SE1020W Просмотр технического описания (PDF) - SiGe Semiconductor, Inc.

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SE1020W

1.25 Gb/s Transimpedance Amplifier Product Preview

SiGe Semiconductor, Inc. 

SE1020W

1.25 Gb/s Transimpedance Amplifier

Product Preview

Functional Description

Amplifier front-end

The transimpedance front-end amplifies an input

current from a photodetector, at pin TZ_IN, to

produce an output voltage with the feedback

resistor Rf determining the level of amplification

(see the functional block diagram on page 1). An

automatic gain control loop varies this resistor, to

ensure that the output from the front-end does

not saturate the output driver stage that follows.

This gain control allows input signals of up to

2.6 mA peak.

The input pin TZ_IN is biased at 1.5 V below the

supply voltage VCC, allowing a photodetector to

have a constant reverse bias by connecting the

cathode to 3.3 V. This enables full single rail

operation.

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

(+3.3 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). Increasing optical input level gives a

positive-going output signal on the OUTP pin.

Automatic Gain Control (AGC)

The AGC circuit monitors the voltages from the

output driver and compares them to an internal

reference level produced 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 typical low

frequency cut-off of 10 kHz.

System Block Diagram

1.25 GHz

2

1.25 Gb/s

2

AGC

Amplifier

Clock

Clock & Data

2

Recovery

Data

2

SE1230

LOS

Receiver Module

SE1020W

PIN

TZ

Amplifier

42-DST-01 Rev 1.3 May 27/02

Confidential

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