configured as a dual

input signal inverting summer or a single tone inverting buffer.

This flexibility will allow for slightly better noise performance

in the single tone mode due to the inherent noise gain

difference in the two amplifier configurations. An optional

feedback capacitor (C9) was added to allow the user additional

out-of band filtering of the input signal if needed.

For two-tone input signals: The user would leave jumpers (JP8)

connected and use IN-1 and IN-2 (J7 and J6) as the connectors

for the input signals.

For signal tone input signal: The user would remove jumper

(JP8) and use only IN-1 as the input signal connector.

Selectable Input Signal Common-Mode Level Source

The input signal’s common-mode level (CML) can be set

by U10.

To use the Input CML generated by U10: Disconnect jumper

JP13 and Connect resistors RX3 and RX4. The CML generated

by U10 is variable and adjustable using the 1 kΩ Variable

Resistor R35.

SHIPMENT CONFIGURATION

The AD9260 Evaluation Board is configured as follows

when shipped:

2.5 V external reference/4.0 V differential full-scale input:

JP5, JP9, and JP10 connected, JP6 and JP7 disconnected.

8× Mode/OSR: JP1 connected, JP2, JP3, and JP4

disconnected.

Full Speed Power Bias: R2 = 2 kΩ and connected.

CSB pulled low: R6 = 49.9 Ω and connected, R29

disconnected.

RESETB pulled high: R7 = 10 kΩ and connected, R30

disconnected.

READ pulled high: R28 = 10 kΩ and connected, R5

disconnected.

Single Tone Input: JP8 removed, input applied via IN-1

(J7).

Input signal common-mode level set by Variable Resistor

R35 to 2.0 V: Jumper JP12 is disconnected and resistors

R×4 and R×3 are connected.

AC-Coupled Clock: JP12 connected and JP11

disconnected. Note: 50 Ω terminated by R27.

QUICK SETUP

Connect the required power supplies to the Evaluation

Board as illustrated in Figure 28:

± 5 VA supplies to P5—Analog Power

+5 VA supply to P4—Analog Power

+5 VD supply to P3—Digital Power

+5 VD supply to P2—Driver Power

Connect a Clock Source to CLKIN (J1):

Note: 50 Ω terminated by R1.

Connect an Input Signal Source to the IN-1 (J7).

Turn on power.

The AD9260 Evaluation Board is now ready for use.

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