Skip to main content Accessibility help
×
Home
  • Print publication year: 2015
  • Online publication date: June 2015

6 - Polar transmitter principles

from Part I - Motivations, definitions, and principles

Summary

A polar transmitter by definition operates in accordance with one or more of the principles shown in Figure 2-3. By far the most common implementation is direct control of output signal magnitude from (2.8) and (2.9) and illustrated in Figure 2-3(a). The implementation shown in Figure 2-3(b) is actually a phase modulator, and is usually also implemented ahead of the stage controlling output magnitude.

History of the technique

Polar modulation, defined as a signal process implementing Figure 2-3(a), has been in use for nearly a century. Early in the implementation of AM broadcasting, it was discovered that the energy efficiency of class A transmitter power amplifiers was unacceptably low. Many alternatives were attempted [6-1], including constant current modulation, variable gain (controlled grid) modulation, and plate modulation.

The technique that won this competition is plate modulation.

6.1.1 Plate modulation (predates 1920)

The controlled port of a vacuum tube (valve) is called the “plate.” It was found before 1920 that the output power from an amplifiers can be made to vary if the power supply applied to the amplifiers varied. This output signal variation was roughly proportional to the power supply value, as long as the amplifiers operated in compression [1-1]. The proportionality was not perfect, but for the modulation requirements of AM broadcasting it was good enough. Later it was learned that when class C bias was used, along with very large drive signals to achieve sufficient output compression, the operation of a plate modulated transmitter could achieve efficiency values greater than 90% at AM band frequencies [4-3]. Plate modulation of class C biased power amplifiers dominated AM broadcast transmitter designs for more than 60 years, making it a very successful technology.

Plate modulation, as used for AM broadcasting, is a single coordinate polar signal process. Only signal magnitude is varied according to the information signal.

[6-1] R. A.Heising, Heising,“Modulation Methods,”Proceedings of the Institute of Radio Engineers, vol. 50, no. 5, May 1962, pp. 896–901.
[6-2] L. R.Kahn, Kahn,“Single-Sideband Transmission by Envelope Elimination and Restoration,”Proceedings of the Institute of Radio Engineers, vol. 40, no. 7, July 1952, pp. 803–806.
[6-3] H.Swanson, Swanson,“Digital AM Transmitters,”IEEE Translations on Broadcasting, vol. 35, no. 2, Feb. 1989, pp. 131–133.
[6-4] J., Staudinger et al. “800 MHz Power Amplifier Using Envelope Following Technique,”Proceedings of the 1999 IEEE Radio and Wireless Conference (RAWCON'99), Denver, CO, Aug. 1–4, 1999.
[6-5] W.Camp, Camp,J.Schlang, Schlang,G.Gore, Gore,R.Boesch, Boesch, and D.Arpaia, Arpaia, “Circuit and Method for I/Q Modulation with Independent, High Efficiency Amplitude Modulation,” US Patent 6194963, issued Feb. 27, 2001.
[6-6] W. B.Sander, Sander,S. V.Schell, Schell, and B. L.Sander, Sander,“Polar Modulator for Multi-mode Cell Phones,”Proceedings of the 2003 IEEE Custom Integrated Circuits Conference (CICC), San Jose, Sept. 2003.
[6-7] E.McCune, McCune,“High-Efficiency Multi-mode, Multi-band Terminal Power Amplifiers,”IEEE Microwave Magazine, March 2005.
[6-8] W. H.Doherty, Doherty,“A New High Efficiency Power Amplifier for Modulated Waves,”Proceedings ofthe Institute ofRadio Engineers, vol. 24, no. 9, Sept. 1936, pp. 1163–1182.
[6-9] E.McCune, McCune,“Polar Modulation and Bipolar RF Power Devices,”Proceedings of the IEEE Bipolar Circuits and Technology Meeting (BCTM), Santa Barbara, Oct. 2005.
[6-10] S.Schell, Schell,W.Sander, Sander,R.Meck, Meck, and R.Bayruns, Bayruns, “Power Control and Modulation of Switched-mode Power Amplifiers with One or More Stages,” US Patent 6734724, issued May 11, 2004.
[6-11] S.Schell, Schell,W.Sander, Sander,R.Meck, Meck, and R.Bayruns, Bayruns, “Power Control and Modulation of Switched-mode Power Amplifiers with One or More Stages,” US Patent 7042282, issued May 9, 2006.
[6-12] E.McCune, McCune, “Variable Bias Control for Switch-mode RF Amplifier,” US Patent 6323731, issuedNov. 27, 2001.
[6-13] W.Sander, Sander,R.Meck, Meck, and E.McCune, McCune, “Communication Signal Amplifiers Having Independent Power Control and Amplifier Modulation,” US Patent 7010276, issued March 7, 2006.
[6-14] W.Sander, Sander,R.Meck, Meck, and E.McCune, McCune, “Communication Signal Amplifiers Having Independent Power Control and Amplifier Modulation,” US Patent 7035604, issued April 25, 2006.
[6-15] W.Sander, Sander,R.Meck, Meck, and E.McCune, McCune, “Communication Signal Amplifiers Having Independent Power Control and Amplifier Modulation,” US Patent 7444125, issued Oct. 28, 2008.
[6-16] W.Sander, Sander,R.Meck, Meck, and E.McCune, McCune, “Communication Signal Amplifiers Having Independent Power Control and Amplifier Modulation,” US Patent 7515885, issued April 7, 2009.
[6-17] D.Flowers, Flowers, “Mode Shift Calibration in Power Amplifiers,” US Patent 8000663, issued Aug. 16,2011.
[6-18] E.McCune, McCune,G.Do, Do, and W.Lee, Lee, “Transmission Power Controller,” US Patent 8064855, issued Nov. 22, 2011.
[6-19] W.Sander, Sander, “Saturation Prevention and Amplifier Distortion Reduction,” US Patent 6528975, issued March 4, 2003.
[6-20] W.Lee, Lee, “Methods and Apparatus for Reconstructing Amplitude Modulation Signals in Polar Modulation Transmitters,” US Patent 7991336, issued Aug. 2,2011.
[6-21] S.Schell, Schell,W.Sander, Sander, and E.McCune, McCune, “Method and System of Amplitude Modulation Using Dual/Split Channel Unequal Amplification,” US Patent 6751265, issued June 15, 2004.
[6-22] J.Sevic, Sevic,W.Sander, Sander, and S.Schell, Schell, “Differential RF/Microwave Power Amplifier Using Independent Synchronized Polar Modulators,” US Patent 6653896, issued Nov. 25, 2003.
[6-23] W.Sander, Sander, “Efficient Precise RF Modulation Using Multiple Amplifier Stages,” US Patent 6690233, issued Feb. 10, 2004.
[6-24] H.Wang, Wang,P.Liang, Liang,R.Booth, Booth,S.Schell, Schell, and T.Biedka, Biedka, “Methods and Apparatus for Conditioning Communications Signals Based on Detection of High-Frequency Events in Polar Domain,” US Patent 8331490, issued Dec. 11, 2012.
[6-25] P. Liang and R.Strandberg, Strandberg, “Apparatus and Method for Conditioning a Modulated Signal in a Communication Device,” US Patent 7675995, issued March 9, 2010.
[6-26] P.Liang, Liang,K.Takinami, Takinami, and T.Matsuura, Matsuura, “Transmitter Utilizing a Duty Cycle Envelope Reduction and Restoration Modulator,” US Patent 8131234, issued March 6, 2012.
[6-27] H. Wang and P.Liang, Liang, “Methods and Apparatus for Reducing High-frequency Events in Polar Domain Signals,” US Patent 8300729, issued Oct. 30, 2012.
[6-28] S. Schell and R.Booth, Booth, “Method and Apparatus for Reducing Peak-to-RMS Amplitude Ratio in Communication Signals,” US Patent 7639098, issued Dec. 29, 2009.
[6-29] S. Schell and R.Booth, Booth, “Method and Apparatus for Reducing Peak-to-RMS Amplitude Ratio in Communication Signals,” US Patent 8050352, issued Nov. 1,2011.
[6-30] M. Mow and R.Booth, Booth, “Signal Enhancement in RF Transmitters Employing Non-linear Filtering,” US Patent 8010063, issued Aug. 30, 2011.
[6-31] H.Chireix, Chireix,“High Power Outphasing Modulation,”Proceedings of the Institute of Radio Engineers, vol. 23, no. 11, Nov. 1935, pp.1370–1392.
[6-32] K., Takinami and P.Liang, Liang, “Adaptive Impedance ConverterAdaptivelyControls Load Impedance,” US Patent 8140030, issued March 20, 2012.
[6-33] T.Biedka, Biedka,P.Liang, Liang, and G.Do, Do, “Selective Envelope Modulation Enabling Reduced Current Consumption,” US Patent 7688157, issued March 30, 2010.
[6-34] S.Schell, Schell, “High-Quality Power Ramping in a Communications Transmitter,” US Patent 6983025, issued Jan. 3, 2006.
[6-35] S.Schell, Schell, “High-Quality Power Ramping in a Communications Transmitter,” US Patent 7227909, issued June 5, 2007.
[6-36] B.Sander, Sander,W.Sander, Sander, and S.Schell, Schell, “Multi-mode Communications Transmitter,” US Patent 7158494, issued Jan. 2, 2007.