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Advanced Circuits for Emerging Technologies by Krzysztof Iniewski

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Chapter 13

RF Transceivers for Wireless Applications

Alireza Zolfaghari, Hooman Darabi, and Henrik Jensen

Broadcom, Irvine, CA, USA

13.1 Transmitter Architectures

13.1.1 Modulation Overview

To have a better understanding of transmitter architectures, first we briefly study the modulation types by categorizing them into two groups: constant-envelope and variable-envelope modulations.

13.1.1.1 Constant-Envelope Modulation

If the transmitter signal is specified as A(t) cos (ωct + Φ(t)), for a constant-envelope modulation, as the name implies, A(t) is fixed. This gives significant flexibility in the implementation of the transmitter because the transmitter signal is not affected by any nonlinearity in the transmitter. This especially provides considerable advantage for the power amplifier (PA) using a nonlinear class for higher efficiency. One good example of this type of modulation is the Gaussian minimum shift keying (GMSK) used in the global system for mobile communication (GSM) and general packet radio service (GPRS). Since that nonlinearity in this case does not change the zero crossing of the signal, it distorts only the amplitude of the carrier. This distortion does not produce any “spectral regrowth” and generates only harmonics of the carrier that can be substantially attenuated by the amplifier low-Q filters (LC tank).

13.1.1.2 Variable-Envelope Modulation

Although constant-envelope modulation is a very attractive option due to its relaxed linearity requirements and improved ...

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