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Maxim > Design Support > Technical Documents > Application Notes > Battery Management > APP 668
Maxim > Design Support > Technical Documents > Application Notes > Power-Supply Circuits > APP 668
Keywords: cellular telephones, noise, power supply, conducted, radiated, layout, GSM, TDMA
APPLICATION NOTE 668
Managing Noise in Cell-Phone Handsets
By: Bob Kelly, Senior Applications Engineer
Jan 24, 2001
Abstract: Presents cellular telephone handset issues impacting noise performance. Power supply layout
improvements are shown to reduce noise problems. Linear regulators are employed to reduce noise at
low frequencies. Power amplifier bias modulates noise on to the RF output. Low dropout regulator output
noise is explained.
To best handle the problem of cell-phone noise, you should apply an understanding of the phone's
noise-coupling mechanisms, noise-sensitive circuit nodes, and noise-generating circuits.
Figure 1. Switch-mode and linear regulators distribute power cleanly and efficiently.
Modern hand-held cellular-radio transceivers have the almost impossible task of selecting and
demodulating a desired signal in the midst of many unwanted signals. For a typical cellular radio, the
desired signal amplitude may be only 0.35 µV—this is more than 100dB below the amplitude of nearby
unwanted signals. To amplify this signal to a level suitable for demodulation, cellular radios often
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