Wonhoon Jang

Nonlinear RF circuits and systems simulation when driven by several modulated signals

The simulation of nonlinear RF circuits and systems driven by digitally modulated signals with a large number of carriers is addressed by combining the envelope transient harmonic balance method with the artificial frequency mapping technique. The co-simulation of low-pass equivalent behavioral models with circuit based models is addressed by simulating the overall wireless communication path. Several application examples are considered, in particular, the modeling of complete wireless communications circuits and systems incorporating the radio channel model.

Simulation of nonlinear RF circuits driven by multi-carrier modulated signals

The simulation of nonlinear RF circuits driven by digitally-modulated signals with multiple carriers is addressed by combining the envelope transient harmonic balance method with the artificial frequency mapping technique. Specific application examples are considered, in particular the modeling of OFDM-based communications circuits. A mixer subject to a modulated RF signal and an amplifier excited by a multi-carrier modulated stimulus are studied. Here an envelope time-marching scheme is coupled to an artificial frequency mapping based harmonic balance engine.

A Broadband Almost-Digital RF Transmitter With an Efficient Power Amplifier

A new architecture of an almost-digital RF transmitter is proposed. It consists of easy-to-have functional modules. Among the modules, a broadband Doherty amplifier is focused through a modified design approach. A proof-of-concept transmitter is built and measured. It demonstrates quite comparable performances: more than 40% of power-amplifier efficiency, adjacent channel leakage ratios between -26 and -37 dB, and average 2.6% of error vector magnitude over a frequency band from 0.7 to 1.1 GHz, which corresponds to a fractional bandwidth of 44%, when it is driven by a signal with 5.6 dB of peak-to-average power ratio.

Designing Harmonic-Controlled Drivers for Switching Power Amplifiers

A driver for a switching power amplifier is designed by an iterative least squares method. With only one stub and two lines in each input and output matching network, amplitude and phase responses up to ninth-order harmonic frequencies have been controlled. The designed amplifier is built, and the method is verified with measurements.

GaN MMIC active arrays with space power combination

This paper discusses the implementation of a K/Ka band GaN MMIC for developing space active arrays with space power combination, as a way to overcome TWTA needs. The obtained results, including the MMIC GaN characterization will be presented and the overall system demonstrator discussed.

MMIC GaN power amplifier with bidirectional operation for RF-to-DC conversion

GaN technology has shown improved characteristics at high power and high frequency conditions, playing a key opportunity in the space industry. In this way, this paper presents a GaN-based MMIC power amplifier (PA), designed for X-band space applications. The PA design consists of a single stage class-B and achieves 10.5 dB gain at 9 GHz and an output power of 32 dBm. It is verified that the MMIC can operate also as a rectifier, with a conversion efficiency of around 40 % for a CW input signal of 28 dBm at 8 GHz. Additionally, two-tone measurements are performed and compared to the CW ones.

Crest factor reduction through scaling and recovering by frame in OFDM communication systems

A new scheme for reducing crest factor in orthogonal frequency division multiplexing (OFDM) communication systems has been proposed. The reduction is achieved by simply scaling all symbols in a frame that exceeds a desired level on the transmitter side. The scaled symbols are recovered by scaling back on the receiver side. All of those operations can be achieved by adding simple functions such as level detection and summation of symbol amplitudes in baseband. The major advantage is that there is no extra information to be sent to the receiver for those operations due to a fixed scaling factor already shared between the transmitter and receiver. Also, the scheme does not degrade adjacent channel power ratio (ACPR) and error vector magnitude (EVM) at all due to the frame-based scaling and recovering so it does not require filtering after crest factor reduction (CFR) as in clipping. One of the limitations is that this scheme achieves only a CFR of about 2.5dB. For validation of the scheme, the processes in baseband and in RF have been conducted with Simulink and measurement with a power amplifier respectively.

Deterministic and Stochastic Behavioral Modeling of RF Front Ends

Behavioral models developed using discrete-tone characterization can be used to capture the response of an RF front end to stochastic signals. It is important that the model architecture capture all nonlinear effects and that the proper translation of the derived envelope model be transformed into an instantaneous model. Here the requirements for the transformation are presented, a multi-slice model architecture that can capture complex behavior from narrow-band measurements is presented together with an extraction procedure