Ka-Band and W-Band Millimeter-Wave Wideband Linear Power Amplifier Integrated Circuits at 30 GHz and 90 GHz with Greater Than 100 mW Output Powers in Commercially-Available 0.12 um Silicon Germanium HBT Technology

Abstract

This dissertation presents several fully-integrated power amplifiers (PAs) within Ka-band (26.5-40 GHz) and W-band (75-110 GHz) with >100 mW output powers in commercially-available 0.12 um silicon germanium HBT-transistor technology (ft = 200 GHz, BVCEO = 1.8 V).

Linear PAs are by far the highest power-consuming component in wireless communication circuits. As wireless standards push into millimeter-wave frequencies for high data rates, challenges created by point-to-point propagation require transceiver phased arrays for antenna-beam steering to maintain optimal channel links. Integration of high-output-power, linear silicon PAs is key in enabling compact and efficient transmitter arrays.

Linear power amplification is especially difficult in silicon at millimeter-wave frequencies because limited transistor gains, low transistor breakdown voltages, and high-loss, high-parasitic passive-circuit components typically result in low output powers and poor power efficiencies. Moreover, at 90-100 GHz, integrated-circuit PAs are sensitive to process skews and HBT modeling errors, as transistor model-to-hardware correlations degrade after 60 GHz.

These SiGe PAs demonstrate record Class-A/AB linear output powers by pushing limits of voltage, power, and frequency while maintaining reliability-aware design.

To overcome voltage limitations of impact ionization, base-ballasting techniques using the lowest reported HBT base-biasing resistance of 20 ohms push operational collector voltages well above the native BVCEO. Additional novel inverted microstrip quarter-wave transmission-line structures, created below the RF global ground plane and terminated by resonant MIM capacitors, present the necessary high-impedance at the fundamental frequency and Class AB harmonic terminations to the HBT base terminal.

This is the first SiGe work to pack unit-cell SiGe HBT transistors at maximum density in 2-D arrays to synthesize large power transistors, circumventing needs for transistor-level power splitting and power combining at W-band. Measured data is used to model thermal coupling and provide custom HBT thermal impedance models for stability.

Resonant capacitor structures are used throughout the 3-stage PA to provide ultra-compact, low-impedance RF references and to synthesize, along with short transmission lines, very low values of DC-blocked, shunt inductance required for interstage power matching of large power HBTs.

Performance impacts from HBT-modeling errors at high frequencies and foundry-process skews are mitigated using a unit-cell design approach throughout the PA, from device level to system level. Identical or similar-characteristic components are used throughout the PA as unit cells: transistors, matching-network capacitors, resonant capacitors, resistors, transmission lines, bias circuits, and matching-network topologies. Additionally, fine bias-adjustment provisions for each gain stage allow tuning of critical DC operating points as collector voltages are pushed higher.

For integration into arrays, the designs integrate wideband capacitor-filtering arrays for stability and follow reliability guidelines for 100,000 power-on-hours operation at 100 C. A single Ka-band chip is tested for >1000 hours and a W-band chip for >500 hours with no measurable performance degradation.

The W-band 90-GHz power amplifier achieves a maximum saturated output power of 19.9 dBm (98 mW), 14.6 dB gain with 20% fractional 3-dB bandwidth from 79-97 GHz, and peak power-added efficiency (PAE) of 15.4%. The Ka-band 33-GHz power amplifier achieves a maxmium saturated output power of 24.2 dBm (260 mW), 14.6 dB gain with 55% fractional 3dB-bandwidth from 20.5-36 GHz, and peak PAE of 22.3%.

In an extended collaboration, the W-band PA has been successfully integrated within a 3x3 SiGe transmit array using quasi-optical free-space combining techniques to achieve 3.2 watts EIRP, the highest reported power at 90-98 GHz in SiGe technology.