1. Field of the Invention
The present invention relates to integrated circuits and, more particularly, to microwave monolithic integrated circuits (MMICs) for use in high-frequency applications, such as those in the microwave and millimeter-wave frequency regions.
2. Description of Related Art
Integrated circuits have gained widespread use in many electronic applications. In early hybrid integrated circuits, active elements (such as diodes and transistors) and passive elements (such as resistors, capacitors, and inductors) were typically discrete components mounted (e.g., soldered or bonded) to a dielectric slab or substrate. In contrast, in a monolithic integrated circuit (or “monolithic circuit”), circuit components including active and passive elements are integrated monolithically, i.e., formed directly on a common semiconductor substrate.
Typically, depending on the operating frequency, monolithic integrated circuits may be formed on different types of substrates. As an example, the monolithic integrated circuits operating up to 1-2 GHz may be fabricated on silicon (Si) substrate. At higher operating frequencies, such as microwave and millimeter-wave frequencies (approximately between 1-300 GHz), the substrate is usually gallium arsenide (GaAs) and these circuits are commonly referred to as monolithic microwave integrated circuits, or MMICs. Some of the advantages of MMICs include their small sizes, the inclusion of multiple functions (e.g., radio frequency (RF) and logic) on a single semiconductor chip, and a wider frequency-bandwidth performance that is often difficult to achieve with discrete devices due to bandwidth-limiting parasitics associated with discrete-device packaging.
Typically, RF signals at microwave and millimeter-wave frequencies can easily penetrate harsh environments such as dust, smoke, and snow, and are very attractive due to their high spatial resolution, resulting in a compact chip size and small antenna dimension. As such, MMICs find use in various commercial, military, and space applications. For example, in addition to the traditional use in radars, microwave and millimeter wave techniques are finding applications in such diverse areas as forward-looking automotive radar, Synthetic Vision Systems (SVS) for aircraft landing, Concealed Weapon Detection (CWD) systems, industrial sensors and accelerometers.
Typically these systems employ a stable transmitter and highly sensitive receiver incorporating a mixer and a local oscillator. However, increasing use of microwave and millimeter-wave frequency bands for communication, radar and measurements have created the need for more sophisticated methods for controlling the frequency, power and phase of these sources of radiation. For example, coherent radar systems have for years relied on phase-locked or injection-locked transmitters as well as phase-locked local oscillator for receivers. In addition to down-converters, IF amplifiers, and phase detectors, typically these techniques use a directional coupler and a power divider to meet the required specifications.
In general, the coupler and power divider are either coaxial/waveguide or fabricated using hybrid microstrip technology. The latter does generally reduce the overall component size, but it still does not lead to a compact, low cost design. Moreover, many newer applications require RF power monitoring capability for accurate control of output power.
Thus, there is a general need for a MMIC, which incorporates the functions of power distribution and power monitoring over a large bandwidth in the microwave and millimeter-wave frequency range.