A 1.5 kW Radio-Frequency Tunable Matching Network Based on Phase-Switched Impedance Modulation

Abstract

Dynamically-tunable impedance matching is a key feature in numerous radio-frequency (RF) applications at high frequencies (10 s of MHz) and power levels (100s-1000 s of Watts and above). This work develops techniques that enable the design of high power tunable matching networks (TMN) that can be tuned orders of magnitude faster than with conventional tunable impedance matching techniques, while realizing the high power levels required for many industrial applications. This is achieved by leveraging an emerging technique -known as phase-switched impedance modulation (PSIM), which involves switching passive elements at the rf operating frequency -that has previously been demonstrated at rf frequencies at up to a few hundred Watts. In this paper, we develop design approaches that enable it to be practically used at up to many kilowatts of power at frequencies in the 10 s of MHz. A detailed analysis of the factors affecting the losses as well as the tradeoffs of a basic PSIM-based element is provided. Furthermore, it is shown how incorporating additional stages to the PSIM-based element, including impedance scaling and / or the addition of series or shunt passive elements, influences the losses and enables the efficient processing of high power levels given the limitations of available switches. A PSIM-based TMN that matches load impedances to 50 and delivers up to 1.5 kW of power at frequencies centered around 13.56 MHz is implemented and tested over a load impedance range suitable for various industrial plasma processes.

Comparison of Radio-Frequency Power Architectures for Plasma Generation

“…To obtain insight from equation (6), one can consider the dependence of k 2 F (k) on k for values of m that are typical of variable-load inverters, somewhere between 0.75 and 3 1 [4], [29]. One can then notice that the quantity k 2 F (k) rapidly increases beyond 1 as k increases, resulting in rapid efficiency degradation as output power backs off.…”

“…In this context, the primary purpose of a TMN block is to present an impedance that is suitable for the inverter and power combining system (e.g., Z L in Fig. 4(a)); several such suitable TMNs have been reported in the literature [6], [7], [33]- [36]. The next two subsections outline two dc-torf architectures demonstrating the usefulness of multiple power control schemes in achieving fast and efficient wide-powerand wide-load-range operation at HF, and present supporting simulation results.…”

“…Fig. 5 shows an example of a dc-to-rf architecture that utilizes a combination of discrete supply modulation (DSM) and outphasing as a means for achieving power control, and a TMN to compress the wide load impedance range [6], [7], [33]- [36]. In this architecture, which is referred to as multilevel outphasing [19], [20], two power amplifier (PA) blocks fed from power supplies that may be switched among different levels are outphased and combined to deliver a desired output power.…”

“…Fig. 7(a) shows another dc-to-rf architecture, termed multiinverter discrete back-off (MIDB) [37], that uses a form of structural modulation and outphasing to achieve control of output power, along with a TMN to compress the wide load impedance range [6], [7], [33]- [36]. This architecture consists of two sets of identical amplifiers, where the amplifiers in each set are in phase and are combined such that the voltage at the combiner output is the average of the individual amplifier output rf voltages within the set.…”

1 kW MHz Wideband Class E Power Amplifier

“…The literature also has references describing various techniques to extend the power amplifier's operational bandwidth to address the need for frequency tuning in many applications [2,[16][17][18]. These include using switched-capacitors, dual-band multi-stage converters, manually changing components in the output network, and applying reactance compensation [19][20][21][22][23]. Among all of these options, reactance compensation provides the benefits of simple circuit design, component count reduction, and elimination of manual tuning during operation.…”