EMI/ESD Filters for Cellular Phones

EMI/ESD Filters for Cellular Phones
Cellular phones, as with all handheld and wireless devices are susceptible to the
damaging effects of Electrostatic Discharge (ESD) transients. As much as 40 kilovolts of
ESD can be generated by the human body or through air discharge. In addition, cellular
phones, because of their higher operating frequencies, are more sensitive to EMI/RFI
interference. Global authorities are now imposing very strict regulations to ensure that
cellular phones are electrically 'clean' before being released to the market.
Unwanted radiated electromagnetic fields or conducted voltages and currents cause EMI.
The coupling path may involve one or more of the following mechanisms
• Conduction – electric current
• Radiation – electromagnetic field
• Capacitive Coupling – electric field
• Inductive Coupling – magnetic field
ESD Transients are normally
• Less than 8.4µs in duration
• Characterized by sinusoidal or exponential waveform
• Normally associated with high impedance sources
• Can range from a few millivolts to 18,000 Volts under normal conditions
The IEC 61000-4-2 (ESD) transient is characterized as shown below
Figure 1 ESD Transient Waveform
A double exponential waveform with a rise time tR of 0.7ns to 1.0ns and fall time of 30ns
measured at 50% of the decay.
If not suppressed, an ESD transient applied to the external interface of a cell phone
causes untold permanent and latent damage to sensitive CMOS type devices. The picture
shown below is actual damage on a transceiver chip that contained 2kV internal
protection for manufacture handling. The transient applied was 8kV contact discharge as
per IEC 61000-4-2.
Figure 2 ESD Damage to Transceiver before TVS was added
Responding to the need for space-efficient, noise filtering and ESD protection
components, ProTek Devices has introduced a series of convenient devices:
EMIFx-100x Series: Chip scale modular devices in 2,4,6,8 line configurations with
line capacitance values of 18pF, 30pF, 49pF and 60pF
EM10Q-100, EM8Q-100: Quad, Flat, No-lead Packages For LCD Displays
EM4D-100L, EM6D-100L: Dual-in-line, Flat, No-lead Packages
EM1402: ESD/EMI filter for application specific SIM Modules
ProTek Devices EMI/ESD Filters are designed and characterized to safely dissipate ESD
strikes at levels well beyond the maximum requirements set in the IEC 61000-4-2
standard. The IEC 61000-4-2 (ESD) pulse requires 8Kv (contact) 15Kv (air discharge).
All I/Os are rated at greater than ±25kV using the IEC 61000-4-2 (1/30nSec) contact
discharge method. Using the MIL-STD-883D (Method 3015) specification for Human Body
Model (HBM) ESD, all pins are protected for contact discharges to greater than ±30kV.
The C-R-C combination of the EMI filter device will filter out high frequency signals such
as 800 MHz 900MHz and 1900MHz that are frequencies used by most GSM cellular
phones. It will also attenuate Bluetooth and Wireless LAN 802.11B (2.4GHz) frequencies
better than –25dB. High integration of the components minimizes the parasitic selfinductances and, compared to discrete solutions, provides much better attenuation.
Figure 3 Two-Stage ESD Protection Circuit
The C-R-C filter also acts as a two-stage ESD protection circuit, by utilizing the TVS
diodes that are designated as the capacitive part of the low pass PI filter. The first stage
D1 will clamp (Vc1) the incoming transient and the second stage D2 will clamp (Vc2) any
residual pulse that passes through the first stage.
Figure 4 Overshoot & Clamping Voltage
The EM6D-100L contains 6 Filters in a 3mm x 1.5mm DFN package.
Each is an independent second-order –40dB/decade low pass filter, the
component values are 10pF-100Ω -10pF this allows a cutoff frequency of
160MHz and an attenuation of greater than -25dB for the frequency band
800MHz – 2.4 GHz
Figure 5 EMI Filter
In standby mode, the integrated TVS filter has a very low leakage current (less than
100pA); an essential feature for battery powered handheld devices. In addition, the low
profile durable 12-pin DFN package is useful in many applications.
Digital Crosstalk between the adjacent channels for the cutoff frequency and maximum
attenuation, is minimal as shown in the figures below
Figure 7 Attenuation at 1.0GHz
Figure 6 Adjacent Channel Crosstalk
Test board for ESD, Insertion and crosstalk measurement
Showing the EM8Q-100 mounted.
Transient In
Top connectors are
throughputs for calibration of
network analyzer
Clamped Transient
The EM1402 provides a bi-directional filter and protection for all the signals and power
line on the SIM. SIM cards are found in all GSM cellular phones and in other handheld
devices and card readers.
SIM card
The TVS diodes protect the controller against possible ESD transients that may occur
when connector pins are exposed for insertion and removal of the SIM card.
Figure 8 SIM Card Application
The EMI filter suppresses all high frequency noise, preventing the unwanted EMI signal
from both entering and exiting the main board. The signals that interface with the SIM
card (Reset, Clock and bi-directional data) is also cleaned up by the filter characteristics
removing unwanted spikes preventing data corruption.
For best results both ground bumps should be directly connected to the ground plane.
An additional 1µF is required for stability of the supply rail.