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Radio Frequency Amplifier Basics
Published in Abdullah Eroglu, Introduction to RF Power Amplifier Design and Simulation, 2018
The compression point for an amplifier is the point where the amplifier gain becomes 1 dB below its ideal linear gain, as shown in Figure 1.12. Once the 1-dB compression point is identified for the corresponding input power range, the amplifier can be operated in linear or nonlinear mode. Hence, the 1-dB compression point can also be conveniently used to identify the linear characteristics of the amplifier.
A Multi-Box Behavioural Nonlinear Mixer Model
Published in International Journal of Electronics, 2023
Ali Ozgun, Tayfun Nesimoglu, Simsek Demir
The nonlinear behaviour of a microwave device is analysed in two steps. Firstly, we observe nonlinearity in the spectral analysis with the generation of IMD components. These components are sum and difference products of input tones and their harmonics. The second analysis of nonlinearity is the behaviour of each frequency component concerning input amplitude modulation. There are two different effects of input amplitude modulation at the output. The distortion at the output amplitude due to the input amplitude modulation is called AM/AM distortion. Similarly, distortion at the output phase response due to the input amplitude modulation is called AM/PM distortion. In general, for an amplifier or a mixer, if the device input level is far below the compression point, fundamental and IMD components have proportional responses in logarithmic scale with input amplitude modulation. In this region, fundamental tones change with a 1:1 ratio and -order IMD changes with a 1:n ratio with input amplitude change. Also, relative phases of fundamental and IMD components are stable under input amplitude sweep. In this case, it is sufficient to model the device for a single input power level to simulate frequency domain nonlinearity. But, with higher drive levels, fundamentals and IMD components show the nonlinear amplitude and phase responses with respect to input amplitude modulation.
A Holistic Experimental Static Bias Point Identification Method for Low Power Wireless RF Amplifier
Published in IETE Journal of Research, 2022
Saroj K. Patro, Rabindra K. Mishra, Ajit K. Panda
The small signal swept frequency simulated performance of the amplifier is shown in Figure 4. As observed, the small signal gain of the amplifier is approximately 18.25 dB in the mid-band with an overall flatness of better than 0.7 dB. Also, the amplifier obtained good input and output return loss. The large signal swept power simulated performance is shown in Figure 5 which depicts three parameters such as the power gain, 1 dB gain compression Power (P1 dB) and 3 dB gain compression Power (P3dB) levels. As observed here, the P1dB for the amplifier is about +37.03 dBm and P3dB is about +38.13 dBm at 1960 MHz. The P1dB and the P3dB are the 1-dB and 3-dB gain compression points of the device and these simulated values are in accordance with the device datasheet predicted performance. These gain data clearly depict the linear and non-linear region of the amplifier before the compression point is reached.
Broadband analogue predistortion using a distortion generator based on two-stage RF mixer topology
Published in International Journal of Electronics, 2018
The output spectrum of a two-tone test at 1.6 GHz with ∆f = 1 MHz is shown in Figure 9(a), where the system is optimised to suppress IM3 and IM5 by 15 and 5 dB, respectively. The output spectrum of a two-tone test with ∆f = 20 MHz is shown in Figure 9(b), where 16 dB IM3 and 6 dB IM5 suppression is achieved. These correspond to output third-order intercept point improvements of 7.5 and 8 dB, respectively. The predistorted amplifier reaches to 1 dB gain compression point1 (P1dB = 15 dBm) at 17 dB input power whereas the amplifier without predistorter reaches to same P1dB at 14 dBm input power. Noise power measurements at the PA’s output indicate only 0.24 dBm/Hz increase in the noise level when linearisation is applied, which is negligible. The LO frequency is 1.2 GHz and its power is set to 7 dBm which is the required LO drive level of the RF mixers. The LO power requirement may be reduced by using lower level RF mixers such as level-3 or 4 (mixer ‘level’ describes the required LO drive power requirement in dBm). In all tests, suppression of IMD is achieved without any reduction in fundamental signals. IM3 may be reduced close to the noise floor by compromising IM5 suppression. This demonstrates that the predistorter characteristic should be improved to match that of the PA. This may be achieved by better choice of RF mixers employed in the distortion generator.