This oscillator uses a single-emitter 0.3-μm InP heterojunction bipolar transistor (HBT) device with maximum frequency of oscillation (fmax) greater than 500 GHz. Due to high conductor and substrate losses at submillimeter-wave frequencies, a primary challenge is to efficiently use the intrinsic device gain. This was done by using a suitable transmission-line media and circuit topology. The passive components of the oscillator are realized in a two-metal process with benzocyclobutene (BCB) used as the primary transmission line dielectric. The circuit was designed using microstrip transmission lines.
The oscillator is implemented in a common-base topology due to its inherent instability, and the design includes an on-chip resonator, output-matching circuitry, and an injection-locking port, the port being used to demonstrate the injection-locking principle. A free-running frequency of 311.6 GHz has been measured by down-converting the signal. Additionally, injection locking has been successfully demonstrated with up to 17.8 dB of injection-locking gain. The injection-locking reference signal is generated using a 2–20 GHz frequency synthesizer, followed by a doubler, active tripler, a W-band amplifier, and then a passive tripler. Therefore, the source frequency is multiplied 18 times to obtain a signal above 300 GHz that can be used to injection lock the oscillator. Measurement shows that injection locking has improved the phase noise of the oscillator and can be also used for synchronizing a series of oscillators.
A signal conductor is implemented near the BCP-InP interface and the topside of the BCB layer is fully metallized as a signal ground. Because the fields are primarily constrained in the lower permittivity BCB region, this type of transmission line is referred to as an inverted microstrip. In addition, both common-emitter and common-base circuits were investigated to determine optimum topology for oscillator design. The common-base topology required smaller amount of feedback than the common-emitter design, therefore preserving device gain, and was chosen for the oscillator design.
The submillimeter-wave region offers several advantages for sensors and communication systems, such as high resolution and all-weather imaging due to the short-wavelength, and improved communication speeds by access to greater frequency bandwidth. This oscillator circuit is a prototype of the first HBT oscillator operating above 300 GHz. Additional development is necessary to increase the output power of the circuit for radar and imaging applications.
This work was done by Todd Gaier, King Man Fung, and Lorene Samoska of Caltech and Vesna Radisic, Donald Sawdai, Dennis Scott, and W.R. Deal of Northrop Grumman Corporation for NASA’s Jet Propulsion Laboratory. This work was partially supported by the DARPA SWIFT Program and Army Research Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-44968
This Brief includes a Technical Support Package (TSP).
A 311-GHz Fundamental Oscillator Using InP HBT Technology
(reference NPO-44968) is currently available for download from the TSP library.
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Overview
The document discusses the development of a 311-GHz fundamental oscillator using InP HBT (Heterojunction Bipolar Transistor) technology, marking a significant advancement in high-frequency oscillator design. This work, part of NASA's Technical Support Package NPO-44968, highlights the oscillator's potential applications in aerospace and other fields requiring high-frequency signal generation.
Traditionally, fundamental oscillators are favored for their simplicity and ease of injection locking, provided the device technology can support high maximum frequencies of oscillation (fmax). While high electron mobility transistor (HEMT) technology has achieved fundamental oscillators up to 213 GHz, HBT technology is preferred for its lower 1/f noise characteristics, making it more suitable for oscillator applications.
The oscillator described in the document was developed by colleagues at Northrop Grumman Corporation (NGC) and operates at a frequency of 311.6 GHz, which is the highest frequency achieved with HBT technology to date. The design utilizes a single-emitter 0.3 μm x 15 μm InP HBT device, which has an fmax exceeding 500 GHz. The oscillator's passive components are fabricated using a two-metal process, with benzocyclobutene (BCB) serving as the primary dielectric for transmission lines. The circuit employs microstrip transmission lines and is implemented in a common base topology, which is known for its inherent instability.
Key features of the oscillator include an on-chip resonator, output matching circuitry, and an injection locking port. The design has successfully demonstrated injection locking with gains of up to 17.8 dB. The document also includes a spectrum analysis of the free-running and injection-locked signals, which were down-converted using a subharmonic mixer.
This oscillator represents a novel contribution to the field of sub-millimeter wave technology, being the first fundamental HBT oscillator to operate above 300 GHz. The research was partially supported by the DARPA SWIFT Program and the Army Research Laboratory, indicating its relevance to advanced military and aerospace applications.
Overall, the document emphasizes the significance of this technological advancement, showcasing the potential for further developments in high-frequency oscillators that could benefit various scientific and commercial applications.
