7 Capella Court
Nepean, ON, Canada
K2E 7X1+1 (613) 224-4700
www.optiwave.com© 2009 Optiwave Systems, Inc.

OptiSystem applications:
Optical receiver analysis (PIN-TIA-LA)

Introduction

PIN-TIA-LA modellingThe overall performance of a point-to-point optical communication link is normally defined based on
the minimum average optical power, measured at the input to the optical receiver, that is required toachieve a given BER. Known as optical receiver sensitivity, this key parameter can be used tocompare different receiver configurations in order to determine the right design components for anapplication.

For direct detection intensity modulated (IMDD) systems the optical receiver will usually consist of aPIN photodetector (to convert the optical field to current), followed by a transimpedance amplifier (TIA)
which amplifies and converts the current to a voltage, and then a limiting amplifier which conditions(limits) the voltage waveform for processing by a decision circuit (using a voltage decision threshold).

In this application note we will present an optical receiver sensitivity calculation model for an opticalreceiver system that includes a PIN-TIA and PIN-TIA-LA configuration. The noise models for theseconfigurations are based on application notes from Maxim Integrated  [1, 2]

The reference file for this application note is: PIN_TIA_LA_Analysis Version 1_0.osd

REF 1: "Accurately Estimating Optical Receiver Sensitivity", Application Note HFAN-3.0.0 (Rev. 1; 04/08), Maxim Integrated,
www.maximintegrated.com
REF 2: "Optical receiver performance evaluation", Application Note 1938 HFAN-03.0.2, Maxim Integrated,
www.maximintegrated.com

2

PIN-TIA configuration (1)This example demonstrates a directly modulated 10 Gb/s system with a PIN-TIA receiver configuration. It is assumed thatthe total noise impact on the system performance results from the input referred noise current of the TIA (thus the thermal
noise current of the PIN is assumed to be zero). It is also assumed that the shot noise from the PIN is negligible for thisanalysis.
For this design the noise current is assumed to be 0.4 uA RMS, Responsivity = 0.5, Tx ER = 9 dB, and the target BER is 1e12 (Ref 1)
Based on these settings the minimum required Optical Modulation Amplitude is set to 11.2 uWpp (Q=7) and the associatedReceiver sensitivity = 7.25 uW. The formulas (based on Ref 2) can be found in the Component Script of the TIA component(see next slide)

REF 1: "Accurately Estimating Optical Receiver Sensitivity", Application Note HFAN-3.0.0 (Rev. 1; 04/08), Maxim Integrated,
www.maximintegrated.com
REF 2: "Optical receiver performance evaluation", Application Note 1938 HFAN-03.0.2, Maxim Integrated, www.maximintegrated.com

Layout: PIN-TIA Rx Analysis

An Eye Diagram Analyzer is used to estimate
the Q factor based on statistical noise analysis
of Logic 1 and 0 signals.
Global parameter settings for directmodulation link with PIN-TIA receiver3

PIN-TIA configuration (2)The VBScript below is associated with the TIA Component (Layout: PIN-TIA Rx Analysis)

This part of the TIA component script is usedto access the global parameter settings

Calculations are performed here to determine:
OMA Minimum = Irms*2*Q/Responsivity
where Irms is the input referred noise current of the TIA
Optical Sensitivity = (OMA/2) x (ER+1)/(ER-1)
where ER is the extinction ratio setting of transmitted
optical waveform

The calculation results are exported to the TIA
Component Results panel using the SetResultValue
operation. These values are displayed after completionof the simulation.

4

PIN-TIA-LA configuration (1)This example demonstrates a directly modulated 10 Gb/s system with a PIN-TIA-LA receiver configuration. It is assumed
that the total noise impact on the system performance is based on the input referred noise current of the TIA (thus thethermal noise current of the PIN is assumed to be zero) and the input sensitivity of the LA (which is converted to an
equivalent input referred noise).
For this design the TIA gain and noise current is assumed to be 2000 ohm and 0.4 uA RMS, the LA input sensitivity = 10mV (peak-to-peak), Responsivity = 0.5, Tx ER = 9 dB, and the target BER is 1e-12 (Q=7)
Based on these settings the minimum required Optical Modulation Amplitude is set to 15 uWpp (Q=7) and the associatedReceiver sensitivity = 9.65 uW.
The formulas (based on Ref 2) can be found in the Component Script of the TIA component (see next slide)

Layout: PIN-TIA-LA Rx Analysis

The TIA component script is used to calculate the receiver sensitivity (for a givenQ) based on the noise characteristics of the TIA and LA. The input referred noise ofthe TIA is set based on the combined noises of the TIA and the LA.

Global parameter settings for directmodulation link with PIN-TIA-LA receiver5

PIN-TIA-LA configuration (2)The VBScript below is associated with the TIA Component (Layout: PIN-TIA-LA Rx Analysis)Calculations are performed here to determine:
Noise current LA (NLA) = (LASensitvity)/(2*Q*TIAGain)
where TIAGain is the gain setting of the TIA and LASensitivity isthe input voltage sensitivity of the TIA (normally included in thevendor specification sheet)
Total noise current (NoiseReceiver) = Itotal = sqrt(Irms2 + ILA2)OMA Minimum = Itotal*2*Q/Responsivity
Optical Sensitivity = (OMA/2) x (ER+1)/(ER-1)
where ER is the extinction ratio setting of transmitted opticalwaveform

6