DC/DC Converter Controlled Power Amplifier module for WCDMA Applications Jongsoo Lee, Eddie Spears, Jeff Potts Outline • Motivation for DC/DC Converter PA • DC/DC converter • Power Detector • Integrated Power Amplifier with DC/DC converter • Results • Conclusions 2 Improve efficiency of PA at back off Urban Current*Probability Vcc=3.2Volts, Frequency=1.88GHz, Switch Point=20 dBm 0.3 Adaptive bias control is a lab experiment and is manually adjusted to maintain -48dBc ACPR Current(mA)*Probability 0.25 0.2 0.15 0.1 0.05 0 -50 -40 -30 -20 -10 0 10 20 Power Output (dBm) Load Switch RF6000-3 RF6100-3 RF6100-3 ABC PAA Load Switch ABC PA Efficiency at Back Off - Parallel Amplifier • • • • Two different sizes of PAs for high and low power At back-off, only small size of PA works Chain match at the output is important Good performance / hard for multi-band Ref : J. Kim et al, “An MMIC smart power amplifier of 21% PAE at 16dBm power level for W-CDMA mobile terminals,” GaAs IC Symposium2002 PA Efficiency at Back Off - Doherty Amplifier • • • • Main (smaller size) and Peaking amplifier At low power, only main amp works Load pulling effect to give lower load line at peak output power Good performance but bulky size for mobile applications PA Efficiency at back off - DC/DC Converter PA RF Input PA Efficiency at back off - DC/DC Converter PA • Good things • No need for dedicated matching at output • typical output matching network is used • good PAE at back off power • suitable for multi-band applications • better performance with buck-booster converter over load mismatch (VSWR variation) • and so on… Efficiency of PA at back off - DC/DC Converter PA • Bad things • Need two different dies (Si & GaAs) • Difficult to achieve module size smaller than • 4x4 mm2 • Requires big inductor and capacitor (added cost) • Noise from DC/DC converter • and so on… DC/DC converter & Power detector DC/DC Converter DCR < 0.1 RFMD DC/DC converter (0.5m CMOS) DC/DC Converter – measured RLOAD = 5 4 100 90 3.5 80 3 Vout (V) 2.5 60 2 50 Vout - 5 Ohms 1.5 40 30 Efficiency - 5 Ohms 1 20 0.5 10 0 0 Vset (V) Efficiency (%) 70 Power Detector Design VBIAS1 VBIAS2 R4 VBIAS4 R3 INPUT (RF) VOUT1 Q1 R1 R8 R7 C2 Q5 C1 Q4 Q3 ICS4 VBIAS3 VOUT2 Q2 R2 Attenuator R5 ICS1 R6 C3 R9 ICS2 ICS3 Decision Circuit • Non-diode detector – high speed & wide band • Temperature compensated current source • Maintain minimum VSET to DC/DC OUTPUT (DC) Power Detector Design VBAT = 3.4V Voltage drop due to DCR of inductor 3.5 Power Detector 3 DC/DC Output Voltage (V) 2.5 VCC2MIN = 1.2V for linearity requirement 2 1.5 1 0.5 0 0 5 10 15 20 Output Power (dBm) 25 30 Integrated PA Module with DC/DC Converter WCDMA PA from RFMD • RF5198 WCDMA PA (3x3mm2) • 1920MHz ~ 1980MHz • 3V WCDMA region 1 • 27.5dBm peak output power • 43% PAE at Pout • -40dBc ACPR @ 5MHz • Integrated Power detector (diode type) Power Amplifier with DC/DC Converter VCBIAS VREG RFIN RFOUT VBAT Cout DC/DC Converter (4.7 F) Output Lout (1.5 H) • Laminate size : 6x6 mm2 • 3D EM simulation • Eval board : Rogers • Include wire bonding effect • Lout =1.5H (0.078 DCR) • 4.7F 0603 cap • used for co-simulation in ADS Power Amplifier with DC/DC Converter 45 0 PAE 35 Room Temp 1950MHz 3GPP Signal ACPR (5MHz offset) -10 30 -20 25 -30 20 15 -40 10 -50 Pout = 16dBm 5 0 -60 0 5 10 15 Pout (dBm) 20 25 30 ACPR (dBc) 40 Gain (dB) / PAE (%) Pout = 27.5dBm Gain Power Amplifier with DC/DC Converter 45 40 DC/DC Converter Control 35 Fixed 3.4V Supply Voltage PAE (%) 30 Room Temp 1950MHz 3GPP Signal 25 16.8% @ 16dBm 20 15 10 8.6% @ 16dBm 5 0 0 5 10 15 Pout (dBm) 20 25 30 Power Amplifier with DC/DC Converter 600 DC/DC Converter Control Total Current (mA) 500 Fixed Supply Voltage 400 Room Temp 1950MHz 3GPP Signal 300 200 136.6mA @ 16dBm 100 70.7mA @ 16dBm 0 0 5 10 15 Pout (dBm) 20 19 25 30 Power Amplifier with DC/DC Converter -120 -123dBm/Hz 322KHz RxNP (dBm/Hz) -125 2.5MHz Room Temp 1950MHz 3GPP Signal -130 -135dBm/Hz -135 -140 -145 RBW = 30KHz -150 0 5 10 15 20 Pout (dBm) 25 30 35 Conclusion • Integrated PA module with DC/DC converter is demonstrated. • Overall PA module size is 6x6mm2. • Closed loop type of power detector is presented. • DC/DC buck converter controls VCC2 of PA. • PAE has been improved from 8.6% to 16.8% @ 16dBm. • PAE at peak power is 40%. • ACPR @ 27.5dBm is -39dBc at 5MHz offset. • Receive band noise is reduced to -135dBm/Hz.