Articles
Control Loop Design For GSM Mobile Phone Applications
October 8, 2008
By <%=Company1%>
Control of output power level on GSM mobile phones
Why do we need to control the output power level of mobile phones? There are a number of very good reasons: to prevent intermodulation of base station receivers, to prevent interference with other mobile phones and to minimize power consumption depending on the distance between mobile and base station.
The 3GPP GSM standards body defines GSM specifications in the TS 45.005 Radio Transmission and Reception technical specification. This document specifies the nominal output power levels and accepted tolerance of GSM mobile transmitters under nominal and extreme conditions. The nominal conditions refer to ambient temperature with nominal voltage supply and the latter refers to a combination of extreme values of voltage and temperature. The radio transceiver operating voltage for most components in the current mobile phone technology is 2.8V, set by voltage regulators operating from the phone battery. However, the PA needs to be connected directly to the battery, as a higher level of DC current is required to deliver the necessary output power. Therefore it is battery response that determines the PA extreme voltage conditions. As an example, GSM TS specifies that three NiCd battery cells with a nominal 3.6 V should have a minimum tolerance of -0.36 V. With regards to temperature variations, GSM TS specifies conditions between –20 and +55°C.
Control of output power level is done in 2 dB steps. The normal maximum output levels for GSM handset mobile station are 33 dBm for GSM 850/900 MHz and 30 dBm for 1800/1900 MHz. Dynamic range of power control is 28 dB for the 850/900 MHz band and 30 dB for the 1800/1900 MHz band.
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