Abstract:
The present invention is directed to an apparatus and method for varying the power level of a transmitted signal, such as a transmitted radio frequency signal, of high power, high transmission rate systems in a relatively straightforward, cost efficient manner. Exemplary embodiments can provide a range of stable DC control voltages for driving a power level attenuator, wherein the control voltages possess essentially no AC component (e.g., in exemplary embodiments, at a 5 volt DC output, virtually no AC component in the millivolt range is present), and possess a high current capability (e.g., at a 5 volt DC output exemplary embodiments can accommodate currents in excess of 0.5 amps (A) up to 7 A or greater). The ability to provide very stable, high current capability transmission power attenuation is especially desirable for communication systems, and in particular, wireless communication systems wherein conservation of energy is important, and wherein transmission rates are on the order of 125 Mb/s or higher, and transmission power is on the order of 0.5 to 2 watts (W) or higher. Because of its high current capability, power level attenuation of a transmitted signal in accordance with exemplary embodiments of the present invention is suitable for use in conjunction with high power (e.g., 0.5 W) monolithic millimeter wave integrated circuits (MMICs).

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. application Ser. No. 09/185,579, filed Nov. 4, 1998 and entitled: METHOD AND APPARATUS FOR HIGH FREQUENCY WIRELESS COMMUNICATION, and now U.S. Pat. No. 6,442,374, the the disclosure of which is hereby incorporated by reference in its entirety. In addition, the present application relates to U.S. application Ser. No. 09/227,832, filed on even date herewith, and entitled: METHOD AND APPARATUS FOR PROVIDING HIGH CURRENT POWER REGULATION, and now U.S. Pat. No. 6,259,237, relates to U.S. application Ser. No. 09/227,831, filed on even date herewith, and entitled: METHOD AND APPARATUS FOR GENERATING A COMMUNICATION BAND SIGNAL WITH REDUCED PHASE NOISE, and now U.S. Pat. No. 6,522,868, relates to U.S. application Ser. No. 09/227,835, (Attorney Docket No.  017750-408 ) filed on even date herewith, and entitled: METHOD AND APPARATUS FOR INTERFACING WITH AN ETHERNET ARCHITECTURE (now abandoned), and relates to U.S. application Ser. No. 09/227,834, (Attorney Docket No.  017750-409 ) filed on even date herewith, and entitled: METHOD AND APPARATUS FOR INTERFACING WITH AN ETHERNET ARCHITECTURE (now abandoned), the disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to communication systems and methods, and more particularly, to reliably varying the power level of a transmitted signal, such as a transmitted radio frequency (RF) signal. 
     2. State of the Art 
     Communication systems which employ wireless transceivers are well known. However, as is the case with most electronic technologies today, there is an ever increasing demand to improve information transmission rates and range (that is, power output), while at the same time, reducing the influence of noise and improving the quality of transmission. In addition, there is always increasing demand to broaden the applicability of wireless communications to technologies still dependent on wired or fiber linked communication, such as mainframe-to-mainframe communications where high data rate and high power requirements have precluded the use of conventional wireless communications. To satisfy these competing concerns, a compromise is often reached whereby some sacrifice in transmission rate is accepted to enhance the integrity of the data transmitted. In addition, sacrifices in transmission range, and in transmitter options, such as an ability to vary the transmit power, are accepted to reduce the transceiver&#39;s circuit complexity and cost. 
     An ability to adjust the power level of a transmitter output signal is desirable in conjunction with applications such as communication systems, in particular, with wireless communication systems, wherein output power requirements can change based on conditions including, but not limited to, weather conditions and distances over which wireless communication is to be performed. For example, a sunny day does not require the same transmitter power output as a rainy day. Accordingly, it would be desirable to reduce power output of the transmitter on sunny days to save power and to avoid saturation of the receiver (which results in signal distortion). Similarly, a transmission over a shorter distance permits, or can require, power output of the transmitter to be reduced. Variable output voltage attentuators are not presently available which would be suitable for the high power requirements of systems which employ high power monolithic millimeter wave integrated circuits (MMICs). Available attentuators are noisy, and are unable to provide a stable DC output which can be varied in response to an attenuator drive circuit that includes components, such as digital to analog converters. 
     Accordingly, it would be desirable to provide an apparatus and method for varying the power level of a transmitter output signal using a cost effective, straightforward approach that can accommodate high power requirements (e.g., 0.5 to 2 watts (W), or higher), high transmission rate systems (e.g., having operating frequencies on the order of 18-40 gigahertz (GHZ) spectrums or wider, and actual transmission rates on the order of 100 to 125 megabits per second (125 Mb/s) or higher). It would also be desirable to provide variations of the transmission power level in incremental steps which permit fine adjustment of the transmitted signal power. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an apparatus and method for varying the power level of a transmitted signal, such as a transmitted radio frequency signal, of high power, high transmission rate systems, in a relatively straightforward, cost efficient manner. Exemplary embodiments can provide a range of stable DC control voltages for driving a power level attenuator, wherein the control voltages possess essentially no AC component (e.g., in exemplary embodiments, at a 5 volt DC output, virtually no AC component in the millivolt range is present), and possess a high current capability (e.g., at a 5 volt DC output exemplary embodiments can accommodate currents in excess of 0.5 amps (A) up to 7 A or greater). The ability to provide very stable, transmission power attenuation is especially desirable for communication systems, and in particular, wireless communication systems wherein conservation of energy is important, and wherein transmission rates are on the order of 125 Mb/s or higher, and transmission power is on the order of 0.5 to 2 watts (W) or higher. Because of its high current capability, a power level attenuation controller in accordance with exemplary embodiments of the present invention is suitable for use in conjunction with high power (e.g., 0.5 W) monolithic millimeter wave integrated circuits (MMICs). 
     Generally speaking, exemplary embodiments of the present invention are directed to an apparatus and method for varying the power of a signal, comprising: means for receiving a regulated input voltage; means for varying said regulated input voltage to provide at least one variable control voltage having a stable voltage over a range of outputs which includes approximately 5.0 volts and a current capability of at least 0.5 amps; and means, responsive to said variable control voltage, for varying a power level of a signal to be transmitted. An exemplary apparatus for attenuating the power level of a transmitted signal includes means for converting a digital input into an analog output voltage; and means for driving a monolithic millimeter wave integrated circuit attenuator with said variable control voltage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments, in conjunction with the accompanying drawings, wherein like reference numerals have been used to designate like elements, and wherein: 
     FIGS. 1A-1D show an exemplary block diagram of a power level attenuator in accordance with the present invention, which can be used, for example, to vary the power level of a transmitter output signal in a communication system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Power supplies often include an on-board voltage regulator or regulators. In an exemplary embodiment of a communication system transmitter as described in the aforementioned copending application, three such voltage regulators are included: a first regulator for a data input means and a data processing means of the transmitter, a second regulator for the portion of the power output means used to establish output amplification channels, and a third regulator for recombining the signals from the power amplification channels into a single RF output. Of course, those skilled in the art will appreciate that a single regulator, or any number of regulators can be used to provide the power supplies to the various components of the circuits. In communication system applications such as this, a voltage output of the regulator which can be varied can be used to, for example, adjust a power level of a transmitted signal provided variations in the voltage output do not detract from stable, reliable transmitter operation. 
     FIGS. 1A-1D illustrate an apparatus for varying the power level of a transmitted output signal in a cost effective, straightforward approach. The FIG. 1 apparatus is configured as a power level attenuation controller  100 . The attenuation controller  100  includes a selection means  102  for receiving a digital output from, for example, a computer  120  used to control the power of a transmitted signal (e.g., a continuous wave RF signal). The selection means  102  includes input nodes  104  and an isolation means  106  for isolating downstream attenuation controller components from the relatively noisy environment of the computer&#39;s output. 
     The attenuation controller includes means for converting the output of the isolation means  106  from a digital signal to an analog signal using a digital-to-analog converter  130 . The analog signal from the converting means is supplied as a variable magnitude DC voltage signal to an attenuator drive means  110 , which drives a high power attenuator  112 , such as two series connected millimeter monolithic integrated circuit (MMIC) attenuators. MMIC attenuators are available from manufacturers, such as Hewlett Packard (e.g., the HP MMIC HMMC-1002 attenuator) and others. 
     In exemplary embodiments of the present invention, an attenuator  112  is selected which can respond to control inputs to provide a step change in the power level of an RF input signal (such as an RF signal to be transmitted by a transmitter portion of transceivers configured in accordance with the copending application Ser. No. 09/185,579) over a desired range of interest. For purposes of the exemplary FIG. 1 embodiment, where an MMIC HMMC-1002 attenuator is selected, attenuation can be provided over an exemplary range from 0 to 60 decibels or greater, in steps on the order of 0.1 dB (or more, or less) for the frequencies specified herein. For example, each of the series connected attentuators can provide 30-45 dB of attenuation. Where a 38 GHZ RF input signal is supplied to these attentuators with a power of −10 dBm, and the attentuators provide 60 dB of attenuation, the power of the RF output will be reduced to −70 dBm. However, as mentioned previously, any desired range of attenuation and associated adjustable steps can be used in accordance with the specific application for which the attenuation controller is to be used. 
     The attenuation controller  100  can include an optional power level monitoring means  118  for detecting the transmission signal power and providing a display of the detected power at a monitor associated with the computer  120  used to select the output power. Generally speaking, the monitoring means  118  receives a power level input signal from a coupler  119  (e.g., inductive current sensor), via a filter  121 , to detect the power level, and then supplies it to a display of the computer  120  via an amplifier, an analog-to-digital conversion means and an isolation means. 
     The components of the FIG. 1 attenuation controller  100  will now be described in further detail according to the exemplary embodiment illustrated. The input nodes  104  of the voltage selection means  102  are supplied by computer  120  and include a clock input  122 , a data input  124  and a select (i.e., enable) input  126 . The data input  124  from computer  120  specifies the desired output power level of the transmitter, and thus, the amount of attenuation which must be provided by attenuator  112 . The three inputs  122 ,  124  and  126  are used to drive the digital-to-analog converter  130  via optocouplers  132  and  134  of the isolation means  106 . The digital-to-analog converter can, for example, be any readily available D/A converter, including that available from Linear Technology Corporation and designated LTC1451IS8. The optocouplers can be those available from Hewlett Packard, and designated HCPL-0661. 
     The input nodes  104  further include a clock input  136  for driving the analog-to-digital converter of the monitoring means  118  via a portion of optocoupler  134 . A voltage input and associated return of the attenuation controller  100  are received via nodes  138  and  140  (i.e., a voltage input isolated from the regulated voltage used to drive components on the attenuator side of the optocoupler), and are supplied to optocouplers  132  and  146 . 
     An analog-to-digital converter enable signal is received via an input  142 , and is supplied to the analog-to-digital converter of the voltage monitor means  118 . 
     The voltage inputs and the analog-to-digital converter enable signal received on the nodes  138 ,  140  and  142  are supplied to the attenuation controller through optocoupler  134  and through additional optocouplers  144  and  146 . An output from the monitoring means  118  is supplied back to the computer via a node  148  and optocoupler  144 . 
     The optocouplers constitute an exemplary isolation means which can be used to avoid noisy signals of the computer from affecting the radio frequency circuitry located downstream of the attenuation controller. Although optocouplers are used, those skilled in the art will appreciate that any isolation means can be used which can receive the digital input signals from the selection means  102  and supply them to the attenuation controller in electrically isolated fashion. The selection supplied via the input nodes  104  passes through the digital-to-analog converter  130 , and onto the drive means  110 . 
     In an exemplary embodiment, a voltage reference generator  114  is provided for supplying a stable voltage (e.g., for a voltage of 5.0 V, no AC peak-to-peak ripple component, of greater than approximately one millivolt) from a regulated 5.0 volt DC voltage supply  116  (e.g., as produced in accordance with the aforementioned U.S. Pat. No. 6,259,237) to components on the attenuator side of the optocouplers (e.g., the digital-to-analog converter and the components of the drive means  110 ). The output of the digital-to-analog converter thus constitutes a varied voltage from the regulated DC supply having a voltage selected in accordance with the inputs on input nodes  104 . The exemplary drive means  110  includes operational amplifiers  150  and  152 , configured as inverting op amps. The op amps supply four control voltages  154 ,  156 ,  158  and  160  for use by the high power attenuator to select the power level of the signal from the attenuator  112 . In an exemplary embodiment, the four control voltages are a set of stable, variable DC voltages (as selected by input nodes  104 ) suitable for driving a Hewlett Packard HMMC-1002 MMIC attenuator in steps of 0.1 dB (or more, or less). 
     Although additional signal path components are shown in the exemplary FIG. 1 embodiment, the exact values shown for the elements identified (such as pull-up resistors R 33 , R 27 , R 28 , R 29  and so forth) are not critical. Rather, the components shown, along with their respective values, are intended to be illustrative of an exemplary embodiment for implementing an attenuation controller in accordance with the present invention. 
     Having described an attenuation controller for varying the power of a signal, attention will now be directed to the monitoring means  118 . In the exemplary FIG. 1 embodiment, the output power is received via a detection node  162  from a coupler which measures the power level of a signal being transmitted (e.g., an RF signal, or any other signal coupled to coupler  119 ). The detected DC voltage is supplied via a non-inverting operational amplifier  164  to an analog-to-digital converter  166 , such as that available from Analog Devices, Inc., and designated AD7823YR. An output from the analog-to-digital converter, representing a digital version of the power level, is supplied through optocoupler  144  to the computer via node  148 . The computer can then optionally display the transmitter power in any format desired. In an exemplary embodiment, the output from the analog-to-digital converter  166  is supplied to the optocoupler  144  via a driver  168  (e.g., a NAND gate) for providing sufficient current to drive the optocoupler (when an optocoupler is used for isolation). 
     The FIG. 1 block diagram can be used, for example, with a transmitter configured to transmit information, such as data, at actual information rates on the order of 100 to 125 Mb/s, or lower or higher. Those skilled in the art will appreciate that this actual transmission rate must account for overhead, such as conventional error correction, clock synchronization signals, and so forth. As such, the rate with which the data is transmitted will be somewhat lower (for example, 100 Mb/s). Although FIG. 1 illustrates a variable attenuation controller for use with a transmitter, those skilled in the art will appreciate that the attenuation controller can be configured as part of a transceiver which includes both a transmitter (such as that of FIG. 1) and a receiver, or with a receiver alone, or for use in any application where attenuation is desired. 
     The exemplary FIG. 1 embodiment is configured for use with a transmitter that can produce a power output on the order of 0.5 to 2 W using four parallel 0.5 W channels. For example, high power (e.g., 0.5 W) monolithic millimeter wave integrated circuits (MMICs), previously used in radar technology, can be used in the transmitter and receiver portions of a transceiver according to exemplary embodiments of the present invention to achieve full duplex, high power wireless communications with a simple circuit design. The high power outputs and fast information transmit/receive rates enable the use of wireless communications for broadband networking technologies and interconnectivity medium standards such as the synchronous digital hierarchy (SDH) known as the synchronous optical network SONET/SDH (e.g., SONET ring architectures having self-healing ring capability). Using available MMICs, such as high quality, low noise MMIC amplifiers, a five decibel (dB) noise figure or lower can be realized in a receiver portion. A transmitter configured using one or more MMICs can be used in conjunction with a receiver of the transceiver to provide point-to-point full duplex operation at operating frequencies in a fixed wireless spectrum range of 18-40 GHz (e.g., on the order of, for example, 20 GHz to 40 GHz) or wider, in contiguous 50 megahertz (MHZ) segments (or any other specified operating frequency range), over a range of the order of 2 kilometers (km) with, for example, 40 dB range attentuation or higher. Such transmitters are suitable for a variety of applications including, but not limited to, point-to-point wireless communications between computers, such as between personal computers, between computer networks and between mainframe computers over broadband networks with high reliability. 
     Although a plurality of separate integrated circuits are available to implement the various functions of the FIG. 1 embodiment, those skilled in the art will appreciate that all of the functions can be configured onto a single substrate to further enhance compactness using a monolithic device. 
     Although exemplary embodiments of the present invention have been described in the context of communication systems which use transmitters and receivers, those skilled in the art will appreciate that the invention is not so limited. Rather, exemplary embodiments of the present invention can be used whenever a power level control is desired. The applicability of the exemplary embodiments will, of course, be suitable for those applications where high current demands exist. Exemplary embodiments can thus be used in conjunction with any computer or computer applications. 
     It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.