Abstract:
Systems and methods are described for a band switchable voltage controlled oscillator. A method comprises: operating said voltage controlled oscillator in a first frequency band by switching a first capacitive circuit having a capacitance that varies with a tuning voltage; and operating said voltage controlled oscillator in a second frequency band by switching a second capacitive circuit having a capacitance that does not vary with the tuning voltage. An apparatus comprises: a switchable variable capacitance circuit; a switchable fixed capacitance circuit coupled to the switchable variable capacitance circuit; a controller for selectively switching said switchable fixed and variable capacitance circuits; a fixed tank capacitance circuit coupled to the switchable fixed capacitance circuit; a main tuning voltage variable capacitance circuit coupled to the fixed tank capacitance circuit; a tank inductance coupled to the main tuning voltage variable capacitance circuit; and an amplifier circuit coupled to the tank inductance.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to the field of oscillators. More particularly, the invention relates to voltage controlled oscillators. 
     2. Discussion of the Related Art 
     A voltage-controlled oscillator (VCO) is a circuit that generates an oscillating signal at a frequency proportional to an externally applied control voltage. These types of circuits find several applications in telecommunications, and are useful for tracking and matching signal frequencies as they shift due to thermal variations, power supply fluctuations, and other sources of frequency shifts. 
     Modern electronics often require a VCO to operate over large frequency ranges. Nevertheless, increasing the tuning bandwidth often degrades the signal-to-noise ratio (SNR) of the VCO&#39;s output. While multi-band products can use multiple VCO&#39;s for multiple frequency ranges, this adds to chip area and require undesirable switching of signal paths. 
     U.S. Pat. No. 3,813,615 to Okazaki describes an oscillator circuit suitable to operate at low and high band frequencies by switching of an inductance. While an inductance switching VCO may tend to keep a constant tuning range, it is not practical given current integrated circuit (IC) technology. 
     Capacitance can be switched by changing the voltage across a tuning element such as a voltage variable capacitor (VVC). Nevertheless, the more capacitance is switched in for operation in lower frequency ranges, the more the tuning range decreases. Thus, compromises have to be made between tuning tolerance on the low range and noise on the high range. 
     Until now, the requirements of providing a method and/or apparatus for a band switched voltage controlled oscillator with constant tuning range that is suitable for use with current IC technology have not been met. 
     SUMMARY OF THE INVENTION 
     There is a need for the following embodiments. Of course, the invention is not limited to these embodiments. 
     According to an aspect of the invention, a method for operating a band switchable voltage controlled oscillator in at least two different frequency bands of substantially equal bandwidth comprises: operating said voltage controlled oscillator in a first frequency band by switching a first capacitive circuit having a capacitance that varies with a tuning voltage; and operating said voltage controlled oscillator in a second frequency band by switching a second capacitive circuit having a capacitance that does not vary with the tuning voltage. According to another aspect of the invention, a band switchable voltage controlled oscillator, comprises: a switchable variable capacitance circuit; a switchable fixed capacitance circuit coupled to the switchable variable capacitance circuit; a controller for selectively switching said switchable fixed and variable capacitance circuits; a fixed tank capacitance circuit coupled to the switchable fixed capacitance circuit; a main tuning voltage variable capacitance circuit coupled to the fixed tank capacitance circuit; a tank inductance coupled to the main tuning voltage variable capacitance circuit; and an amplifier circuit coupled to the tank inductance. 
     These, and other, embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating various embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many substitutions, modifications, additions and/or rearrangements may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such substitutions, modifications, additions and/or rearrangements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings accompanying and forming part of this specification are included to depict certain aspects of the invention. A clearer conception of the invention, and of the components and operation of systems provided with the invention, will become more readily apparent by referring to the exemplary, and therefore nonlimiting, embodiments illustrated in the drawings, wherein like reference numerals (if they occur in more than one view) designate the same elements. The invention may be better understood by reference to one or more of these drawings in combination with the description presented herein. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale. 
     FIG. 1 is a block diagram of a band switchable voltage controlled oscillator, representing an embodiment of the invention. 
     FIG. 2 is a circuit diagram of a first dual-band, band-switchable voltage controlled oscillator, representing an embodiment of the invention. 
     FIG. 3 is a circuit diagram of a second dual band, band-switchable voltage controlled oscillator, representing another embodiment of the invention. 
     FIG. 4 is a simplified graph of capacitance versus voltage, illustrating an embodiment of the invention. 
     FIG. 5 is a circuit diagram of a third dual-band, band switchable voltage controlled oscillator, representing an embodiment of the invention. 
     FIG. 6 is a graph of a simulated dual-band, band switchable voltage controlled oscillator circuit output, illustrating an embodiment of the invention. 
     FIG. 7 is a circuit diagram of a multi-band, band switchable voltage controlled oscillator, representing an embodiment of the invention. 
     FIG. 8 is a graph of a simulated multi-band, band switchable voltage controlled oscillator output, illustrating an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     The invention and the various features and advantageous details thereof are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be understood that the detailed description, while indicating specific embodiments of the invention, is given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to one of ordinary skill in the art in light of this disclosure. 
     Referring to FIG. 1, a block diagram of a band switchable voltage controlled oscillator  100  is presented in accordance with an exemplary embodiment of the invention. A band selection circuit  101  is coupled to a band switchable circuit  102 . The band switchable circuit  102  is coupled to a tank circuit  103 . The tank circuit  103  is coupled to an amplifier circuit  104 . The amplifier circuit  104  is coupled to a bias circuit  105 . The bias circuit  105  may enable operation of the voltage controlled oscillator  100 . 
     Still referring to FIG. 1, in the illustrated embodiment, the band switchable circuit  102  comprises a switchable variable capacitance circuit  120  coupled to a switchable fixed capacitance circuit  121 . The band selection circuit  101  provides a first band control voltage V B  to the switchable variable capacitance circuit  120  and a second control voltage V C  to the switchable fixed capacitance circuit  121 . The tank circuit  103  comprises a fixed tank capacitance  130  coupled to a main tuning capacitance  131 . The tank circuit  103  also comprises a tank inductance  132  coupled to the main tuning capacitance  131 . 
     Still referring to FIG. 1, a tuning voltage (Vtune) is applied to the switchable fixed capacitance circuit  121  and to the main tuning capacitance  131 . The tuning voltage (Vtune) may tune the tank circuit  103  and determine the frequency of an output voltage (Vout). The tank circuit  103  has the ability to store energy and produce a continuous alternating current output. The output voltage (Vout) may be differentially probed in the amplifier circuit  104 . 
     Still referring to FIG. 1, the band selection circuit  101  determines the band of operation of the VCO  100  by applying complementary control voltages V C  and V B  to the band switchable circuit  102 . According to one aspect of the invention, the bandwidth of the band of operation is proportional to ratio between fixed and variable capacitances within band switchable circuit  102  and tank circuit  103 . The band switchable circuit  102  comprises a combination of variable and fixed capacitances which may be switched in and out of the circuit to change the band of operation of the VCO  100  while minimizing and/or eliminating tuning range variations among the different bands. In FIG.  1  and in all circuit block diagrams and schematics in the present disclosure, wires connected by dots indicate an electrical connection. Crossing wires without dots in their intersection are not electrically connected. 
     Referring to FIG. 2, a circuit diagram of a first dual-band, band-switchable voltage controlled oscillator  200  is depicted according to one aspect of the invention. The band selection circuit  101  comprises a switch  201  and an inverting amplifier  202 . The band switched circuit  102 A includes a switchable variable capacitance circuit  120 A and a switchable fixed capacitance circuit  121 A. Capacitors  204 - 207  are voltage variable capacitors (VVCs), such as, for example, MOS capacitors, and capacitors  208  and  209  are fixed value capacitors, such as, for example, metal-insulator-metal capacitors (MIMs). In the tank circuit  103 , a main tuning capacitance comprises a pair of VVCs  214 ,  215 , while the fixed tank capacitance comprises a pair of MIMs  212 ,  213  and the tank inductance comprises a pair of inductors  216 ,  217 . A capacitor  218  serves as an AC coupling in the tank circuit  103 . In operation the combined capacitance within band-switched circuit  102 A and tank circuit  103  together determine the oscillation frequency of VCO  200 . 
     Still referring to FIG. 2, the switch  201  produces a control voltage V B  which takes one of two logic states, a reference voltage or ground. The output of the switch  210  is fed to a node between resistors  210 ,  211  and to the input of inverting amplifier  202 . The inverting amplifier  202  feeds the complement of V B , i.e. V C , to the band switchable circuit  102 A via a resistor  203 . A tuning voltage (Vtune) is applied to a node between capacitors  206 ,  207 , and to a node between capacitors  214 ,  215 , determining the frequency output of the VCO. The VCO  200  output oscillates at a frequency proportional to Vtune. 
     Still referring to FIG. 2, while the capacitances of capacitors  206 ,  207  vary proportionally to Vtune, capacitors  204 ,  205  assume two distinct capacitance values. When the control voltage V B  is at a high logic state, the control voltage V C  is at low logic state and the VCO  200  operates in a low frequency band. In this low frequency band, capacitors  206 ,  207  may be tuned by Vtune and the capacitances of  204 ,  205  assume high capacitance values. In this low frequency band, Vtune is used to tune capacitors  206 ,  207  as well as capacitors  214 ,  215  within the main tuning capacitance  131  of the tank circuit  103 . When the control voltage V B  is at a low logic state, the control voltage V C  is at high logic state and the VCO  200  operates in a high frequency band. In this high frequency band, capacitors  206 ,  207  cannot be tuned by Vtune and become substantially fixed value capacitors, while and the capacitances of  204 ,  205  assume substantially fixed low capacitance values. In this high frequency band, Vtune is used to tune only capacitors  214 ,  215  within the main tuning capacitance  131  of the tank circuit  103 . In accordance with one aspect of the present invention, the ratio of fixed capacitance to variable capacitance within band switched circuit  102 A and tank circuit  103  remains substantially constant regardless of the state of control voltages V B  and V C . This results in VCO  200  having two substantially constant oscillation bandwidths. 
     Referring to FIG. 3, a circuit diagram of a second dual band, band-switchable voltage controlled oscillator  300  is depicted according to one aspect of the invention. The band switched circuit  102 B includes a switchable variable capacitance circuit  120 B and a switchable fixed capacitance circuit  121 B. Capacitors  305 ,  306 ,  309 ,  310  are voltage variable capacitors and capacitors  303 ,  304 ,  307 ,  308  are fixed value capacitors. In this embodiment, when the control voltage V B  is at a high logic level (V C  is low), capacitors  309 ,  310  may be tuned by Vtune, capacitors  305 ,  306  assume a substantially fixed high capacitance state and the VCO  300  operates in a low frequency band. When the control voltage V C  is at a high logic level (V B  is low), capacitors  309 ,  310  cannot be tuned by Vtune and become substantially fixed value capacitors, while and capacitors  305 ,  306  assume a substantially low capacitance state and the VCO  300  operates in a high frequency band. As in FIG.  2  and in accordance with one aspect of the present invention, the ratio of fixed capacitance to variable capacitance within band switched circuit  102 B and tank circuit  103  remains substantially constant regardless of the state of control voltages V B  and V C . This results in VCO  300  having two substantially constant oscillation bandwidths. 
     Referring to FIG. 4, a simplified piece-wise linear graph of capacitance versus voltage across a VVC is depicted, illustrating an aspect of the invention. Curve  400  shows how the capacitance of a VVC in the band switchable circuits  102 A and  102 B of FIGS. 2 and 3, respectively, may vary as a function of the voltage across it (C-V curve). The voltage across the VVC may be a function of Vtune. 
     Referring to FIGS. 2 and 4, the operation of capacitors  204 ,  205  and  206 ,  207  is illustrated in Table I. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Operation of VVCs detailed in FIG. 2 
               
             
          
           
               
                   
                   
                 Voltage (volts) 
                   
               
             
          
           
               
                   
                   
                 204, 
                   
                 Capacitance (picoFarad) 
               
             
          
           
               
                   
                 V C   
                 V B   
                 205 
                 206, 207 
                 204, 205 
                 206,207 
               
               
                   
               
             
          
           
               
                 Low Band 
                 0 
                 2.5 
                 2.5 
                 1 
                 [+/−1.5] 
                 2 
                 1.5 +/− 0.5 
               
               
                 High Band 
                 2.5 
                 0 
                 −2.5 
                 −1.5 
                 [+/−1.5] 
                 1 
                 1 
               
               
                   
               
             
          
         
       
     
     When the VCO  200  is operating in a low band (V B  is high and V C  is low), the voltage across each of capacitors  204 ,  205  is 2.5 volts and they are substantially fixed with a 2 pF capacitance value. For capacitors  206 ,  207 , as Vtune varies between 0 and 3 Volts, the voltage applied across capacitors  206  and  207  varies between 2.5 and −0.5 Volts and their capacitances may vary between 1 and 2 pF, i.e. operation is centered around point  401  of curve  400 . When the VCO  200  is operating in a high band (V B  is low and V C  is high), the voltage across each of capacitors  204 ,  205  is −2.5 volts and they are substantially fixed with a 1 pF capacitance value. Capacitors  206 ,  207  cannot be tuned by Vtune and are also substantially fixed with a 1 pF capacitance value. 
     Referring to FIGS. 3 and 4, the operation of capacitors  305 ,  306  and  309 ,  310  is illustrated in Table II. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Operation of VVCs detailed in FIG. 3 
               
             
          
           
               
                   
                   
                 Voltage (volts) 
                   
               
             
          
           
               
                   
                   
                 305, 
                   
                   
                 Capacitance (picoFarad) 
               
             
          
           
               
                   
                 V C   
                 V B   
                 306 
                 309, 310 
                 305, 306 
                 309, 310 
               
               
                   
               
             
          
           
               
                 Low Band 
                 0 
                 2.5 
                 2.5 
                 1 
                 [+/−1.5] 
                 2 
                 1.5 +/− 0.5 
               
               
                 High Band 
                 2.5 
                 0 
                 0 
                 −1.5 
                 [+/−1.5] 
                 1 
                 1 
               
               
                   
               
             
          
         
       
     
     When the VCO  300  is operating in a low band (V B  is high and V C  is low), the voltage across each of capacitors  305 ,  306  is 2.5 volts and they are substantially fixed with a 2 pF capacitance value. For capacitors  309 ,  310 , as Vtune varies between 0 and 3 Volts, the voltage applied across capacitors  309  and  310  varies between 2.5 and −0.5 Volts and their capacitances may vary between 1 and 2 pF, i.e., operation is centered around point  401  of curve  400 . When the VCO  300  is operating in a high band (V B  is low and V C  is high), the voltage across each of capacitors  305 ,  306  is 0 volts and they are substantially fixed with a 1 pF capacitance value. In this state, capacitors  309 ,  310  cannot be tuned by Vtune and are substantially fixed with a 1 pF capacitance value. 
     As one of ordinary skill in. the art will recognize in light of this disclosure, while the circuits detailed in FIGS. 2 and 3 may provide similar functionality, the selection of a particular topology may depend on several factors, including the reference and tune voltages available, the type of variable element, and the layout. 
     Referring to FIG. 5, a circuit diagram of a third dual-band, band switchable voltage controlled oscillator  500  is depicted according to an aspect of the invention. The band switched circuit  102 C includes a switchable variable capacitance circuit  120 C and a switchable fixed capacitance circuit  121 C. Capacitors  503 ,  504 ,  509 ,  510  are voltage variable capacitors and capacitors  505 - 508  are fixed value capacitors. When the VCO  500  is to operate in a low frequency band, the control voltage V B assumes a high state (V C  is low) and it is applied to the switchable variable capacitance circuit  120 C via a pair of resistors  501 ,  502 , and a tuning voltage may be applied to a node between capacitors  507 ,  508  and  503 ,  504 . When the VCO  500  is to operate in a high frequency band, control voltage V C  assumes a high state (V B  is low) and it is applied to the switchable fixed capacitance circuit  121 C via a pair of resistors  511 ,  512 . In this high frequency band, capacitors  503 ,  504  are essentially fixed value capacitors. As in FIGS. 2 and 3, the ratio of fixed capacitance to variable capacitance within band switched circuit  102 C and tank circuit  103  remains substantially constant regardless of the state of control voltages V B  and V C . This results in VCO  500  having two substantially constant oscillation bandwidths 
     Still referring to FIG. 5, circuit element values may be chosen to provide a desired band shift and tuning range for each band. For a given value of tank inductance  132  (FIG.  1 ), a main tuning capacitance  131  and a fixed tank capacitance  130  may be selected to cover an upper band range. A center frequency F of a band of operation may be:          F   =     1       2                 π                 LC           ;                          
     where L is the equivalent inductance and C is the equivalent capacitance of the band switchable circuit  102  and tank circuit  103  of the VCO  500 . 
     For example, with Vtune at 0.5 volts and a target oscillation (center frequency) of F=3.22 Ghz, values for inductance and capacitance are L=390 pH and C=6.26 pF, respectively. For the low band, in order to arrive at a new target of 3.02 Ghz (with Vtune still at 0.5V), the capacitance increases to 7.12 pF total. The fixed and variable capacitances have a low capacitance when V B  is low and a high capacitance when V B is high, and a ratio of high to low capacitance is of about 2. Thus, the overall band switch capacitance may be increased by about 2 times the 0.86 pf difference in order to establish the required bandshift. The main tuning capacitance  131  may be designed taking the minimum band switch capacitance into account in order for the VCO  500  to stay at the upper band frequencies. 
     Still referring to FIG. 5, in order to maximize the effectiveness of the VVC pair  503 ,  504 , their series MIM capacitors  505 ,  506  may be chosen to be approximately twice the maximum VVC value. For the same reason, fixed value capacitors  507 ,  508  may be chosen to have about twice the capacitance of VVCs  509 ,  510 . In one embodiment, the desired ratio of total variable to fixed capacitance remains the same for each band and the VCO  500  maintains a substantially constant center frequency and bandwidth for each band. 
     Still referring to FIG. 5, according to one aspect of the invention, adjustments to the switchable fixed and variable capacitances  121 C,  120 C may be made to center each band with the desired bandwidth by observing that increasing either switchable fixed  121 C or switchable variable capacitance  120 C can increase the band shift and lower the low band of operation. Also, increasing the switchable fixed capacitance  121 C can decrease the low band bandwidth. Further, increasing the switchable variable capacitance  120 C can increase the low band bandwidth. 
     Referring to FIG. 6, a graph of the simulated dual-band, band switchable voltage controlled oscillator circuit output detailed in FIG. 5 is depicted illustrating an embodiment of the invention. The vertical axis is the frequency output of the VCO  500  in GHz, and the horizontal axis is the tuning voltage Vtune in volts. Plots  601  and  602  respectively show tuning curves for a higher and a lower band of operation of the VCO  500 . The results are summarized as illustrated in Table III. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE III 
               
             
             
               
                   
               
               
                 Summary of Results for Dual-Band VCO 
               
             
          
           
               
                   
                 0.5-3 V 
                   
                 Bandshift 
                 overall 
               
               
                   
                 tuning range 
                 Bandwidth 
                 (low/high) 
                 range 
               
               
                   
                   
               
             
          
           
               
                 High Band 
                 3.22-3.82 GHz 
                 600 MHz 
                 — 
                 — 
               
               
                 Low Band 
                 3.02-3.58 GHz 
                 560 MHz 
                 200/240 MHz 
                 800 Mhz 
               
               
                   
               
             
          
         
       
     
     In Table III, the bandshift column indicates the change in frequency from the lowest frequency of the low band to the lowest frequency of the high band, and the change in frequency from the high frequency of the low band to the high frequency of the high band. 
     Still referring to FIG. 6, the 0.5-3V tuning range can be read on the horizontal axis, while the bandwidth, band shift and overall range can be read from the vertical axis. For the lower range (low band), the VCO  500  has substantially the same bandwidth as the upper band. 
     As one of ordinary skill in the art will recognize in light of this disclosure, additional pairs of switched fixed and variable capacitance circuits may be added to the circuit in order to obtain constant bandwidth within more bands. The invention can include and N-band switched voltage controlled oscillator with constant tuning range, where N is an integer greater than 1. 
     Referring to FIG. 7, circuit diagram of a multi-band, band switchable voltage controlled oscillator  700  is depicted, representing an embodiment of the invention. The design of the three-band voltage controlled oscillator is similar to the one described for the dual-band circuit detailed above. A first band switchable circuit  102 D includes first switchable variable and fixed capacitances  120 D,  121 D and it is coupled to a second band switchable circuit  102 E. The second band switchable circuit  102 E, includes second switchable variable and fixed capacitances  120 E,  121 E. 
     Still referring to FIG. 7, a first pair of control voltages V D , V A , may be applied to the first band switchable circuit  102 E, and a second pair of voltages V B , V C  may be applied to the second band switchable circuit  102 E. These voltages are generated by a the control circuit  101 A. The VCO  700  can produce an output frequency with substantially constant bandwidth in up to four different frequency bands. In one embodiment, the VCO  700  may be designed to operate in three different frequency bands. Once again, and in accordance with one aspect of the present invention, the ratio of fixed capacitance to variable capacitance within band switched circuits  102 D and  102 E and tank circuit  103  remains substantially constant regardless of the state of control voltages V A , V B , V C  and V D . This results in VCO  700  having three substantially constant oscillation bandwidths. 
     Referring to FIG. 8, a graph of the simulated multi-band, band switchable voltage controlled oscillator output detailed in FIG. 7 is depicted illustrating an embodiment of the invention. The vertical axis is the frequency output of the. VCO  700  in GHz, while the horizontal axis is the tuning voltage Vtune in volts. Plots  801 ,  802 , and  803  show tuning curves for a high, mid, and low bands of operation of the VCO  700 , respectively. A set of results are summarized as illustrated in Table IV. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE IV 
               
             
             
               
                   
               
               
                 Summary of Results for Three-Band VCO 
               
             
          
           
               
                   
                 0.5-3 V tuning range 
                 Bandwidth 
                 Bandshift (low/high) 
               
               
                   
                   
               
             
          
           
               
                 High band 
                 3.55-4.22 GHz 
                 670 MHz 
                 — 
               
               
                 Mid band 
                 3.41-4.06 GHz 
                 650 MHz 
                 140/160 MHz 
               
               
                 Low band 
                 3.18-3.82 GHz 
                 640 MHz 
                 230/240 MHz 
               
               
                   
               
             
          
         
       
     
     In Table IV, as in Table III, the bandshift column indicates the differences between the lowest frequencies of the three bands and the differences between the highest frequencies of each of the three bands. 
     Still referring to FIG. 8, the 0.5-3V tuning range can be read on the horizontal axis, while the bandwidth, band shift and overall range can be read from the vertical axis. As may be seen with reference to FIG. 8, the bandwidths for the upper range (high band), middle range (mid band), and low range (low band) are substantially equal. 
     According to one embodiment of the invention, a tuning circuit, a band shift inverting circuit, and/or a bias and enable circuit may be used to provide operational voltages and/or controls to a band switchable voltage controlled oscillator. The tuning circuit may provide a tuning voltage Vtune. A band shift inverting circuit may provide a first selection voltage V B  and a second selection voltage V C . Another band shift inverting circuit may provide a third control voltage V A  and a fourth control voltage V D . As one of ordinary skill in the art will recognize in light of this disclosure, such circuits may assume a variety of forms known in the art. 
     The terms a or an, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. The term substantially, as used herein, is defined as at least approaching a given state. 
     Further, although the band switched voltage controlled oscillator with substantially constant tuning range described herein can be a separate module, it will be manifest that the band switched voltage controlled oscillator with constant tuning range may be integrated into the system with which it is associated. Furthermore, all the disclosed elements and features of each disclosed embodiment can be combined with, or substituted for, the disclosed elements and features of every other disclosed embodiment except where such elements or features are mutually exclusive. 
     The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” and/or “step for.” Subgeneric embodiments of the invention are delineated by the appended independent claims and their equivalents. Specific embodiments of the invention are differentiated by the appended dependent claims and their equivalents.