MAX3657(2004) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX3657
(Rev.:2004)

155Mbps Low-Noise Transimpedance Amplifier

Maxim Integrated 

155Mbps Low-Noise Transimpedance

Amplifier

AMPLITUDE

AMPLITUDE

INPUT FROM PHOTODIODE

Figure 1. MAX3657 Limited Outputs

TIME

OUTPUT (SMALL SIGNALS)

OUTPUT (LARGE SIGNALS)

TIME

INPUT AFTER DC CANCELLATION

Figure 2. Effects of DC Cancellation on Input

Photocurrent Monitor

The MAX3657 includes an average photocurrent monitor.

The current at MON is approximately equal to the DC cur-

rent at IN. Best monitor accuracy is obtained when data

input edge time is longer than 500ps.

Design Procedure

Select Photodiode

Noise performance and bandwidth are adversely affected

by stray capacitance on the TIA input node. Select a

low-capacitance photodiode to minimize the total input

capacitance on this pin. The MAX3657 is optimized for

0.5pF of capacitance on the input. Assembling the

MAX3657 in die form using chip and wire technology

provides the lowest capacitance input and the best

possible performance.

Select CFILT

Supply voltage noise at the cathode of the photodiode

produces a current I = CPD ∆V/∆t, which reduces the

receiver sensitivity (CPD is the photodiode capaci-

tance). The filter resistor of the MAX3657, combined

with an external capacitor, can be used to reduce the

noise (see the Typical Application Circuit). Current gen-

erated by supply-noise voltage is divided between

CFILT and CPD. To obtain a good optical sensitivity,

select CFILT > 400pF.

Select Supply Filter

The MAX3657 requires wideband power-supply decou-

pling. Power-supply bypassing should provide low

impedance between VCC and ground for frequencies

between 10kHz and 200MHz. Use LC filtering at the

main supply terminal and decoupling capacitors as

close to the die as possible.

Select RMON

Connect a resistor between MON and ground to moni-

tor the average photocurrent. Select RMON as large as

possible:

RMON

=

2.1V

IMONMAX

where IMONMAX is the largest average input current

observed.

Select Coupling Capacitors

A receiver built with the MAX3657 has a bandpass fre-

quency response. The low-frequency cutoff due to the

coupling capacitors and load resistors is:

LFCTERM

=

2π

x

1

RLOAD x

CCOUPLE

Select CCOUPLE so the low-frequency cutoff due to the

load resistors and coupling capacitors is much lower than

the low-frequency cutoff of the MAX3657. The coupling

capacitor should be 0.1µF or larger, but 1.0µF is recom-

mended for lowest jitter. Refer to Maxim Application Note

HFAN-1.1: Choosing AC-Coupling Capacitors for more

information.

Layout Considerations

Figure 3 shows a suggested layout for a TO header for

the MAX3657.

Wire Bonding

For high-current density and reliable operation, the

MAX3657 uses gold metalization. For best results, use

gold-wire ball-bonding techniques. Use caution if

attempting wedge bonding. Die size is 41 mils x 48 mils,

(1040µm x 1220µm) and die thickness is 15 mils (380µm).

The bond pad is 94.4µm x 94.4µm and its metal thickness

is 1.2µm. Refer to Maxim Application Note HFAN- 8.0.1:

_______________________________________________________________________________________ 7

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