Class E broadband amplifier with C-LC shunt network

Transcription

1 San Diego, CA Jan 09 CLASS E RF/MICROWAVE POWER AMPLIFIERS Class E broadband amplifier with C-LC shunt network Basic theory, simulation and prototype A. Mediano, K. Narendra 2, C. Prakash 2, I3A, University of Zaragoza, Zaragoza, Spain 2 Motorola Technology, Penang, Malaysia RWW 2009 IEEE Topical Symposium on Power Amplifiers for Wireless Communications Motivation: Class E and broadband Class E amps very interesting in modern communication systems - Large number of channels for a long period from a small-size battery. - Power amplifier is a main consumer of dc power from a battery. - Class E offers high operating efficiency near 00 % for ideal case. Class E amplifiers are narrowband by concept. - Output network tuned to one frequency. - Nominal operation if switch see a nominal impedance at fo and harmonics. - Published results for broandband operation: Grebennikov, Raab, Al-Shahrani, Gudimetla, Qin, Quach, Tat Hung, Tayrani, Everard, Pajic, etc. Design of a broadband class E UHF amplifier... - With choke in drain to supply, - With C parallel with device (or more) included in output network Bandwidth: MHz Rated power: 4W Load: 50Ω Efficiency: Pout=5W Power supply: 7.5V Harmonic spectrum: Aditional filter for harmonic rejection.

2 Class E: basics of the idea Nominal switching VDC Lchk IDC ZLOAD ψ RLOAD + fo = nfo; n=2,3,... XLOAD ir vd isw ic Co fo RLOAD nfo; n=2,3,... vr Load network Device Cout + Cext ZT ϕ Try a new output network designed to show almost ZLOAD for the complete broadband, MHz. Broadband: output network Choke! resonant to center of band ZB ZA Virtual load To absorb too much Cout for Class E To avoid DC short and/or to add new goals in design Analysis was done with similar method as Raab 76. 2

3 Broadband: equations for the design () Considering: i) the ZLOAD to show to device at fo; ii) the angle of ZLOAD to show to device (49º); iii) the slope of that angle =0 for broadband design; iv) the resonant frequency of LB-CB must be fo and v) the CA value must be a low impedance versus LA impedance. LBx( ωx, ψx, Cx, Cdx, Nratiox) := ωx 2 Cx 2 ( Nratiox. ) 75. ( tan( ψx) ) Cx tan( ψx) ( tan( ψx) ) Cx Nratiox tan( ψx) Cdx Nratiox Cdx Nratiox tan( ψx) 2 CBx( ωx, ψx, Cx, Cdx, Nratiox) 250. Cx 2 Nratiox. := 75. ( tan( ψx) ) Cx tan( ψx) ( tan( ψx) ) Cx Nratiox tan( ψx) Cdx Nratiox Cdx Nratiox tan( ψx) 2... Analysis was done with similar method as Raab 76. Broadband: equations for the design (2) ( ) tan( ψx) LAx( ωx, ψx, Cx, Cdx, Nratiox) := 7 Nratiox ωx tan( ψx) Nratiox Cx 25. tan( ψx) Cx Cdx Nratiox ( tan( ψx) ) 7. Cdx ( tan( ψx) ) 2 ( tan ψx Rx( ωx, ψx, Cx, Cdx, Nratiox).28 ( )2 + ) := Cx ωx ( ) CAx( ωx, ψx, Cx, Cdx, Nratiox) := Nratiox Cdx tan( ψx) Cdx ( tan( ψx) ) Cx tan( ψx) tan( ψx) 2 +. Analysis was done with similar method as Raab 76. 3

4 The design: using the equations Transistor RD07MVS(Mitsubishi): Nominal Ron=0.8R Cout=60pF From classical narrowband class E theory: Co = 403MHz, fo ; 470MHz Using equations: Cx := 5.5 pf fx := MHz ψx:= 49 deg ωx:= 2 π fx Cdx := 45 pf Nratiox := 0 Cd 45 pf LB 7.6 nh LA.7 nh CA 78 pf CB 7.5 pf Cx := 5.5 pf fx := MHz ψx := 49 deg ωx:= 2 π fx Cdx := 45 pf Nratiox := 0 LBx( ωx, ψx, Cx, Cdx, Nratiox) = 7.63 nh CBx( ωx, ψx, Cx, Cdx, Nratiox) = 7.462pF LAx( ωx, ψx, Cx, Cdx, Nratiox) =.702 nh Rx( ωx, ψx, Cx, Cdx, Nratiox) = 0.04 Ω CAx( ωx, ψx, Cx, Cdx, Nratiox) = pF ZLOAD( fx, Cx) = j Ω ZLOAD( fx, Cx) = Ω The design: output network simulation MHz Deg MHz Deg ZIN[] (L) Schematic Ang(ZIN[]) (R, Deg) Schematic MHz Deg MHz MHz MHz Frequency (MHz)

5 The design: block diagram FUNCTION: To help M in the switching action BIAS Vdd 7.5V Parallel capacitance of device (if bigger that optimum value for desired Pout, the excess will be included in LOAD NET). L CHOKE ZLOAD = RLOAD + jxload = ZLOAD ψ RF SOURCE DRV 50Ω INPUT MATCH M 50Ω M LOAD NETWORK LN Ro Ro OUTPUT MATCH M2 RL 50Ω FUNCTION: To generate drive signal for the input of our amplifier FUNCTION: To match 50ohm to input impedance of device FUNCTIONS: ) to show to device the nominal ZLOAD 2) to compensate the excess in Cdevice FUNCTION: The matching network is a broadband one with low pass topology to match the 50 ohms load to the Ro calculated value in previous stage.. The design: matching driver About the input matching network M... DRV INPUT MATCH M M 50Ω 50Ω 50Ω (-j3) Ω ZIN = Ω 430MHz [23pF] Broadband Lowpass response. Maximum saturated gain in PA Topology... L L2 L3 50ohms C C2 (-j3) Ω 5

6 The design: output matching Simple (low parts count) and ladder L topology for broadband. Theoretical design... Ro =6-0 Ω L C L2 C2 L3 50ohms C3 The design: simulation (time domain) 6

7 Prototype: the driver Arturo Mediano Bias Measurement with E7402A Agilent Spectrum Analyzer with tracking generator set to 0dBm, VDD=7.V (IDD=490mA), VGG=3V. A 30dB (5W) attenuator is used in the setup and corrections are included on screen. Prototype: the class E PCB CHOKE OUTPUT MATCHING INPUT MATCHING XTOR OUTPUT NETWORK 7

8 Prototype: characterization setup BIRD Rfin sensor BIRD Rfout sensor RFIN RFOUT From RF generator 0-5W driver CLASS E AMPLIFIER To 50hm load through a 30dB att Arturo Mediano Prototype: measurements Efficiency (%) 90% 80% 70% 60% 50% 40% 30% 20% 0% 0% 4,44 79,6% 8,8% 4,05 3,70 75,4% 63,6% 47,9% 3,46 3,39 49,2%,66 Eff_drain (%) PAE (%) Pout (W) Frequency (MHZ) ,0 4,5 4,0 3,5 3,0 2,5 2,0,5,0 0,5 0,0 Output power (W) 8

9 Conclusions Analytical expresions for a class E design with a C-LC output network for broadband, with choke in drain and excess in device output capacitance compensation-absortion were shown. An UHF amplifier was designed, simulated and optimized with real world components and prototype parasitics with good results. A big transistor with excess in Cout was used for the design. A prototype has been built to work in broadband. Main problems were found in the model of transistor as a switch and the output inductance of device. This exploration has lead to the conclusion that the C-LC series output branch in the Class E amplifier is an attractive solution for radios where operation over a large number of channels for a long period and from a small size battery is typical. Thanks for your attention... Dr. Arturo MEDIANO a.mediano@ieee.org 9