With the growing
demand for advanced multimedia capabilities, higher resolution
displays, and camera modules, system characteristics of cell phone
applications have evolved tremendously over the past few years. A
consequence of this growth is the significant increase in signal speed
and the number of lines between the host processor, the display
subsystem, and the imager to transfer media-rich content. As a result,
for handset designers who are worried about maintaining good signal
integrity, finding a solution for electromagnetic interference (EMI)
filtering with low channel capacitance and robust electrostatic
discharge (ESD) protection is a critically important concern.
In handsets with clamshell or slider configurations, a flexible cable connects the main system board to the liquid crystal display (LCD) module. When signals are transmitted through the flexible cable at high frequency, the cable behaves as an antenna and radiates EMI to the external environment. Therefore, high performance EMI filters, combined with a high level of ESD protection, are required to suppress radiated frequencies and preserve the best signal integrity possible on high speed signals.
The industry has reached the point where traditional architectures, based upon resistor-capacitor (RC) pi filters, impose limitations in terms of signal integrity and system robustness, and advanced integrated passive solutions based on a new architecture are required.
When selecting an optimal EMI filter for wireless handset applications, designers should consider multiple factors to ensure superior filter performance and robust ESD protection while maintaining excellent signal integrity. These factors include: greatest level of attenuation within the carrier frequency band (800MHz to 2.5GHz); highest cutoff frequency to support high data rates and preserve a high level of signal integrity; minimum insertion loss in the pass band; minimum propagation delay; high level of integrated ESD protection; minimum footprint; and cost efficiency.
Pi filters based upon an RC architecture have been the most popular for addressing EMI issues in wireless handsets. As handsets handle increased amounts of data transferred at higher speeds, higher cutoff frequencies are required to preserve excellent levels of signal integrity. However, the requirement to deliver the greatest level of attenuation at critical carrier frequencies (800MHz to 2.5GHz) remains unchanged.
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