AN RFMD® APPLICATION NOTE SZA-2044 Biasing, VPC Selection, and Performance versus Supply Voltage RFMD Multimarket Products Group Overview The SZA-2044 is a very flexible amplifier in terms of biasing. It can run deep class AB for best efficiency and up to near class A for best linearity. The power on/off control voltages are accessible for each of the three stages and nominal currents are set via externally chosen series resistors for each stage. It can support power on voltage logic (VPC) from +2.9V to +5V by simply choosing the right resistor network for the desired quiescent current and VPC power enable voltage. This application note addresses VPC resistor selection, VPC voltage selection, associated performance tradeoffs of the various configurations over temperature, and performance over supply voltage variation. VPC Power Enable Bias Resistor Selection for Various VPC Voltage Levels Information is shown below for the recommended IQ setting of 302mA for V+=VCC =5V. Table 1 shows resistor values for VCC =5V and VPC range of 2.9V–5V. Table 2 shows resistor values for other VCC and VPC level combinations. Figure 1. Application Schematic RF MICRO DEVICES®, RFMD®, Optimum Technology Matching®, Enabling Wireless Connectivity™, PowerStar®, POLARIS™ TOTAL RADIO™ and UltimateBlue™ are trademarks of RFMD, LLC. BLUETOOTH is a trademark owned by Bluetooth SIG, Inc., U.S.A. and licensed for use by RFMD. All other trade names, trademarks and registered trademarks are the property of their respective owners. ©2006, RF Micro Devices, Inc. AN068 090319 7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical support, contact RFMD at (+1) 336-678-5570 or [email protected]. 1 of 5 SZA-2044 Biasing, VPC Selection, and Performance versus Supply Voltage Table 1 VPC =2.9V to 5.0V VCC =5.0V ICQ=302mA Stage 1 (75mA) Stage 2 (227mA) VPC R1 (Ω) R2 (Ω) R5 (Ω) 2.9 34.8 27.4 OUT 3 121 105 OUT 3.1 205 182 OUT 3.2 287 261 OUT 3.3 374 332 OUT 5 1.82K 1.10K 4.75K Table 2 ICQ=302mA Stage 1 (75mA) Stage 2 (227mA) VCC =4.9V to 5.5V VPC =2.9V to 5V 3.3 2.9 10 0 OUT 3.3 3 82.5 68.1 OUT 3.3 3.1 165 140 OUT 3.3 3.2 243 200 OUT 3.3 3.3 316 274 OUT 4.8 5 1.78K 1.10K 4.75K 4.9 2.9 33.2 24.3 OUT R1 (Ω) R2 (Ω) R5 (Ω) 4.9 3 118 100 OUT 4.9 3.1 200 178 OUT 4.9 3.2 280 255 OUT 4.9 3.3 365 332 OUT 4.9 5 1.82K 1.10K 4.75K 5 2.9 34.8 27.4 OUT 5 3 121 105 OUT 5 3.1 205 182 OUT 5 3.2 287 261 OUT 5 3.3 374 332 OUT 5 5 1.82K 1.10K 4.75K 5.1 2.9 37.4 29.4 OUT 5.1 3 124 107 OUT 5.1 3.1 210 187 OUT 5.1 3.2 294 267 OUT 5.1 3.3 374 340 OUT 5.1 5 1.82K 1.13K 4.75K 5.2 2.9 39.2 32.4 OUT 5.2 3 124 110 OUT 5.2 3.1 210 191 OUT 5.2 3.2 294 267 OUT 5.2 3.3 383 348 OUT AN068 090319 7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical support, contact RFMD at (+1) 336-678-5570 or [email protected]. 2 of 5 SZA-2044 Biasing, VPC Selection, and Performance versus Supply Voltage Table 2 5.2 5 1.82K 1.15K 4.75K 5.3 2.9 41.2 34 OUT 5.3 3 127 113 OUT 5.3 3.1 215 196 OUT OUT 5.3 3.2 301 274 5.3 3.3 383 357 OUT 5.3 5 1.82K 1.15K 4.75K 5.4 2.9 43.2 37.4 OUT 5.4 3 130 118 OUT 5.4 3.1 215 196 OUT 5.4 3.2 301 280 OUT 5.4 3.3 392 357 OUT 5.4 5 1.87K 1.15K 4.75K 5.5 2.9 46.4 39.2 OUT 5.5 3 133 121 OUT 5.5 3.1 221 200 OUT 5.5 3.2 309 280 OUT 5.5 3.3 392 365 OUT 5.5 5 1.87K 1.18K 4.75K The temperature range and required performance of the application should be considered when choosing a VPC power enable voltage. The higher VPC values have better performance over temperature because Iq varies less with temperature. Figure 2 shows Iq variation over temperature for VPC enable set voltages ranging from 2.9V to 5V. . SZA-2044 Icq vs Vpc vs Temp. 450 400 Vpc(V) Icq(mA) 350 2. 9v 3. 0v 300 3. 1v 250 3. 2v 3. 3v 200 5v 150 100 -45 -35 -25 -15 -5 5 15 25 35 45 55 65 75 85 95 Temp(C) Figure 2. SZA-2044 ICQ versus VPC versus Temperature AN068 090319 7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical support, contact RFMD at (+1) 336-678-5570 or [email protected]. 3 of 5 SZA-2044 Biasing, VPC Selection, and Performance versus Supply Voltage Another consideration is the variation in VPC enable voltage and the impact on performance. Performance is optimized when the VPC power enable is regulated and controlled. Figure 3 shows IQ versus swept VPC for the nominal cases of VPC enable=2.9V to 5V at 25°C. . SZA-2044 Icq vs swept Vpc, Constant Vcc=5V, T=25C (Icq=302mA) 0.5 0.4 Icq(A) 0.3 0.2 0.1 0 0 Vpc Config. 1 2 3 4 5 6 VPC(V) 2.9v 3.0v 3.1v 3.2v 3.3v 5v Figure 3. SZA-2044 ICQ versus Swept VPC, Constant VCC =5V, T=25°C The variation in current over temperature has impact on EVM over temperature. Figure 4 shows the EVM at POUT =22.5dBm versus temperature and VPC enable set voltage. . EVM(%) @ Pout=22.5dBm vs Vpc vs Temp, F=2.4GHz 5.0 EVM(%) 4.0 3.0 2.0 1.0 -45 -35 -25 -15 -5 5 15 25 35 45 55 65 75 85 95 Temp(C) Vpc Config. 2.9v 3v 3.3v 5v Figure 4. EVM (%) at POUT =22.5dBm versus VPC versus Temp, F=2.4GHz AN068 090319 7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical support, contact RFMD at (+1) 336-678-5570 or [email protected]. 4 of 5 SZA-2044 Biasing, VPC Selection, and Performance versus Supply Voltage The variation in VCC also has an impact on EVM. Figure 5 shows the POUT at 3% EVM versus temperature and fixed VPC voltage=5.0V. . Pout @ 3% EVM vs Vcc, F=2.4GHz, Constant Vpc=5V, Icq=302mA 25 24. 5 Pout(dBm) 24 23. 5 23 22. 5 22 21. 5 21 4.8 4.9 5 5. 1 5.2 5.3 5.4 5.5 Vcc(V) -40c -20c 0c +25c +70c +85c Figure 5. POUT at 3% EVM versus VCC, F=2.4GHz, Constant VPC =5V, ICQ=302mA AN068 090319 7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical support, contact RFMD at (+1) 336-678-5570 or [email protected]. 5 of 5