High efficiency power amplifiers for RF and Microwaves. Grupo de Ingeniería de Radio

Transcription

1 High efficiency power amplifiers for RF and Microwaves. Grupo de Ingeniería de Radio

2 INDEX 1. INTRODUCTION. 2. WIDEBAND CLASS-E HF POWER AMPLIFIER. 3. WIDEBAND VHF CLASS-E AMPLIFIER. 4. S and L BAND HEPAs BASED ON GaN TECH. 5. CONCLUSION. 2

3 INTRODUCTION. Communicatton circuits usually exhibit low power efficiency. Efficiencies as low as 10% are usual in communications hardware. These low efficiency figures cause important technical problems: high power consumption, low battery life, bulky cooling systems, etc. Comunication circuits are inneficient because they use low efficiency power amplifiers (PAs) in their amplification line-up. Several techniques have been proposed to improve the efficiency of PAs, however they have not benn extensively used. 3

4 INTRODUCTION. High efficiency power amplifiers use Amplification classes transistors in switch mode, but switching operation is difficultat RF & MW. High efficiency switch-mode power amplifiers are nonlinear but nowadays communicattion services require lineal amplification => challenging linearization techniques, The high efficiency amplification problem requires a complex solution combining: high frequency electronics + power electronics + solid state technology + digital signal processing. A, AB, B: No switching D, E, F: switching Ƞ: LIN: Ƞ: LIN: 4

5 WIDEBAND CLASS-E HF POWER AMPLIFIER. 5

6 WIDEBAND CLASS-E HF POWER AMPLIFIER. Load impedance synthesis concept is specially useful for switchmode power amplifier design at RF & MW. The load required to operate into Class-E by this transistor was shynthesized over a one octave bandwidth The driver of this amplifier was also designed according to the load synthesis technique. The target was to produce proper waveforms at he gate of the power transistor (3 db gain imrpovement). The amplifier exibited 60% fractional bandwith, 90% peak efficiency and 50W poeak power. 6

7 WIDEBAND CLASS-E HF POWER AMPLIFIER. AMPLIFIER MEASURED PERFORMANCE 6 MHz 7 MHz 8 MHz 2f 0 f 0 12 db 20 db 25 db 3f 0 f 0 32 db 42 db 57 db Harmonic rejection 7

8 WIDEBAND CLASS-E HF POWER AMPLIFIER. This PA is completely nonlinear => only useful to amplify constant enevelope communication signals: FM, FSK, GSM, etc, Modern broadband communication services (WCDMA, DVB, WiFi, etc.) use very complex non constant envelopes. Switchomde amplifers (such as this one) must be linearized to be used with new services. Envelope Elimination and restoration (EER) and Envelope Tracking (ET) are some of the most effective linearization techniques for switchmode amplifiers. 8

9 WIDEBAND CLASS-E HF POWER AMPLIFIER. ET (Envelope Tracking) EER (Envelope Elimination Restoration) Efficiency is improved powering a LINEAR amplifer with an aproximate replica (sligthly higher) of the amplified signal envelope. A NONLINEAR amplifier is powered and simultaneously amplitude modulated by the envelope of the amplified signal. 9

10 WIDEBAND CLASS-E HF POWER AMPLIFIER. EER LINEARIZATION PERFORMANCE (WITHOUT PREDISTORTION) Potencia (dbm) Average Power Potencia DC Frecuencia (MHz) Potencia salida Rendimiento (%) Drain Efficiency Frecuencia (MHz) C/I (db) Frecuencia (MHz) 10

11 WIDEBAND VHF CLASS-E AMPLIFIER. 11

12 WIDEBAND VHF CLASS-E AMPLIFIER. This amplifier was esigned upon the load impedance shynthesis technique. A Silicon LDMOS transistor was chosen to build it. The relatively high output power of this amplifier combined with a relatively low drain voltage yielded a low and difficult to shynthesize load impedance. The parasitics of the package made the design even more difficult. A special high frequency transformer was designed to overcome this problem. The amplifier exhibited a 40% fractional bandwidth, 90% peak efficiency and 145 W peak output power. 12

13 WIDEBAND VHF CLASS-E AMPLIFIER. AMPLIFIER PERFORMANCE Gain and harmonic rejection Frequency (MHz) I DC 28V V f harmonic rejection (dbc)

14 WIDEBAND VHF CLASS-E AMPLIFIER. LINEARIZATION BY MEANS OF EER TECHNIQUE AND PREDISTORTION 14

15 WIDEBAND VHF CLASS-E AMPLIFIER. LINEARIZATION RESULTS, TWO TONES TEST. 88 MHz 100 MHz 114 MHz Carrier frequency (MHz) Without predistortion IMD3 (dbc) With predistorstion Improvement (db)

16 WIDEBAND VHF CLASS-E AMPLIFIER. OFDM LINEARITY 512 carriers --- Without predistortion --- With predistortion --- Feedthrough 2048 portadoras --- Without predistortion --- With predistortion --- Feedthrough 16

17 WIDEBAND VHF CLASS-E AMPLIFIER. EFFICIENCY COMPARATIVE AGAINST NON SWITCHMODE AMPLIFIERS 17

18 S and L BAND HEPAs BASED ON GaN TECH. 18

19 S and L BAND HEPAs BASED ON GaN TECH. GaN advantages at RF and MW GaN High Breakdown Voltage High Power Density Low Capacitances High Load impedance Compact design High efficiency capability at MW 19

20 S and L BAND HEPAs BASED ON GaN TECH. AMPLIFIER ARCHITECTURE IN OUT DRIVER NPTB00004 SOIC-8 4W@ 28V μ = 70% G = 18 db Subopt. Class-E HEPA RF3931 Flanged - ceramic 30W@ 48V μ = 75% G = 14 db F -1, B, B-E Linealización de amplificadores de alto rendimiento mediante EER 20

21 S and L BAND HEPAs BASED ON GaN TECH. Designed upon the load impedance shynthesis technique. GaN HEMTs solid state devices. Non linear HB simulation. Measuring waveforms is impossible => simulation + load impedance measurements. AMPLIFIER DESIGN Pacakaged devices used (no packaged in near future). The package parasitics preclude correct implementation of some amplification classes. Load-pull technique used to test and trim the amplifier both simulated an real. Linealización de amplificadores de alto rendimiento mediante EER 21

22 S and L BAND HEPAs BASED ON GaN TECH. LOAD-PULL SIMULATION Linealización de amplificadores de alto rendimiento mediante EER 22

23 CONCLUSION. 1. High efficiency power amplifiers (HEPAs) have been researched for one century but only recent advances in solid state technology, circuit theory and DSP have made it possible in a practical way. 2. At this moment there are HEPAs examples in scientific literature from HF to W bands exhibiting effiencies ranging from 90% to 20%. 3. Linearity is an extra requirement for modern HEPAs that demnads the combination of RF electronics, power electronics and DSP knowledge. 4. Three examples of HEPAs have been shown from HF to S band. They were designed to be part of linear HEPAs for modern digital communication services. Linealización de amplificadores de alto rendimiento mediante EER 23