MAX3744/MAX3745 Evaluation Kit

_____________Component Suppliers

SUPPLIER

PHONE

FAX

AVX

803-946-0690

803-626-3123

Coilcraft

847-639-6400

847-639-1469

Murata

814-237-1431

814-238-0490

Note:

Please

indicate

that

you

are

using

the

MAX3744/MAX3745

when

contacting

thes e

component

suppliers.

________________________Quick Start

1)

Connect a signal source to IN at J3. Set the signal

amplitude to 100mVp-p (this may require some

attenuation

between

the

source

and

the

MAX3744/MAX3745 EV kit.) The signal should

have a data rate of 2.5Gbps.

2)

Connect OUT+ and OUT- to the 50O inputs of a

high-speed oscilloscope at J6 and J7.

3)

Remove the shunt from jumper JU1.

4)

Connect a +3.3V supply to the VCC terminal and

ground to the GND terminal.

5)

The differential signal at the oscilloscope should

be

greater

than

280mVp-p

(140mVp-p

on

MAX3744 EV Kit).

______________Detailed Description

The MAX3744/MAX3745 EV kit allows characterisation

without a photodiode. The kit is designed to emulate a

DC-coupled photodiode input. Diode currents may

from 10uA to 1mA. The high-speed current source of

the photodiode is emulated on the EV kit using

separate AC and DC paths. The AC signal is supplied

from a standard 50O lab source that delivers power to

an on board termination resistor. A current is then

generated from the voltage signal by a resistor with low

stray capacitance. The effect of the DC photodiode

current may be emulated by a current source at TP1.

An isolation resistor prevents the DC source from

loading the AC path.

The values of the series resistive element, R3 and R4,

have been carefully selected so that the bandwidth of

the transimpedance amplifier is not altered. Surface-

mount resistors have parasitic capacitance that may

reduce their impedance at frequencies above 1GHz.

____________Photodiode Emulation

The following procedure can be used to emulate the

high-speed current signal generated by a photodiode:

1)

2)

ρ

⋅

=

1000

10

I

)

10

/

P

(

AVE

AVE

(?= photodiode responsivity in A/W)

3)

Calculate the AC signal current and adjust the

signal generator to obtain it.

1

r

1

r

I

2

I

e

e

AVE

AC

+

−

⋅

⋅

=

For example: To emulate a photodiode with an average

power of –16dBm and an extinction ratio of 10;

1)

–16dBm optical power will produce 25µA of

average

input

current

(assume

photodiode

responsivity of 1A/W). Set the DC current input to

25µA at TP1.

2)

To generate this current through the 1000O input

resistors, set the signal source to produce an

output level of

41µA*1000 O = 41mVp-p.

______________Noise Measurement

Remove R3 and R4 before attempting noise

measurements to minimize input capacitance. With R3

and R4 removed the total capacitance at the IN pin is

approximately 0.85pF.

__________________RSSI (MAX3744)

The Average Power at the MAX3744 input is indicated

by the common mode output measured at TP2 and

TP3. Refer to the MAX3744 data sheet for details.

_____________________________________Adjustments and Control Descriptions

COMPONENT

NAME

FUNCTION

JU1

OFFSET CORRECTION

Instal JU1 to disable offset correction.

TP1

DC CURRENT INPUT

Apply DC current for photodiode simulation.

TP2, TP3

OUTPUT COMMON MODE

MAX3744 RSSI Signal