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Broadband Oscillator-free 0.03–1.1 THz Pulse Generation and Radiation Based on Direct Digital-to-Impulse Architecture

     Broadband 0.03–1.1 THz signal generation and radiation are demonstrated based on an oscillator-free direct digital-to-impulse architecture with a 1.9-ps full width at half maximum and 130-GHz 3-dB bandwidth (BW) (200-GHz 10-dB BW) centered at 160 GHz. The radiated pulse achieves a peak pulse effective isotropic-radiated power of 19.2 dBm and peak pulse-radiated power of 2.6 mW. An ON/OFF impulse shaping technique is introduced and implemented to suppress undesired ringing and to increase dc-to-radiated efficiency. The frequency-comb spectrum of the radiated pulse train with 5.2-GHz repetition rate is measured up to 1.1 THz. At a distance of 4 cm, the measured received SNR at 1 and 1.1 THz is 28 and 22 dB, respectively. A 1.1-THz tone is measured with a 10-dB spectral width of 2 Hz, demonstrating an extremely narrow spectral line width (two parts per trillion). Time-domain picosecond pulses are characterized using a custom femtosecondlaser-based terahertz time-domain spectroscopy system. Coherent spatial combining from two widely spaced chips is demonstrated. It is shown that the starting time of the radiated pulses is locked to the edge of the input digital trigger with a timing jitter of 270 fs. The chip is fabricated in a 130-nm SiGe BiCMOS process technology.


Time-Domain Characterization of Silicon-based Integrated Picosecond Impulse Radiator

     A direct time-domain method for the characterization of broadband silicon-based integrated radiators using a femtosecond laser-gated optoelectronic sampling technique is developed. In the proposed system, a 1550 nm femtosecond laser source is used to generate an electrical trigger signal fed to a picosecond impulse radiator, and another synchronized 1550 nm femtosecond laser source is used to gate a photoconductive detector. Technical challenges are addressed to synchronize the silicon radiators with the optoelectronic sampling system. This paper presents the details of the proposed technique and characterization of  impulses radiated by custom silicon chips.


Broadband THz Spectroscopic Imaging Based on a Fully Integrated 4×2 Digital-to-Impulse Radiating Array with a Full-Spectrum of 0.03–1.03 THz in Silicon

     This work presents a broadband THz frequency-comb spectroscopic imager based on a fully-integrated 4×2 picosecond Direct Digital-to-Impulse (D2I) radiating array. By employing a novel trigger-based beamforming architecture, the chip performs coherent spatial combining of broadband radiated pulses and achieves an SNR>1 BW of 1.03THz (at the receiver) with a pulse peak EIRP of 30dBm. Time-domain radiation is characterized using a fsec-laser-based THz sampler and a pulse width of 5.4ps is measured. Spectroscopic imaging of metal, plastic, and cellulose capsules (empty and filled) are demonstrated. This chip achieves signal generation with an available full-spectrum of 0.03-1.03THz. The 8-element single-chip array is fabricated in a 90nm SiGe BiCMOS process.


Terahertz Trace Gas Spectroscopy Based on a Fully Electronic Frequency-Comb Radiating Array in Silicon

      A GHz-repetition-rate picosecond pulse radiating array that generates and radiates a tunable frequency comb characterized between 0.03-1.03THz is used to demonstrate gas detection and broadband spectroscopy experiments. The chip consists eight radiating elements and performs coherent spatial combining, resulting in a peak pulse radiated power of 10mW and a peak pulse EIRP of 1W. Measurement of the frequency tones shows a line-width of 2Hz at THz frequencies ensuring a narrow line-width and ultra-stable frequency tone necessary for the detection of narrow absorption lines with large integration times to increase sensitivity.


Broadband Beamforming of Terahertz Pulses with a Single-Chip 4×2 Array in Silicon

     In this work, a single-chip impulse antenna array is presented that performs spatial combining of picosecond impulses radiated from eight elements. A new broadband beamforming architecture is introduced that controls the timing of impulses radiated from each antenna by delaying a trigger signal, with resolution steps of 300fsec. This method eliminates the distortive and narrowband effects of delay blocks in conventional phased arrays by separating the delay path from the information path. Frequency domain measurements are performed up to 1.03THz and array directivities of 22dBi at 0.33THz, 25dBi at 0.57THz, and 27dBi at 0.75THz are achieved. The 8-element array is fabricated in a 90nm Silicon Germanium BiCMOS process technology.


A Fully Integrated Digitally Programmable 4×4 Picosecond Digital-to-Impulse Radiating Array in 65nm Bulk CMOS

     In this work, a fully integrated 4×4 direct digital-to-impulse radiating array with a programmable delay at each element is reported. Coherent spatial combining from 16 elements is successfully demonstrated. The combined signal from 16 elements achieves a jitter of 230fsec, a pulse width of 14psec, and an EIRP of 17dBm. Each array element is equipped with an 8-bit digitally-programmable delay that provides a step resolution of 200fsec and a dynamic range of 20psec. The chip is implemented in a 65nm bulk CMOS process.


Picosecond Impulse Generator in Silicon

     This work presents a picosecond electrical pulse generator with a measured record pulse-width of 8psec and an output peak pulse power of 6mW. It is shown that the timing of the generated impulses can be locked to the edge of an input trigger with a high timing accuracy. It is also shown that the peak amplitude of the impulses can be programmed. In addition to time-domain measurements, frequency-domain spectrum is measured from DC to 75GHz. At 75GHz, the generated impulses have a line width of better than 4Hz at 20dB below peak corresponding to more than 99.8% of the tone power confined in less than 4Hz. The impulse train has a timing jitter of better than 240fsec from its input reference to the generated pulse. The chip is fabricated in a 130nm SiGe BiCMOS process.


A 9-psec Differential Lens-Less Digital-to-Impulse Radiator with a Programmable Delay Line in Silicon

    A lens-less impulse radiator is reported in this project that radiates 9-ps pulses with a peak pulse EIRP of 10dBm. The radiator employs a differential pair of inverted cone impulse antennas. The spacing between the two antennas and the substrate thickness are tuned to achieve a maximized antenna efficiency within the band of interest, avoiding loss through substrate modes in this lens-less radiator. A digitally programmable delay chip is implemented and used to control the timing of radiation by delaying the trigger signal with steps of 150fs having a large dynamic range of 400ps. This is necessary for precision coherent combining of radiators spaced at 12cm. The lens-less radiator is fabricated in a 180nm SiGe BiCMOS process and the delay line chip is fabricated in a 45nm SOI CMOS process.


An 8-psec 13dBm Peak EIRP Direct Digital-to-Impulse Radiator with an On-chip Slot Bow-tie Antenna in Silicon

      This paper reports a new method of broadband and phase-linear signal generation in the mm-wave and THz regimes based on Direct Digital-to-Impulse architecture. In this method, a DC current stores a magnetic energy in a slot bow-tie antenna and consequently, by disrupting the circulating current, the energy is radiated in the form of an electromagnetic impulse. The first step in the design process of such radiator is the impulse antenna. A slot bow-tie antenna with curved edges is used that its impulse response has a flat gain and constant group delay. The active core switching circuit used in this method is a pair of fast bipolar transistors available in a commercial a SiGe BiCMOS process. A group of digital buffers and an edge-sharpening amplifier precede the output switching stage to reduce the rise time of the input trigger from 150psec to less than 10psec and to increase its amplitude. This chip radiates impulses with pulse widths of shorter than 8psec and a peak pulse EIRP of 13dBm. It has been shown that the starting time of the radiated impulses is locked to the edge of the input trigger with an added jitter of less than 270fsec. Based on this high timing accuracy, coherent combining of radiated impulses in space from two distantly spaced radiators is performed. This experiment demonstrates that massive sparse arrays of individual impulse radiators can be used to combine impulse radiation in a 3-D point in space within an effective spatial volume of with dimensions of a few hundred microns.