Abstract:
A cellular telephone utilizing a variable power voltage control oscillator that may achieve a high dynamic range in output power is disclosed. In some embodiments, a microprocessor may be provided to adjust the amplitude of the variable power voltage control oscillator in response to transmitted commands that may be received.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to cellular telephones.  
         BACKGROUND OF THE INVENTION  
         [0002]    New cellular technologies, such as Wideband Code Division Multiple Access (“WCDMA”) promises to bring to users new capabilities such as packet-switched data such as high-speed Internet applications and electronic multimedia mail. WCDMA technology may also offer high-capacity circuit-switched capabilities for delivery of full-motion video services and high quality voice communications.  
           [0003]    However, the WCDMA standard uses cellular telephones or other mobile transmitters to be manufactured having large dynamic ranges of a transmitted Radio Frequency (“RF”) power. For example, WCDMA standards may uses as much as a 70 dB range of transmit power. If the peak-to-minimum power fluctuations of the modulation, such as from a voice peak, are added to this number, a large dynamic range of greater than 90 dB may be needed.  
           [0004]    To keep manufacturing cost low, WCDMA transmitters may be designed to integrate a considerable portion of the radio frequency circuits, and other circuits, within a few intergraded circuits. For example, a WCDMA transmitter may be designed with as many of the RF circuits, such as voltage control oscillators, integrated on a single integrated circuit that may be considered a transmitter function block.  
           [0005]    However, the isolation between the input and the output of any transmitter function block may limit the dynamic range of that block by the amount of isolation that may be considered Pmin. In order to decrease power below Pmin, an effective increase in the isolation path must be achieved. An increase in isolation may typically be accomplished by physically distributing system components of the variable gain amplifier across a plurality of chips. This however may result in increased chip count and may increase manufacturing costs.  
           [0006]    In cellular telephones, a signal source such as a voltage controlled oscillator (VCO) may be amplified by one or more variable gain stages. The minimum output power of the cellular telephone may therefore be limited for the reasons detailed above with the result that unwanted signal source power may be present in the cell phone RF output. Therefore, a need exists to improve the dynamic range of a transmitter such as WCDMA mobile transmitters. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a block diagram of a embodiment of a cell phone in accordance with the present invention.  
         [0008]    [0008]FIG. 2 is a block diagram of a radio frequency section of a cell phone in accordance with a embodiment of the present invention.  
         [0009]    [0009]FIG. 3 is a block diagram illustrating a variable power vco in accordance with a embodiment of the present invention.  
         [0010]    [0010]FIG. 4 is a block diagram of a variable power voltage control oscillator in accordance with a embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0011]    In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However it would be understood by those of ordinary skill in the art that the present invention might be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in details so as not to obscure the present invention.  
         [0012]    It should be understood that the present invention might be used in a variety of applications. Although the present invention is not limited in this respect, the circuit disclosed herein maybe used in many apparatuses such as in the transmitters of a radio system. Radio systems intended to be included within the scope of the present invention include by way of example only, cellular radio telephone communications system, two way radio communications systems, one way pagers, two way pagers, personal communications systems (PCS), and the like.  
         [0013]    Types of cellular radio telephone communication systems intended to be within the scope of the present invention include, although are not limited to, direct sequence- code division multiple access (DS-CDMA) cellular radio telephone communications systems, wideband CDMA and CDMA  2000  cellular radio telephone systems, global systems for mobile communications (GSM) cellular radio telephone systems, North American Digital Cellular (NADC) cellular radio telephone systems, time division multiple access (TDMA) systems, enhanced data for GSM evolution (EDGE), Universal Mobile Telecommunication Systems (UMTS) and WCDMA.  
         [0014]    Referring now to FIG. 1, a cellular telephone  10  may include an antenna  12  coupled to a radio frequency interface  14 . The cellular telephone  10  may be in accordance with any of the available communications standards. The interface  14  may communicate with a base band processor  16  over a bus  15 . Likewise, the base band processor  16  may communicate with an applications processor  22  over an interface  20 . The base band processor  16  maybe coupled to a memory  18  and the application processors  22  maybe coupled to a memory  24 . In some embodiments, both the base band processor  16  and the applications processor  22  may be integrated into the same integrated circuit. In other embodiments, they may be on separate integrated circuits.  
         [0015]    A display  28  and a keyboard  30  may be coupled to the applications processor  22 . Additionally, in some embodiments, a base band processor  16  may also be coupled to a variable power voltage controlled oscillator (VPVCO)  34 . The base band processor  16  may control the output power of the voltage controlled oscillator  34  through one or more control signals  38 . VPVCO  34  maybe coupled to the radio frequency interface  14  through one or more signal lines  36 .  
         [0016]    As will be discussed in more detail subsequently, a base band processor  16  may control the output power of the VPVCO  34  and, in that manner, may effectively provide for an increased dynamic range in the output power of the cell phone  10 .  
         [0017]    Referring now to FIG. 2, a portion  200  of the radio frequency interface  14  is illustrated. A digital signal processor (DSP)  201  may receive a signal over bus  15  and produce two constant envelope vectors I and Q,  203  and  205  respectively, which may provide inputs to a modulator  207 . An output  209  from modulator  207  may provide inputs to a phase detector  211  and an amplitude detector  213 . An output  215  from the phase detector  211  may be coupled to a signal generator  217 . The signal generator  217  may include a loop filter and a VPVCO not illustrated. A variable power input  38  may also be coupled to a signal generator  217 . Output  219  of the signal generator  217  may be coupled to an out phasing signal generator  221 . Amplitude detector  213  may be coupled to a signal shaping circuit  223  that, in some embodiments, may be coupled to an input signal  225  that may comprise a GSM-EDGE signal. Outputs  227  and  229  of the signal shaping circuit  223  may provide additional inputs to the out phasing signal generator  221 . Outputs  231  and  233  of the out phasing generator  221  may provide inputs to a combiner and a radio frequency power amplifier circuit  235 .  
         [0018]    Output  12  of the combiner and radio frequency amplifier  235  maybe coupled to an antenna and to a feedback circuit  237 . An output  239  of the feedback circuit  237  may provide an additional input to the phase detector  211 .  
         [0019]    In some embodiments, feedback circuit  237  may include a step attenuator to step down the output power from the combiner and radio frequency amplifier  235  to a lower level. Additionally, feedback circuit  237  may include an RF mixer and phase splitter that may serve, in some embodiments, to mix down the frequency of the output of the combiner and RF amplifier  235  to a lower frequency and to adjust the phase of that signal prior to the input of phase detector  211 .  
         [0020]    Phase detector  211 , in some embodiments, may generate a phase error signal that may represent the difference in the phase between the feedback signal  239  and the signal  209  from the input modulator  207 . This error signal may then be utilized by the signal generator  217  to adjust a frequency of an internal VPVCO (not shown).  
         [0021]    Referring now to FIG. 3, in some embodiments, signal generator  217  may include a loop filter  301  that maybe coupled to a VPVCO  303  by an error signal  305 . Loop filter  301  in some embodiments, receives the output of phase detector  211  and filters the output of phase detector  211  to provide the error signal  305  to the variable power vco  303 . The VPVCO  303  maybe designed such that changes in the signal  305  may cause the VPVCO  303  to change frequency in response to variations in error signal  305 . Also, the output power of the VPVCO, in some embodiments, may change in response to changes in the variable power control signal  38 .  
         [0022]    Referring now to FIG. 4, a differential VCO  401  may produce two output signals  403  and  405  that maybe of similar amplitude but phase shifted by  180  degrees from each other. These signals  403  and  405  may, in some embodiments, be buffered by buffer amplifier  407  that may be coupled through signal lines  219  to the out phasing signal generator  221  (shown in FIG. 2). To change the amplitude of the output signals  403  and  405 , in some embodiments, the current provided by controlled current source  409  may be varied and thereby may change the current through transistors  411  and  413 . The amplitude of the oscillation on signals  403  and  405  may be proportional to the dc current through transistors  411  and  413  since the dc current may define both the large and small signal transconductance of the transistors  411  and  413 .  
         [0023]    The variable frequency resonator  415  may be, in some embodiments, a voltage controlled oscillator. The voltage control oscillator  415  may be constructed as a Colpits, Hartley, or other oscillator type. The adjustment of the frequency of the VCO  415  may be accomplished by changing a voltage that may be applied to a voltage sensitive capacitor such as, in some embodiments, a varactor diode. As a voltage across a varactor diode varies, the net capacitance applied to an oscillator circuit, which incorporates the varactor diode, may also change thereby effecting a frequency shift. In some embodiments, error signal  305  may be coupled to a varactor diode, not illustrated, that may be part of the VCO  415  to effect a frequency shift of VCO  415 .  
         [0024]    To provide a feedback path for detecting the oscillation amplitude of the differential VCO  401 , in some embodiments, output signal lines  403  and  405  may be coupled to a low pass filter  419  by a signal feedback circuit  431 . The signal feedback circuit  431  may serve, in some embodiments, to combine the output signals  403  and  405 , that may be differential signals, to provide an input  433  to the low pass filter  419 . Signal  417  may include an alternating current (AC) signal and a direct current (DC) component that may be proportional to the amplitude of the oscillation of the differential VCO  401 . Signal  417  may also include an offset voltage due to the current dependent voltage of the controlled current source  409 .  
         [0025]    The output  421  of the low pass filter may be coupled to one input of a differential amplifier  423 . Another input to differential amplifier  423  may be provided by a reference voltage circuit  425  that may be coupled to an output  427  of a second difference amplifier  429 . The output  427  of the differential amplifier  429  may also be coupled to the controlled current source  409  to provide adjustment of the controlled current provided by the controlled current source  409 . An output from the differential amplifier  423  may be coupled to an input of differential amplifier  429 . A second input to differential amplifier  429  maybe provided by signal  38  that may be coupled to base band processor  16  (shown in FIG. 1).  
         [0026]    In some embodiments, the detection of the oscillation amplitude of the differential VCO  401  maybe achieved by filtering signal line  417 . Signal line  417  may include an alternating current (AC) frequency signal, a direct current (DC) component that may be proportional to the amplitude of the oscillation of differential voltage control oscillator  401  and a voltage offset due to the current dependent voltage of the control current source  409 . The detection of the amplitude may be achieved by filtering signal  417  with the low pass filter  419  and then subtracting a reference voltage  425  with a differential amplifier  423 . The obtained signal,  431 , may then be combined, in some embodiments, with the variable power control signal  38  with the differential amplifier  429  and then coupled to the current source  409 .  
         [0027]    The reference voltage circuit  425  may produce a voltage reference voltage that may be the current dependent voltage of the controlled source  409 . In some embodiments, reference voltage circuit  425  may include a VCO that may be coupled to controlled current source (not illustrated). Manufacturing the reference voltage circuit  425  on the same integrated circuit and in close proximity to the differential VCO  401  may significantly reduce both process and temperature variation affects.  
         [0028]    As discussed above, the output amplitude of the differential VCO  401  may be adjusted by adjusting signal  38 . The base band processor  16 , or other processor, to control, in part, the transmitter power in accordance with WCDMA or other standards, may adjust signal  38 . The processor  16  or other processor may receive a power command from the cellular or other system commanding a reduction or an increase in transmitter output power. In response thereto, the processor  16  or other processor may effect a change in the VPVCO output amplitude and may change the gain in one or more RF amplifiers that receive, in part, the VPVCO output signal(s) or a signal or signals derived, in part, from the VPVCO output signal(s). In some embodiments, this reduction in the differential voltage controlled oscillator output may serve to effectively increase the dynamic range of the transmitting circuit, in part, by reducing the input signal to subsequent amplifier stages in a transmitter. This increase in dynamic range may be achieved utilizing a single integrated circuit that may contain the VPVCO and other coupled amplifiers although the scope of the present invention is not limited in this respect. The integration of the VPVCO and other coupled amplifiers onto a single integrated circuit may provide for manufacturing and other efficiencies.  
         [0029]    While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalence will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes has fall within the true spirit of the invention.