Brush up on the theory before designing a high power Class‐E amplifier: Page 7 of 15

June 29, 2016 //By Alfio Scuto, Roberto Cammarata, ST Microelectronics
The most promising switched-mode PA for RF applications, among the several types available, is the Class-E for several reasons: high efficiency, simplicity of the load network, and a satisfying performance even with a non-optimal drive signal.

3.4. Finite DC‐feed inductance

Using a finite DC feed inductance instead of an RF-choke has significant benefits (5), (6):

  • Higher load resistance then less losses on the output matching network (7).
  • Possibility to use devices with lower breakdown voltage.

To analyze a circuit with DC finite feed, the inductance is quite complex, and a practical approach (3) is to choose the RF choke reactance higher in comparison to the reactance of the shunting capacitor, i.e.,

→ Equation 24

 

→ Equation 25

 

4. Design a 500 W Class‐E at 13.56 MHz

The target specifications for the design are shown in the table below.


Table 2: Target specifications.

 

4.1 Device selection and circuit simulation

Using the Advanced Design System (ADS) from Keysight (Agilent), we have analyzed the RF performances of the switch mode Class-E power amplifier. The analysis of the circuit was done using the transient envelope and the harmonic balance simulation. With the transient envelope, we optimized the values of the output components (Figure 4) in Class-E conditions (Equation 6, Equation 7).


Figure 4: Transient envelope simulation.

 

Design category: