A tutorial review on the modulation-doped field-effect transistor (MODFET) and its application to ultra-low-noise, medium-power, and ultra-wide-band traveling-wave amplifiers as well as ultra-high-speed digital logic circuits is presented. It is believed that with further advances in material growth and device scaling significant improvements in cutoff frequencies, switching speed, noise, and power will be achieved in the near future. >

Ultra-high speed modulation-doped field-effect transistors: a tutorial review

A dynamic termination circuit is disclosed that has a plurality of parallel termination elements that respond successively to a signal transition and which are selectively enabled and disabled to provide a desired impedance match with a transmission line Each termination element includes a first dynamic resistive path between a voltage supply line and that termination element's output and a second dynamic resistive path between the termination element output and ground, both resistive paths including field-effect transistors whose control gates are responsive to a signal received from the transmission line via an input to the circuit For successive response, a series of delay elements are provided between the circuit input and the respective termination circuit elements For selective enablement, logic gates connected between the termination element inputs and the field-effect transistor control gates have enable inputs receiving user-programmable enable signals for the respective termination elements In addition to the impedance provided by the main dynamic resistive paths to voltage supply and ground, at least one of the termination elements may have supplemental dynamic resistive paths in parallel with the main paths and responsive to a TRIM bit to allow adjustment of the actual impedance to manufacturing tolerances

Programmable dynamic line-termination circuit

Optical logic gates are constructed from Mach-Zehnder interferometer (MZI) optical circuits. A multi-mode interference (MMI) splitter divides a continuous-wave input into two branches of the interferometer. Each branch has a semiconductor optical amplifier (SOA). When a logic input having a logic-high power level is applied to one of the SOA's, cross-phase modulation occurs in the SOA. The phase shift increases through the SOA. The branch coupled to the logic input has a relative phase shift of π compared with the other branch. When two branches with the π phase difference are combined, destructive interference occurs, producing a logic low. An MMI combiner or an equivalent phase shifter is used to combine the two branches. The MMI splitter adds a phase shift of π/2 to the upper branch but not to the lower branch, while the MMI combiner also adds π/2 shifts.

All optical logic using cross-phase modulation amplifiers and mach-zehnder interferometers with phase-shift devices

A method of photonic analog-to-digital conversion including the steps of using an analog signal to modulate a laser, splitting the modulated optical output into 2 N paths, attenuating the different paths along a gradient, then splitting each path again and recombining with an adjacent path in such a way that only one path has significant energy. An implementation architecture is also provided which includes a laser source, a modulator for modulating the laser source in accordance with an analog input signal, a first splitter section for splitting the modulated optical output into 2 N paths, and for attenuating the different paths along a gradient, an interferometer section for splitting each path again and for recombining the signals in such a way that only one path has significant energy, and a decoder section for outputting a digital word corresponding to the analog input signal.

Photonic analog-to-digital converter

An optically sampling device optically samples an optical analog signal using a sampled signal having a predetermined sampling frequency, and outputs control light having a pulse train of an optically sampled optical analog signal. A signal generating device generates a pulse train of signal light which is synchronized with the sampled signal. An optical encoding device optically encodes the pulse train of the signal light according to the control light, by using optical encoders each including nonlinear optical loop mirrors, and outputs pulse trains of optically encoded signal light from said optical encoders, respectively. An optically quantizing device performs optical threshold processing on the pulse trains of optically-encoded signal light to optically quantize them, by using at least one of optical threshold processors each of which is connected to each of said optical encoders and includes a nonlinear optical device, and outputs optically quantized pulse trains as optical digital signals.

Optical Signal Processing Device For A/D Converter Including Optical Encoders With Nonlinear Loop Mirrors

An active load applied to the gate transmission line termination of distributed power devices reduces the low frequency noise power appearing at the output of the device. The active load, including at least one active device such as a field effect transistor, operates by transforming the input impedance of a low noise amplifier to the desired load impedance. The active load is connected to one end of an input transmission line having a plurality of impedances connected in electrical series. An input terminal is connected to the opposite end. An output transmission line, also having a plurality of impedances connected in series, has an output terminal at one end and a terminating output impedance at the other. A plurality of active devices are connected to junction points between the series connected impedances of the input and output lines.

Active load applications for distributed circuits

The authors describe the technology development leading to a family of high-electron-mobility transistor (HEMT) monolithic low-noise amplifiers (LNAs), and present modeled and measured performance data on LNAs covering the 2-20 GHz frequency band. These amplifiers achieve noise figures comparable to their counterpart in hybrid HEMT technology. The amplifiers are configured in a cascadable design, with simultaneous low input and output VSWR, and flat gain response. Performance results include measured and modeled data for a 2-7 GHz LNA with 2.5-dB noise figure, a 2-20-GHz distributed amplifier with 9.5-dB flat gain and 3.5-dB noise figure, and a 5-11-GHz and >3.5 balanced LNA with 10-dB gain and >

A family of 2-20 GHz broadband low noise AlGaAs HEMT MMIC amplifiers

An optical inverter (10) that uses a saturable absorber (28) to distinguish between a logical one and a logical zero. A low power laser (18) generates an optical beam that is split into a first beam that propagates among a first beam path (24) and a second beam that propagates along a second beam path (26). The saturable absorber (28) is an optical switch that is positioned in the first beam path (24), and is switched from an opaque mode to a transparent mode when it receives an optical input signal. The first beam and the second beam are recombined as an optical output beam in an optical combiner (30). The first beam path (24) and the second beam path (26) have a length relative to each other such that the first and second beams are 180° out of phase when they reach the optical combiner (30). Therefore, if the saturable absorber (28) is switched to the transparent mode, the first and second beams combine destructively and the optical output beam is dark, or a logical zero. When the saturable absorber (28) is in the opaque mode, the first beam is blocked so that the optical output beam is the second beam, providing a logical one. A second saturable absorber (34) can be provided to receive the optical output beam from the combiner (30) to absorb residual light when the output beam is dark. Additionally, an optical amplifier (36) can be provided to receive the optical output beam from the combiner (30) to amplify the optical output beam to a consistent, predetermined output level.

Saturable absorber based optical inverter

An optical analog-to-digital converter (10) which fully operates in the optical domain and utilizes an upward-folding successive approximation approach for conversion. The converter (10) includes a plurality of optical stages (14, 16, 18) where each stage (14, 16, 18) generates a digital bit. Each stage (14, 16, 18) includes an optical threshold switch (30, 56, 78) that sets the bit high when the switch (30, 56, 78) is closed. When a sample amplitude of the analog signal is compared to a threshold value and found to exceed the threshold value, the bit is set to "high" and the sample is passed directly onto the next stage (14, 16, 18). If the sample amplitude is found to be less than the threshold value, the bit is set to "low" and an intensity equal to the maximum signal intensity minus the threshold intensity is added to the sample amplitude. Each successive stage (14, 16, 18) compares the normalized signal sample to thresholds growing closer and closer to the maximum signal intensity. Multiple bits can be obtained by cascading stages.

Upward-folding successive-approximation optical analog-to-digital converter and method for performing conversion

A frequency modulation-based optical analog-to-digital converter utilizes a downward-folding, successive approximation approach. A series of stages is utilized to generate bits in the digital signal. In each stage, complementary low and high bandpass filters collectively cover a bandpass frequency range from a low frequency to a high frequency. The high frequency filtered signal from the high bandpass filter is observed to obtain a bit in the digital word. By performing the folding operations in the frequency domain, the converter avoids the difficult task of optical power subtraction, relying instead on frequency down-conversions. The high frequency filtered signal passed by the high bandpass filter is then downconverted and added to the low pass filter signal to generate a modulated signal for the next stage.

Juan C. Carillo

Papers

Active load applications for distributed circuits

A family of 2-20 GHz broadband low noise AlGaAs HEMT MMIC amplifiers

Saturable absorber based optical inverter

Upward-folding successive-approximation optical analog-to-digital converter and method for performing conversion

Frequency modulation-based folding optical analog-to-digital-converter