2014 2016 Linearity Enhancement for Ga N HEMT

2014 2016 Linearity Enhancement for Ga. N HEMT Amplifier using Parallel Transistors with Independent Gate Bias Control Kanika Saini 1, Amin K Ezzeddine 2, Ho C Huang 2, Sanjay Raman 1 1 Virginia Tech, Arlington, VA 2 AMCOM Communications, Gaithersburg, MD Kanika@vt. edu

Outline 2012 2016 • • Introduction and Motivation. Linearity Discussion and Simulation. Amplifier Prototype design and Measurement Results. Conclusion and Future Works. 4/12/2016 2

Outline 2012 2016 • • Introduction and Motivation. Linearity Discussion and Simulation. Amplifier Prototype design and Measurement Results. Conclusion and Future Works. 4/12/2016 3

Introduction and Motivation 2012 2016 • Ga. N HEMT’s have – high output power density – high efficiency – poor intermodulation performance. • Linearization techniques like feedforward, digital pre distortion and Cartesian feedback are quite complex to implement. • We present a simple method to linearize Ga. N HEMT at device and MMIC level, that has minimum impact on output power and efficiency. 4/12/2016 4

Outline 2012 2016 • • Introduction and Motivation. Linearity Discussion and Simulation. Amplifier Prototype design and Measurement Results. Conclusion and Future Works. 4/12/2016 5

Linearity Discussion 2012 2016 • Expression for the drain current is given for a common source transistor is given as [1] • IMD 3 can be expressed as • plays an important role in the non-linearity. 4/12/2016 [1] B. Kim, J. -S. Ko, and K. Lee, “A new linearization technique for MOSFET RF amplifier using multiple gated transistors, ” IEEE Microw. Guid. Wave Lett. , vol. 10, no. 9, pp. 371– 373, Sep. 2000. 6

Linearity Discussion Contd. 2012 2016 • Wi. N Semiconductor devices (0. 25 μm process) are biased in the region (-3 V to -2 V ), closer to pinch off. • I-V characteristics of 0. 5 mm Wi. N Semiconductor Ga. N HEMT were measured and was computed. • has a negative peak which exacerbates the nonlinearity (pink curve). 4/12/2016 7

Prior Work 2012 2016 CMOS 0. 5 μm process, Frequency = 900 MHz, Improvement in IMD 3 = 6 d. Bm @ Pout = -4. 7 d. Bm [1] B. Kim, J. -S. Ko, and K. Lee, “A new linearization technique for MOSFET RF amplifier using multiple gated transistors, ” IEEE Microwave and Guided Wave Letters, vol. 10, no. 4/12/2016 9, pp. 371– 373, Sep. 2000. 8

MATLAB Simulation 2012 2016 • A program was written in Matlab to shift in the target range of second device w. r. t first one. • Optimum solution is reached when least value for minimization function (Mf) is obtained in the target range. • This step is tried for increasing the number of devices (4 max). 4/12/2016 9

MATLAB Simulation (0. 5 mm parallel transistors) 2012 2016 • The gate bias voltage of two transistors is varied w. r. t each other with drain bias kept constant. • Vgs bias of transistor B shifted by +1 V. • Improvement in the minimization function is 60% if the Vgs 1 = -2. 5 V and Vgs 2 = -1. 5 V. A+B B B 4/12/2016 A A 10

MATLAB Simulation (0. 5 mm parallel transistors) 2012 2016 • The gate bias voltage of two transistors is varied w. r. t each other with drain bias kept constant. • Vgs bias of transistor B shifted by +1 V. • Improvement in the minimization function is 60% if the Vgs 1 = -2. 5 V and Vgs 2 = -1. 5 V. 1 mm Ga. N HEMT A+B B 4/12/2016 A 11

MATLAB Simulation ( 4 parallel transistors) 2012 2016 • Simulation was performed with four devices in parallel (Shifted in Vgs values of each). B A C D A+B+C+D 4/12/2016 12

MATLAB Simulation ( 4 parallel transistors) 2012 2016 • Simulation was performed with four devices in parallel (Shifted in Vgs values of each). 2 mm Ga. N HEMT B A C D A+B+C+D 4/12/2016 13

Comparison Table for simulation 2012 2016 Values of Vgs and Error computed Mf W/O Mf with # of Tx Shift 1 0. 187 N/A 2 0. 374 0. 1396 3 0. 5609 0. 1356 4 0. 7479 0. 0628 Vgs Percentage Value Improvement -2. 5 V N/A -1. 54 V 62. 72% -3. 43 V 75. 82% -4. 37 V 91. 60% Comparison table for the percentage improvement with Vgs bias values of various devices. 90% improvement. 4/12/2016 14

Outline 2012 2016 • • Introduction and Motivation. Linearity Discussion and Simulation. Amplifier Prototype design and Measurement Results. Conclusion and Future Works. 4/12/2016 15

Amplifier Prototype Design (2 parallel transistors) 2012 2016 A B • • 0. 8 – 1. 0 GHz, Pout = 40 d. Bm , PAE = 40% Wi. N Semiconductor 1. 25 mm Ga. N HEMT devices. 4/12/2016 16

Measurement Results (Two Tone linearity) 2012 2016 2 d. B 4 d. B • Vgs 1 = -2. 5 V, Varying Vgs bias of the second transistor by +/-1 V. • If the second device is biased at Vgs 2 = -2. 0 V, the IMD 3 improves by 4 d. Bc up to Pout of 30 d. Bm. • If the Tx 2 is biased at Vgs 2= -3. 0 V, the IMD 3 improves by 2 d. Bc for higher output power level. 4/12/2016 17

Measurement Results Contd. 2012 2016 • • Comparison of PAE with IMD 3. PAE improves with Vgs bias = -3. 0 V at output power > 30 d. Bm. 4/12/2016 18

Comparison of IMD 3 and PAE 2012 2016 Comparison of IMD 3 and PAE for different Vgs values. Gate Bias of 2 nd Tx (Vgs 2) -3. 5 V N/A IMD 3 improvement None -3. 0 V 30 – 34 d. Bm 2 d. Bc 5% -2. 5 V Baseline -- -- -2. 0 V 18 - 31 d. Bm ~ 3. 5 d. Bc -1. 5 % -1. 5 V 20 - 32 d. Bm ~ 3. 5 to 4. 3 d. Bc -1. 5 to -2% 4/12/2016 Pout (range) PAE change None 19

Outline 2012 2016 • • Introduction and Motivation. Linearity Discussion and simulation. Amplifier Prototype design and Measurement Results. Conclusion and Future Works. 4/12/2016 20

Conclusion 2012 2016 • We demonstrated a method of improving linearity by applying different gate bias voltages. • The method breaks the transistor into multiple parallel gates and apply different gate voltages to minimize the gm” over the desired region of operation • Improvement in IMD 3 by 4 d. Bc with 2% loss in PAE up to Pout of 30 dbm and 2 d. Bc with 5 % improvement in PAE at Pout > 30 dbm with two parallel gate transistors. • Simple technique and widely applicable. 4/12/2016 21

Future Work 2012 2016 • Experimental demonstrations with 4 transistors in parallel will be done. • Design of Ga. N PA MMIC using this technique at higher frequencies will be investigated. 4/12/2016 22

2012 2016 Questions? 4/12/2016 23