SY88903AL
3.3V, Burst Mode 1.25Gbps PECL HighSensitivity Limiting Post Amplifier with TTL
Loss-of-Signal
General Description
Features
The SY88903AL, burst mode, high-sensitivity limiting
post amplifier is designed for use in fiber-optic receivers,
specially optimized for passive optical networks (PONs).
The device connects to typical transimpedance
amplifiers (TIAs). The linear signal output from TIAs can
contain significant amounts of noise and may vary in
amplitude over time. The SY88903AL quantizes these
signals and outputs PECL level waveforms.
The SY88903AL operates from a single +3.3V power
supply, over temperatures ranging from –40oC to +85oC.
Signals with data rates from 622Mbps up to 1.25Gbps,
and as small as 5mVpp, can be amplified to drive
devices with PECL inputs.
The SY88903AL generates a Loss-of-Signal (LOS)
open-collector TTL output. A programmable Loss-ofSignal level set pin (LOSLVL) sets the sensitivity of the
input amplitude detection. LOS asserts high if the input
amplitude falls below the threshold set by LOSLVL and
de-asserts low otherwise. The enable bar input (/EN)
de-asserts the true output signal without removing the
input signal. The LOS output can be fed back to the /EN
input to maintain output stability under a loss-of-signal
condition. Typically, 3.4dB LOS hysteresis is provided to
prevent chattering.
All support documentation can be found on Micrel’s web
site at: www.micrel.com.
• Single 3.3V power supply
• Fast LOS release/assert ( 3.3V, IOH-MAX < 160µA
2.4
V
VCC < 3.3V, IOH-MAX < 160µA
2.0
V
IOL = +2mA
mA
0.5
V
Notes:
1. Permanent device damage may occur if absolute maximum ratings are exceeded. This is a stress rating only and functional operation is not
implied at conditions other than those detailed in the operational sections of this data sheet. Exposure to absolute maximum rating conditions for
extended periods may affect device reliability.
2. The data sheet limits are not guaranteed if the device is operated beyond the operating ratings.
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SY88903AL
AC Electrical Characteristics
VCC = 3.0 to 3.6V; RL = 50Ω to VCC-2V; TA = –40°C to +85°C, typical values at VCC = 3.3V, TA = 25°C.
Symbol
Parameter
tr, tf
Output Rise/Fall Time
(20% to 80%)
tJITTER
Condition
Min
Typ
Note 3
Max
260
Units
ps
Deterministic
Note 4
15
psPP
Random
Note 5
5
psRMS
VID
Differential Input Voltage Swing
See Figure 1
VOD
Differential Output Voltage
Swing
VID > 18mVPP, See Figure 1
tOFF
LOS Release Time
Note 8
40
500
ns
tON
LOS Assert Time
125
500
ns
5
1800
mVPP
mVPP
1500
LOSAL
Low LOS Assert Level
Note 8
RLOSLVL = 15kΩ, Note 6
2.3
mVPP
LOSDL
Low LOS De-assert Level
RLOSLVL = 15kΩ, Note 6
3.4
mVPP
HSYL
Low LOS Hysteresis
RLOSLVL = 15kΩ, Note 7
3.4
dB
LOSAM
Medium LOS Assert Level
RLOSLVL = 5kΩ, Note 6
LOSDM
Medium LOS De-assert Level
RLOSLVL = 5kΩ, Note 6
HSYM
Medium LOS Hysteresis
RLOSLVL = 5kΩ, Note 7
LOSAH
High LOS Assert Level
RLOSLVL = 100Ω, Note 6
LOSDH
High LOS De-assert Level
RLOSLVL = 100Ω, Note 6
HSYH
High LOS Hysteresis
RLOSLVL = 100Ω, Note 7
B-3dB
3dB Bandwidth
AV(Diff)
Differential Voltage Gain
S21
Single-Ended Small-Signal Gain
2
4.2
mVPP
6.2
9
mVPP
2
3.4
5
dB
8
10.8
2
30
mVPP
16.4
21
mVPP
3.4
5
dB
1
GHz
42
dB
36
dB
Notes:
3. Amplifier in limiting mode. Input is a 200MHz square wave.
4. Deterministic jitter measured using 1.25Gbps K28.5 pattern, VID = 10mVPP.
5. Random jitter measured using 1.25Gbps K28.7 pattern, VID = 10mVPP.
6. See “Typical Operating Characteristics” for a graph showing how to choose a particular RLOSLVL for a particular LOS assert and its associated
de-assert amplitude.
7. This specification defines electrical hysteresis as 20log (LOS De-assert/LOS Assert). The ratio between optical hysteresis and electrical
hysteresis is found to vary between 1.5 and 2 depending upon the level of received optical power and ROSA characteristics. Based on that ratio,
the optical hysteresis corresponding to the electrical hysteresis range 1dB-4.5 dB, shown in the AC characteristics table, will be 0.5dB-3dB
Optical Hysteresis.
8. In real world applications, the LOS Release/Assert time can be strongly influenced by the RC time constant of the AC-coupling cap and the 50Ω
input termination. To keep this time low, use a decoupling cap with the lowest value that is allowed by the data rate and the number of
consecutive identical bits in the application (typical values are in the range of 0.001µF to 1.0µF).
February 2007
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SY88903AL
Typical Operating Characteristics
VCC = 3.3V, TA = 25°C, RL = 50Ω to VCC-2V, unless otherwise stated.
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SY88903AL
Functional Block Diagram
Detailed Description
The SY88903AL high-sensitivity limiting post amplifier
operates from a single +3.3V power supply, over
temperatures from –40°C to +85°C. Signals with data
rates from 622Mbps up to 1.25Gbps, and as small as
5mVpp, can be amplified. Figure 1 shows the allowed
input voltage swing. The SY88903AL generates an LOS
output, allowing feedback to /EN for output stability.
LOSLVL sets the sensitivity of the input amplitude
detection.
Input Amplifier/Buffer
Figure 2 shows a simplified schematic of the input
stage. The high-sensitivity of the input amplifier allows
signals as small as 5mVpp to be detected and amplified.
The input amplifier allows input signals as large as
1800mVpp. Input signals are linearly amplified with a
typically 42dB differential voltage gain. Since it is a
limiting amplifier, the SY88903AL outputs typically
1500mVpp voltage-limited waveforms for input signals
that are greater than 12mVpp. Applications requiring the
SY88903AL to operate with high-gain should have the
upstream TIA placed as close as possible to the
SY88903AL’s input pins to ensure the best performance
of the device.
Output Buffer
The SY88903AL’s PECL output buffer is designed to
drive 50Ω lines. The output buffer requires appropriate
termination for proper operation. An external 50Ω
resistor to VCC–2V for each output pin provides this.
Figure 3 shows a simplified schematic of the output
stage.
February 2007
Loss-of-Signal
The SY88903AL generates a chatter-free loss-of-signal
(LOS) open-collector TTL output with internal 4.75kΩ
pull-up resistor as shown in Figure 4. LOS is used to
determine that the input amplitude is too small to be
considered a valid input. LOS asserts high if the input
amplitude falls below the threshold set by LOSLVL and
de-asserts low otherwise. LOS can be fed back to the
enable (/EN) input to maintain output stability under a
loss of signal condition. /EN de-asserts low the true
output signal without removing the input signals.
Typically, 3.4dB LOS hysteresis is provided to prevent
chattering.
Loss-of-Signal-Level Set
A programmable LOS level set pin (LOSLVL) sets the
threshold of the input amplitude detection. Connecting
an external resistor between VCC and LOSLVL sets the
voltage at LOSLVL. This voltage ranges from VCC to VREF.
The external resistor creates a voltage divider between
VCC and VREF, as shown in Figure 5.
Hysteresis
The SY88903AL provides typically 3.4dB LOS electrical
hysteresis. By definition, a power ratio measured in dB
is 10log (power ratio). Power is calculated as V2IN/R for
an electrical signal. Hence, the same ratio can be stated
as 20log (voltage ratio). While in linear mode, the
electrical voltage input changes linearly with the optical
power and hence, the ratios change linearly. Therefore,
the optical hysteresis in dB is half the electrical
hysteresis in dB given in the data sheet. The
SY88903AL is an electrical device, this data sheet refers
to hysteresis in electrical terms. With 3.4dB LOS
hysteresis, a voltage factor of 1.5 is required to assert or
de-assert LOS.
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SY88903AL
Figure 1. VIS and VID Definition
Figure 2. Input Structure
Figure 3. Output Structure
Figure 4. LOS Output Structure
Figure 5. LOSLVL Setting Circuit
Note: Recommended value for RLOSLVL is 15kΩ or less.
Related Product and Support Documentation
Part Number
Function
Data Sheet Link
Application Notes
Notes on Sensitivity and Hysteresis in Micrel
Post Amplifiers
http://www.micrel.com/product-info/app_hints+notes.shtml
February 2007
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Micrel, Inc.
SY88903AL
Package Information
10-Pin MSOP (K10-1)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http:/www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for
its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a
product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for
surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant
injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk
and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.
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