This paper presents a power amplifier (PA) designed as a part of a transceiver front-end fabricated in 130-nm SiGe BiCMOS. The PA shares its output antenna port with a low noise amplifier using a low-loss transmission/reception switch. The output matching network of the PA is designed to provide high output power, low AM-AM distortion, and uniform performance over frequencies in the range of 24.25-29.5GHz. Measurements of the front-end in TX mode demonstrate peak S21 of 30.3dB at 26.7GHz, S21 3-dB bandwidth of 9.8GHz from 22.2to 32.0GHz, and saturated output power (Psat) above 20dBm with power-added efficiency (PAE) above 22% from 24 to 30GHz. For a 64-QAM 400MHz bandwidth orthogonal frequency division multiplexing (OFDM) signal, -25dBc error vector magnitude (EVM) is measured at an average output power of 12.3dBm and average PAE of 8.8%. The PA achieves a competitive ITRS FoM of 92.9.

When confirming the ACLR (adjacent channel leakage power ratio), which are representative indicators of distortion in the design of PA (power amplifier), it is well known how to calculate the AM-AM/PM characteristics of PA, input time series data of modulated signals, and analyze the output by Fourier analysis. In 5G (5th generation) mobile phones, not only QPSK (quadrature phase shift keying) modulation but also 16QAM (quadrature modulation), 64QAM, and 256QAM are becoming more multivalued as modulation signals. In addition, the modulation band may exceed 100MHz, and the amount of time series data increases, and the increase in calculation time becomes a problem. In order to shorten the calculation time, calculating the total amount of distortion generated by PA from the probability density of the modulation signal and the AM (amplitude modulation)-AM/PM (phase modulation) characteristics of PA is considered. For the AM-AM characteristics of PA, in this paper, IMD3 (inter modulation distortion 3) obtained from probability density and IMD3 by Fourier analysis, which are often used so long, are compared. As a result, it was confirmed that the result of probability density analysis is similar to that of Fourier analysis, when the nonlinearity is somewhat small. In addition, the agreement between the proposed method and the conventional method was confirmed with an error of about 2.0dB of ACLR using the modulation waves with a bandwidth of 5MHz, RB (resource block) being 25, and QPSK modulation.

Since 2020, the service of the 5th generation (5G) mobile phone has been started. In order to increase the transmission speed in 5G mobile phones, the multi-level of the modulated signal is advanced, and for that, the power amplifier (PA) high linearity is required even at low output power. In accordance with this, the review of the linearization technology of a PA has become important. As a performance index of the distortion of the PA, the output power dependence of the gain and phase, the AM (Amplitude Modulation)-AM/PM (Phase Modulation) characteristic is well known. There has been a lot of consideration for the AM-AM/PM characteristics of PA. The AM-AM/PM characteristics are affected by both source and load impedances. In this paper, a single-stage HBT (Hetero-junction Bipolar Transistor) PA is described by a simple linear equivalent circuit with multiple parameter sets. Each parameter set is defined according to the PA output power level. With this simple model, we investigated the change of AM-AM/PM characteristics when the reactance parts of source and load impedances was changed. It has become clear that change in the AM-AM/PM characteristics of the PA when the parameters were changed was mainly due to the change in the AM-AM/PM characteristics at the base node.