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Slide 1
LINEARIZERS 101
LINEARIZERS –DISTORTION REDUCTION IN HIGH POWER AMPLIFIERS
BY: DR. ALLEN KATZ
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Slide 2
OUTLINE
n WHY LINEARIZEn LIMITATIONS/IDEAL LIMITERn DECISION TO LINEARIZEn TYPES OF LINEARIZERSn PREDISTORTION LINEARIZERSn SOME RESULTSn MEMORY EFFECTSn EXTENDING THE LIMITS n CONCLUSIONS
Slide 3
WHY LINEARIZE
-MUST OPERATE AMPLIFIER AT REDUCEDPOWER LEVEL (BACKOFF FROM SATURATION)
IR≥BW[1+log2(S/N)]
Slide 4
ALLOWS OPERATION CLOSER TO SAT
Slide 5
CHANGE IN PHASE WITH LEVEL
Slide 6
DISTORTION DUE AM/AM & AM/PM
dn(gain)/d(Pin)n & dn(Ø)/d(Pin)n
Slide 7
IDEAL HPA CHARACTERISTIC
WANT CONSTANT GAIN AND PHASESETS A LIMIT ON WHAT CAN ACHIEVE
Slide 8
IDEAL HPA CHARACTERISTIC
WANT CONSTANT GAIN AND PHASEüSETS A LIMIT ON WHAT CAN ACHIEVE
Slide 9
IDEAL HPA CHARACTERISTIC
WANT CONSTANT GAIN AND PHASEüSETS A LIMIT ON WHAT CAN ACHIEVE
WHY PAR IS SO IMPORTANT
ONCE ABOVE SAT, NOTHING YOU CAN DO
Slide 10
PAR LIMITS IDEAL PERFORMANCE
Slide 11
IDEAL HPA CHARACTERISTIC
CREST FACTOR REDUCTION (CFR)
WHY PAR IS SO IMPORTANT
ONCE ABOVE SAT, NOTHING YOU CAN DO
Slide 12
FIRST RULE
YOU CAN’T LINEARIZE AN AMPLIFIERTHAT IS ALREADY LINEAR!
WANT TO OPTIMIZE EFFICIENCY AND SATURATED POWER, NOT LINEARITY
Slide 13
DECISION TO LINEARIZEn PRIMARILY ECONOMICn THE MORE NONLINEAR A DEVICE IS, THE GREATER THE ADVANTAGE OF LINEARIZATION
n THE MORE LINEARITY REQUIRED, THE GREATER THE ADVANTAGE OF LINEARIZATION - FOR MANY APPLICATIONS C/I ~ 30 dB ENOUGHn FOR MANY HPAs [GaN] CAN ACHIEVE- 3 TO 6 dB MORE POWER- MORE THAN DOUBLING OF EFFICIENCY- REDUCED SIZE AND WEIGHT
BY LINEARIZATION
Slide 14
IMPROVED EFFICIENCY
TYPICAL LINEARIZER EFFICIENCY IMPROVEMENT
Slide 15
n LINEARIZERS ALSO OFFER HPAs REDUCED THERMAL LOAD
n SINCE LIN COST IS ~ FIXED, THE BIGGER THE HPA, THE MORE ECONOMICAL IT BECOMES- LINEARIZING A 10 kW PA IS MUCH MORE COSTEFFECTIVE THAN A 1 W PA
n LINEARIZATION IS ALSO EASIER TO JUSTIFY AT HIGHER FREQ WHERE POWER IS MORE $$
DECISION TO LINEARIZE
Slide 16
n THREE COMMON FORMS:1) FEEDFORWARD2) FEEDBACK3) PREDISTORTION
n + TECHNIQUES TO IMPROVE EFFICIENCY USING NL PAs
TYPES OF LINEARIZATION
Slide 17
FEEDFORWARD
§ RELATIVELY COMPLEX & LIMITED EFFECIENCY § NOT EFFECTIVE FOR OPBOs < 6 dB§ MOST USEFUL FOR VERY HIGH LINEARITY APPS
Slide 18
FEEDBACK
Slide 19
FEEDBACK
< ~ 10 MHz MAX(1 MHz)
Slide 20
WAYS TO IMPROVE EFF WITH NL PAs
n MANY WAYS TO ACCOMPLISH.n CLASSICAL “KHAN METHOD” DEMODS ENVELOPE & LIMITS SIGNAL. THEN REMODULATES AT OUTPUT PA
n LINC SYSTEMS OBTAINS LINEAR AMPLIFICATION BY COMBINING TWO NON-LINEAR PAs.
n LOAD MODULATION AND OUTPHASING (DOHERTY – MOST SUCCESSFUL EXAMPLE)
Slide 21
PREDISTORTION
Slide 22
DIGITAL PDL DOMINANT
(CAN’T EASILY COMBINEMULTIPLE SIGNALS)~ALL USE ADAPTIVE APP.
Slide 23
DIGITAL VS. ANALOG PDL• DIGITAL PDL– IF DIGITAL MODULATOR AVAILABLE AND SUFFICIENTLY NARROW BAND – NO BRAINER!• ANALOG PDL– AS BW INCREASES ANALOG GAINS THE ADVANTAGE AS DIGITAL’S COST AND POWER OVERHEAD INCREASE– HAS ADVANTAGE FOR SIGNAL BW > ~ 25 MHz– SELECTION DEPENDS ON BENEFIT PROVIDED– FOR MANY APPS PERFORMANCE SIMILAR– FOR MULTI GHz/MULTI OCTAVE OPERATION ANALOG IS THE ONLY PRACTICAL OPTION (DIGITAL CANNOT EASILY ADJ NL WITH FREQ)
Slide 24
SOME RESULTS – GaN HPAs
n FOR C/I = 30 dB, ALMOST 2.5 dB MORE POWER
n AND AN INCREASE IN EFFICIENCY > 60%
n FOR C/I = 30 dB, > 7 dB MORE POWER
n AND AN INCREASE IN EFFICIENCY > 200%
Slide 25
SOME RESULTS – GaN HPAs
Slide 26
ME ARE CHANGES IN A HPA’S NONLINEARITY DUE TO PAST HISTORY OF THE INPUT SIGNAL
Vo = f(Vin, time)SOURCES OF ME
- Frequency ME- Drain/collector ME- Gate/base ME- Device related ME- Thermal ME
MEMEORY EFFECTS (ME)
Slide 27
GAIN VS. INPUT POWER IS AFFECTED BY FREQUENCY
PHASE VS. INPUT POWER IS AFFECTED BY FREQUENCY
n Standard DPD look-up tables have the same correction for every frequency
n Real PA nonlinearities do change with frequency
Slide 28
TWO KINDS OF BANDWIDTH1) STATIC BANDWIDTH - ABILITY OF LIN MAG/PHASE TRANSFER RESP TO
EQUALIZE AMP AT ALL FREQ OF INTEREST
2) DYNAMIC BANDWIDTH - ABILITY OF LIN MAG/PHASE TRANSFER RESP TO FOLLOW ENVELOPE OF SIGNALS
- MEAS WITH 2 CLOSE SPACED TONES AT ALL FREQ OF INTEREST
- MEAS WITH 2-TONE SIGNAL IN WHICH THESPACING OF THE TONES IS INCREASED
Slide 29
Slide 30
MAJOR CAUSE OF DEGRADATION --
ENVELOPE FREQUENCY Fe = FΔ/2
TRANSFER CHARACTERISTICS CHANGE WITH Fe
INABILITY OF AMPLIFIERS TO FOLLOW RAPIDLY CHANGING ENVELOPE
Slide 31
IMDS CAUSED BY THE PA NONLINEARITY SUBTRACT FROM THE RIPPLE INDUCED IMDS
Slide 32
A LOW IMPEDANCE NETWORK AT ENVELOPE FREQUENCIES ACROSS THE DRAIN AND EFFECTIVE POWER SUPPLY DECOUPLING CAN MINIMIZE ME
Slide 33
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Slide 35
n GAIN AND PHASE (TD) MUST BE MAINTAINED OVER FREQUENCY – CAN CORRECT WITH EQUALIZER
n GAIN RIPPLE A MAJOR PROBLEM – LIMITS CORRECTION
35
WB LIMITATIONS
Slide 36
n LINEARIZER DESIGNED FOR 4 TO 18 GHz GaN MMIC SSPA
n USED 2 ACTIVE FET NON-LINEAR GENERATORS, COMBINED USING 180°HYBRID MAGIC TEE BALUNS
36
WB GaN LINEARIZER
Slide 37
1 dB CP MOVED > 6 dB CLOSER TO SAT FROM 6 TO 16 GHz PHASE SHIFT REDUCED FROM > 30°TO < 10 °OVER BAND
37
WB GaN LINEARIZER
Slide 38
2-TONE CARRIER TO INTERMOD (C/I) IS A COMMON MEASURE OF
DISTORTION REDUCTION
38
WB GaN LINEARIZER
At 6, 10, & 16 GHz:C/I INCREASE OF 5-11 dB FOR OPBOs OF 5–8 dB
Slide 39
Slide 40
Slide 41
Slide 42
FOR A C/I OF 25 dB, LINEARIZATION PROVIDES ~ 5 dB MORE POWER
MOVED P1dB 7 dB CLOSER TO SAT & ∆PHASE <5°
Slide 43
n LINEARIZERS ESSENTIAL FOR BW-EFFICIENT, HIGH DATA RATE COMMUNICATIONS
n INCREASE HPA’s EFF POWER AND EFFICIENCYn DIGITAL PDL DOMINANT WHEN HPA IS USED WITH A DIGITAL MODULATOR AND SIGNAL BW NARROW ENOUGH
n ANALOG PDL GAINS THE ADVANTAGE FOR WIDEBAND APPLICATIONS
n UNDERSTANDING LIMITATIONS ENABLES BETTER HPA DESIGNS
n LINEARIZERS FOR MULTI GHz/OCTAVE AND TO > 100 GHz AVAILABLE
Slide 44
n A. Katz, “Linearization: Reducing Distortion in Power Amplifiers,” IEEE Microwave Magazine, pp. 37-49, December 2001.
n M. Franco, A. Guida, A. Katz, and P. Herczfeld, “Intermodulation Distortion Products in Radio Frequency Power Amplifiers with Digital Predistortion Linearization,” MTT-S International Microwave Symposium Digest, San Francisco, CA, June 11-16, 2006.
n A. Katz, B. Eggleston and D. McGee, “A Linear GaN UHF SSPA with Record High Efficiency,” MTT-S International Microwave Symposium Digest, Boston, MA, , pp. 769 – 772, June 7-12, 2009.
n A. Katz, M. Kubak and G. DeSalvo, “A 6 to 16 GHz Linearized GaN Power Amplifier,” MTT-S International Microwave Symposium Digest, San Francisco, CA, pp. 1364-1367, June 11-16, 2006.
n M. Franco, and et al, “Minimization of Bias-Induced Memory Effects in UHF Radio Frequency High Power Amplifiers with Broadband Signals,” 2007 IEEE Radio and Wireless Sym., Long Beach, CA, pp. 369-372, Jan. 9-11, 2007
n A. Katz, R. Gray and R. Dorval, “Truly wideband linearization,” IEEE Microwave Magazine, Vol. 10, Issue 7, Part Supplement, pp. 20-27, December 2009.
n A. Katz, and et al, “Wide/Multi-band Linearization of TWTAs Using Predistortion,” IEEE Trans. on Electron Devices, Vol. 56, pp. 959-964, May, 2009.
n A. Katz, M. Chiappetta and R. Dorval, “Predistortion Linearization to 100 GHz,” Radio and Wireless Symposium, PAWR Topical Conference Proceedings, Austin, TX, Jan. 20-23, 2013.