Abstract:
A distributed amplifier for wide-band, high power application is disclosed. The amplifier consists of an analysis module, a gain module and a synthesis module. In the analysis and synthesis modules, inductors such as transmission lines are connected to gain elements of the gain modules with a newly disclosed “pi” configuration, by which the number of inductors, or transmission lines, is reduced. This invention may be applied to wide-band and high-speed communications.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from the following U.S. Provisional Patent Application, the disclosure of which is incorporated by reference in its entirety for all purposes: U.S. Provisional Patent Application Ser. No. 60/292,487, Cheh-Ming Jeff Liu and Neng-Haung Sheng entitled, “DISTRIBUTED AMPLIFIER WITH PI-CONFIGURATION ANALYSIS AND SYSTHESIS LINES,” filed May 21, 2001. 
    
    
     BACKGROUND 
     1. Field of Invention 
     The present invention relates to distributed amplifiers and, in particular, distributed amplifiers suited for wide-band and high-power applications. 
     BACKGROUND 
     2. Description of Prior Art 
     Distributed amplifiers are widely used in part to overcome the gain-bandwidth limitation due to inherent capacitance of the active devices associated with the resistive loads. Inductors and transmission lines are commonly employed to resonate with the device capacitance. The combinations of inductors and capacitors are approximately equivalent to delay elements (e.g., transmission lines) and thereby increase the operational bandwidth. FIG. 1A shows a conventional distributed amplifier  10  comprised of an analysis module  20 , a gain module  30  and a synthesis module  40 . The gain elements of the gain module  30  are identical and uniformly distributed in conjunction with the inductors. An equivalent-circuit model of an elementary section  50  of the distributed amplifier  10  is shown in FIG.  18 . The elementary section  50  is composed of two series inductors  51  and  52 , and a shunt capacitance  53  in the format of a T-configuration. The inductors  51  and  52  are the inductors in the analysis  20  or synthesis module  40 , while the capacitor  53  represents the device capacitance at the input or the output of the gain element. As the operation frequencies are lower than the resonance frequency of the components  51 ,  52 , and  53 , the elementary section  50  is approximately equal to a piece of transmission line  60  as shown in FIG.  1 C. Virtually, a transmission line is a delay element with infinite bandwidth. Therefore, by combining device&#39;s capacitance  53  with the inductors  51  and  52  into a transmission line  60 , amplifiers with these types of analysis module and synthesis module can be operated over very wide frequency range. However, for the integrated circuit, the size of the inductor is comparably larger than the one for an active gain element. Moreover, the inductors in the analysis and synthesis modules are of two values, L and L/2, where L/2 is the inductance value on one arm of the T-configuration. This increases the complexity of the resulting design and implementation of the conventional analysis and synthesis modules. A simple architecture for the analysis and synthesis modules of the distributed amplifier is desirable and provided by the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention is embodied as a circuit for a distributed amplifier where the analysis and synthesis lines are implemented in formats of a new π-configuration. In accordance with a preferred embodiment of the present invention, the connection of the inductors and the capacitive devices is in a format of a π-configuration, that is, two shunt device capacitances with a series inductor. The number of inductors is less by two than the number associated within a conventional distributed amplifier, in which the connection is in a format of a T-configuration. Moreover, according to the present invention, all the inductances of the synthesis, or analysis, lines are of the same value as opposed to the two different values in a conventional distributed amplifier. This sameness of value of the inductances is also present in the analysis lines of the present invention. 
     A distributed amplifier, according to the present invention, features compactness of integration and less complexity in designing the analysis and synthesis modules. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and for further features and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: 
     FIGS. 1A,  1 B and  1 C illustrate prior art of distributed amplifiers; 
     FIG. 2 illustrates the circuitry of a preferred embodiment of the present invention; 
     FIGS. 3A,  3 B and  3 C respectively illustrate equivalent-circuit models for the input circuit of the present invention, an elementary section and its equivalence; 
     FIGS. 4A,  4 B and  4 C respectively illustrate equivalent-circuit models for the output circuit of the present invention, an elementary section and its equivalence; and 
     FIG. 5 illustrates an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 shows a preferred embodiment of the present invention in which a distributed amplifier  100  consists an analysis module  110 , the gain module  120  and a synthesis module  130 . The analysis module  110  consists of N identical, or substantially similar, inductors  111  of a value L I  and is terminated with a load  112  of a value R I  at one end. The gain module  120  is composed of 2N identical, or substantially similar, gain elements  121 . The synthesis module  130  consists of N identical, or substantially similar, inductors  131  of a value L o  and is terminated with a load  132  of a value R o  at one end. 
     FIG. 3A shows an equivalent-circuit model  200  for the analysis module  110  and the input of the gain module  120 . The input of each of a plurality of gain elements is characterized by an equivalent capacitor C r . The inductance L I  is designed to satisfy the equation:                R   I     =         L   I       2        C   I                   [   1   ]                                
     FIG. 3B shows a representative input elementary section  210  of the analysis module  110  and the input of the gain module  120 . The input elementary section  210  is of a π-configuration as opposed to a T-configuration delay element  50 , as shown in FIG. 1B, which is used in conventional distributed amplifiers. The input elementary section  210  is approximately equivalent to a segment of transmission line  220 , as shown in FIG. 3C, with a characteristic impedance of R I  and a delay of τ I ={square root over (L I ·2C I )}. This approximation is valid and effective so long as the operational frequencies are much less than 1/(2πτ I ). With the distributed π-configuration of  200 , all inductors are of the same value and the number of inductors is reduced by two as compared to the conventional distributed amplifiers (FIG. 1A.) 
     FIG. 4A shows an equivalent-circuit model  300  for the synthesis module  130  and the output of the gain module  120 . The output of each of a plurality of gain elements is characterized by a capacitor C o . Similarly, the inductance L o  is designed to meet the equation:                R   O     =         L   O       2        C   O                   [   2   ]                                
     FIG. 4B shows a representative output elementary section  310  of the synthesis module  130 . The output elementary section  310  is composed of two output-equivalent capacitors C o  of gain elements symmetrically in conjunction with an inductor L o  of synthesis module  130  in a format of a π-configuration. The output elementary section  310  is approximately equivalent to a piece of transmission line with a characteristic impedance of R o  and a delay of τ o ={square root over (L o ·2C o )} as the operation frequencies are much less than 1/(2πτ o ). In order to reduce the phase distortion due to the different delays between the analysis modules  110  and the synthesis module  130 , the gain element of gain module  120  is designed to minimize the difference of τ I  and τ o . 
     Detailed Description of an Alternative Embodiment 
     FIG. 5 shows an alternative embodiment of the present invention. The distributed amplifier  500  consists of an analysis module  510 , a gain module  520  and a synthesis module  530 . The analysis module  510  consists of a plurality of N identical transmission lines  511  and is terminated with a load  512  at one end. The gain module  120  is composed of a plurality of 2N identical gain elements  521 . The synthesis module  530  consists of N identical transmission lines  531  and is terminated with a load  532  at one end. 
     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims. 
     The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself. 
     The definitions of the words or elements of the following claims are, therefore, defined in this specification to include not only the combination of elements which are literally set forth, but all equivalent structure, material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. 
     In addition to the equivalents of the claimed elements, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements. 
     The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention.