1  Converter Design and simulation

A simplified schematic of the Class-E RF power amplifier (Sokal and Sokal 1975) you will implement in the laboratory is shown in Figure 1.1.

Figure 1.1: Class-E switched mode power amplifier

1.1 Class-E amplifier design and initial simulation

Following the design guidelines discussed in the lecture, determine the component values required to design a Class-E inverter that meets the specifications listed in Table 1.1.

Table 1.1: Class-E specifications

Parameter	Value	Units
\(f_s\)	6.78	MHz
\(V_i\)	12	V
\(R_{load}\)	5	\(\Omega\)

In the idealized Class-E inverter shown in Figure 1.1, the choke inductor \(L_{choke}\) is assumed to be very large, allowing the input current \(i_{in}(t)\) to be considered constant. In practice, however, a finite and realizable inductance must be used. For the Class-E inverter constructed in this laboratory, you may assume a choke inductance satisfying \[L_{choke}\geq 5\times L_s\]

For your design, assume that the gate drive signal \(v_g(t)\) is square-wave with sufficient amplitude to fully enhance the switch and a fixed duty cycle of 50%.

Complete the following tasks:

• Simulate your design using LTspice with an ideal switch.
• Provide a list of all component values used in your design.
• Plot three full cycles of the following steay-state waveforms: \(v_g(t), v_{ds}(t)\) and \(v_{load}(t)\).
  
• Report the simulated output power and the ratio \(\frac{\max\left(v_{ds}(t)\right)}{V_i}\).

1.2 Matching network design and updated simulation

Although the class-E in Chapter 1 is designed for a \(5~\Omega\) load, a \(50~\Omega\) RF attenuator will be used in the laboratory to enable more accurate performance measurements. Consequently, you must design a \(6.78~\textrm{MHz}\), matching network that transforms a \(50~\Omega\) load to an effective \(5~\Omega\) load, as shown in Figure 1.2.

Figure 1.2: Matching network

Update your LTspice simulation to include the matching network. Note that some elements of the matching network may be combined with the resonant components of the Class-E amplifier, thereby reducing the total number of components required.

Complete the following tasks:

• Provide the component values of your \(6.78~\text{MHz}\), \(50~\Omega\)–to–\(5~\Omega\) matching network.
• List the component values of the updated design, clearly indicating any combined elements.
• Plot three full cycles of the steady-state waveforms \(v_g(t)\), \(v_{ds}(t)\), and \(v_{load}(t)\). In this simulation, the load resistance should be \(50~\Omega\).
• Report the simulated output power and the ratio \(\frac{\max!\left(v_{ds}(t)\right)}{V_i}\).
• Briefly discuss the differences between the simulation results with and without the matching network.

Sokal, N. O., and A. D. Sokal. 1975. “Class E-A New Class of High-Efficiency Tuned Single-Ended Switching Power Amplifiers.” IEEE Journal of Solid-State Circuits 10 (3): 168–76. https://doi.org/10.1109/JSSC.1975.1050582.