RFIC DESIGN ELEN 351 Lecture 4 Power Amplifier Design Dr Allen Sweet Copy right 2003 ELEN 351 1 Power Amplifier Classes Indicate Efficiency and Linearity Class A Most linear max efficiency is 50 Class AB linear max efficiency is 60 Class B More nonlinear max efficiency is 75 Class C Very nonlinear max efficiency is 85 Classes D E F Switching modes 85 95 Copy right 2003 ELEN 351 2 Linearity Metrics Scaled Linearity OIP3 P 1 dB Linear Efficiency 10 LOG OIP3 Pdc Adjacent Channel Power Ratio Main Channel average power Adjacent Channel average power Copy right 2003 ELEN 351 3 GaAs HBT Performance Expectations PAE Matched Feedback amps 45 to 65 Darlington amps 15 to 25 OIP3 P 1 dB 10 dB to 20 dB 10 LOG OIP3 Pdc 5 dB to 15 dB ACPR 50 dB to 65 dB Copy right 2003 ELEN 351 4 Matching for Maximum Gain Zl Copy right 2003 ELEN 351 5 Smith Chart Display of S11 and S22 and Zl for Maximum Pout Match for Gain Match for Power Copy right 2003 ELEN 351 6 MESFET Power Amplifier Load Line Analysis Copy right 2003 ELEN 351 7 Load Line Resistance Calculation With no Restrictions on Voltage Copy right 2003 ELEN 351 8 Load Line for a One Finger GaAs HBT Using the G P Model Bias Point Bias Point Copy right 2003 ELEN 351 9 Calculate HBT PA Load Line Resistance Based on Pout Assume the Requirement is for Pout 1 watt from a class A amplifier Assume 50 conversion efficiency and Vcc 6 0 volts Pdc 2 watts and Ic 2watts 6 volts 333 mA The number of emitter fingers is N 333 10 33 fingers Load Resistance Rl 580 33 17 5 Ohms Copy right 2003 ELEN 351 10 Pure Class A Load Line Analysis Copy right 2003 ELEN 351 11 Simulated Wave Forms for Pure Class A Operation Copy right 2003 ELEN 351 12 Simulated Pin vs Pout for Pure Class A Operation Copy right 2003 ELEN 351 13 Class AB Operation Low DC Current Copy right 2003 ELEN 351 14 Class AB Current and Voltage Wave Forms Copy right 2003 ELEN 351 15 Pin vs Pout for Class AB Operation Copy right 2003 ELEN 351 16 Load Line Analysis for Low Voltage Class A Operation Copy right 2003 ELEN 351 17 Current and Voltage Wave Forms for Low Voltage Operation Copy right 2003 ELEN 351 18 Pin vs Pout for Low Voltage Operation Copy right 2003 ELEN 351 19 Ways to Test an Amplifier s Stability Instability K factor K 1 0 is Unconditionally stable 0 K 1 0 is conditionally stable and K 0 is Unstable S11 or S22 greater than 1 0 or positive if expressed in dB s is unstable Stability circles ADS element under Simulation S parameter Palette Show Unstable Impedance Regions BE SURE TO TEST STABILITY OVER A WIDE RANGE OF FREQUENCIES Copy right 2003 ELEN 351 20 Circuit Elements which Enhance an Amplifier s Stability Parallel or Series Feedback Place a series R L network in shunt with the amplifier s input to cure low frequency instabilities Place a series R C network in shunt with the amplifier s input to cure high frequency instabilities Copy right 2003 ELEN 351 21 Amplifier Stability Analysis Demonstrating a Problem Copy right 2003 ELEN 351 22 Improved Stability after Modifying Component Values Copy right 2003 ELEN 351 23 Simulating Power Linearity and DC with ADS Harmonic Balance Use Harmonic Balance and a One Tone Frequency Source to Simulate Pin vs Pout Use Harmonic Balance and an N Tone Frequency Source to Simulate OIP3 Use DC Control Icon to Annotate DC conditions Copy right 2003 ELEN 351 24 ADS Harmonic Balance Schematic For Simulating Pin vs Pout Name output node on Schematic Vout Copy right 2003 ELEN 351 25 ADS Display Trace Expression for Pin vs Pout Choose dBm Not dB for power Copy right 2003 ELEN 351 26 ADS Harmonic Balance Schematic for Simulating OIP3 Note be sure to Name the output Node vout Copy right 2003 ELEN 351 27 ADS Display Trace for OIP3 Simulations Copy right 2003 ELEN 351 28 Types of GaAs HBT PAs Darlington Simple Inherently Stable Medium Power 15 to 25 Efficient Very Broad Bandwidth Minimum off chip components Feedback Simple High Power High Efficiency 50 to 60 Some off chip Components Required Balanced 3 dB Power Combining Inherently Good in out matches Many off chip components Push Pull 3 dB Power Combining Natural Impedance Transformation for matching Off chip Copy right 2003 ELEN 351 29 Darlington Amplifiers Simple Topology Two Transistors 4 Resistors No on chip Capacitors No on chip Inductors Flat Broadband Gain Response Extends down to D C and Rolls off at a High Corner Frequency determined by the device sizes Inherently Stable Power and OIP3 trade off with corner Frequency Device Area determines Gain and Power Gain to 20 dB P 1 db to 25 dBm OIP3 to 45 dBm but not all at once Use for Low and Medium Power Stages Copy right 2003 ELEN 351 30 Darlington Amplifier Topology OUT IN Vbe for both Transistors must be About 1 4 volts Normally Zero Ohms Copy right 2003 ELEN 351 31 Darlington Amplifier Frequency Response Copy right 2003 ELEN 351 32 Homework 3 A Darlington Amplifier with Layout Parasitic Elements Copy right 2003 ELEN 351 33 Darlington Amplifier DC Simulation Copy right 2003 ELEN 351 34 Menu Pick for DC Annotation Copy right 2003 ELEN 351 35 Blow up of Darlington Circuit R1 Input Pad Collector line Base Line Q1 Q2 Output Pad Emitter Base Line R2 R5 R3 Copy right 2003 ELEN 351 36 Darlington Amplifier Simulated Performance Peaking is caused By a transmission line From Q1 s emitter to Q2 s base Copy right 2003 ELEN 351 37 Darlington Schematic for Simulating OIP3 Copy right 2003 ELEN 351 38 Darlington OIP3 Simulation Linearity Metrics dBm OIP3 P 1 10 dB 10LOG OIP3 Pdc 5 dB Copy right 2003 ELEN 351 39 Darlington Schematic for Simulating Pin vs Pout Copy right 2003 ELEN 351 40 Simulated Pin vs Pout for the Darlington Amplifier P 1 dB Copy right 2003 ELEN 351 PAE 21 41 Darlington Amplifier Layout W 50 microns Resistors have A Resistance in Ohms equal to Their length in microns Copy right 2003 ELEN 351 42 Layout Detail 1 M1 to M2 VIA Copy right 2003 ELEN 351 43 Layout Detail 2 M1 to M2 VIAS Copy right 2003 ELEN 351 44 Feedback Amplifiers Highest Power Efficiency and Linearity Feedback promotes Stability and Suppresses Harmonics and Spurious signal Well matched over Narrow Band Segments only Output Matching is done off chip to reduce losses at the high power side of the Amplifier PAE up to 60 P 1 dB up to 32 dBm OIP3 up to 50 dBm Copy right 2003 ELEN 351 45 Feedback Amplifier Topology with Resistive Base Bias Copy right 2003 ELEN 351 46 Feedback Amplifier Topology with Current Mirror Base Bias for Improved Temp Stability Copy right 2003 ELEN 351 47 Layout of a Large A 24