Large-signal vector characterization of LDMOS devices for analysis and design of broadband Doherty high-power amplifiers

Abstract

We present a novel broadband large-signal vector characterization technique, suitable for high-power broadband Doherty amplifiers (DPAs). It consists of characterizing the DPA three-port sub-circuit composed of the main and peak power devices that are inter-connected by the input network. We discuss a suitable way to extract the three-port X-parameters of a DPA sub-circuit, which is based on a pair of high-power Silicon Laterally Diffused MOSFETs (LDMOSs) for UHF applications. It is then applied to the analysis of a high-power broadband DPA developed on the basis of the same DPA sub-circuit. This technique permits the broadband analysis of the operation of the DPA, as well as to get insight on the load modulation for both the peak and main devices, while they mutually interact through the input network. Measurements and simulated data in the 700–960 MHz bandwidth are compared so as to demonstrate the feasibility of three-port X-parameters characterization for high-power DPAs in UHF band.

High‐power UHF Doherty amplifier output combiner network optimization by 3‐port sub‐circuit X‐parameters characterization

“…The DPA sub-circuit is composed of the two power devices, namely the main and peak devices, an input network capable of splitting properly the input signal through the two devices, as well as the devices' gate bias networks: this subcircuit was already adopted in. 5,6 In this letter the DPA subcircuit is completed by two output networks suitable for device drain proper loading and characterization, as well as the devices' drain bias networks. A block diagram for this 3-port test fixture is shown in Figure 1A, where the reference sections are defined respectively at the DPA input port and at the devices drain terminal.…”

“…The DPA subcircuit implements the commercial PTVA042502FC, the same adopted in, 5,6 which integrates in the same package a pair of high power Si-LDMOS for ultra high frequencies (UHF) applications. At the devices drain reference sections, the test fixture terminates the two devices with their optimum device impedance.…”

“…The test-fixture characterization set-up is based on a threechannel nonlinear vector network analyzer, derived from that introduced in. 5,6 The set-up adopts two sources sequentially synchronized at the operating frequencies and corresponding levels, which are capable of stimulating the DPA subcircuit with a large signal, while injecting tick signals for the extraction of the X-parameters.…”

“…2 The adoption of X-parameters characterization for DPAs was already pursued in, 3,4 and for analysis purposes in. 5,6 In this letter we extend the approaches of 3,4 by extracting the 3-port X-parameters model of a pair of DPA radio frequency (RF) devices along with the input network, as a whole. During the characterization stage, the two power devices were terminated with multisection artificial transmission lines (TLs) capable to absorb the devices drain parasitic capacitance, and thus to exhibit the optimum impedance at the intrinsic device reference plane.…”

“…We report the optimized DPA performance comparison with a previous analogous design presented by the authors in. 5,6 This latter and the optimized implementations share the same device technology, as well as the same input network.…”