Abstract:
Briefly, according to embodiments of the invention, there is provided a method and an apparatus to compensate for a closed loop response error of a transfer function of a phase locked loop unit.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Transmitters and/or receivers of wireless communication systems such as, for example, a cellular radio communication system, wireless local area network (WLAN) and the like, may include an offset phase locked loop (OPLL) unit. The OPLL may receive for example a Gaussian minimum shift keying (GMSK) modulated signal and may upconvert the GMSK signal into a radio frequency (RF) signal. The RF signal may be transmitted by a transmitter. For example, in a cellular radio transmitter, an OPLL unit may be used to upconvert an intermediate frequency (IF) signal into the RF signal.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0002]     The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanied drawings in which:  
         [0003]      FIG. 1  is a schematic illustration of a wireless communication system according to an exemplary embodiment of the present invention;  
         [0004]      FIG. 2  is a block diagram of a radio device according to some exemplary embodiments of the present invention;  
         [0005]      FIG. 3  is a schematic block diagram of an offset phase locked loop according to some exemplary embodiments of the invention; and  
         [0006]      FIG. 4  is a schematic block diagram of an offset phase locked loop according to another exemplary embodiment of the invention. 
     
    
       [0007]     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0008]     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to obscure the present invention.  
         [0009]     Some portions of the detailed description, which follow, are presented in terms of algorithms and symbolic representations of operations on data bits or binary digital signals within a computer memory. These algorithmic descriptions and representations may be the techniques used by those skilled in the data processing arts to convey the substance of their work to others skilled in the art.  
         [0010]     Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system&#39;s registers and/or memories into other data similarly represented as physical quantities within the computing system&#39;s memories, registers or other such information storage, transmission or display devices. In addition, the term “plurality” may be used throughout the specification to describe two or more components, devices, elements, parameters and the like. For example, “plurality of mobile stations” describes two or more mobile stations.  
         [0011]     It should be understood that the present invention may be used in a variety of applications. Although the present invention is not limited in this respect, the circuits and techniques disclosed herein may be used in many apparatuses such as transmitters and/or receivers of a radio system. Transmitters and/or receivers intended to be included within the scope of the present invention may be included, by way of example only, within a wireless local area network (WLAN), two-way radio communication system, digital communication system, analog communication system transmitters, cellular radiotelephone communication system, and the like.  
         [0012]     Types of cellular radiotelephone communication system intended to be within the scope of the present invention include, although are not limited to, Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communication (GSM), General Packet Radio Service (GPRS), extended GPRS extended data rate for global evolution (EDGE), and the like.  
         [0013]     Turning to  FIG. 1 , a wireless communication system  100  in accordance with exemplary embodiment of the invention is shown. Although the scope of the present invention is not limited in this respect, wireless communication system may include at least one base station (BS)  110  and at least one mobile station  120 . In this exemplary embodiment of the invention, MS  120  may include a PLL  130 , a transceiver  140  and antennas  150  and  160 .  
         [0014]     Although the scope of the present invention is not limited in this respect types of antennas that may be used for antenna  150  and/or antenna  160  may include an internal antenna, a dipole antenna, an omni-directional antenna, a monopole antenna, an end fed antenna, a circularly polarized antenna, a micro-strip antenna, a diversity antenna and the like.  
         [0015]     Although the scope of the present invention is not limited in this respect, in some embodiments of the invention, PLL unit  130  may include an OPLL unit. According to embodiments of the invention PLL unit  130  may include one or more compensation filters to compensate the closed loop transfer function of the PLL unit  130  if desired.  
         [0016]     Although the scope of the present invention is not limited to this embodiment, OPLL unit  130  may provide an RF signal to transceiver  140 . For example, transceiver  140  may include at least one GSM receiver and/or at least one GSM transmitter, if desired. Transceiver  140  may receive from OPLL unit  130  the RF signal which may be transmitted through antennas  150  and  160 , if desired. It should be understood by persons skilled in the art that transceiver  140  may include any suitable type of a cellular transceiver, a WLAN transceiver, a two-way radio transceiver, a digital radio transceiver, or the like.  
         [0017]     Turning to  FIG. 2 , a schematic block diagram of a radio device  200  according to an exemplary embodiment of the invention is shown. Although the scope of the present invention is not limited in this respect, radio device  200  may include a PLL unit  300  and a transmitter  250 . Transmitter  250  may be able to transmit a signal (e.g. RF signal) via antennas  260  and  270 . In some exemplary embodiments of the invention, transmitter  250  may include a power amplifier (PA)  240 .  
         [0018]     Although the scope of the present invention is not limited in this respect, PLL  300  may include a compensation filter  305 , for example, a digital filter, or any other suitable type of filter. According to some embodiments of the present invention, compensation filter  305  may compensate the closed loop transfer function of the PLL unit  300 , for example OPLL unit. PLL unit  300  may further include a phase detector PD)  320  to detect a phase of an input signal, a loop filer  330 , a voltage controlled oscillator (VCO)  340 . A feedback path of PLL unit  300  may include a mixer  345  operably coupled to a local oscillator (LO)  310  and other filters (not shown).  
         [0019]     Although the scope of the present invention is not limited in this respect, PLL unit  300  may receive an intermediate frequency (IF) signal. One or more components of PLL unit  300  may upconvert the IF signal into a corresponding signal carried by a final carrier frequency, e.g., a RF signal, if desired. In this embodiment, VCO  340 &gt;may upconvert the IF signal into a corresponding RF signal. Mixer  345  and LO  310  may downconvert the RF signal into an IF signal which may be inputted to PD  320 . The RF signal may be amplified by PA  240  and may be transmitted via antenna  260 , if desired.  
         [0020]     Turning to  FIG. 3 a  block diagram of an OPLL unit  400  according to some exemplary embodiments of the invention is shown. Although the scope of the present invention is not limited in this respect, OPLL unit  400  may include a digital section  410 , an analog section  440 , and a RF section  460 . In this exemplary embodiment, digital section  410  may include compensation filters  415 ,  420  and digital to analog converters (DAC)  425  and  430 . Analog section  440  may include analog reconstruction filters (ALPF)  445 ,  450 , an image reject mixer (IRM)  455 , a local oscillator (LO)  460 , a phase detector (PD)  465 , a loop filter  470  and an image reject filter (IRF)  475 . RF section  480  may include a VCO  485 , a mixer  490  and a LO  495 .  
         [0021]     According to this exemplary embodiment of the invention, OPLL  400 , which may also be referred to as a translation loop transmitter, may translate an input modulated signal into a RF signal at an output terminal of VCO  485 . According to some embodiments of the invention, the input modulated signal may include one or more base band signals. In some others embodiment of the present invention, the input modulated signal may include one or more IF signals, although the scope of the present invention in no way limited in this respect.  
         [0022]     According to exemplary embodiments of the invention, compensation filters  415 ,  420  may compensate for the known closed-loop response of the OPLL unit. For example, compensation filters  415 ,  420  may be designed to yield flat frequency response of the OPLL closed-loop transfer function, if desired. According to other embodiment of the invention, compensation filter  415 ,  420  may be designed to compensate the closed loop response transfer function of the OPLL unit  400 . Furthermore, embodiments of the invention may include compensation filters  415 ,  420  which include Pre-Emphasis filters, if desired. Furthermore, compensation filter  415  may compensate an in-phase closed loop transfer function of OPLL unit  400  and compensation filter  420  may compensate a quadrature closed loop transfer function of OPLL unit  400 .  
         [0023]     Although the scope of the present invention is not limited in this respect, compensation filters  415 ,  420  may be implemented by hardware or by software or by any combination of hardware and/or software. For example, compensation filters  415 ,  420  may be implemented by a digital signal processor (not shown), if desired.  
         [0024]     Although the scope of the present invention is not limited in this respect an exemplary closed loop transfer function H of OPLL  400  may be depicted as follows:  
       H   =           θ   0     ⁡     (   s   )           θ   i     ⁡     (   s   )         =         K   d     ⁢     K   0     ⁢     F   ⁡     (   s   )           s   +       K   d     ⁢     K   0     ⁢     F   ⁡     (   s   )                   
 
 Where, 
 
         [0025]     s may be the complex frequency in the Laplas domain (i.e, jω);  
         [0026]     Kd may be the phase detector coefficient (in units of [Volt/Rad]);  
         [0027]     K0 may be the VCO coefficient (in units of [Hz/Volt]); and  
         [0028]     F(s) may be the loop filter&#39;s transfer function.  
         [0029]     In some exemplary embodiments of the present invention, a digital signal, for example an In-Phase (I) signal, may be inputted to compensation filter  415  and a digital signal, for example a Quadrature phase (Q) signal, may be inputted to compensation filter  415 . DACs  425 ,  430  may convert the filtered I and Q signals into corresponding analog signals. ALPFs  445 ,  450  may suppress spectral replicas of the converted signals, if desired.  
         [0030]     Although the scope of the present invention is not limited in this respect, IRM  455  may include a quadrature modulator. The quadrature modulator may yield a modulated signal, centered at a designated intermediate frequency. In some embodiment of the invention, LO  460  may provide a reference signal, if desired. IRM  455  may combine and upconvert the I and Q signals and may output a modulated signal to PD  465 . For example, PD  465  may be implemented in the discrete digital domain by using trigonometric functions, or by exclusive-OR designs or the like.  
         [0031]     According to this exemplary embodiment of the invention loop filter  470  may filter a phase detected signal and VCO  485  may upconvert the modulated signal into a corresponding RF signal. Mixer  490 , LO  495  for example, a tuned local oscillator and IRF  475  may down convert the RF signal into a feedback signal to be fed to PD  465 .  
         [0032]     Turning to  FIG. 4 a  block diagram of an OPLL  500  according to some other exemplary embodiments of the invention is shown. Although the scope of the present invention is not limited in this respect, OPLL  500  may include a digital section  510 , an analog section  540 , and an RF section  560 . In this exemplary embodiment, digital section  510  may include compensation filters  515 ,  520 , an image rejection modulator (IRM)  530 , a phase detector (PD)  540 , a digital loop filter  550 , a digital to analog converter (DAC)  560 , and analog to digital converters (ADC)  565 . Analog section  540  may include analog reconstruction filters (ALPF)  570  and an image reject filter (IRF)  475 . RF section  580  may include a VCO  585 , a mixer  590  and a LO  595 .  
         [0033]     According to this exemplary embodiment of the invention, digital section  510  may be implemented by digital hardware (e.g. DSP) or by software, or by any combination of hardware and software. Compensation filters  515 ,  520  may be digital filters which may be able to compensate for the known closed-loop response of OPLL  500 . For example, compensation filters  415 ,  420  may be designed to yield a flat frequency response of the OPLL closed-loop transfer function. According to other embodiment of the invention, compensation filter  515 ,  520  may be designed to compensate a closed loop response error of a transfer function of OPLL unit  500 . Additionally, embodiments of the invention may include compensation filters  515 ,  520 , which may include Pre-Emphasis filters, if desired.  
         [0034]     According to this exemplary embodiment, digital signals I and Q may be filtered by compensation filters  515 ,  520 . IRM  520  may digitally combine compensated I and Q signals into a modulated digital signal. However, according to another embodiment of the invention, I and Q signal may be inputted directly to IRM  520  and the IRM may compensate for the closed loop response error of a transfer function of OPLL unit  500 , although the scope of the present invention is not limited to this embodiment.  
         [0035]     PD  540  may detect a phase of the digital modulated signal. The digital modulate signal may be filtered by DLPF  550 . For example, in some embodiments of the invention, DLPF  550  may be a digital filter that operates as a loop-filter for the phase-locked-loop. Furthermore, DLPF  550  may be a software reconfigurable loop filter to configure a closed loop bandwidth of OPLL unit  500 . DLPF  550  may be used to attenuate loop noises and/or to shape the closed loop response of the OPLL unit  500 , if desired. DAC  560  may convert the digital signal into a corresponding analog signal, and the converted analog signal may be filtered by ALPF  570 . VCO  585  may up-convert the converted analog signal into a corresponding RF signal.  
         [0036]     Although the scope of the present invention is not limited in this respect, a feedback path of OPLL  500  may include mixer  590 , LO  595 , IRF  575  and ADC  565 . According to these exemplary embodiments, one or more components of the feedback path may down-convert a portion of the RF signal into a digital signal that may be fed to PD  540 , although the scope of the present invention is not limited to this exemplary embodiment of the invention.  
         [0037]     While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.