Patent Application
20060160500
The present invention relates to the field of communications, and more particularly, this invention relates to the field of Block Up Converters (BUC's), for example, used in Very Small Aperture Terminal (VSAT) communications systems.
In the early days of satellite communications, there were few downlink earth stations. Those few stations in existence were essentially large antenna dishes operative with wired communications hubs. Any communications signals received at these large earth stations were distributed through wires and cables to numerous destinations, including other communications hubs. As a result, many earth stations were positioned in metropolitan areas and acted as communications hubs, which distributed communication signals in broadcast fashion to other communications hubs, regional communications centers, or local home and residence sites via cable. It was not convenient to have a large number of smaller, earth station terminals using this prior art wired technology as described.
This scenario changed with the advent of Very Small Aperture Terminal (VSAT) communications systems and networks. VSAT systems are cost-effective communications networks that allow many smaller VSAT terminals to be geographically dispersed and located in many different areas, including rural and metropolitan areas. VSAT networks support internet, voice/fax, data, LAN and many other communications formats, broadening the range of communications services and lowering the overall system, network and communications costs to previous prior art systems using wired technology.
A VSAT network usually includes a large central earth station, known as a central hub (or master earth station), a satellite transponder, and a large number of geographically disbursed, remote VSATs. The satellites are typically positioned in a geostationary orbit about 36,000 kilometers above the earth. A VSAT terminal receives and transmits signals via the satellite to other VSAT's in the network. The term “very small” used in the name VSAT refers to the small antenna dish commonly seen in various locales typically about three (3) to about six (6) feet in diameter and mounted in an accessible but adequate location for communications, such as a roof, building wall, or on the ground. A VSAT terminal has an outdoor unit (ODU), which includes an antenna, low noise blocker (LSB) in some instances, and a VSAT transceiver as part of the outdoor electronics and other components. The antenna usually includes an antenna reflector, feed horn and an antenna mount or frame. The outdoor electronics constitute part of the outdoor unit and usually include low noise amplifiers (LNA) and other transceiver components, for example, a millimeter wave (MMW) transceiver. Many of these VSAT terminals include converter circuits, for example, a Block Up Converter (BUC), which converts L-band signals to Ka-band signals, for example. In a BUC, an incoming IF signal could be mixed with a local oscillator (LO) signal, filtered, and amplified to produce a Ka-band signal to an antenna.
The indoor unit (IDU) is typically operative as a communications interface. It could be formed from various functional components, for example, a desktop box or PC, and contains the electronics for interfacing and communicating with existing in-house equipment, such as local area networks, servers, PC's and other equipment. The indoor unit is usually connected to the outdoor unit with a pair of cables, e.g., usually a coaxial cable. Indoor units also include basic demodulators and modulators for operation.
In the next few years a number of Ka-band (27.5 to 30 GHz) satellites will be launched that will enable remote Internet access via two-way communications with user terminals. To compete successfully with other internet services, such as Digital Subscriber Line (DSL) and cable modem, the cost of these Very Small Aperture Terminals (VSAT's) must be further reduced. As noted before, each Very Small Aperture Terminal typically includes an antenna, a diplexer, and a millimeter wave (MMW) transceiver. To compete successfully with these other internet service providers, the costs of these ground terminals must be driven to very low levels.
In many current VSAT designs, the millimeter wave (MMW) transceiver circuit accounts for almost 75% of the total cost of the VSAT terminal. Unlike most lower frequency Ku-band transceivers, which can be built from low cost discrete components using low cost soft board, for example, Rogers board, a Ka-band transceiver requires tighter tolerances because of its inherent shorter wavelength in the millimeter wave range. One current method used by many manufacturers for manufacturing these transceivers is to pre-package the Ka-band MMIC chips in surface mount packages using traditional surface mount technology (SMT) assembly methods. Although this method is widely used throughout the industry, it has not been a successful approach for driving down the costs of VSAT's because the packaging of MMIC's and their required tuning after assembly has been expensive.
In addition to this cost issue, as the number of VSAT terminals increases to perhaps millions of units in the next few years, the amount of power transmitted from a ground unit operative as a VSAT terminal to any satellite transponders will have to be better controlled not only for cost considerations, but also because of the larger number of terminals in one area. For example, most VSAT terminals require low power to operate in clear weather, while higher power is required to overcome adverse weather conditions and maintain a high rate of service availability. The well-known practice of continuously “blasting,” i.e., transmitting high power signals, would reduce transceiver reliability, as maximum heat is constantly generated, shortening component life.
It is therefore an object of the present invention to provide a Very Small Aperture Terminal (VSAT) transceiver that overcomes the disadvantages of packaging millimeter wave (MMW) Monolithic Microwave Integrated Circuit (MMIC) chips in surface mount packages using traditional surface mount technology assembly methods.
It is yet another object of the present invention to provide an efficient Block Up Converter (BUC) chip for use in VSAT and similar applications.
In accordance with the present invention, a Block Up Converter chip is integrated into a single surface mount technology chip, resulting in substantial costs and space savings.
In accordance with the present invention, the Block Up Converter chip includes a base board formed from a dielectric material and opposing top and bottom metal layers. These form a respective top ground and bottom RF ground. The top metal layer has radio frequency (RF) circuits and the bottom metal layer has ground and signal pads. Microwave Monolithic Integrated Circuit (MMIC) chips are carried by the base board and operative with the RF circuits and ground signal pads for receiving and up converting signals. A top cover is positioned over the base board for protecting the MMIC chips.
In one aspect of the present invention, the MMIC chips include a sub-harmonic mixer MMIC chip that receives and mixes together an intermediate frequency (IF) signal and local oscillator (LO) signal and up converts the IF signal into a higher frequency RF signal. The MMIC chips can also include a driver amplifier MMIC and high power amplifier (HPA) MMIC operatively connected to the sub-harmonic mixer MMIC chip for amplifying the RF signal.
In yet another aspect of the present invention, the top cover includes an inside surface over the MMIC chips and has channelization providing isolation between RF circuits and MMIC chips. A metallized layer can be formed on the inside surface of the top cover and form a waveguide channel. Vias can extend through the base board and connect the top and bottom RF grounds. Other vias can extend from a top metal layer to bottom signal pads for carrying input and output signals. A bottom metal layer can be configured for surface mounting on an RF board or flanges can be included for mounting the base board, wherein the flanges include signal terminals operative with the MMIC chips and RF circuits.
In yet another aspect of the present invention, surface mounted by-pass capacitors can be mounted on the base board with wire bonds interconnecting by-pass capacitors and MMIC chips to RF circuits. Cut-outs can be formed within the base board which receive respective MMIC chips. A conductive epoxy can be used for securing the MMIC chips within the cut-out to a bottom metal layer.
In yet another aspect of the present invention, filters are formed on the base board and operative with the RF ciruits and HPA MMIC, driver amplifier MMIC, and sub-harmonic mixer MMIC. A surface mounted IF amplifier is operatively connected to the sub-harmonic mixer MMIC for amplifying the IF signal into the sub-harmonic mixer MMIC.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the invention which follows, when considered in light of the accompanying drawings in which:
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments.
One prior art method of building Ka-band and similar wavelength Block Up Converters (BUC's) is to prepackage MMIC chips in surface mount packages, which in turn, are secured to a board using traditional SMT assembly methods to produce the final BUC product. Although this method is widely used by many manufacturers, it has not been successful for driving down the manufacturing costs because the packaging of the MMIC's and their final tuning required after assembly processes, which proved expensive.
The present invention solves these prior art problems and is directed to a low cost, preferably Ka-band Very Small Aperture Terminal (VSAT) Block Up Converter (BUC) formed as a single Surface Mount Technology (SMT) chip. The present invention provides a low cost, miniature VSAT BUC that integrates all functions on a single chip, allowing about a 10:1 reduction in size as compared to prior art Block Up Converters that were similar in function. The VSAT BUC chip of the present invention uses a low cost soft board as a base carrier for the MMIC's and filter synthesis. A chip cover can be made from low cost plastic or other similar material and is used to protect the bare MMIC chips or die and other components. The base formed from an RF board and the chip cover when assembled form a Surface Mount Technology (SMT) chip that mounts directly to a main board, for example, a larger and much thicker Radio Frequency (RF) board. This miniature SMT BUC chip simplifies manufacturing by incorporating all millimeter wave (MMW) functions into a single BUC chip. The VSAT BUC chip of the present invention also improves efficiency by reducing losses that result in reduced power dissipation.
This BUC chip 100 includes all the functions of a typical BUC circuit of the prior art, such as described relative to
The RF board 126 typically will have various circuits that are etched or formed with stripline and microstrip circuits, as illustrated. The IF input 150 is connected to a surface mounted IF amplifier 152, which is connected to a sub-harmonic mixer MMIC 156. This sub-harmonic mixer MMIC 156 receives a local oscillator input signal at a local oscillator input 154 connected to a high frequency generator circuit or other circuit for producing a local oscillator signal. The sub-harmonic mixer MMIC 156 is received within a board cut-out 158. The signal is passed into a printed filter 160 and to a driver amplifier MMIC 162, which is connected to various circuits using various wire bonds 164. This driver amplifier MMIC 162 is also received in a cut-out 158. The signal from the driver amplifier MMIC 162 is passed into another printed filter 166 and into a high power amplifier (HPA) MMIC chip 168 and output through the printed filter 170 to an RF output terminal 172. Other components include ground vias 172, signal vias 174, by-pass capacitors 176, and various surface mount capacitors 178, as illustrated. The sub-harmonic mixer MMIC 156, driver amplifier MMIC 162, and HPA MMIC 168 are contained in various board cut-outs 158 as illustrated.
The filters 160, 166, 170 can be formed in a manner similar to that disclosed in commonly assigned U.S. Pat. No. 6,483,404, the disclosure which is hereby incorporated by reference in its entirety. Other etching or printing techniques for forming the filters could also be used. The RF board 126 forming the base of this BUC chip 100 can be formed from a glass microfiber reinforced PTFE composite, such as manufactured by Rogers Corporation, under the designation RT/Duroid® 5870/5880, high frequency laminate. This type of board can be designed for exacting stripline and microstrip circuits. It has low electrical loss, low moisture absorption, chemical resistance, and uniform electrical properties over different frequencies. It is also isotropic. This type of board can be cut easily and is usually supplied as a laminate with an electrode deposited metal layer on top and bottom. The thickness of the metal layers can vary, but typically it is as little as one-fourth to as much as two ounces per square foot (8-70 micrometer) on both top and bottom. The top and bottom metal layers could be formed and clad with rolled copper foil. The cladding could also be formed from different types of metals, including aluminum, copper or brass plate. The board usually includes a dielectric located between the metal plate layers. The boards can have a standard thickness with as little as 0.005 inches (0.127 mm). Of course, the boards come in very large sizes of about 0.125 inches thick, but this type of thickness would not be anticipated for use in the present invention except in rare circumstances.
The high temperature, surface mount capacitors 178 can be operative to temperatures up to about 200° C. or more with rated working voltages varying depending on the end use. These capacitors can handle high power voltage levels in many different RF applications. In one example of the present invention, 0402 capacitors can be used. In some designs, better, improved 0403 capacitors could be used. Both, however, provide high “Q” chip geometries and can be formed as lower cost P-NPO ceramic capacitors. They have high solderability and a varying temperature coefficient with high insulation resistance, dielectric strength and capacitance.
The RF board 126 has a number of ground vias 172 to provide any required isolation. Signal vias 174 can be used to interconnect various components. By-pass capacitors 176 can have appropriate connections for signal vias 174. The high power amplifier MMIC 168 is connected by the printed filter 170 to the RF output terminal 172. Another printed filter 166 interconnects the HPA MMIC 168 and the driver amplifier MMIC 162, which includes various wire bonds 164 for circuit connection, and a printed filter 160 interconnecting the driver amplifier MMIC 162 and the sub-harmonic mixer MMIC 156. The local oscillator input 154 connects to the sub-harmonic mixer MMIC 156. The surface mounted technology intermediate frequency (IF) amplifier 152 is connected to the IF input 150 and various Surface Mount Technology (SMT) capacitors 178.
The cover 130 shown in
The composite BUC chip 100 measures approximately 15 mm×14 mm×2 mm in one non-limiting example, as shown by the x, y and z dimensions in
For this non-limiting application, a one to two ounce copper layer forming the respective top and bottom metal layers 126b, 126c has been found adequate. The top metal layer 126b is used for creating a top ground and etched RF circuits, such as 50 ohm lines and filters. The bottom metal layer 126c is used as a base for the chip and can be etched to create any signal and ground pads (
After the MMIC chips are assembled and the epoxy is cured, automatic wire bonding can be used to connect the MMIC chips and any associated by-pass capacitors 176 to other circuits. The channelized cover 130 is installed, which is preferably made from low cost dielectric material or plastic. It is placed over the base carrier using epoxy or solder. Some area of the cover may require metallization to improve isolation between different circuits and provide a waveguide channel for the filters.
As shown in
Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
