AC89 - Nortel Networks - Product.Network

AC89

2.5 Gb/s Transimpedance

Amplifier, 5.0 Volt supply

Preliminary Data Sheet

Preliminary

Information

Features

Single +5 V power supply

operation

Input noise current = 270 nA rms

in 2 GHz band width with a 0.5 pF

detector

Transimpedance gain = 4.0 kΩ

(differential)

On-chip automatic gain control

gives input current overload of

2.6 mA pk and max output

voltage swing of 300 mV pk-pk

differential

50 Ω single-ended or 100 Ω

differential wire bond selectable

outputs

On-chip power supply rejection

achie ves 40 dB rejection up to1

MHz

Bandwidth (- 3 dB): DC to 2.2 GHz

Constant photodiode reverse

bias = 3 V, (anode to input,

cathode to VCC)

Photodiode may be anode or

cathode connected

-40°C to + 100°C junction

temperature operation

Available as bare die

Manufactured using a high yield,

silicon bipolar process

Applications

SONET OC-48

Fibre optic data modules

The Nortel Networks AC89 is a

monolithic, silicon bipolar

transimpedance amplifier, providing

wideband, low noise preamplification

of signal current from a photodetector.

It features differential outputs with a

single-ended bond option and

optimized noise performance, and

incorporates an Automatic Gain

Control (AGC) mechanism to increase

dynamic range. When u sing differen tial

outputs, a supply decoupling capacitor

is the only external circuitry required.

Noise performance is optimized for 2.5

Gb/s operation, with a sensitivity of -27

dBm for 10-10 bit error rate, using a

detector with 0.5 pF capacitance and a

responsivity of 0.85 A/W.

Nortel Networks offers a portfolio of

optical networking ICs for use in high-

performance optical receiver and

transmitter applicatio ns. The AC89

provides for power and chip-count

savings to the designer of fiber-based

Datacom or Telecom solutions.

System block dia gram

Preliminary

Information

Page 2 of 6 AC89 - 2.5 Gb/s Transimpedance Amplifier, 5.0 Volt supply

Functional descrip tion

Amplifier front-end

The transimpedance front-end amp lifies an input current from

a photodetector, at pin TZ_IN, to produce an output with the

feedback resistor Rf determining the level of amplification

(see “Functional block diagram” below). An automatic gain

control loop varies this resistor, to ensure that the output from

the front-end does not saturate th e outpu t driver stage that

follows. This gain control allows input signals of up to 2.6 mA

peak. The input transistor and feedback are optimized for

noise performance at 2.5 Gb/s.

The input pin TZ_ IN is biased at 3 V below th e supply volt age

VCC, allo wing a photodetector to ha v e a constant re v erse bias

by connecting the cathode to VCC. This enables full single

rail operation. Alternatively the photodetector may be

connected between TZ_IN and GND which provides 2 V

nominal reverse bias.

The front-end stage has its own supply ground connection

(VEE2) to achieve optimum noise performance and maintain

integrity of the high-speed signal path. The front-end shares

the VCC (+5 V) connection with the remainder of the

circuitry, which has a separate ground (VEE1).

Output driver stage

The output driver acts as a buffer stage, capable of swinging

up to 300 mVpk-pk differential into a 100 Ω load. The small

output swings allow ease of use with low voltage post

amplifiers (e.g. 3.3 V parts).

Automatic Gain Control (AGC)

The AGC circuit monitors the voltages from the output d river

and compares them to an internal r eference le v el produ ced via

the on-chip bandgap reference circuit . When this level is

exceeded, the gain of the front-end is reduced by controlling

the feedback resistor Rf.

A long time-constant integrator is used within the control loop

of the AGC with a low frequency cut-off of 5 kHz.

Functional block diagram

Preliminary

Information

AC89 - 2.5 Gb/s Transimpedance Amplifier, 5.0 Volt supply Page 3 of 6

Absolu te maximum ratings

These are stress ratings only. Exposure to stresses beyond

these maximum ratings may cause permanent damage to, or

affect the reliability of the device. Avoid operating the device

outside the r ecommended operating conditions defined below.

Recommended operating conditions

DC electrical characteristics

Symbol Parameter Minimum Maximum Units

VCC Supply voltage -0.7 6.0 V

Tstg Storage Temperature -65 150 °C

Tj Junction temperature -40 120 °C

Symbol Parameter Minimum Typical Maximum Units

VCC Supply voltage 4.7 5.0 5.3 V

Tj Operating junction temperature -40 100 °C

Symbol Parameter Minimum Typical Maximum Units

ICC Supply Current 65 95 mA

Vin Input Bias Voltage VCC -3.5 VCC -3.0 VCC -2.5 V

Vout Output Bias Voltage 2.8 3.1 3.4 V

Tr Transresistance 6.0 8.0 10.0 kΩ

Rout Output res ist anc e 50 Ω

Preliminary

Information

Page 4 of 6 AC89 - 2.5 Gb/s Transimpedance Amplifier, 5.0 Volt supply

AC cha racteristics

The above parameters are specified differentially under the

following conditions:

• Supply Voltage (VCC) = 4.7 V to 5.3 V

• Junction Te mperature (T j) = -40°C to 100°C

• Load Resistor (RL) = 2 x 50 Ω AC-coupled via 100 nF

capacitors

• Photodetector Ca pacitance (Cd) = 0.5 pF

• Photodetector Responsivity = 0.85 A /W

• Transimpedance ( Tz) me asured wi th <36 µA peak

photocurrent

Applications information

For maximum performance it is recommended that the device

be used in differential mode with the circuit shown in the

“Connections for differential operation” diagram.

Symbol Parameter Minimum Typical Maximum Units

BW (3dB) Small Signal Bandwidth at -3dB point 1.7 2.2 3.3 GHz

Flfc Low frequency cut-off 5kHz

DRi Input data rate 50 2500 Mb/s

Iagc AGC Threshold 36 µA peak

Tz Differential transimpedance (f = 100 mHz) 3.0 4.0 5.0 kΩ

Iol Input current before overload (2.5 Gb/s NRZ data) 2600 3000 µA peak

Pol Optical overload +1.8 +2.5 dBm

Nrms Input noise current (in 2 Ghz) 270 365 nA rms

Sens Optical Sensitivity (10-10 B.E.R.) -27 -25.6 dBm

PSR Power supply rejection (up to 1 MHz) 30 40 dB

Connections for differ ential operation

Preliminary

Information

AC89 - 2.5 Gb/s Transimpedance Amplifier, 5.0 Volt supply Page 5 of 6

In situations where it is necessary to use the device in a single-

ended mode, this can be achieved using the circuit shown in

the “Connections for single-ended operation” diagram.

Connections for single-ended operation

Bond pad assignment

Pad No. Pad Name Type Description Function

1, 8, 11 VCC PSupply Positive Supply (+5 V)

2BIAS-MON ITest Test Pad (leave unconnected)

3TZ_IN IAnalog Input Pad (connect to photodetector)

4 VEE2 P Supply Negative Supply (0V) - Note this is a separate ground for the

input stage, which is AC coupled on chip. There is no DC

current through this pad.

5, 7 VEE1 PSupply Negative Supply (0V)

6-ACGND PSupply Single-ended bond option. Connect to GND (0V) through

minimum 1 nF for single-ended output on S_OUTP. Leave

open-circuit for differential outputs. See “Connections for single-

ended operation” diagram on page 5.

9 S_OUTN O Analog Negative differential voltage output. Leave open-circuit for

single -end ed operatio n.

10 S_OUTP OAnalog Positive differential voltage output. Also positive single-ended

output if -AC GND is connected to GND (0V) via 1 nF capacitor.

Preliminary

Information

Fo r addi tional info rmation on Norte l Netw orks pro ducts an d service s

offered, please contact your local representative.

Nortel Networks

High Performance Optical Component Solutions

attn: Mark etin g Depa rtm ent

2745 Iris Street

6th Flo or

Ottawa, Ontario

Canada K2C 3V5

Tel: 1-800-4 NORTEL

Fax: 1-613-763-8416

Email: opt icalcompo nents@nortelnetworks.co m

www.nortelnetworks.com/hpocs

Nortel, Nortel Networks, the Nortel Net wo rks corporat e logo, an d the

globemark design are tradema rks of Nort el Networks Corporation. Any third-

party tradema rks are the property of thei r respe ctive owners.

Prelimi na ry informa ti on docum ent s contain information on produc ts in thei r

formative or design phase of dev e lopment. Features, characteristic data and

other specifications are subject to change with out notice. Contact Nortel

Networks for current informatio n on this produc t.

The information contained in this document is considered to be accurate as of

the date of publication. No liability is assumed by Nortel Networks for use of

any information contained in this document, or for infringement of any patent

rights or any other propriet ary rights of third parties which may result from

suc h us e. No license is grant e d by impl ication or ot herwi s e un der any patent

right or any other propriet ary right of Norte l Ne tworks.

Publication # 84018.37/03-01 Issue 3 Issued: 7 March 2001 Pag e 6 of 6

Pad layout diagram

Note: This diagram is not to scale. Bondpad openings are

82 µm x 82 µm. There are three VCC pads for ease of wire bonding - these pads are connected on-chip and only one pad is

required to be bonded out.