To save power, amplifiers in TDMA mobile phones are only fed with current during the active slot. For this purpose, the bias voltage of the amplifier is usually applied in pulsed form, in the case of GSM for example with a pulse width of about 1/8 of the total 4.615 ms period. The noise figure, an important parameter also in power amplifiers, can only be determined with conventional measuring equipment if the amplifier is in a continuous mode, which may overload it and corrupt the result. Now there is a convenient way of determining the noise figure of amplifiers with a pulsed power supply: using Spectrum Analyzer FSP, Noise Measurement Software FS-K3 [1] and a function or pulse generator.
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