Analog Devices EVALZ-ADN2871 Scheda tecnica

- 1 -

Introduction:

This technical note describes 24-Lead ADN2871/ADN2873 laser diode driver evaluation kit. The

evaluation kit provides an AC-coupled, differential optical evaluation platform for the device

ADN2871/ADN2873, called device under test (DUT) below. The evaluation kit supports two DUT

operation modes to set laser optical average power (Pav) and extinction ratio(ER) outputs: Voltage setting

mode and Resistor Setting mode. The voltage settings mode uses a micro-converter’s DAC voltage outputs

to DUT pin PAVREF and ERREF. The resistor setting mode uses potentiometers connected to DUT pin

PAVSET and ERSET, respectively.

This document describes how to configure the evaluation kit to either voltage or resistor setting mode to

correctly set the DUT optical average power and extinction ratio driving capabilities. The document

contains:

1. Board Description

2. Capacitor Selection

3. Quick Start Operation using Voltage setpoint Calibration

4. Quick Start Operation using Resistor setpoint Calibration

5. Description of board settings

6. BOM and Schematic of board

7. Laser to PCB footprints

8. Discussions

Board Description:

The EVALZ-ADN2871/ADN2873 board provides on-board configurable jumpers to setup the DUT in

either voltage or resistor setting mode. The board is convenient to evaluate the DUT optical performance

worked with various differential TOSA lasers, and to optimize, debug, and confirm new optical transmitter

design.

The DUT is a 3.3V, APC (average power control) single loop capable, laser diode driver device, available

for data rate support from 50Mbps up to 4.25Gbps. To evaluate the DUT performance, a suitable coax laser

diode must be soldered onto the evaluation board. A photo-current, produced from the laser companion

monitor photo diode, MPD, is fed into the DUT to close the APC loop. This board is configured for

differential ended coaxial lasers only. LEDs on board present the DUT power supply, and FAIL alarm

status.

Capacitor Selection

The EVALZ-ADN2871/ADN2873 needs only one high isolation impedance capacitor: PAVCAP for the

stable APC loop control. The bandwidth of APC control loop is centered between a maximum bandwidth to

avoid data dependency and loop instability, and a minimum bandwidth to ensure compliance to SFP start

up time. The following equations can be used to determine the nominal values of the average power loop

capacitor (PAVCAP) for a design based on the laser slope efficiency and the required average output

power. There is a +/-15% tolerance allowed for the capacitors value calculated.

- 2 -

VOLTAGE SETPOINT CALIBRATION:

At the voltage setting calibration mode, The PAVCAP should be:

Pav

Pavcap 



6

1028.1

(F)

RESISTOR SETPOINT CALIBRATION:

At the resistor setting calibration mode, The PAVCAP should be:

Pav

Pavcap 



6

102.3

(F)

where: LI (mW/mA) is the typical laser slope efficiency at 25 Degrees Celsius.

PAV is the average power (mW) required.

For example, if a designed transmitter needs optical average power output of -4dBm, the selected laser has

about typical 0.07mW/mA slope efficiency, the calculated Pavcap in

Voltage Setting Mode: Pavcap = 225nF

Resistor Setting Mode: Pavcap = 560nF

Quick start for voltage setpoint calibration of Pav:

In Voltage setpoint calibration, the evaluation board offers two different methods of providing the

controlled reference voltages to DUT pin PAVREF and ERREF. The ADN2871/ADN2873 evaluation

board has on board voltage regulators and potentiometers that allow the user to adjust the reference

voltages to DUT pin PAVREF and ERREF that set the average power and extinction ratio. Alternatively

the user can provide two external reference voltages to DUT pin PAVREF and ERREF.

Voltage Setting Method 1:

JP1

JP2

JP6 JP7

JP5

JP4

JP3

R21

R24

Figure 1. Jumper settings for voltage setpoint calibration using external DAC reference

voltages to DUT pin PAVREF and ERREF.

- 3 -

To operate an EVALZ-ADN2871 in Voltage Setting mode using external DACs input, verify the

following:

1. Remove jumper K2 and connect jumpers JP1, JP2, JP3, JP5 to JP6 to position A (connected as shown

in black box), JP4 and JP7 to position B as shown in figure 1.

2. The power supply is diode protected to ensure the DUT safety if a negative power supply is

accidentally connected. The user may connect Jumper K1 (short circuit) and power up the board by

applying +3.3V to the POWER input SMA, J1. If Jumper K1 is not connected then the user should

supply the sufficiently +3.3V to jumper K1, on the head connected to pin R1 and C2. The actual DUT

supply voltage can be confirmed at the anode of D1.

3. Connect external power supplies, PAVREF and ERREF reference voltages to J2 and J3. Adjust both

external supply reference voltages to 0.1volt.

4. Apply a differential signal, typically 500mV p-p, to J4 and J5 (DATAN and DATAP). Single ended

operation may result in a degraded eye.

5. The optical eye and switching characteristics of the DUT may be observed using a digital

communications analyzer which has an optical input channel with the required bandwidth.

6. The bias and modulation currents can also be monitored by observing Ibmon and Immon respectively.

Ibmon is a 1:100 ratio of Ibias and Immon is a 1:50 ratio of Imod. Both are terminated with resistors

and so can be viewed at test points TP2 and TP1 using a voltmeter or oscilloscope.

7. To establish the desired optical average power and extinction ratio the user should do:

Turn on the power supply to the evaluation board, and hook up a differential data signal,

Slowly increase the external voltage supplied to pin PAVREF to establish the desired average

optical power.

After satisfy the initial average optical power output, slowly increase the external voltage

supplied to pin ERREF to increase the extinction ratio. The bias current will decrease as the

modulation current increases. The bias and modulation currents can be monitored using Ibmon

and Immon (through test points TP2 and TP1).

When adjusting the extinction ratio the user should allow adequate time for the eye to settle. The range of

allowable voltage supplied to DUT pin (PAVREF) for average power is 0.1volt to 1.0volt and the

allowable voltage range supplied to input (ERREF) for at extinction ratio is between 0.1volt and 1.0 volt.

Voltage Setting Method 2:

JP1

JP2

JP6 JP7

JP5

JP4

JP3

R21

R6 R24

R21

Figure 2. Jumper settings for voltage setpoint calibration using on board regulator

voltages for PAVREF and ERREF.

- 4 -

To operate the evaluation board using voltage setpoint calibration using on board regulators for

PAVREF and ERREF, verify the following:

1. On the evaluation board remove jumper K2 and connect jumpers JP2 and JP4 to position B and

connect jumpers JP1 (connected as shown in black box), JP3, JP5, JP6 and JP7 to position A as

shown in figure 2.

2. With the power supply turned off adjust potentiometer R6 (ERSET) to approx zero ohms.

3. With the power supply turned off adjust potentiometers R21 and R24 (shown in grey) to approx

25K ohms.

4. The power supply is diode protected to ensure the DUT safety if a negative power supply is

accidentally connected. The user may connect Jumper K1 (short circuit) and power up the board

by applying +3.3V to the POWER input SMA, J1. If Jumper K1 is not connected then the user

should supply the sufficiently +3.3V to jumper K1, on the head connected to pin R1 and C2. The

actual DUT supply voltage can be measured at the anode of D1.

5. Apply a differential signal, typically 500mVp-p, to J4 and J5 (DATAN and DATAP). Single

ended operation may result in a degraded eye

6. The optical eye and switching characteristics of the DUT may be observed using a digital

communications analyzer which has an optical input channel with the required bandwidth.

7. The bias and modulation currents can also be monitored by observing Ibmon and Immon

respectively. Ibmon is a 1:100 ratio of Ibias and Immon is a 1:50 ratio of Imod. Both are

terminated with resistors and so can be viewed at test points TP2 and TP1 using a voltmeter or

oscilloscope.

8. To establish the desired average power and extinction ratio the user should follow the below

procedure:

Power up the evaluation board and hook up a switching data signal, reduce the value of

potentiometer R21 to establish the desired average optical power.

Reduce the value of potentiometer R24 to increase the modulation current, and hence increase the

extinction ratio. The bias current will decrease as the modulation current increases. Monitor the

bias and modulation currents by using Ibmon and Immon (through test points of TP2 and TP1).

When adjusting the extinction ratio the user should allow adequate time for the eye to settle. The range of

allowable voltage supplied to DUT pin (PAVREF) for average power is 0.1volt to 1.0volt and the

allowable voltage range supplied to input (ERREF) for at extinction ratio is between 0.1volt and 1.0 volt.

- 5 -

Quick start for Resistor Setting Mode of average power Pav:

JP1

JP2

JP6 JP7

JP5

JP4

JP3

R21

R6 R24

Figure 3. Jumper settings for resistor setpoint calibration using potentiometers

connected to the PAVSET and ERSET pins.

To operate the evaluation board in resistor setpoint calibration using potentiometers at the PAVSET and

ERSET pins, verify the following:

1. Connect Jumper K2, connect jumpers JP1,JP3 and JP6 to position B (connected as shown in black

box) and connect jumpers JP4 and JP5 to position A as shown in figure 3.

2. The power supply is diode protected to ensure the DUT safety if a negative power supply is

accidentally connected. The user may connect Jumper K1 (short circuit) and power up the board

by applying +3.3V to the POWER input SMA, J1. If Jumper K1 is not connected then a +3.3V

should be supplied to jumper K1, on the head connected to pin R1 and C2. The actual DUT supply

voltage can be measured at the anode of D1.

3. Apply a differential signal, typically 500mVp-p, to J4 and J5 (DATAN and DATAP). Single

ended operation may result in a degraded eye.

4. The optical eye and switching characteristics of the ADN2870 may be observed using a digital

communications analyser which has an optical input channel with the required bandwidth.

5. The bias and modulation currents can also be monitored by observing Ibmon and Immon

respectively. Ibmon is a 1:100 ratio of Ibias and Immon is a 1:50 ratio of Imod. Both are

terminated with resistors and so can be viewed at test points TP2 and TP1 using a voltmeter or

oscilloscope.

6. To establish the desired average power and extinction ratio, user should follow the procedure:

• turn off the power supply, adjust potentiometers R3 (PAVSET) and R6 (ERSET) (shown in grey)

to approximately 20k.

• turn on the board power supply and the data signal switching, reduce the value of potentiometer

R3 to establish the desired average optical power.

•after get satisfied Pav, reduce potentiometer R6 value to increase the modulation current, and

Hence to increase the extinction ratio. The bias current will decrease as the modulation current

increases. The bias and modulation currents are available from monitoring IBMON and IMMON.

When adjusting the extinction ratio the user should allow adequate time for the eye to settle. The allowable

resistance range at the Power Set Input (PAVSET) and the allowable resistance at the Extinction Ratio Set

- 6 -

Input (ERSET) is between 1Kohm and 20K ohm. Resistors R4 and R7 ensure that the resistance at these

nodes never falls below the minimum allowable value. If the node resistances increase above 25Kohm the

DUT may not operate within its specifications.

With a known laser diode, there is a quick way to get Rpavset and Rerset values:

Assume the known laser diode a has a typical slope efficiency = 0.07mW/mA, the typical threshold current

is about 10mA, the companion MPD responsivity = 0.85mA/mW, and requested average optical power is

about 0.4mW, ER = 5dB.

61.3

85.04.0

23.1

23.1 









Pav

Rpavset

(kohm)

325.8

91.5

4023.14023.1

Re 









MOD

rset

(kohm)

The above Rpavset and Rerset resistance values could be a good start to get the fine tuned optical

performance in resistor setting mode.

Description of Board Settings:

COMPONENT

NAME

FUNCTION

POWER

+3.3V power input to board

PAVREF

PAVREF external reference input

ERREF

ERREF external reference input

DATAN

Data N input

DATAP

Data P input

ALS

ALS external input

TP1

IMMON

Imod Current Mirror Monitor

TP2

IBMON

Ibias Current Mirror Monitor

TP3/TP4

PAVREFmon

PAVREF reference voltage

TP5/TP6

ERREFmon

ERREF reference voltage

PAVSET

POTENTIOMETER Adjusts bias current (in Resistor set mode)

ERSET

POTENTIOMETER Adjusts mod current (in Resistor set mode)

R21

PAVREF

POTENTIOMETER Adjusts bias current (in Voltage set mode)

R24

ERREF

POTENTIOMETER Adjusts mod current (in Voltage set mode)

Jumper to bypass supply protection diode

Jumper for PAVSET (in Resistor set mode)

JP1

Jumper to select voltage or resistor mode for PAVREF

JP2

Jumper to select onboard or external ref for PAVREF

JP3

Jumper to select voltage/resistor mode for RPAV

JP4

Jumper to select external input for ALS

JP5

Jumper to select Immon

JP6

Jumper to select voltage/resistor mode for ERREF

JP7

Jumper to select onboard or external ref for ERREF

- 7 -

EVALZ-ADN2871/ADN2873 Schematic

- 8 -

EVALZ-ADN2871/ADN2873 Bill of Materials

Part No.

Device number

Quantity

Value

Package

AD381(A)

ADR381*

SOT23

CAP+

22UF

TYPE "C" Case

CAP+

220UF

TYPE "C" Case

C3, C8, C9, C13

CAP

10NF

201A

C4*

CAP

Not populated*

805

CAP

560NF

805

C6, C7

CAP

10NF

603

C15, C16, C11, C10

CAP

100NF

402

C50, C51, C52, C53,

C54, C55

CAP

10NF

402

C12

CAP

3.3PF

402

Diode

1N4001

Not populated

LED

LED_SMT

LED

LED_SMT

J1, J2, J3, J4, J5, J6

SMA

SMA CONNECTOR

J10, J11

SMA

Not populated*

SMA CONNECTOR

JP1, JP2, JP3, JP4, JP5,

JP6, JP7

JUMPER2\SIP3

LINK-3P

K1, K2

JUMPER

SIP-2P

IND

10uH

1206

L2, L5

IND

0.6nH*

402

IND

0nH

402

L4, L7

IND

10uH

603

IND

82nH

603

FET

SOT23

RES

330R

603

R2, R12

RES

15R

201

R3, R6, R21, R24

VRES

50K

SMD POT

VRES_SMD

R4, R5, R9, R22, R25

RES

603

R13

RES

603

R7, R8

RES

470

603

R10

RES

330R

603

R11

RES

9K1*

603

R20, R23

RES

1.1K

603

T1 - T6

TESTPOINT

LFCSP-

ADN2873ACPZ

LFCSP-ADN2873-24PIN-

HSN_COAX_LA

SER_TYPEC

Not Populated*

HSN_COAX_LASER_T

YPEC

- 9 -

EVALZ-ADN2871/ADN2873 top layer Layout

In the latest revision D, the PCB offers one option to cut off the BIAS and CCBIS pin

connection. At the Red circled place, one 402 surface mount pad designed in between the

pins BIAS and CCBIS. If populated DUT is ADN2871, an 0 ohm resistor is needed to

connect BIAS and CCBIAS pins. If the DUT is ADN2873, leave this component pad

OPEN, and the pad offers test points for BIAS and CCBIAS pins, respectively.

Laser and EVALZ-ADN2871/ADN2873 footprints

The EVALZ-ADN2871/ADN2873 board supports differential ended coaxial lasers only.

The compliant laser footprint should be like:

- 10 -

On the EVALZ-ADN2871/ADN2873 board, the differential laser footprints are:

PCB Bottom

Look into

the PCB at

the laser

side

As a default setting of the EVALZ-ADN2871/ADN2873 board, the laser diode driver

(DUT) to a laser diode (LD) interface circuit been optimized to work with a VCSEL

TOSA: HFE4192-582.

When use this EVALZ-ADN2871/ADN2873 board to evaluate other differential lasers

LDs, one optimization work is necessary on the circuitry between the DUT to the LD.

Please contact ADI sales for the necessary technical support.

Information furnished by Analog Devices is believed to be accurate

and reliable. However, no responsibility is assumed by Analog Devices

for its use, nor for any infringements of patents or other rights of third

parties that may result from its use. Specifications subject to change

without notice. No license is granted by implication or otherwise under

any patent or patent rights of Analog Devices. Trademarks and

registered trademarks are the property of their respective owners.

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