Datasheet MAX3262CAG, MAX3262C-D Datasheet (Maxim)

________________General Description

The MAX3262 limiting amplifier with its high gain and
wide bandwidth is ideal for use as a post amplifier in
fiber-optic receivers with data rates up to 1Gbps. The
amplifier’s gain can be adjusted between 33dB and
48dB. At maximum gain, signals as small as 6mVp-p
can be amplified to drive devices with PECL inputs.

The MAX3262 has complementary loss-of-signal out­puts for interfacing with open-fiber-control (OFC) cir­cuitry. These outputs can be programmed to assert
with input levels between 9mVp-p and 48mVp-p. LOS
hysteresis for any programmed level is nominally

3.0dB, preserving a balance between noise immunity
and dynamic range.

________________________Applications

1062Mbps Fibre Channel
622Mbps SONET

____________________________Features

♦ 900MHz Bandwidth
♦ 48dB Maximum Gain
♦ Chatter-Free LOS
♦ Programmable LOS Threshold
♦ Single +5V Power Supply
♦ Fully Differential Architecture

_______________Ordering Information

MAX3262

1Gbps, High-Speed Limiting Amplifier with

Chatter-Free Loss-of-Signal Detection

________________________________________________________________

Maxim Integrated Products

1

MAX3262

MAX3260

0.01µF

V

CC

ENB

DIN-

DIN+

RECEIVER WITH
PECL TERMINATIONS

(50Ω TO V

CC

- 2V)

DOUT-

DOUT+

LOSB

GND

OUTPUT

C

IN

C

IN

INPUT

FILTER

LOS

LOSB

LOS

CZN

CZP

V

CC

GND

C

AZ

+5V

+5V

50Ω +5V

+5V

+5V

C1

0.01µF

C1

R2

R1

R

4.7k

R

4.7k

V

CC

A

V

CC

B

V

CC

C

V

CC

D

V

CC

E

V

LOS

DIV2

____________________________________________________Typical Operating Circuit

19-0324; Rev 2; 12/97

PART

MAX3262CAG 0°C to +70°C (T

A

)

TEMP. RANGE PIN-PACKAGE

24 SSOP

Pin Configuration appears at end of data sheet.

MAX3262C/D 0°C to +100°C (TJ) Dice*

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone] ext. 3468.

*Dice are designed to operate over this range but are tested and
guaranteed only at TA= +25°C.

MAX3262

1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

DC ELECTRICAL CHARACTERISTICS

(VCC= +5V, R

LOAD

= 50Ω to VCC- 2V (equivalent), TA= 0°C to +70°C. Typical values are at VCC= 5V and TA= +25°C.)

AC ELECTRICAL CHARACTERISTICS

(VCC= +5V, R

LOAD

= 50Ω to 3V, AC parameters are not tested, TA= +25°C, unless otherwise noted.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Note 1: Input is a 200MHz square wave, tR< 300ps, 8mVp-p.
Note 2: Input is a 200MHz square wave, t

R

< 300ps, 1.8Vp-p.

Note 3: Input-referred noise = RMS output noise/low-frequency gain.

Power Supply, V

CC

- VEE......................................................6.0V

Input Voltage, DIN+, DIN-.....................................................6.0V

CZN, CZP, ENB, VLOS, DIV2, LOS+, LOS-.....-0.3V, V

CC

+ 0.3V

DOUT+, DOUT- (with 50Ω load).......................2.5V, V

CC

+ 0.3V

Continuous Power Dissipation (T

A

= +70°C)

SSOP (derate 10mW/°C above +70°C) ....................500mW°C

Junction Operating Temperature ......................-55°C to +150°C

Storage Temperature Range.............................-55°C to +175°C

Processing Temperature (Die).........................................+400°C

No output load

VCC= 5.0V
I

OUT

= -1.0mA

DIV2 = 0V

CONDITIONS

µA150I

ENB

Enable Input Current

mA60I

VCC

Power-Supply Current

V2.5 3.0V

DIN

Input Bias Voltage

µA120I

LOS

V

LOS

Input Current

V3.5 3.7 3.8Common-Mode Output Voltage
V0.5

LOS+, LOS- Output Low
Voltage

mA0.5DIV2 Short-Circuit Current

UNITSMIN TYP MAXSYMBOLPARAMETER

mV±35

Differential Output Offset,
DOUT+ to DOUT-

MAX3262CAG

MHz

MAX3262C/D

V

OH

- V

OL

1Gbps, 8mVp-p input

V

LOS

= 5V, DIV2 = GND (Note 3)

V

LOS

= 5V, Pattern 27 - 1PRBS

750 810

Peak-to-peak

(Note 1)

(Note 2) µs

Input referred, 55MHz

CONDITIONS

BWSmall-Signal Bandwidth

Differential inputs,
peak-to-peak

mV

10 48

V

SR

LOS Sensitivity Range

800 925

mV400 600 730V

OUT

Output Voltage Amplitude

ps250t

R, tF

Output Edge Speed

ps40PWDPulse-Width Distortion

µV80V

n

Differential Input Noise

dB1.5 3.0 5.0HYSLOS Hysteresis

V

9 48MAX3262C/D

MAX3262CAG

µs0.020 0.5t

OFFL

LOS Release Time,
Minimum Input

0.5t

OFFH

LOS Release Time,
Maximum Input

(Note 1)

dB35PSRRPower-Supply Rejection Ratio

µs0.2 0.5t

ONL

LOS Assert Time

UNITSMIN TYP MAXSYMBOLPARAMETER

0.006 1.8V

ID

Input Voltage Range

MAX3262

1Gbps, High-Speed Limiting Amplifier with

Chatter-Free Loss-of-Signal Detection

_______________________________________________________________________________________

3

70

65

60

55

50

45

40

VCC SUPPLY CURRENT

(NO OUTPUT LOAD) vs. TEMPERATURE

MAX3262-01

SUPPLY CURRENT (mA)

0 10 20 30 40 50 60 70 80 90 100

TEMPERATURE (°C)

5.25V

5.0V

4.75V

0

0

LOS HYSTERESIS

vs. TEMPERATURE

MAX3262-02

TEMPERATURE (°C)

HYSTERESIS (dB)

20 40 60 80 100 120

1

2

3

4

5

6

7

8

1Gbps WITH 1,0 PATTERN

4.0
400

LOS SENSITIVITY

vs. FREQUENCY

MAX3262-03

FREQUENCY (Mbps)

SENSITIVITY (mVp-p)

600 800 1000

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

1-0 PATTERN

K28.5 SEQUENCE
(FIBRE CHANNEL IDLE PATTERN)

PRBS 27-1

4.0

3.0

2.0

1.0

0

3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0

LOS HYSTERESIS vs. V

LOS

MAX3262-04

V

LOS

(V)

5.0

HYSTERESIS (dB)

1Gbps
DIV2 = 0
1,0 PATTERN

25

0

FREQUENCY RESPONSE

MAX3262-05

FREQUENCY (MHz)

GAIN (dB)

200 400 600 800 1000 1200 1400

31

37

43

49

55

V

LOS

= 5V

DIV2 = GND
V

LOS

= 5V

DIV2 OPEN
V

LOS

= 3.4V

DIV2 OPEN

V

LOS

= 3.0V

DIV2 OPEN

EYE DIAGRAM

1Gbps
R

LOAD

= 50Ω to VCC - 2V (EQUIVALENT)

V

IN

= 250mV, V

CC

= +5V, DIV2 = GND, V

LOS

= V

CC

V

LOS

= V

CC

MAX3262-07

+500mV

100mV/div

-500mV
225ps/div

LOS
OUTPUT

DATA
INPUT

LOS OPERATION

MAX3262-06

2µs/div

__________________________________________Typical Operating Characteristics

(VCC= 5V, TA = +25°C, unless otherwise noted.)

MAX3262

1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection

4 _______________________________________________________________________________________

_______________________________________________________________Pin Description

NAME FUNCTION

1 VCCB Positive supply for internal gain stages

PIN

5 VCCA Power supply for the input stage amplifier
6 DIN+ Data Input

10 DIV2

Input stage gain adjust. Grounding this pin forces the input stage gain to maximum (11dB) for applications
where the LOS threshold level will be set for input signals in the 9mVp-p to 20mVp-p range. Leaving this pin
open forces the gain of the input stage to be divided by two (6dB) for applications where the LOS threshold
level will be set for input signal levels in the 15mVp-p to 48mVp-p range.

9

ENB

Output Enable. Output gain stage is disabled and LOS circuitry remains functional.

8 GND Ground for the input stage amplifier

7 DIN- Inverting Data Input

15 VCCD Positive supply for the LOS+/LOS- buffer circuitry

14 GND Ground for the LOS+/LOS- buffer circuitry

13 GND Ground for the power detect/LOS circuitry

12 VCCE Positive supply for the power detect/LOS circuitry

11 VTH Comparator threshold voltage for test only. Leave unconnected.

19 DOUT+ Data Output

18 DOUT- Inverting Data Output

17 LOS+ Loss-of-Signal detect. This pin is asserted high when input power drops below the LOS threshold level.

16 LOS- Loss-of-Signal detect. This pin is asserted low when input power drops below the LOS threshold level.

23 V

CC

Positive supply for output buffers

22 GND Ground for bias generators

21 VCCC Positive supply for bias generators

20 GND Substrate Ground

24 GND Ground for internal gain stages

4 CZN

Offset-correction loop compensation capacitor. This pin should be connected to the CZP pin through a
100nF to 330nF capacitor, which provides the dominant pole for the offset-correction loop.

2 V

LOS

Power detect/LOS level set. Use this input to program the required threshold level for LOS assertion.

3 CZP

Offset-correction loop compensation capacitor. This pin should be connected to the CZN pin through a
100nF to 330nF capacitor, which provides the dominant pole for the offset-correction loop.

_______________Detailed Description

The MAX3262 is an integrated limiting amplifier intend­ed for high-frequency fiber-optic applications. The cir­cuit connects to typical transimpedance amplifiers
found within a fiber-optic link. The linear signal output
from a transimpedance amplifier can contain significant
amounts of noise, and may vary in amplitude over time.
The MAX3262 limiting amplifier quantizes the signal,
and outputs a voltage-limited waveform over a 48dB
input dynamic range.

The MAX3262 provides an offset correction function
that effectively reduces the offset voltage to negligible
levels. In communications systems using NRZ data with
a 50% duty cycle, pulse-width distortion present in the
signal or generated by the transimpedance amplifier
appears as input offset and is partially removed by the
offset correction function. An external capacitor is
required between CZP and CZN to compensate the off­set correction loop, determining the lower 3dB point.

Loss-of-Signal Function

The MAX3262 incorporates a chatter-free loss-of-signal
function, which is used to detect that the input signal
has dropped below the level necessary for acceptable
bit error rate performance, or to indicate an open-fiber
condition. The loss-of-signal function is implemented
with a rectifying peak detector, which samples the sig­nal entering the output stage. The output from the peak
detector is compared against an internally generated
threshold, and is used to assert the LOS+ and LOS­outputs.

The loss-of-signal threshold is adjusted by varying the
amplifier gain. The MAX3262 is configurable for gains
between 33dB and 48dB, allowing LOS thresholds
between 9mVp-p and 48mVp-p. Figure 2 shows the
LOS threshold as a function of the DIV2 and V

LOS

pins.
The DIV2 pin provides a coarse adjustment of 6dB of
gain, while the V

LOS

pin provides a fine gain adjust-

ment between 0dB and 11dB.

MAX3262

1Gbps, High-Speed Limiting Amplifier with

Chatter-Free Loss-of-Signal Detection

_______________________________________________________________________________________ 5

DIN-

DIV2

DIN+

20k

20k

DOUT-

ENB

DOUT+

RMS

DETECT

BIAS

REFERENCE

LOS+
LOS-

C

AZ

OFFSET

CORRECTION

V

LOS

MAX3262

0dB to 11dB5dB/11dB 10dB 10dB 6dB

Figure 1. Functional Diagram

MAX3262

Level-detect hysteresis and a 200ns internal delay
ensure chatter-free LOS outputs when the input signal
level is close to the LOS threshold. The hysteresis for
any programmed loss-of-signal level is nominally 2.5dB.

The LOS+ and LOS- outputs are open-collector,
Schottky-clamped transistors, that require pull-up resis­tors for proper operation (Figure 3). The loss-of-signal
time constant is set externally with the appropriate pull-up
resistor and shunt load capacitance.

The ENB pin allows the user to disable the output sig­nal without removing the input signal.

Wire Bonding Die

For reliable operation, the MAX3262 has gold metaliza­tion. Connections to the die should be made with gold
wire only, using ball bonding techniques. Wedge bond­ing is not recommended. Bond pad size is 4 mils.

__________________Design Procedure

Determining Capacitor Values

The MAX3262 inputs must be AC coupled to allow prop­er operation of the offset correction function. Figure 4
shows the circuit’s input stage. The circuit’s lower -3dB
point is determined by the input coupling capacitors. The
lower -3dB frequency is 1 / [(2π)(1500Ω)(CIN)] Hz.

C

IN

should be large enough to not affect the signal
quality, but small enough to not affect the LOS assert
time. When an open-fiber condition occurs, the input
coupling capacitors must discharge below the LOS
threshold level before the LOS can assert. The worst­case discharge time would occur with the maximum
input signal and the minimum LOS threshold. In this
case, the input capacitor must discharge from 0.9V to

4.5mV. The time required for this to occur is:

t = (1500)(CIN) In(V

MAX

/ V

THRESH

) seconds

Example: If the MAX3262 is configured for 6mV sensi­tivity, CIN= 100pF results in a lower -3dB frequency of
1MHz, and a maximum LOS delay of about 1µs.

The offset correction capacitor (CAZ) must be greater
than 100nF to ensure stable operation. This capacitor is
in series with an internal 40kΩ of resistance. The -3dB
point of the offset zeroing circuit is:

1 / [(2π)(CAZ)(40kΩ)] Hz

For CAZ= 180nF, the bandwidth of the offset correction
circuit is 22Hz. Maxim’s proprietary offset-correction
architecture decouples the input coupling time constant
from the offset correction time constant. This ensures
there is no interaction between these two networks, elimi­nating an additional source of chatter on LOS.

1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection

6 _______________________________________________________________________________________

0

3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1

LOS ASSERT LEVEL

MAX3262-07

V

LOS

(V)

SENSITIVITY (mVp-p)

10

5

15

25
20

30

35

40

45

50

DIV2 OPEN

DIV2 GROUNDED

VCC = 5V

Figure 2. MAX3262 Sensitivity vs. V

LOS

Setting

MAX3262

LOS

BUFFER

LOS+

C

LOS

R

LOS

R

LOS

≥ 3.3kΩ

LOS OUTPUT WITH
DESIRED RISE TIME

+5V

Figure 3. Setting the LOS Time Constant

Output Termination

The MAX3262 outputs must be terminated with a 50Ω
load to (VCC- 2V), or a Thevenin equivalent. Figure 5
shows two possible output termination methods.

Layout and PC Board Design

Since the MAX3262 is a high-frequency component,
the circuit’s performance can largely be determined by
board layout and design. A common problem with
high-gain amplifiers is feedback from the large swing
outputs to the input via the power supply. Some fiber­optic limiting amplifiers suffer from LOS “chatter.” The
act of switching the LOS outputs on or off generates
noise on the power supply, which can cause the LOS
outputs to chatter. With proper board layout, the
MAX3262 ensures chatter-free LOS operation.

The MAX3262 has five ground pins and a substrate
connection. All of these should be connected to the cir­cuit board’s ground. Use multiple PCB vias close to the
part to connect the grounds. Avoid long, inductive runs,
which can degrade MAX3262 performance. The
MAX3262’s six VCCsupply pins must all be connected.
VCCA–VCCE can be collectively decoupled with one
capacitor. VCC(pin 23) should be decoupled separate­ly (see the

Typical Operating Circuit

).

MAX3262

1Gbps, High-Speed Limiting Amplifier with

Chatter-Free Loss-of-Signal Detection

_______________________________________________________________________________________ 7

C

IN

V

IN

C

IN

DIN+

DIN-

V

CC

1.5k

1.5k

MAX3262

DOUT+

+5V

+5V

b) DRIVING A HIGH-IMPEDANCE LOAD

Z

LOAD

>500Ω

DOUT-

82Ω

120Ω

82Ω

120Ω

MAX3262

DOUT+

a) DRIVING A 50Ω LOAD TO GROUND

50Ω

DOUT-

50Ω

330Ω

330Ω

MAX3262

Figure 4. MAX3262 Equivalent Input Circuit

Figure 5. Output Termination Techniques

MAX3262

1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection

___________________Pin Configuration ____________________Chip Topography

24
23
22
21
20

19
18
17

1
2
3
4
5
6
7
8

GND
V

CC

GND
V

CC

C

CZN

CZP

V

LOS

VCCB

TOP VIEW

GND
DOUT+

DOUT-

LOS+

GND

DIN-

DIN+

V

CC

A

16

15

14
13

9
10
11
12

LOS­V

CC

D

GND

GND

V

CC

E

VTH

DIV2

ENB

SSOP

MAX3262

0.080"

(2.032mm)

0.060"

(1.524mm)

CZN

VCCA

DIV2

V

CC

C

GND

DOUT+

DOUT-

LOS+

LOS-

GND

VCCB

V

LOS

CZP

GND

V

CC

DIN+ DIN- GND

ENB

VTH

VCCE

GND

GND

VCCD

TRANSISTOR COUNT: 200
SUBSTRATE CONNECTED TO GND PIN 17

Maxim makes no warranty, representation, or guarantee regarding the suitability of its products for any particular purpose, nor does Maxim assume any lia­bility arising out of the application or use of any product or circuit, and Maxim specifically disclaims any and all liability including, without limitation, conse­quential or incidental damages. “Typical’’ parameters can and do vary in different applications. All operating parameters, including “typicals”, must be
validated for each customer application by customer’s technical experts. Maxim products are not designed, intended, or authorized for use as components
in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the fail­ure of the Maxim product could create a situation where personal injury or death may occur.

8

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