Transcript Slide 1
Final Presentation Fourth Order Very Fast Voltage Regulator for RF PA Performed by: Tomer Ben Oz Yuval Bar-Even Guided by: Shahar Porat Background • Mobile devices such as smartphones, tablet and laptop required to support wireless communication, and yet, to be able to run for a long period of time with out charging. • One of the most energy consumer in wireless module is the Power Amplifier (PA) that connected to the RF antenna. • Recent trend to reduce the total power of the PA, is by applying Envelope tracking (ET) on the PA supply level. By using this technique, the power of the PA will be change as a results of the required power for transmitting. • In order to apply high efficiency ET, there is a need to use Switching Voltage Regulator (SVR), and not Linear Voltage Regulator (LVR). • In order to reduce frequency switching noise on the PA supply, a 4th order SVR is being proposed. Project target • Develop a 4th order, high bandwidth Switching Voltage Regulator (SVR), that will be able to supply RF PA, as describe in the figure below. Project objectives • Design and stabilize a high efficiency, high BW fourth order voltage regulator. • Build a good understanding on how each component affects the stability and accuracy for the “real world” implementation of the voltage regulator. Design Requirements • Very low power consumption. • Ripples and overshoot of below 5%. • SSE of at least 2%. • Phase margin of at least 35°. • 1 [MHz] envelope tracking bandwidth. The phases of the project 1. Simple closed loop design 2. Buck converter 3. Adding a compensator 4. Fourth order system 5. Adding Equivalent Series Resistance Working environment • Simulink via Matlab • Cadence’s virtuoso. Simple closed loop design • Understanding The Principle 𝐴 A Vin A 1 lim Vout Vin Vout A Simple closed loop design • Advantages: • High Bandwidth • Low Overshoot • Simple to design • Disadvantage: • Power Consumption Buck converter - Transient I max I min I T DutyCycle T Vi VO V VDiode T DutyCycle O T (1 DutyCycle) L L VO Vi DutyCycle VDiode (1 DutyCycle) Buck Converter – Block Diagram Our Buck Simulink implementation Buck converter - RLC Vout R || C R Vin R || C sL RLCs 2 Ls R L L2 4 LCR 2 1 2 LRC LC Buck converter - PWM A Vc B DutyCycle Vc B A B VO VDD DutyCycle VDD VO VDD V B Vc DD A B A B VO VDD Vc A Vc B A B Buck converter Frequency domain Buck converter simulation Buck output for given sine wave input f switching 10 LC fsin 1 LC Buck converter – Linear Model Comparator & Driver Replaced by Constant Gain Buck converter - Open Loop Bode On the Cross Over point the phase margin is 8° So What Is A Compensator VOut (1 s R1C1 ) (1 s R2C2 ) VIn s R1C2 f Pole 0 f Zero 1 1 2 R2C2 f Zero 2 1 2 R1C1 Compensator – Bode Diagram Locating the Zeroes give the open loop system 90° boost Considerations of choosing the locations of the Zeros • The zeros should give a phase boost of at least 35° at the Cross Over. • There is a need to filter the switching frequency and it requires a large attenuation. • Increase in the difference of the zeros can move the Cross Over point 0dB. Adding The Compensator Adding The Compensator On the Cross Over point the phase margin is 5𝟏° Various Components Values Poles Location Degrees of freedom in choosing the component values Fourth order system Zeros 1 L5C5 Poles ,1 1 L5C5 Poles ,2 1 L4C4 Canceling each other Dominant in the TF Fourth order system – Bode Diagram After adding the 4th order the system is not stable – Negative phase margin Caused by adding more cross over points Adding Equivalent Series Resistance The ESR of the inductors add complexity to the Transfer Function but due to their low values one can consider only the damping they apply ESR Damping Effect As the ESR increases the damping decreases Final Components Values Name Value R1 10[MOhm ] C1 0.159[pF] R2 0.1[MOhm ] C2 5.59[pF] RL 300[m Ohm] L4 10[nH] C4 25.4[nF] L5 1[uH ] C5 2.56[ uF] Final System – Step Response Settling time < 1[uS] OverShoot < 2% Working Frequency – 1[MHz] Phase Margin - 53° Preparing for Part B • Achieving a good understanding of the affects of each component to the system for: – Stability – Settling time – Sensitivity Questions?