ADN2841ACP-32-REEL7 - Analog Devices

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ADN2841 OPTICAL EVALUATION KIT

HSN TECHNICAL NOTE - HSN TN009

HSN TECHNICAL NOTE -HSN TN009

Introduction:

This Technical Note describes the ADN2841 laser diode driver Rev. C1 evaluation kit. The evaluation kit is a

demonstration board that provides optical evaluation of the ADN2841. This document describes how to config-

ure the board in order to operate the part optically. The document contains the following information:

· Board Description.

· Quick Start for optical operation.

· Description of board settings.

· General Notes.

· Component List.

· Schematic of board.

· Board Layout Information

· Silkscreen Image of board

· Optical Eyes

Board Description:

The ADN2841 is a dual loop 155Mbs to 2.7Gbps laser diode driver. To use the board in an optical configura-

tion, a suitable laser diode driver must be soldered onto the board. The monitor photo diode, MPD, current is

fed into the ADN2841 to control the average power and extinction ratio. The ADN2841 uses automatic power

control, APC, to maintain a constant average power over time and temperature. The ADN2841 uses closed

loop extinction ratio control to allow optimum setting of extinction ratio for every device. This board is configured

for lasers in Minidil packages only. LEDs for Power Supply, DEGRADE, and FAIL are made available for

monitoring purposes.

Power to the evaluation circuitry is -5V only!

Quick Start for Optical Operation:

To ensure proper operation in the optical configuration, verify the following:

1. Jumpers K3 & K4 are connected to A, Jumpers K2 & K5 are connected to B.

2. If the input data is clocked it is necessary to enable the clock select pin (CLKSEL). CLKSEL is enabled by

connecting K4 to B. If the clock inputs are not used, or the input data is not latched, connect K4 to A.

3. The power supply is diode protected to ensure the device is not damaged if a +5V power supply is acci-

dently connected. The user may connect Jumper K1 (short circuit) and power up the board by applying -5V

to the POWER input SMA, J3. If Jumper K1 is not connected then the user should make the power

supply sufficiently negative to enure that the DUT supply is -5V. The actual DUT supply can be measured

at the anode of D1.

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ADN2841 EVALUATION KIT

4. Apply a differential signal, typically 500mV, to J6 and J7 (DATAN and DATAP). Single ended operation may

result in a degraded eye

5. If the clock select pin is enabled by K4, apply a differential clock signal, typically 500mV, to J4 and J5

(CLKN and CLKP).

6. The optical eye and switching characteristics of the ADN2841 may be observed using a digital communica-

tions analyser 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

and Immon are both a 1:100 ratio of Ibias and Imod. Both are terminated with resistors and so can be viewed

at Test Points T3 and T4 using a voltmeter or oscilloscope.

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

 With the power supply turned off adjust potentiometers R20 (ERSET) and R21 (PSET) to approx 20k.

 With the evaluation board powered on reduce the value of potentiometer R21 to establish the desired average

optical power.

 Potentiometer R20 can then be reduced in value to increase the modulation current, and hence 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.

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 (PSET), the Extinction Ratio Set Input (ERSET), and the Alarm Set

(ASET) is between 1Kohm and 25Kohm. Resistors R31-R33 ensure that the resistance at these nodes never

falls below the minimum allowable value. If the node resistances increase above 25Kohm the ADN2841 may

not operate within its specifications.

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ADN2841 EVALUATION KIT

Description of Board Settings:

COMPONENT NAME FUNCTION

J3 POWER -5V power input to board

J1 IDTONE Idtone input.

J4 CLKN Clkn input.

J5 CLKP Clkp input.

J6 DATAP Datap input.

J7 DATAN Datan input.

T1 IMPDMON IMPD Current Mirror Monitor

T2 IMPDMON2 MPD2 Current Mirror Monitor

T3 IBMON Bias Current Mirror Monitor

T4 IMMON Modulation Current Mirror Monitor

R19 ASET POTENTIOMETER Adjusts bias current threshold for disable and fail alarms.

R20 ERSET POTENTIOMETER Adjusts for slope efficiency.

R21 PSET POTENTIOMETER Adjusts the mpd current and thus the average power.

K1 K1 Jumper to bypass supply protection diode.

K2 K2 Jumper for LBWSET

K3 K3 Jumper to exercise ALS

K4 K4 Jumper for CLKSEL

K5 K5 Jumper for IDTONE

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ADN2841 EVALUATION KIT

COMPONENT QTY DESCRIPTION

R19, R20, R21 3 50k trim potentiometer

D1 1 Supply Protection Diode (IN4001)

D2, D3, D4 3 SMD LEDs

C4-C12, C16-C18 8 10nF capacitor

C2 1 220uF capacitor

C13, C14 2 1µF capacitor (Loop Bandwidth Setting)

Q3, Q4 2 Transistor (SOT23)

C1 1 22uF

C15 1 1pF

R10, R15, R18 3 10k resistor.

R3 1 10 Ohm resistor

R5 1 100 Ohm Resistor

R2 1 24 Ohm resistor

R1, R16, R17, 3 330 Ohm resistor.

R6 1 1k Ohm resistor

R31-R33 3 820 Ohm resistor.

R11, R12, R13, R14 4 1k5 Ohm resistor.

R25*, R26, R27*, R28*, R29 5 0 Ohm resistor

K1-K5 4 Pin header jumper sockets

J1, J3-J7, J8* 7 SMA connector.

U1 1 ADN2841

U2* 1 Laser Diode - Not supplied by Analog Devices

L1, L2 2 10µH inductor

*Signifies components which are not populated

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ADN2841 EVALUATION KIT

Figure 1. Schematic of Board

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ADN2841 EVALUATION KIT

Figure 2. PC Component Side Figure 3. PC Ground Plane

Figure 4. -5V Power Plane Figure 5. Solder Side

BOARD LAYOUT

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ADN2841 EVALUATION KIT

Figure 6. Silkscreen Image

Figure 7. Unfiltered 2.5Gbs Optical Eye.

Average Power = -3dBm, Extinction Ratio = 9.5dB.

Eye obtained using a Mitsubishi FU-445-SDF.

Figure 8. Filtered 2.5Gbs Optical Eye.

Average Power = -3dBm, Extinction Ratio = 9dB.

Eye obtained using a Mitsubishi FU-445-SDF