AD8138AR-EBZ - Analog Devices Inc.

Evaluation Board User Guide

UG-130

One Technology Way • P. O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com

Differential Amplifier Evaluation Board for 8-lead SOIC and MSOP Packages

PLEASE SEE THE LAST PAGE FOR AN IMPORTANT

WARNING AND LEGAL TERMS AND CONDITIONS. Rev. B | Page 1 of 8

FEATURES

Flexible board layout

Accommodates AD8131/AD8132/AD8138/AD8139

Accommodates various circuit configurations

Enables quick breadboarding/prototyping

Edge-mounted circuit configuration

Easy connection to test equipment and other circuits

RoHS compliant

GENERAL DESCRIPTION

An Analog Devices, Inc., differential driver evaluation board

makes it easy for designers to obtain quick performance results

for their particular differential driver application circuits. The

board layout is very flexible and allows for many circuit configura-

tions, including traditional four-resistor circuits, circuits with

two different feedback loops, circuits with input and output

transformers, filters, and many others. Most resistors and

capacitors use 1206 packages.

The board accommodates the AD8131, AD8132, AD8138, and

AD8139. The data sheets for these devices should be consulted

in conjunction with this evaluation board user guide.

The AD8131 is a special case because it has internal feedback

networks but can, nonetheless, be evaluated on the board by

• Omitting the R19 and R20 feedback resistors and C3 and

C4 capacitors.

• Using 0 Ω resistors for Gain Resistor R17 and Gain

Resistor R18.

• Ignoring all further references to these components.

DIFFERENTIAL DRIVER EVALUATION BOARD SCHEMATIC

R4 R2 R3

JP1

V+ V– C2

JP2

T1, T3

R5 R18

R17

V–

V+

CW TP4

OCM

DUT

C10 C11 TP3

V–

R20

TP1

R19

R10 R9

JP4 R8

JP3

T2, T4

C13

R15

R16

V+

C12 C8 TP2

R12

R11 PR1

R21

R13

R14

08988-001

TP10TP5 TP6 TP7 TP8 TP9

R23

R24

R22

V–

Figure 1. Evaluation Board Schematic

UG-130 Evaluation Board User Guide

Rev. B | Page 2 of 8

TABLE OF CONTENTS

Features .............................................................................................. 1

General Description......................................................................... 1

Differential Driver Evaluation Board Schematic.......................... 1

Revision History ............................................................................... 2

Evaluation Board Hardware............................................................ 3

Power Supplies .............................................................................. 3

Feedback Networks and Input/Output Terminations ............. 3

VOCM Input ..................................................................................... 3

Measuring Output Common-Mode Voltage .............................3

Input/Output Transformers.........................................................3

SMA Input/Output Connectors ..................................................4

Other Components .......................................................................4

Evaluation Board Artwork ...............................................................5

Ordering Information.......................................................................8

Related Links......................................................................................8

REVISION HISTORY

6/10—Rev. A to Rev. B

Document Title Changed from EVAL-ADDIFFAMP to

UG-130.................................................................................Universal

Changes to Features Section............................................................ 1

Deleted Ordering Guide .................................................................. 4

Added Evaluation Board Artwork Section ................................... 5

Added Figure 2 to Figure 13; Renumbered Sequentially ............ 5

Added Table 1; Renumbered Sequentially .................................... 8

Added Related Links Section .......................................................... 8

1/06—Rev. 0 to Rev. A

Updated Format..................................................................Universal

Change to Figure 1 ........................................................................... 1

10/03—Revision 0: Initial Version

Evaluation Board User Guide UG-130

Rev. B | Page 3 of 8

EVALUATION BOARD HARDWARE

POWER SUPPLIES

Power is applied to the board through P1, a Molex® 3-pin

header, Part 22-11-2032. Pin 1 (square footprint) is for the

positive supply, Pin 3 is for the negative supply, and Pin 2 is

connected to the ground plane of the board. Alternatively,

looped test points can be used; Test Point TP2 connects to the

positive supply, TP3 connects to the negative supply, and TP7

and TP8 connect to the ground plane. The TP5, TP6, TP9, and

TP10 test points also connect to the ground plane.

The board accommodates single or dual supplies. For single-

supply operation, connect the negative supply to the ground plane.

It is very important that the power supply pins of the device

under test (DUT) have broadband decoupling circuitry. The

board layout facilitates this with footprints for two 1206 ceramic

capacitors on each supply. At frequencies beyond the resonant

frequency of the first capacitor and its associated internal and

external inductance, the second capacitor provides the required

low impedance return current path. For optimum performance,

place the smaller of the two capacitances closest to the DUT, in

the C8 and C11 positions. C13 provides the user with the option

of adding differential decoupling between the supplies. Bulk

decoupling is provided by C1 and C2; 10 μF tantalum capacitors

are recommended.

FEEDBACK NETWORKS AND INPUT/OUTPUT

TERMINATIONS

R19 and R17 compose the upper resistive feedback loop (see

Figure 1), and R20 and R18 compose the lower feedback loop.

C3 and C4 are included across the feedback resistors to provide

frequency-dependent feedback, typically used to introduce a

real-axis pole in the closed-loop frequency response.

To minimize summing node capacitances, void the ground

plane under and around Pin 1 and Pin 8 of the DUT and the

copper that connects to them.

R6 and R7 are included as input termination resistors for applica-

tions that have single-ended inputs. Having a place for a shunt

resistor on each input makes it simple to match the two feed-

back factors. A common example of how this is used is when

the input signal originates from an unbalanced 50 Ω source. In

this case, the single-ended termination resistance is 50 Ω and

the Thevenin equivalent resistance seen looking back to the

source is 25 Ω. For the traditional four-resistor configuration,

where R19 = R20 and R17 = R18, the feedback networks are

matched by making the shunt resistor on the input leg opposite

the termination resistor equal to 25 Ω. R5 is provided for differ-

ential termination.

R15 and R16 series termination resistors are provided on each

of the outputs for impedance matching, analog-to-digital

converter (ADC) driving, and other system requirements.

VOCM INPUT

The VOCM input can be set to a dc level by adjusting the R1

potentiometer that spans the power supplies. For the dc case,

C9 is provided at the wiper for decoupling.

An external voltage can be applied to VOCM via TP4 (referenced

to the ground plane of the board). In ADC driving applications,

it is convenient to apply the ADC dc reference voltage output

directly to TP4.

It is also possible to drive the VOCM input from an external ac

source. In this case, omit C9 or reduce it to a value that allows

the desired signal to be passed. For high frequency signals on

VOCM, connect the center conductor of a coaxial cable to TP4

and ground its shield at TP10.

R21 is provided for the high common-mode output impedance

application illustrated in the AD8132 data sheet.

MEASURING OUTPUT COMMON-MODE VOLTAGE

The internal common-mode feedback loop used in the differen-

tial drivers forces the output common-mode voltage to be equal

to the voltage applied to the VOCM input, thereby providing

excellent output balance. R11 and R12 form a voltage divider

across the differential output, and the voltage at the divider tap

is equal to the output common-mode voltage, provided that

R11 and R12 are exactly matched in value. If R11 and R12 are

used to evaluate the output common-mode voltage, they should

be measured and matched to better than 300 ppm to obtain results

commensurate with the DUT output balance error performance

of −70 dB. Test Point PR1 accepts coaxial-type oscilloscope test

points, such as the Berg Electronics 33JR135-1.

INPUT/OUTPUT TRANSFORMERS

The board has the added flexibility of allowing the user to incorpo-

rate transformers on its input and output. This capability can be

especially useful when connecting to single-ended test equipment.

Because both input and output transformers have dual, nested

footprints, the user can select from a wide array of transformers

available from companies such as Mini-Circuits® and Coilcraft®.

The layout provides footprints for connecting resistors to ground

on the primary and secondary transformer center taps, offering

the user a number of options with regard to the common-mode

properties of the evaluation circuit.

JP1, JP2, JP3, and JP4 are jumpers on the backside of the board

that provide direct shunts across their associated transformers.

When not using a transformer, bypassing the transformer is a

simple matter of shorting the appropriate jumpers. When using

a transformer, it is a good idea to verify that the associated

jumpers are open.

UG-130 Evaluation Board User Guide

Rev. B | Page 4 of 8

SMA INPUT/OUTPUT CONNECTORS

The inputs and outputs have edge-mounted SMA connectors

for straightforward connection to coaxial cables. The recom-

mended connector type is Johnson Components™ Part Number

142-0701-801, or equivalent.

OTHER COMPONENTS

The components described in this user guide pertain mostly to

traditional amplifier topologies. Footprints are provided for a

number of other components on the board to allow the user to

be more creative than the traditional designs. A component

labeled as a capacitor need not be a capacitor provided that it

fits the user’s application circuit and the footprint on the board.

In application circuits where footprints for desired components

are not available on the board, the user is encouraged to find ways

to include them. For example, if an additional shunt element is

required, the user can scrape some solder mask away from the

ground plane and trace (if necessary) to make a place for the

additional part. Furthermore, 1206 elements can be stacked on

top of each other to implement a parallel circuit. An example of

this includes stacking capacitors across R17 and R18 to realize a

zero in the closed-loop transfer function. This is one way to

insert preemphasis in a line-driver application.

Evaluation Board User Guide UG-130

Rev. B | Page 5 of 8

EVALUATION BOARD ARTWORK

08988-002

Figure 2. EVAL-ADDIFFAMP-RMZ, Component Side (MSOP)

08988-003

Figure 3. EVAL-ADDIFFAMP-1RZ, Component Side (SOIC)

08988-004

Figure 4. EVAL-ADDIFFAMP-RMZ, Circuit Side (MSOP)

08988-005

Figure 5. EVAL-ADDIFFAMP-1RZ, Circuit Side (SOIC)

UG-130 Evaluation Board User Guide

Rev. B | Page 6 of 8

08988-010

Figure 6. EVAL-ADDIFFAMP-RMZ, Component Side (MSOP)

08988-006

Figure 7. EVAL-ADDIFFAMP-1RZ, Component Side (SOIC)

08988-011

Figure 8. EVAL-ADDIFFAMP-RMZ, Circuit Side (MSOP)

08988-007

Figure 9. EVAL-ADDIFFAMP-1RZ, Circuit Side (SOIC)

Evaluation Board User Guide UG-130

Rev. B | Page 7 of 8

08988-008

Figure 10. EVAL-ADDIFFAMP-RMZ, Component Side (MSOP)

08988-012

Figure 11. EVAL-ADDIFFAMP-1RZ, Component Side (SOIC)

08988-009

Figure 12. EVAL-ADDIFFAMP-RMZ, Circuit Side (MSOP)

08988-013

Figure 13. EVAL-ADDIFFAMP-1RZ, Circuit Side (SOIC)

UG-130 Evaluation Board User Guide

Rev. B | Page 8 of 8

ORDERING INFORMATION

Table 1. Bill of Materials

Qty Reference Designator Package Description

2 C1, C2 3216 10 μF capacitor

10 C3 to C6, C8 to C13 C1206 Capacitor, user-defined value

5 J1 to J5 SMASMT SMA connector

4 JP1 to JP4 JPRSLD02 Jumper

1 P1 PWR_CONN_6-9-2 3-pin header, Molex Part 22-11-2032

1 PR1 SMACON SMA connector

1 R1 3299W 1 kΩ potentiometer

23 R2 to R24 R1206 Resistor, user defined value

2 T1, T2 ETC1-6 Transformer

2 T3, T4 KK81 Transformer

1 TP1 TP Test point

9 TP2 to TP10 TP104 Test point

1 U1 8-lead SOIC and MSOP Device under test

1 PC board