Microchip MIC2297 Handleiding

Microchip Niet gecategoriseerd MIC2297

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ANTC204
SY88149NDL and SY88349NDL
Burst Mode Limiting Post Amplifiers
Introduction
This document explains to use the SY88149NDL and SY88349NDL burst mode limiting amplifiers in different how
applications including 1G/10GEPON, XGPON.1, GE- -PON/GPON, Gigabit Ethernet, Fibre Channel, OC 3/12/24
SONET/SDH, and OBSAI/CPRI.
The SY88149NDL (resp. SY88349NDL) is a high sensitivity limiting post amplifier that can am- plify signals as
small as 5mVPP with data rates up to 1.25Gbps (resp. 2.5Gbps). The parts offer LOS or SD outputs depending on
the LOS/SD SEL option. The LOS/SD output can be fed back to JAM input for output stability when there is no the
data present at the input. LOS/SDLVL sets the threshold for the input signal detection.
Both amplifiers offer a fast SD assert (LOS de assert) time of 5ns and a fast SD de assert (LOS assert) time of - -
5ns if manual RESET is used or 120ns if /AUTORESET is used.
Noise Discriminator
The noise discriminator feature is intended for PON OLT applications with gain burst mode TIAs where noise -high -
can trigger a false LOS de assert or SD assert while no input data is present. The noise discriminator will filter -
input data through a series of specialized circuits that will only trigger LOS/SD on the rising edge of a valid PON
1.244Gbps noise (resp. 2.488Gbps) preamble bit stream (10101). The SY88149NDL (resp. SY88349NDL)
discriminator is designed to accept a 1.244 (resp. 2.488 preamble burst. Any Gbps 300 bps± M Gbps 300 bps)± M
other bit pattern will be rejected. If th ed at any other data rate, the noise discriminator should be is part is us
disabled.
The noise discriminator, implemented in the edge detector circuit, can be selected or bypassed by selecting the
proper resistor value using the settings at as shown in the LOS/SDSEL pin, Table 1.
Table 1. Truth Table for SD/LOS Select and Noise Discriminator function
LOS/SDSEL P LOS/SD Sin election N Doise iscriminator I To O nput JAM utputs
0 SD Ωto VCC Enabled HIGH Enabled
0 SD Ωto VCC Enabled LOW Disabled
16k DisabledΩ SD to VCC HIGH Enabled
16k DisabledΩ SD to VCC LOW Disabled
16k DisabledΩ to GND LOS HIGH Disabled
16k DisabledΩ to GND LOS LOW Enabled
0 Ωto GND LOS Enabled HIGH Disabled
0 Ωto GND LOS Enabled LOW Enabled
Micrel Inc. • 2180 Fortune Drive • Jose, CA 95131 • USA • tel +1 (408) 944 0800 • fax + 1 (408) 474 1000 • San - - http://www.micrel.com
April 23, 2014 Revision 1.1
Micrel, Inc.
AN TC204 −SY88149NDL and SY88349NDL Burst Mode Limiting Post Amplifiers
RESET vs. /AUTORESET Operation in Burst Mode Applications
The user can chose to de assert SD (assert LOS) AUTORESET mode or manual RESET. In - using either /
/ - - -AUTORESET mode, the SD de asserts (LOS as er the last highserts) automatically within 120ns aft to low
transition of the input data burst. If the AUTORESET function is disabled, SD must be de/ -asserted (LOS
asserted) manually by applying a RESET pulse at RESET pin.
AC or DC Coupling and Burst Mode Receiver Challenges
The receiver should be able to support data signals with long strings of consecutive identical bits (CID) and power
shift from strong bursts to weak bursts (and vice versa) to avoid getting errors. These two situations won’t be an
issue if the receiver link from the ph to the limiting amplifier to the CDR is DC coupled and otodiode– TIA (ROSA) -
doesn’t contain any coupling capacitors. Unfortunately, DC coupling the limiting amplifier to the TIA requires the -
output of the TIA and the input of the LA to have compatible common mode voltages, and it is unlikely to find a
TIA- LA on the market that satisfies that condition. Therefore, to have more choice in parts selection, the module
designer will more likely use AC coupling between the TIA and LA.
AC-coupling the TIA to the LA comes with some issues the designer should address by using better architecture
and appropriate component values. The two issues that face the use of AC coupling are the presence of long
strings of consecutive identical digits (CID) and receiver threshold settlement time during large power shift s
b etween strong and weak bursts.
CID
CID is defined as consecutive identical digits and may vary from one protocol to another and may be either
consecutive ‘1’ or consecutive ‘0’. It is up to the module designer to ensure that the module will correctly handle
the number of CIDs for the particular application(s).
Figure 1. Eect of CID “1”
Figure 2 . Eect of CID “0”
A small value coupling capacitor will create off frequency (the cap and the termination creates a a higher low-cut-
high- -pass filter) that may cause errors with low frequency data, especially in the presence of long strings of CID.
Additionally, this condition makes the middle of the data eye wander frequency data components. with low-
Therefore, the value of the cap should be large enough to set the low frequency cut off well below the lowest -
frequency component (created by CID) and minimize DC frequency components.level wander with low-
April 23, 2014 2 Revision 1.1
Micrel, Inc.
AN TC204 −SY88149NDL and SY88349NDL Burst Mode Limiting Post Amplifiers
Receiver Threshold Settling Time in Burst Mode Applications
As can be seen in , when the data at the input of the receiver switches from a strong burst toFigure 3 a weak
burst, the DC components of the data signal decays exponentially with time. If a large value is selected for the
coupling cap, the data’s DC level may not settle to the baseline within allowed deviation during the preamble time
and will lead to errors in data detection. In other words, the time constant created by the coupling cap should be
small enough to make the receiver threshold settlement transparent to stron weak burst transitions.g burst-
Figure 3 Strong -. Eect of Burst Weak Burst Transition
CID and Receiver Threshold Settling Time Solution
To improve the receiver threshold settlement time, which requires a short time constant, and the CID problem,
which requires a long time constant, the circuit can be designed with two low frequency cut off frequencies: one - -
low enough to be used for CID and one high enough to improve the receiver’s settlement time between bursts.
The circuit in Figure 4 below can be used to achieve that.
Figure 4. Solution Based On Two Time Constants
April 23, 2014 3 Revision 1.1

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: MIC2297

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