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High linearity lead-lag style envelope modulator for RF power amplifiers

Published online by Cambridge University Press:  01 April 2015

Gavin T. Watkins  and
Konstantinos Mimis
Gavin T. Watkins*
Affiliation:
Toshiba Research Europe Limited, 32 Queen Square, Bristol, BS1 4ND, UK. Phone: +44 117 906 0740
Konstantinos Mimis
Affiliation:
Toshiba Research Europe Limited, 32 Queen Square, Bristol, BS1 4ND, UK. Phone: +44 117 906 0740
*
Corresponding author: G. T. Watkins Email: [email protected]
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Abstract

A new split frequency envelope modulator for envelope tracking radio-frequency power amplifiers is proposed based on a lead-lag network. By mathematically deriving the transfer functions of the lead-lag modulator and the conventional split frequency type, the lead-lag is shown to have a significantly flatter phase response. The frequency response of the two modulators is verified by simulation, where the phase transient of the lead-lag is significantly less than the 360° of the conventional type. They are further simulated with a 3 MHz bandwidth 3GPP long-term evolution (LTE) signal and the lead-lag shown to reduce the modulator's normalized root-mean-square error (NRMSE) from −27.3 to −39.2 dB. A practical demonstrator was developed around an existing high-efficiency modulator architecture. To maintain system efficiency synthetic impedance was incorporated in the low-frequency switched mode power supply (SMPS) path. This was achieved with voltage and current feedback around the SMPS. The dynamic wideband signal response was investigated by applying a 3 MHz LTE envelope signal to the modulator and comparing the input and output signals. The measured NRMSE was improved from −27.5 to −30.0 dB by adopting the lead-lag structure and the dynamic frequency response verifies correct operation.

Keywords

Active array antennas and componentsPower amplifiers and linearizers
Type
Research Paper
Information
International Journal of Microwave and Wireless Technologies , Volume 8 , Issue 3: Journee Nationale des Micro-ondes (JNM) 2015 , May 2016 , pp. 463 - 470
Copyright
Copyright © Cambridge University Press and the European Microwave Association 2015 

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