A Decade Bandwidth 90 W GaN HEMT Push-Pull Power Amplifier for VHF / UHF Applications K. Krishnamurthy, J. Martin, D. Aichele, D. Runton Defense and Power Business Unit, RFMD, USA. CSICS 2011 Presentation October 19th, 2011 Session : N.4 Agenda 2 1 Motivation 2 RFMD GaN Technology overview 3 Multi-decade band PA topologies 4 45 W Unit Amplifier design and performance 5 90 W Module design and performance 6 Summary Motivation Milcom and Public Mobile Radio Amplifiers PMR Portable Radio Market Drivers • • • • • Improve battery life Multi-standards for inter-operability Wide-band architecture Improve reliability Leverage COTS components Why GaN? JTRS Radio 3 • Higher efficiency – Reduce heatsink requirements, smaller size – Increase battery life • Wide bandwidth – Replace 3 or more amplifiers with 1 amplifier – Improve engineering efficiency Power Frequency (PF2) Limit Maximum Power (Watts) 100,000.0 Th eo ret ica lL 10,000.0 1,000.0 im it f Property Si GaAs GaN Eg (eV) 1.1 1.4 3.4 vs (10 7 cm/s) 0.7 0.8 2.5 X-Band Military Radar or Ga NP ow er Th De eo vic ret es ica Th lL im eo it f ret or ica Ga lL im As it f Po or we Si rD Po evi we ces rD e vic Commercial es Communications Base Stations 100.0 10.0 1.0 Commercial Satcom Transmitters (VSAT – 1MBPS) Commercial Broadband Satcom (VSAT – 16 MBPS) Pmax 0.1 1 10 Frequency (GHz) 4 100 Eg4 v 2s F2 Power Bandwidth Limit • High power density (V, I) enables high impedance, high power density • Low pF/W enables broadband Wideband HPA’s covering multiple communication bands 5 Fo LDMOS LDMOS LDMOS Fhigh Flow QL ln() RFMD GaN HEMT Process Device Schematic Device SEM Process Details: • AlGaN/GaN HFET on 3” SiC • 0.5µm gate length • Dual field plate technology – Gate connected – Source connected • Ti / Al / Ni / Au ohmic contact • Ni / Au Gate For additional detail: Shealy et al., IEEE BCTM 2009, p146-153 6 Processed Wafer GaN Transistor Parameters 2.2 mm device 2500 Vgs: +1V to -4V Parameter Value Units 1500 Idss 800 mA/mm 1000 Id-max 900 mA/mm 500 Peak gm 225 mS/mm Vp -4 V Vbr(GD) >150 V ft 10.5 GHz fmax 16 GHz Power Density 8.4 W/mm 20 Peak Power 18.6 W 10 Peak Drain Eff 71 % Optimum load 31.4+j46.1 Ids (mA) 2000 0 0 10 20 30 40 50 60 Vds (V) 40 GMax (dB) Gain (dB) 30 |H(2,1)| (dB) 0 ft fmax [1] Class AB Bias: Vds=48V, Ids = 20 mA/mm -10 .1 7 1 10 Frequency (GHz) 100 [2] frequency = 2.14 GHz; Broadband PA topologies Topology Resistive FBRf Zo Zo Vin Vgen Zo Vout Zo Q RLC Lossy Match Zo Zo L1 Zo Vgen C1 L2 Vout Zo Q, W Ri matching Zo network Cgs ( ) Distributed Amp Cd reverse termination L Zo RF IN Cdiv L/2 Zo L/2 L Cin 8 RF OUT Advantages - lumped implementation - good S22 Disadvantages - O/P not designed for Zopt - Tuning Zload affects gain flatness and S11 - Rf Pdiss / leakage issues - Rf Layout issues - Simple / lumped design - output optimized for Zopt - Input optimized for gain flatness - Lumped circuit, so - All-pass network at input thermal design is critical implies excellent S11 - best bandwidth and gain - dissipation spread out - Zload optimization for each cell is complicated - poor efficiency - implementation feasibility issues 20 0 15 -5 10 -10 5 -15 0 -20 2.0 0.0 0.5 1.0 1.5 Output Power (dBm) 5 50 80 47 70 44 60 41 50 38 40 35 30 32 20 29 10 26 0 14 17 20 23 26 29 32 Pin (dBm) freq, GHz 9 • Uses 6.6mm device periphery • designed for 25 source and load impedance • frequency target is 30-1000MHz • Multi-chip module approach with GaAs passive die and GaN HEMT active die. • This minimizes SiC die area as the matching circuits are large at low GHz frequencies and below. • Dies are packaged in a Cu package • Performance - Vdq = 50V, Idq = 130mA - Bandwidth: 20 – 1000 MHz - Gain: 17.5±1 dB - Input return loss: < 11 dB - Output power: 50.3 W at 512 MHz - PAE: 70% at 512 MHz Gain(dB) (dB), PAE (%) Gain 25 dB(S(2,2)) dB(S(1,1)) dB(S(2,1)) 45W Amplifier Performance PA Module Topology • Two 25 matched unit amplifiers are combined together. • Broadband 45W amplifiers are first designed for operating in a 25 system. • Two such PAs are combined using a broadband 1:1 Balun at input and output to convert the differential 25 impedance to a 50system. • Gate bias feeds isolated through a resistor, and connected together. • The high-Q bias feed inductors at drain of each device are connected together. • 300 ferrite (at 100 MHz) at the drain bias feed to extend low frequency performance. 10 Balun Design • • • • • • • 11 Broadband coiled balun is formed by winding a rigid coax around a ferrite rod Coiling increases self-inductances and the ferrite improves low frequency cut-off Advances in low-loss ferrites make them suitable for GHz range A 43 material ferrite rod from Fair-Rite corp with 5mm diameter is used provides high permeability at low frequency and low loss at high frequency 50 coax with 0.22dB/ft loss, that can handle 124W at 500MHz is used The center and outer conductor are connected to unbalanced signal and • ground at one end and to the differential balanced signal at the other. The ferrite forces equal and opposing • current at the inner and outer conductor and isolates the 180º signal from the input ground at low frequency For high frequency isolation the coax length is quarter wave long at the upper cut-off frequency. This results in a 4 turn coil for the chosen ferrite diameter. Balun performance • Measured performance - Insertion loss (back-back) : 0.34 dB - Insertion loss per balun : 0.17 dB - Return loss: better than 20 dB 12 PA Module • 2 x 2 inch size • Uses 2 x 45W devices in push-pull configuration • Each device is matched to 25 at the input and drives a 25load • Drain is biased separately through a 160nH high current air coil inductor and a 300ferrite. • 25 microstrip traces with broadband capacitors for DC blocking connect the devices to the differential end of the balun. • A similar coaxial balun is used at the input to split the signal to the two devices. • The backside of the devices and PCB are soldered to the Copper carrier and mounted on an Aluminum heatsink with fins for improved thermal performance. 13 90 W Module Small Signal performance • Bandwidth: 20 – 1100 MHz • Gain: 17 – 19 dB • Input return loss: 12 dB 14 • Vdq = 50V • Idq = 265mA (class-AB) 90 W Module CW performance • Vdq = 50V, Idq = 265mA • Frequency: 100 – 1000 MHz • Gain over band: 15.1 – 16.3 dB • Output power: 82 – 107.5 W • Efficiency: 51.9 – 73.8 % 15 90 W Module CW performance • Vdq = 50V, Idq = 265mA • Frequency : 512 MHz • Pout : 104.2 W • PAE : 67.4 % • Drain efficiency : 69.4 % 16 Two Tone Linearity Performance • Vdq = 50V • Idq = 540 mA • Fc = 512 MHz • Tone spacing = 1MHz • Pout : 52 W • IMD3 : 35 dBc • Drain efficiency : 41 % 17 Summary • Emerging SDR architectures require wideband, high power amplifiers with high efficiency, compact size and low cost • GaN-on-SiC technology adoption continues for high power commercial and military applications • We’ve demonstrated a 90W, 100 – 1000 MHz, 50V GaN HEMT PA module with >51% drain efficiency over the band Output power (W) Bandwidth (MHz) Gain (dB) 82–107.5 100-1000 15.1-16.3 Supply Drain Voltage (V) Efficiency (%) 50 • Future work: - improving efficiency and linearity performance 18 51.9-73.8 Q&A Thank You