Robert A. Marsland

130 GHz GaAs monolithic integrated circuit sampling head

We have fabricated a GaAs diode sampling head which has a bandwidth of 130 GHz, which is a five times improvement over previous room‐temperature designs. This speed is attained with a monolithic sampling head design integrated with two nonlinear transmission lines which serve as the strobe pulse and test signal generators. A 4 ps transition time has been measured with the sampler. We have also measured sinusoidal waveforms to 120 GHz.

Hyperabrupt‐doped GaAs nonlinear transmission line for picosecond shock‐wave generation

Voltage waveforms with 6 V amplitude and 1.6 ps fall time were generated by voltage shock‐wave formation on a hyperabrupt‐doped Schottky diode monolithic GaAs nonlinear transmission line.

Generation of 3.5-ps fall-time shock waves on a monolithic GaAs nonlinear transmission line

It is shown that nonlinear wave propagation on a monolithic GaAs nonlinear transmission line can form shock waves with fall time as short as 3.5 ps. An output fall time of 4.3 ps was measured for a single line driven at 15 GHz (20-ps fall time) while a cascade of two lines driven at 8 GHz (37-ps fall time) produced a 2-V wavefront with 3.5-ps fall time.<<ETX>>

100 GHz GaAs MMIC sampling head

A room-temperature GaAs diode sampling head was fabricated which has an estimated bandwidth of 130 GHz. This speed is attained with a monolithic sampling bridge design which allows integration with a nonlinear transmission line (NLTL) strobe pulse generator on the same GaAs IC. The 4-ps falltime of the test NLTL measured by the diode sampler is shown. The sampler is within 0.5% of linearity from 0 to 0.4 V. The voltage conversion loss is less than 5% at 5 GHz while the power conversion loss is 43 dB due to the relatively high impedance of the equivalent time output. The minimum detectable voltage is 90 nV/ square root Hz. This sampling head IC, when packaged in a coplanar probe, will allow on-wafer measurements at frequencies in excess of 100 GHz.<<ETX>>

Long wavelength In/sub 0.53/Ga/sub 0.47/As photodetectors on GaAs with a thin super lattice buffer

In/sub 0.53/Ga/sub 0.47/As-based, high speed long wavelength photodetectors have been demonstrated on GaAs substrates with a thin In/sub 0.52/Al/sub 0.48/As/AlAs super lattice buffer of 500 /spl Aring/. The photodetector epitaxial material was grown selectively by solid-source Molecular Beam Epitaxy and fabricated by conventional GaAs MMIC processing. Photoresponsivity of over 0.3 A/W has been achieved for strain relaxed In/sub 0.53/Ga/sub 0.47/As photodetectors fabricated on GaAs substrates, with frequency responses measured up to 50 GHz. The successful demonstration of long wavelength photodetectors with strain-relaxed In/sub 0.53/Ga/sub 0.47/As on GaAs substrates, allows long wavelength optoelectronics or OEICs to take full advantages of the well established GaAs MMIC technology.<<ETX>>

Picosecond Pulse Generation Circuits Using a GaAs Nonlinear Transmission Line

Circuits for generation picosecond step and pulse signals have many applications in wide bandwidth time-domain and microwave instrumentation. The silicon step-recovery diode is widely used in sampling oscilloscopes and network analyzers for gating sampling diodes but has limited utility in optoelectronic and ultrafast applications due to its relatively slow speed (30–40 ps). Conversely, photodiodes and photoconductors produce much narrower electrical pulses [1,2] but the real pulse generator is a femtosecond or picosecond mode-locked laser. Using only RF drive, we have measured a 6 V, 1.8 ps falltime step output as well as a 2.4 V, 4.4 ps full width at half maximum (FWHM) pulse output from monolithic GaAs nonlinear transmission line (NLTL) circuits.

Picosecond shock-wave generation on a GaAs nonlinear transmission line

A 3.5-ps falltime shock-wave signal has been generated on a nonlinear transmission line (NLTL). In this circuit a high-impedance transmission line is periodically loaded by Schottky varactor diodes, producing a synthetic transmission line with a voltage-dependent propagation velocity. As a negative-going input voltage transition propagates along the line, the falltime first decreases linearly with distance. As it decreases, dispersion arising from the Bragg periodic-line cutoff frequency and the varactor cutoff frequency competes with the compression arising from the voltage-dependent propagation velocity. A final limited falltime is reached at which the falltime compression per line section equals the falltime broadening per section, so that the resulting shockwave propagates unchanged. A full-scale NLTL design had 50 fF-diodes spaced 160 mu m apart. In a half-scale design, 25-fF diodes were spaced by 80 mu m. Nonlinear circuit simulations using SPICE indicate that the full-scale NLTL has a limiting falltime of 4.7 ps, while the half-scale line will compress to 2.7-ps falltime. A mixed design combined the full- and half-scale structure to utilize the lower minimum falltime of the half-scaled line after reaching the minimum falltime of the lower loss full-scale structure. >