Intermodulation products in the EER technique applied to Class-E amplifiers

Envelope Elimination and Restoration is a relatively old but attractive transmitter technique for high efficiency linear amplification of variable envelope RF signals. EER employs switching mode power amplifiers, which are extremely nonlinear but efficient, and the concept of supply voltage modulation to achieve linear performance. The bandwidth limitations in the envelope modulation path will have a strong impact on performance of the whole EER system. This paper derives analytic relationships between the transfer function in the envelope path of the EER system and IMD products in the output signal. The derived expressions are of generic character and can be used for an arbitrary transfer function in the envelope path. An estimation of the theoretical limit for IMD levels in the EER system based on the Class-E amplifier is given.