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Micrel Semiconductor

SY88993AL Datasheet Preview

SY88993AL Datasheet

3.3V 3.2Gbps High-Speed Limiting Post Amplifier

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SY88993AL
3.3V 3.2Gbps High-Speed Limiting Post
Amplifier with High Input Sensitivity
General Description
The SY88993AL limiting post amplifier, with its wide
bandwidth, is ideal for use as a post amplifier in fiber-optic
receivers with data rates up to 3.2Gbps. Signals as small
as 4mVPP can be amplified to drive devices with CML
inputs or AC-coupled PECL inputs. The SY88993AL
generates a chatter-free Loss-of-Signal (LOS) open
collector TTL output using an external resistor, as shown
Figure 1.
The SY88993AL incorporates a programmable 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 LOSLVL pin the sensitivity of the level detect can be
adjusted. The LOSLVL voltage can be set by connecting a
resistor divider between VCC and VREF, Figure 5.
Datasheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Features
Up to 3.2Gbps operation
Low noise CML data outputs
Chatter-Free LOS generation
Open Collector TTL LOS output
TTL /EN Input
Differential PECL inputs for data
Single 3.3V power supply
Available in a tiny 10-pin (3mm x 3mm) MSOP
Applications
PON
SFP/SFF/GBIC optical transceivers
Gigabit Ethernet
1X and 2X Fibre Channel
SONET/SDH: OC 3/12/24/48 – STM 1/4/8/16
Line driver and line receiver
Markets
FTTX
Datacom/Telecom
Figure 1. LOSLVL resistor configuration
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
September 2008
M9999-093008-A
hbwhelp@micrel.com or (408) 955-1690




Micrel Semiconductor

SY88993AL Datasheet Preview

SY88993AL Datasheet

3.3V 3.2Gbps High-Speed Limiting Post Amplifier

No Preview Available !

Micrel, Inc.
Block Diagram
SY88993AL
Detailed Description
The SY88993AL is a high-sensitivity limiting post
amplifier that operates from a single +3.3V power
supply, over temperatures from –40oC to +85oC. Signals
with data rates up to 3.2Gbps and as small as 4mVPP
can be amplified. Figure 2 shows the allowed input
voltage swing. The SY88993AL generates a LOS output.
LOSLVL sets the sensitivity of the input amplitude
detection.
Input Amplifier/Buffer
Figure 3 shows a simplified schematic of the
SY88993AL’s input stage. The high-sensitivity of the
input amplifier allows signals as small as 4mVPP to be
detected and amplified. The input amplifier also allows
input signals as large as 1800mVPP. Input signals below
6mVpp are linearly amplified with a typical 38dB
differential voltage gain. Since it is a limiting amplifier,
the SY88993AL outputs typically 800mVPP voltage-
limited waveforms for input signals that are greater than
10mVPP. Applications requiring the SY88993AL to
operate with high-gain should have the upstream TIA
placed as close as possible to the SY88993AL’s input
pins to ensure the best performance of the device.
Output Buffer
The SY88993AL’s CML output buffer is designed to
drive 50lines. The output buffer requires appropriate
termination for proper operation. An external 50
resistor to VCC for each output pin provides this. Figure 4
shows a simplified schematic of the output stage.
Loss-of-Signal
The SY88993AL generates a chatter-free LOS open-
collector TTL output which requires an external pull-up
resistor, as shown in Figure 1. LOS is used to determine
that the input amplitude is large enough to be considered
a valid input. LOS asserts high if the input amplitude falls
below the threshold sets by LOSLVL and de-asserts low
otherwise. LOS can be fed back to the enable bar (/EN)
input to maintain output stability under a loss of signal
condition. /EN de-asserts the true output signal without
removing the input signals. Typically, 5.6dB LOS
hysteresis is provided to prevent chattering.
Loss-of-Signal Level Set
The SY88993AL incorporates a programmable 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 LOSLVL pin the sensitivity of the level
detect can be adjusted. The LOSLVL voltage can be set
by connection a resistor divider between VCC and VREF,
Figure 5.
Hysteresis
The SY88993AL typically provides 5.6dB 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
therefore, the ratios change linearly. Thus, the optical
hysteresis in dB is half the electrical hysteresis in dB
given in the data sheet. Since the SY88993AL is an
electrical device, this data sheet refers to hysteresis in
electrical terms. With 5.6dB LOS hysteresis, a voltage
factor of about 2 is required to assert or de-assert LOS.
September 2008
2 M9999-093008-A
hbwhelp@micrel.com or (408) 955-1690


Part Number SY88993AL
Description 3.3V 3.2Gbps High-Speed Limiting Post Amplifier
Maker Micrel Semiconductor
Total Page 8 Pages
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