ENHANCED FILTERING METHOD FOR ENVELOPE ELIMINATION AND RESTORATION AMPLIFICATION
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Aug-02
Many of the second generation cellular and wireless systems have adopted spectrally efficient digital modulation methods and as a consequence, the modulated rf signal envelope in many cases exhibits time varying amplitude characteristics. Due to the amplitude varying envelope, a linear (low distortion) high efficiency power amplifier is required in the transmitter unit in contrast to non- linear saturated ones common to analog FM sys- tems. To achieve the desired level of linearity, typi- cal single ended amplifiers (e.g, class E, F, . ..) must be operated in the gain backoff region where the achievable efficiency is much lower than desired. In general, an inherent trade-off exists between amplifier efficiency and spectral linearity. An alter- native amplifier topology which has the potential to achieve reasonable spectral linearity and simultane- ous high efficiency is the Envelope Elimination and Restoration (EER) class of amplifiers.