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 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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This article first appeared in the May, 2010 issue of NASA Tech Briefs Magazine.

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