Voltage-mode class-D Research Articles

Robust Two-Layer Model Predictive Control for Full-Bridge NPC Inverter-Based Class-D Voltage Mode Amplifier

Finite control set model predictive control (FCS-MPC) is able to handle multiple control objectives and constraints simultaneously with good dynamic performance. However, its industrial application is limited by its high dependence on system model and the huge computational effort. In this paper, a novel robust two-layer MPC (RM-MPC) with strong robustness is proposed for the full-bridge neutral-point clamped (NPC) voltage mode Class-D amplifier (CDA) aiming at this problem. The errors caused by the parameter mismatches or uncertainties of the LC filter and the load current are regarded as lumped disturbance and estimated by the designed Luenberger observer. The robust control can be achieved by compensating the estimated disturbance to the used predictive model. In order to reduce computation of the controller, a two-layer MPC is proposed for the full-bridge NPC inverter with an LC filter. The first layer is used to calculate the optimal output level which minimizes the tracking error of the output voltage. The second layer is used to determine the switching state for the purpose of capacitor voltage balancing. The experimental results show that the lumped model error is observed centrally through only one observer with low complexity. The two-layer MPC further reduced the computation without affecting the dynamic performance.

Design of High-Efficiency Voltage-Mode Class-D RF Power Amplifier for Class-S Transmitter Using Signal Analysis and Additional Multi-Section Bandpass Filter

This paper proposes a high-efficiency voltage-mode class-D (VMCD) RF power amplifier (PA) for class-S transmitter, which includes additional multi-section bandpass filter (BPF). For an accurate analysis of class-S transmitter, the output signals of band pass delta sigma modulator (BPDSM) are described with probability distribution functions (PDF) versus pulse widths of quantized signals. Usually, the results show that magnitudes of sub-harmonic terms increases for high peak-to-average power ratio signal such as long term evolution (LTE) signal. For a high efficiency and appropriate linearity of class-S transmitter, we propose a VMCD PA utilizing a multi-section BPF. The proposed architecture effectively improves the linearity without deterioration the efficiency. For the LTE signal, the efficiency is 25.82% and adjacent channel power ratio (ACPR) is -52.44dBc when using a one-section BPF. By using the multi-section BPF, ACPR and efficiency have been improved up to 11.88dB and 13.44% respectively. The effectiveness of the proposed design is demonstrated for various input signals.

On‐coil multiple channel transmit system based on class‐D amplification and pre‐amplification with current amplitude feedback

A complete high-efficiency transmit amplifier unit designed to be implemented in on-coil transmit arrays is presented. High power capability, low power dissipation, scalability, and cost minimization were some of the requirements imposed to the design. The system is composed of a current mode class-D amplifier output stage and a voltage mode class-D preamplification stage. The amplitude information of the radio frequency pulse was added through a customized step-down DC-DC converter with current amplitude feedback that connects to the current mode class-D stage. Benchtop measurements and imaging experiments were carried out to analyze system performance. Direct control of B1 was possible and its load sensitivity was reduced to less than 10% variation from unloaded to full loaded condition. When using the amplifiers in an array configuration, isolation above 20 dB was achieved between neighboring coils by the amplifier decoupling method. High output current operation of the transmitter was proved on the benchtop through output power measurements and in a 1.5T scanner through flip angle quantification. Finally, single and multiple channel excitations with the new hardware were demonstrated by receiving signal with the body coil of the scanner.

DEVELOPMENT OF A WIDEBAND HIGHLY EFFICIENT GAN VMCD VHF/UHF POWER AMPLIFIER

A 50 to 550MHz wideband gallium nitride (GaN) HEMT power amplifler with over 43dBm output power and 63% drain e-ciency has been successfully developed. The demonstrated wideband power amplifler utilizes two GaN HEMTs and operates in a push-pull voltage mode Class D (VMCD). The design is based on a large signal simulation to optimize the power amplifler's output power and e-ciency. To assure a wideband operation, a coaxial line impedance transformer has been used as part of the input matching network; meanwhile, a wideband a 1:1 ferrite loaded balun and low pass fllters are utilized on the amplifler's output side instead of the conventional serial harmonic termination.

CMOS Outphasing Class-D Amplifier With Chireix Combiner

This letter presents a CMOS outphasing class-D power amplifier (PA) with a Chireix combiner. Two voltage-mode class-D amplifiers used in the outphasing system were designed and implemented with a 0.18-mum CMOS process. By applying the Chireix combiner technique, drain efficiency of the outphasing PA for CDMA signals was improved from 38.6% to 48% while output power was increased from 14.5 to 15.4 dBm with an adjacent channel power ratio of -45 dBc.

Current-mode class-D power amplifiers for high-efficiency RF applications

We show that current-mode class-D (CMCD) power amplifiers can achieve high efficiency at RF frequencies. In contrast with conventional voltage-mode class-D amplifiers, the CMCD features "zero voltage switching," which eliminates the output capacitance discharge loss. Experimental CMCD amplifiers with 76.3% power-added efficiency (PAE) at 290-mW output and 71.3% PAE at 870-mW output are demonstrated using GaAs FETs at 900 MHz.