Texas Instruments Corporation

Gailon E Brehm

Bentley N Scott

Randall E Lehmann

David J Seymour

Varactors are incorporated in a monolithic microwave integrated circuit (MMIC) to provide voltage-programmable impedance matching at inputs and/or outputs. This permits the impedance variations normally caused by manufacturing variations in (e.g.) doping or epitaxial thickness to be easily compensated by adjusting the varactor bias, after all major manufacturing steps are completed. Integrated varactors are also used to provide temperature compensation in an MMIC. A temperature-sensitive voltage is generated off-chip and supplied to each on-chip varactor. Each varactor may include a respective voltage-shifting network, so that different varactors implement different capacitance (temperature) functions, to optimally compensate different portions of the MMIC.

Varactor trimming for MMICs

In order to provide low and exactly repeatable common lead inductance (gate lead inductance) and low feedback parasitics in a common-gate low noise amplifier, a GaAs FET connects the gate electrode to ground at various points along its width by means of an air bridge crossover structure. This structure crosses over the input (source) lines with very low capacitance. Since the gate lead inductance is low in this design, and because in monolithic form this inductance does not vary as is the case for a device grounded using bond wires, common-gate circuit stability is assured. This device preferably uses the well-known pi-gate configuration to provide low drain-gate parasitic capacitance and equal phasing to all parts of the device.

Common-gate GaAs FET design for monolithic microwave integrated circuits

A monolithic amplifier having a common-gate input stage with a device transconductance which is higher than required for input match, and a load impedance presented to the common-gate stage which is not conjugate matched. The present invention teaches a common-gate configuration using an FET with higher transconductance and a higher output load impedance. Over narrower bandwidths, excellent input match is thus obtained with noise figures at least as good as those obtained with the common-source approach. This combination of noise figure and input match is achieved in a compact monolithic structure.

Monolithic low noise common-gate amplifier

A monolithic microwave voltage-controlled oscillator including one or more FETS integrated with a wide-ratio varactor. The varactor includes interdigitated anode and cathode patterns laid out on a single thin epitaxial layer. The punch through voltage of the epitaxial layer, and hence the resistivity-thickness product of the epitaxial layer, must be low. Since the substrate is semi-insulating, punch through to the substrate does not become uncontrollable, but simply permits modulation of the capacitance over a very wide range. The FETS are formed in the same epitaxial layer with the varactor, and complicated doping profiles are not required.

Monolithic microwave wide-band VCO

A microwave voltage-controlled oscillator includes a varactor-controlled tuned circuit connected to the gate of an FET. The gate of the FET forms a Schottky barrier contact with the channel region. This Schottky barrier operates to clip the RF voltages generated in the gate circuit, and this clipping is used to provide the necessary gate bias to set the operating point of the VCO. No other source of bias is provided, and thus no DC return path from the gate circuit to the source or drain of the FET exists. Thus, the other circuit elements normally required to establish the gate operating point, which would have high frequency resonances, are eliminated. This permits operation of a microwave VCO over an extremely broad bandwidth.

Growing community of inventors

Plano, TX, United States of America

Gailon E Brehm