Application Note
AN3028
ESD Protection of Broadband GaAs CATV & FTTx Amplifiers
Rev. V2
Introduction
Increasing protection from electrostatic discharge
(ESD) for GaAs devices in various applications is
critical to long term reliability of the final products. This
application note explains how a simple anti-parallel pair
of diodes delivers protection levels of 8kV contact
discharge Human Body Model (HBM) as per the
commercial IEC-61000-4-2 specification.
The Protection Components
The ESD protection circuit is an inexpensive pair of
anti-parallel diodes, either Fairchild Semiconductor
BAV99 or LL4148. The BAV99 is an anti-parallel diode
pair packaged in a single SOT-23 package. The
LL4148 is a single diode per package requiring two
with opposite polarity. See the Fairchild Semiconductor
website for complete product information.
Figure 1.
Diode pair location in CATV STB applications
Implementation
The level of protection provided is independent of diode
pair location. Placement can be adjacent to the external
signal input (connector input) or near the broadband
amplifier requiring protection. However it is good ESD
protection practice to locate the protection device as
physically close as possible to the physical input source
of the ESD strike so as to shunt the ESD energy to
ground as early as possible in the system.
The schematic diagrams in Figures 1 & 2 show
examples using the MAAMSS0042 broadband amplifier
which operates from 50 to 1000 MHz (see
MAAMSS0042 data sheet for off-chip component
values). The protection location is shown for two
different applications. Figure 1 shows the diode pair
located on the input of the broadband amplifier for a
typical CATV set-top box (STB). In this application the
RF input is exposed to potentially harmful external
signals through an F-type connector on the input to the
system. Figure 2 shows the location of the diode pair
for FTTx applications where the RF output of the
broadband amplifier is exposed to external signals
through a SMB connector at the output.
It is critical in both applications that the diodes be
located electrically outside of the series DC blocking
capacitors as shown in Figures 1 & 2. The BAV99
device (single part) is shown in red in Figures 3 & 5.
The LL4148 (two parts) is shown in blue in Figures 4 &
6.
Figure 2.
Diode pair location in FTTx applications
Verification & Results
The level of ESD protection provided was verified
through a design of experiments (DOE). This DOE
varied component placement and component type.
The variations included:
BAV99 adjacent to connector
LL4148 pair adjacent to connector
BAV99 adjacent to amplifier
LL4148 pair adjacent to amplifier
All amplifier circuit variations with either choice of
diode pair remained functional after 25 ESD strikes of
8kV (HBM) contact discharge.
Recommendation
For ESD protection of broadband (50-1000 MHz)
amplifiers, an anti-parallel diode pair is placed in
shunt along the RF transmission line
requiring
protection. The component location is flexible, and
since these devices are available in small outlines,
little additional board space is required to implement
this circuit.
1
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changes to the product(s) or information contained herein without notice.
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