Search

Interpolation involves the process of estimating values at positions in between the adjacent samples, which has very fundamental and applied implications in signal processing and communication systems. In this work, a new method of cubic spline interpolation (CSI) is proposed and derived mathematically from the input samples respecting the time-domain boundary conditions, and the corresponding piecewise polynomials are optimized in the frequency domain to achieve good spectral properties. A comparative analysis of several prior arts, including arbitrary frequency response polynomial (AFRP) and basis spline (B-spline) is also presented, giving a clear overview of the advantages associated with the proposed technique in terms of implementation complexity, latency, and in-band and out-of-band spectral performance. The measurement results with three different radio frequency (RF) power amplifier (PA) prototypes using an input stimulus comprised of different instantaneous bandwidth (iBW) carrier aggregated 5G new radio (NR) waveform are demonstrated to highlight the improved performance in the context of digital predistortion (DPD) correction. Finally, the architecture of the proposed method is illustrated, which is suitable for real-time high-speed digital implementation. [ABSTRACT FROM AUTHOR]

This paper presents a new method of reactive-combiner structure to be used as part of a multiphase digital pulsewidth modulated polar transmitter (DPWMPT). It overcomes the limitations of previous implementations of the multiphase pulse-modulated polar transmitter related to terminating pulsewidth modulation (PWM) harmonics located outside the passband, thereby improving both PWM harmonic suppression by using multiphase aliasing-free digital PWM technique and increasing overall efficiency by using reactive combining. For validation, a prototype transmitter was implemented and tested with a 64-QAM 20-MHz bandwidth long-term evolution (LTE) downlink signal with a 7.5-dB peak-to-average power ratio at 2140 MHz. The prototype dual-phase DPWMPT architecture achieved an output power level of 37 dBm and power-added efficiency of 33.5% while passing the stringent spectral requirements of the LTE standard for small-cell base stations using only simply memoryless predistortion correction. [ABSTRACT FROM AUTHOR]

This letter presents a study of thermal memory effect reduction for pulse-modulated polar transmitters (PMPTs). PMPTs using pulse modulation have shown very low memory effects even when operated at high-power levels in the previous literature. In this letter, thermal simulations were performed to study the effects of pulse modulation. The simulation results show that the pulse modulation not only reduces the increase of temperature but also temperature variation. Temperature variation is the main source of thermal-related memory effect since temperature change affects parameters such as internal transconductance, resistances, and capacitances. Furthermore, the simulation and measurement results indicate that modern 4G and 5G signals with high peak-to-average power ratios actually help reduce thermal-related memory effects in PMPTs. [ABSTRACT FROM AUTHOR]

The pulse-modulated polar transmitter (PMPT) uses envelope information to pulse modulate phase information to implement highly linear and highly efficient polar transmitters. Previous implementations of the PMPT successfully achieved bandwidths up to 5 MHz. However, as the bandwidth of the signal increases, nonidealities of the PMPT limit the performance of this architecture. The nonidealities are predominantly aliasing from pulsewidth modulation (PWM) and distortions from switching, which degrade the spectral performance. By using aliasing-free digital PWM and digital pre-distortion concurrently, spectral performance of the PMPT can be improved for wide bandwidth applications. For validation, a prototype transmitter was tested with a 20-MHz bandwidth downlink long-term evolution (LTE) signal at 836.5 MHz. Using the proposed method, the prototype transmitter achieved an output power of 19.8 dBm and drain efficiency of 24.4% while passing the spectral requirements of the LTE standard for femtocell base stations. [ABSTRACT FROM AUTHOR]

This paper presents a wideband power recycling technique for pulse-modulated polar transmitters (PMPTs). The technique allows unwanted out-of-band modulation spurs in PMPTs to be rectified and recovered back to the power supply for efficiency improvement. By configuring the power amplifiers as a balanced amplifier with dual-phase digital pulse-width modulation, the odd modulation spurs can be extracted directly from the isolation port of the output-combining quadrature coupler. Using the proposed architecture, the prototype transmitter achieved 59.1% drain efficiency at an output channel power of 26.2 dBm using a 10-MHz bandwidth long-term evolution 16-quadrature amplitude modulation test signal at 836.5 MHz. After output signal restoration by a surface-acoustic-wave filter, an output power level of 24.8 dBm and 42.8% drain efficiency were achieved while passing the spectral and receive-band-noise requirements without using any digital pre-distortion techniques. [ABSTRACT FROM AUTHOR]

This letter presents an aliasingfree multilevel pulse modulation (MLPM) architecture to implement a linear Doherty power amplifier (PA). This letter is believed to be the first reported results of this type of Doherty architecture to achieve linear amplification rather than the usual situation of a continuous amplitude modulated carrier and continuous load modulation. Our results show that both high efficiency and good linearization can be achieved with simple memoryless digital predistortion. Doherty operation with MLPM is believed to have benefits in linearization due to the MLPM discrete drive as less power is dissipated by the PA, leading to less thermal-related memory effects. A prototype transmitter system is constructed using a commercially available Doherty PA for validation. Measurements are performed using a 64-QAM long-term evolution (LTE) downlink signal at 2140 MHz with 20-MHz bandwidth. The overall system achieved an output power level of 40.1 dBm with a power-added efficiency of 39.5% while passing the −45-dBc downlink spectral requirements of the LTE standard. [ABSTRACT FROM AUTHOR]

This letter presents a broadband power amplifier (PA) for improving the linearity of an aliasing-free pulse-modulated polar transmitter. For this letter, a broadband input matching deep class-C PA is designed. The input matching bandwidth is over 650 MHz around the center frequency. To validate the proposed system, a prototype transmitter system is constructed using commercially available components. The overall system achieved an output power level of 35.5 dBm with a power-added efficiency of 32.8%. Spectral requirements using a 10-MHz bandwidth 64-QAM long-term evolution downlink signal at 2140 MHz was passed for small-cell base stations without the use of any digital predistortion techniques. [ABSTRACT FROM AUTHOR]

The pulse-modulated polar transmitter (PMPT) uses the envelope information to pulse modulate the phase information to implement a highly linear and highly efficient polar transmitter. The bandwidth of the PMPT is primarily determined by the pulsewidth modulation sampling frequency of the envelope information. For wide bandwidth applications such as long-term evolution (LTE), finite rise and fall times of the RF pulses distort the envelope information. In this paper, the nonideal RF pulses are analyzed and an envelope correction method is proposed to reduce the distortion in wide bandwidth applications using the PMPT architecture. For validation, a cellular-band prototype transmitter system was constructed using commercially available components. Using a 20-MHz bandwidth 16-QAM LTE signal at 836.5 MHz, the prototype transmitter achieved an output power of 22.7 dBm and drain efficiency of 33% while passing the spectral requirements of the LTE standard. [ABSTRACT FROM AUTHOR]

This letter presents a method for improving the efficiency of a power amplifier (PA) under load mismatch by recycling the reflected power. By configuring the PA as a balanced PA, the reflected power will be directed to the isolation port of a 90^\circ hybrid coupler. The reflected power can then by rectified and converted back to dc power to assist in supplying the PA. A prototype system was built to validate the concept and tested under various load phase angles with 2:1 and 4:1 VSWR using a W-CDMA voice signal at 836.5 MHz. Measurement results show that the power recycling technique improves the overall efficiency by as much as 22.1% when the output power level is 25 dBm. Under load conditions and power levels where the rectifier cannot provide sufficient output voltage level to supply the PA, the proposed technique simply maintains the original PA efficiency with no degradation. [ABSTRACT FROM PUBLISHER]