DESCRIPTION
s
Up to 1.25Gbps operation
s
Low noise
s
Chatter-Free LOS Generation
s
Open Collector TTL LOS Output
s
TTL /EN Input
s
Differential PECL inputs for data
s
Single power supply
s
Designed for use with SY88902 and SY88904
s
Available in a tiny 10-pin (3mm) MSOP
The SY88903 limiting post amplifier with its high gain
and wide bandwidth is ideal for use as a post amplifier in
fiber-optic receivers with data rates up to 1.25Gbps.
Signals as small as 5mVp-p can be amplified to drive
devices with PECL inputs. The SY88903 generates a
chatter-free Loss of Signal (LOS) open collector TTL
output.
The SY88903 incorporates a programmble level detect
function to identify when the input signal has been lost.
This information can be fed back to the /EN input of the
device to maintain stability under loss of signal conditions.
Using LOS
LVL
pin the sensitivity of the level detect can
be adjusted. The LOS
LVL
voltage can be set by
connecting a resistor divider between V
CC
and V
REF
,
Figure 3. Figure 4 shows the relationship between input
level sensitivity and the voltage set on LOS
LVL
. Figure 5
shows the relationship between input level sensitivity and
resistor divider ratio.
The LOS output is a TTL open collector output that
requires pull-up resistor for proper operation, Figure 1.
SY88903
LOS
+5V
2k
Figure 1. LOS Output with Desired Rise Time
FEATURES
1.25Gbps HIGH-SPEED
LIMITING POST AMPLIFIER
SY88903
APPLICATIONS
s
1.25Gbps Gigabit Ethernet
s
531Mbps and 1062Mbps Fibre Channel
s
622Mbps SONET
s
Gigabit Interface Converter
BLOCK DIAGRAM
Limiting
Amplifier
D
IN
D
IN
Level
Detect
ECL
Buffer
Enable
D
OUT
D
OUT
LOS
LVL
LOS
GND
V
CC
EN
V
REF
PIN CONFIGURATION
1
/EN
D
IN
/D
IN
V
REF
LOS
LVL
10 V
CC
D
OUT
/D
OUT
LOS
GND
9
8
7
6
2
3
4
5
MSOP
K10-1
1
Rev.: G
Amendment: /1
Issue Date: July 2000
2
SY88903
Micrel
Pin
Type
Function
D
IN
Data Input
Data Input
/D
IN
Data Input
Inverting Data Input
LOS
LVL
Input
Loss of Signal Level Set
/EN
TTL Input
Output Enable (active Low)
LOS
TTL Output
Loss of Signal Indicator
(Open Collector)
(active High)
GND
Ground
Ground
D
OUT
PECL Output
Data Output
/D
OUT
PECL Output
Inverting Data Output
V
CC
Power Supply
Positive Power Supply
V
REF
Output
Reference Voltage Output
for LOS Level Set (see Fig. 3)
General
The SY88903 is an integrated limiting amplifier intended
for high-frequency fiber-optic applications. The circuit
connects to typical transimpedance amplifiers found within
a fiber-optics link. The linear signal output from a
transimpedance amplifier can contain significant amounts
of noise, and may vary in amplitude over time. The SY88903
limiting amplifier quantizes the signal and outputs a voltage-
limited waveform.
The TTL /EN pin allows the user to disable the output
signal without removing the input signal.
PIN NAMES
GENERAL DESCRIPTION
Symbol
Rating
Value
Unit
V
CC
Power Supply Voltage
0 to +7.0
V
D
IN
, /D
IN
Input Voltage
0 to V
CC
V
D
OUT
, /D
OUT
Output Voltage (with 50
load)
V
CC
2.5, V
CC
+0.3
V
T
A
Operating Temperature Range
40 to +85
C
T
store
Storage Temperature Range
55 to +125
C
ABSOLUTE MAXIMUM RATINGS
(1)
NOTE:
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 RATlNG conditions for extended
periods may affect device reliability.
3
SY88903
Micrel
T
A
= 40
C
T
A
= 0
C
T
A
= +25
C
T
A
= +85
C
Symbol
Parameter
Min.
Max.
Min.
Max.
Min.
Typ.
Max.
Min.
Max.
Unit
I
CC
Power Supply Current
(1)
--
35
--
35
--
21
35
--
35
mA
I
IL
/EN Input LOW Current
0.3
--
0.3
--
0.3
--
--
0.3
--
mA
I
IH
/EN Input HIGH Current
--
20
(5)
--
20
(5)
--
--
20
(5)
--
20
(5)
A
--
100
(6)
--
100
(6)
--
--
100
(6)
--
100
(6)
V
CMR
Common Mode Range
GND +2.0
V
CC
-1.0
GND +2.0
V
CC
-1.0
GND +2.0
--
V
CC
-1.0
GND +2.0
V
CC
-1.0
V
V
offset
Differential Output Offset
--
100
--
100
--
--
100
--
100
mV
LOS
LVL
LOS
LVL
Level
V
REF
V
CC
V
REF
V
CC
V
REF
--
V
CC
V
REF
V
CC
V
V
OL
LOS Output Low
--
0.5
--
0.5
--
--
0.5
--
0.5
V
Level
(2)
I
OH
LOS Output Leakage
(3)
--
250
--
250
--
--
250
--
250
uA
V
OH
D
OUT
and /D
OUT
V
CC
-1085
V
CC
-880
V
CC
-1025
V
CC
-880
V
CC
-1025
V
CC
-955
V
CC
-880
V
CC
-1025
V
CC
-880
mV
HIGH Output
V
OL
D
OUT
and /D
OUT
V
CC
-1830
V
CC
1555 V
CC
-1810 V
CC
1620
V
CC
-1810
V
CC
1705 V
CC
1620
V
CC
-1810
V
CC
1620
mV
LOW Output
V
REF
Reference Supply
(4)
V
CC
-2.625 V
CC
2.325 V
CC
-2.625 V
CC
2.325 V
CC
-2.625 V
CC
2.475 V
CC
2.325 V
CC
-2.625 V
CC
2.325
V
V
IH
/EN Input HIGH Voltage
2.0
--
2.0
--
2.0
--
--
2.0
--
V
V
IL
/EN Input LOW Voltage
--
0.8
--
0.8
--
--
0.8
--
0.8
V
NOTES:
1. No output load
2. I
OL
= + 2mA
3. V
OH
= 5.5V
DC ELECTRICAL CHARACTERISTICS
V
CC
= +5V
10%, R
LOAD
= 50
to V
CC
-2V, T
A
= 40
C to +85
C
4. I
REF
must be limited to be within -0.8mA (source) and 0.5mA (sink).
5. V
IN
= 2.7V
6. V
IN
= V
CC
T
A
= 40
C
T
A
= 0
C
T
A
= +25
C
T
A
= +85
C
Symbol
Parameter
Min.
Max.
Min.
Max.
Min.
Typ.
Max.
Min.
Max.
Unit
Conditions
PSRR
Power Supply
(1)
--
--
--
--
--
35
--
--
--
dB
Input referred,
Rejection Ratio
55MHz
V
ID
Input Voltage Range
5
1800
5
1800
5
--
1800
5
1800 mVp-p
t
r,
t
f
Output Rise/Fall Time
--
350
--
350
--
200
350
--
350
ps
V
ID
> 100mVp-p
--
--
--
--
--
t
rin
,t
fin
--
--
--
V
ID
< 100mVp-p
V
OD
Differential Output
--
--
--
--
--
600
--
--
--
mV
V
ID
= 15mVp-p
Voltage Swing
(2)
--
--
--
--
--
200
--
--
--
mV
V
ID
= 5mVp-p
t
OFFL
LOS Release Time
(3)
--
0.5
--
0.5
--
0.1
0.5
--
0.5
s
Minimum Input
t
OFFH
LOS Release Time
(4)
--
0.5
--
0.5
--
0.1
0.5
--
0.5
s
Maximum Input
t
ONL
LOS Assert Time
(3)
--
0.5
--
0.5
--
0.2
0.5
--
0.5
s
V
SR
LOS Sensitivity Range
5
50
5
50
5
--
50
5
50
mVp-p
HYS
LOS Hysteresis
2
8
2
8
2
4.6
8
2
8
dB
AC ELECTRICAL CHARACTERISTICS
V
CC
= +5V
10%, R
LOAD
= 50
to V
CC
- 2V, T
A
= 40
C to +85
C
NOTES:
1. Input referred noise = RMS output noise/low frequency gain.
2. Input is 622MHz square wave.
3. Input is a 200MHz square wave, tr < 300ps, 8mVp-p.
4. Input is a 200MHz square wave, tr < 300ps, 1.8Vp-p.
4
SY88903
Micrel
PRODUCT ORDERING CODE
Ordering
Package
Operating
Code
Type
Range
SY88903KC
K16-1
Commercial
Output Termination
The SY88903 outputs must be terminated with a 50
load to V
CC
2V (or Thevenin equivalent).
Layout and PCB Design
Since the SY88903 is a high-frequency component,
performance can largely be determined by board layout
and design. A common problem with high-gain amplifiers is
feedback from the large swing outputs to the input via the
power supply.
D
IN
D
IN
+
V
REF
0.1F
0.1F
50
50
0.1F
Figure 2. Differential Input Configuration
APPLICATION INFORMATION
The SY88903 ground pin should be connected to the
circuit board ground. Use multiple PCB vias close to the
part to connect to ground. Avoid long, inductive runs which
can degrade performance.
NOTES:
Resistor Divider = R2/ (R1 + R2)
R1 + R2
5k
LOS
LVL
V
REF
R1
R2
V
CC
Figure 3. LOS
LVL
Circut
5
SY88903
Micrel
PERFORMANCE CURVE
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
2.53
2.65
2.77
2.90
3.02
3.14
3.27
3.39
3.52
3.64
3.76
3.89
4.01
4.13
4.26
4.38
4.51
4.63
4.75
4.88
5.00
LOSlvl (V)
Level (mV)
Deassert
Assert
Figure 4. LOS Assert and Deassert Levels vs LOS
LVL
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
Resistor Divider R
2
/ (R
1
+ R
2)
Level (mV)
Deassert
Assert
Figure 5. LOS Assert and Deassert Levels vs Resistor Divider
PDF 
ZIP