M. Mahdi Assefzadeh

An 8-psec 13dBm peak EIRP digital-to-impulse radiator with an on-chip slot bow-tie antenna in silicon

In this paper, a direct digital-to-impulse transmitter is implemented that radiates impulses with EIRP of 13dBm and a record pulse-width of shorter than 8psec. It is shown that the starting time of the radiated impulses can be locked to the edge of the input trigger with a high timing accuracy. It is demonstrated that two widely spaced chips can generate coherent impulses in space with timing jitter of better than 270fsec. It is also shown that the frequency stability of the radiated impulses is better than 10Hz at 220GHz. 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

In this paper, a lens-less digital-to-impulse radiator is implemented that radiates impulses with EIRP of 10dBm and a record pulse-width of shorter than 9psec using an on-chip differential inverted cone antenna. It is shown that the starting time of the radiated impulses can be locked to the edge of the input trigger with high timing accuracy. A digitally programmable delay line is implemented and used at the input of the radiator. The delay line has a resolution step of 150fs and a dynamic range of 400ps. It is shown that by programming the delay line, the starting time of the radiated impulses in the air can be controlled.

Terahertz trace gas spectroscopy based on a fully-electronic frequency-comb radiating array in silicon

A silicon integrated circuit is reported for radiating picosecond pulses with tunable repetition rate, covering frequencies from 30 GHz to 1.03 THz. This source is used in a gas spectroscopy setup to measure the absorption lines of ammonia and water in the terahertz region.

A Nonlinear Q-Switching Impedance Technique for Picosecond Pulse Radiation in Silicon

This paper presents a nonlinear Q-switching impedance (NLQSI) technique for picosecond pulse radiation in silicon. A prototype chip is designed with four NLQSI-based impulse generation channels, which can produce picosecond pulses with a reconfigurable amplitude. An on-chip impulse-coupling scheme combines the outputs from four channels and delivers the combined signal to an on-chip antenna. In addition, an asynchronous optical-sampling measurement system is used to characterize the radiated picosecond pulses in the time domain. The prototype chip can radiate 4-ps pulses with an SNR > 1 bandwidth of 161 GHz. Furthermore, pulse amplitude modulation is experimentally demonstrated. The prototype chip is fabricated in a 130-nm SiGe BiCMOS process technology with a die area of 1 mm2.

Broadband THz spectroscopic imaging based on a fully-integrated 4×2 Digital-to-Impulse radiating array with a full-spectrum of 0.03–1.03THz in silicon

This paper 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.

Gone in a Picosecond: Techniques for the Generation and Detection of Picosecond Pulses and Their Applications

The technology for generating and detecting electromagnetic waves has evolved significantly over the last 120 years. In the early 1890s, Guglielmo Marconi used a spark-gap transmitter to build a wireless telegraphy system. In his design, he charged a capacitor to a high dc voltage and connected it to a parallel combination of an inductor, a second capacitor, and an antenna through an air gap. In this configuration, when the dc voltage of the first capacitor reaches the breakdown voltage of the gap, the air in the gap ionizes and reduces the resistance across the gap. This results in a large step voltage applied to the parallel combination of the inductor, second capacitor, and the antenna and converts the dc energy stored in the first capacitor to a damped oscillation at a low megahertz range that is radiated from the antenna. Marconi?s design used the spark gap as a fast high-voltage switch. The technology for generating electromagnetic waves then evolved further with the invention of vacuum tubes in the mid-1920s. Vacuum tubes enabled oscillatory signals to be amplified in the megahertz range and provided enough bandwidth for transferring audio signals.

Broadband Oscillator-Free 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 femtosecond-laser-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.

Picosecond digital-to-impulse generator in Silicon

In this paper, a direct digital-to-impulse architecture is presented that generates impulses with a measured record pulse-width of shorter than 8psec and an output peak 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 frequency stability of better than 4Hz at 20dB below peak. The impulse train also achieves a timing jitter of better than 240fsec. The chip is fabricated in a 130nm SiGe BiCMOS process.

A fully-integrated digitally-programmable 4×4 picosecond digital-to-impulse radiating array in 65nm bulk CMOS

In this paper, a fully-integrated 4×4 digital-toimpulse 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.

Time-Domain Characterization of Silicon-Based Integrated Picosecond Impulse Radiators

A direct time-domain characterization of silicon-based integrated picosecond impulse 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 4.8 ps impulses radiated by a custom silicon chip.