Yu.A. Bryukhanov1, K.S. Krasavin2

1,2 P.G. Demidov Yaroslavl State University (Yaroslavl, Russia)

The output power amplifier is operated in nonlinear mode to increase its efficiency, at which the signal is distorted more. The goal is to analyze effects of nonlinearity on the modulating signal of angle-modulated signal distortions for single-ended and push-pull output power amplifiers with memory and without it. The amplifier characteristic ic(vBE) is preset by the cubic polynomial. The output voltage of memoryless amplifier uout(t) is found by Ohm's law. And in case with amplifier with memory, the output voltage uout(t) is found by Complex amplitude method with a Fourier series of function ic(t). The output voltage uout(t) is represented as the narrowband process with envelope of the waveform U1(t) and initial phase Ф1(t) to determine the angular modulation law Ф1(t) at the amplifier output. The function U1(t) is defined as combination of in-phase А(t) and quadrature В(t) components.

The distortion estimate based on Total Harmonic Distortion (THD). The measurement of THD is defined as the ratio of the RMS amplitude of a set of higher harmonic frequencies to the RMS amplitude of the first harmonic. The spectrum of function Ф1(t) is represented a Fourier series.

In single-ended memoryless amplifier and non-cutoff mode, the THD decreases as m increases and THD of modulating signal is {37.6; 18.8; 6.3%} at m  {0.5; 1; 3}. In cutoff mode, the smallest THD is {15.18; 5.13%} at m  {1; 3} as θ = 140o.

In push-pull memoryless amplifier and θ = 90o, the THD is {22.2; 11.1; 3.7%} at m  {0.5; 1; 3} which is 1.7 times less than in a single-ended amplifier without cutoff. This is due to compensation even-order harmonic of amplified signal at the output of a pushpull amplifier. In this case of memoryless amplifier, the transistor load is a parallel RLC circuit. The distortion decreases under m increases at first (up m is 1.5), but then rapidly increases (from m is 1.7). This is due to increase of the parasitic harmonics level caused by the nonlinearity of the phase-frequency characteristic of RLC circuit. The calculations show that THD of modulating signal is 3.35, 9.02 and 22.88 % at Q = 10 and m  {0.5; 1; 3}, respectively. In cutoff mode, the smallest THD is at θ = 90o and it does not depend on θ at large values of m. In push-pull amplifier with memory, the THD is 2.8, 2.5 and 3.0 times less than for a singleended amplifier without cutoff at Q  {2.5; 5; 10}, respectively.

The results of this paper can be used for the design of signal processing systems.

Bryukhanov Yu.A., Krasavin K.S. Nonlinear distortion of angle modulation signal in output power amplifiers. Radiotekhnika. 2021.  V. 85. № 9. P. 86−94. DOI: https://doi.org/10.18127/j00338486-202109-08 (In Russian)

1. Mamonkin I.G. Usilitel'nye ustrojstva. M.: Svjaz'. 1966. 400 s. (In Russian)
2. Liang C., Jong J., Stark W.E., East J.R. Nonlinear Amplifier Effects in Communications Systems. IEEE Transactions on Microwave Theory and Techniques. August 1999. V. 47. № 8. P. 1461-1466.
3. Jantunen P., Gamez G., Laakso T. Measurements and Modelling of Nonlinear Power Amplifiers. Proceedings of the 6th Nordic Signal Processing Symposium. NORSIG-2004. Espoo, Finland. June 2004. P. 328-331.
4. Lin F-L., Chen S-F., Chuang H-R. Effects of RF-circuit Nonlinear Distortion on Digitally Modulated Signals in Wireless Communication. Microwave Journal. September 2000. V. 43. № 9. P. 126-138.
5. Smirnov A.V. Issledovanie jeffekta AM-RM iskazhenij pri vysokojeffektivnom usilenii moshhnosti. Jelektrosvjaz'. 2016. № 4. S. 61-64 (In Russian).
6. Aschbacher E., Rupp M. Modelling and Identification of a Nonlinear Power-Amplifier with Memory for Nonlinear Digital Adaptive PreDistortion. 4th IEEE Workshop on Signal Processing Advances in Wireless Communications. SPAWC-2003. Rome, Italy. August 2004. P. 658-662 (In Russian).
7. Brjuhanov Ju.A., Krasavin K.S. Nelinejnye iskazhenija signalov v vyhodnom usilitele. Radiotehnicheskie i telekommunikacionnye sistemy. 2018. № 3(31). S. 54-58 (In Russian).
8. Baskakov S.I. Radiotehnicheskie cepi i signaly. M.: LENAND. 2016. 528 s.
9. Kharchenko V., Grekhov A., Ali I. Influence of Nonlinearity on Aviation Satellite Communication Channel Parameters. Proceedings of the National Aviation University. 2015. № 4(65). P. 12–21. 
10. Evtjanov S.I. Perehodnye processy v priemno-usilitel'nyh shemah. M.: Svjaz'izdat. 1948. 211 s. (In Russian).
11. Gonorovskij I.S., Demin M.P. Radiotehnicheskie cepi i signaly: Ucheb. posobie dlja vuzov. M.: Radio i svjaz'. 1994. 418 s. (In Russian).
12. Janke E., Jemde F., Ljosh F. Special'nye funkcii: per. s nem. pod red. L.I. Sedova. M.: Nauka. 1968. 344 s. (In Russian).