Class-E PA Appendix

        On this page we give a little more background information for the design as well as the design process used for the  Class-E Power amplifier.

Below is a list of all the topics we cover in this page. Click on any of these links to go to that section.

CLASS-E PA OVERVIEW

            The class-E Power Amplifier (PA) is a switch mode PA which has a potential theoretical efficiency of approximately 100%. Being a switching mode PA, the Power FET is used as an ON-OFF switch. Using the basic switching mode PA with the circuit topology seen in image (a) below, we can only achieve a maximum efficiency of ~81% due to losses from all other odd harmonics besides the fundamental. To overcome this efficiency limitation, first a series resonator (LC) is added at the output to act like a short at the fundamental frequency, and an open at all other harmonics. Next a capacitor (Cp) placed in parallel with the switch to store charge when the switch is closed and to provide current when it is open. Finally an inductor (Ls) is put in series with the resonator to phase shift the current to ensure it is 0 (zero) Amps at the switch closing point. The resulting Class-E circuit topology is shown in image (b).

Ideal Class-E Circuit Topology

            The Class-E PA was used within our Magnetically Coupled Resonant, Wireless Power Transmission  system (or MCR-WPT system) based on the now obsolete Rezence WPT standard (superceded by Qi). This is mainly due to the high efficiency of the Class-E PA which results in most of the power going to the Transmitter coils of the Rezence system. Also, the fundamental load of the Class E PA is inductive, which is good for driving WPT coils.

            For more detailed information on the basic theory of the Class-E PA, the design methodology used, design specifications and results, check out section 2.3 of the thesis. For more brief overview of the Rezence WPT standard, see section 1.1.1 The thesis can be obtained from the Ryerson University library by clicking the button below.

Ryerson Library Thesis Download
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DESIGN COMPONENT VALUES

        This section provides the list component values used in the design of the Class-E Power Amplifier. The list is broken down into the 4 groups below:

  • Ideal Class E Parameters
  • Output Matching Network
  • Input Matching Network
  • Miscellaneous
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PARAMETERVALUE
VDC36V
Cp-external68pF
Cp-internal68pF
Lshift+Lres15uH
Cres39pF

PARAMETERVALUE
C2470pF
C3620pF (150+470)
L3500nH

PARAMETERVALUE
C62750pF (1600+820+330)
C710nF
C8220pF
L6500nH

PARAMETERVALUE
Choke Inductors (L1 and L4)15uH
Input bias voltage3V
Input Power2 Watts
Input impedance27Ω
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EFFICIENCY DIFFERENCES

        The main source of the efficiency decrease was due to the 39pF Cres capacitor with 2% tolerance used within the prototype. It was found to have a measured capacitance of 40pF. A harmonic balance simulation with this value shows efficiency drops by more than 10%.

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EXAMPLE DESIGN FLOW WALKTHROUGH

Operating Frequency              6.78MHZ
Target Efficiency                     >=85%


Device                                    FQPF3N25 MOSFET
Datasheet                               located HERE on ON Semiconductor’s website

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Ideal Class-E Circuit Topology
Device
Parameter		ValueClass-E Design
Parameter		ValueReliability
Requirement		Pass
Cint/Cdev25.3pFCp415.4pFCp > Cint/Cdevyes
Vmax250VVpeak(2 x VDC x 3.6)172.8VVmax < Vpeakyes
Imax9.2AIpeak1AImax < Ipeakyes
Class-E feasibility and reliability check (VDC =36V)
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Ideal Class-E Schematic Setup

Ideal Class-E Circuit Schematic Setup

Ideal Time and Frequency Domain Simulation

Ideal Class-E Time and Frequency Domain Simulation Results
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FQPF3N25 Class-E Output Matching Schematic

FQPF3N25 Class-E Circuit Output Matching Schematic Setup

FQPF3N25 Class-E Output Matching Simulation Results

FQPF3N25 Class-E Circuit Output Matching Simulation Results
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FQPF3N25 Class-E Input Matching Schematic

FQPF3N25 Class-E Circuit Input Matching Schematic Setup

FQPF3N25 Class-E Input Matching Simulation Results

FQPF3N25 Class-E Circuit Input Matching Simulation Results
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FQPF3N25 Class-E Final Circuit Schematic

FQPF3N25 Class-E Final Circuit Schematic Setup

FQPF3N25 Class-E Final Circuit Simulation Results

FQPF3N25 Class-E Circuit Final Circuit Simulation Results
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