Abstract:
A television receiver includes a digital TV preamp for amplifying a received RF signal within a first frequency range, a satellite TV preamp for amplifying the received RF signal within a second frequency range, a first mixer having inputs coupled to the output of either the digital or satellite TV preamp according to a mode selection signal, a digital TV band-pass filter for filtering the output of the first mixer centered at a first center frequency being selectively coupled to the output of the first mixer according to the mode selection signal, a satellite TV band-pass filter for filtering the output of the first mixer centered at a second center frequency being selectively coupled to the output of the first mixer according to the mode selection signal, and a second mixer stage having inputs coupled to the output of the digital TV filter stage and the satellite TV filter stage.

Description:
CROSS REFERENCE To RELATED APPLICATIONS  
       [0001]    This is a continuation-in-part of application Ser. No. 10/604,018, filed on Jun. 22, 2003, entitled “Passive Harmonic Mixer” and assigned to the same assignee, the contents of which are incorporated herein by reference. This is also a continuation-in-part of application Ser. No. 10/707, 319, filed on Dec. 4, 2003, entitled “Harmonic Mixer Based Television Tuner And Method of Processing a Received RF Signal” and assigned to the same assignee, the contents of which are incorporated herein by reference. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to television tuners, and more particularly, to a dual mode television tuner for processing both satellite TV signals and digital TV signals.  
           [0004]    2. Description of the Prior Art  
           [0005]    One of the most significant costs in television manufacturing is the cost of the tuner. Furthermore, with the increasing desire to integrate TV functions into personal computer (PC) systems and other electronic devices, the cost of the tuner needs to be reduced. Additionally, television tuners are no longer just used for processing analog TV signals. Satellite TV and digital TV are both increasing in popularity everyday.  
           [0006]    Traditionally, tuners have been comprised of two basic components. The first component performs high frequency to intermediate frequency (RF to IF) conversion. Subsequently, the second component performs IF to baseband conversion. The TV tuner was originally designed for broadcast television reception within a television set, which is essentially a stand-alone unit containing a cathode ray picture tube. So, TV tuners were originally integral parts embedded in a single-purpose device.  
           [0007]    Presently, however, state-of-the-art consumer electronic devices use TV tuners that are not a built-in part of a television set. The tuner is a separate element that is connected to a cathode ray picture tube at some point, but the tuner is not an integral part of the monitor. As previously mentioned, TV tuners may be fabricated on circuit boards and then installed in personal computer systems, thereby allowing the PC to function as a television set. These tuners convert a radio frequency television signal into a baseband (or low frequency) video signal, which can then be passed on to other elements in the PC for video processing applications.  
           [0008]    [0008]FIG. 1 shows a highly integrated television tuner  100  on a single microcircuit as disclosed by U.S. Pat. No. 5,737,035. The television tuner  100  includes an adjustable low noise amplifier  101 ; a first mixer  102 ; a first local oscillator  104 ; a band-pass filter  106 ; a second mixer  108 , which is an image rejection type mixer; a second local oscillator  110 ; a first intermediate frequency amplifier  112 ; a second band-pass filter  114 ; and a variable intermediate frequency amplifier  116 . However, as the television tuner  100  requires the use of a special image rejection mixer for the second mixer  108 , the cost of the tuner is increased. Additionally, the first local oscillator  104  is used in conjunction with the first mixer  102  to up-convert a particular channel selected from an incoming RF signal. This means the first local oscillator  104  must be a variable frequency local oscillator having a large operating frequency range. Because the phase noise over the operating frequency range of the first local oscillator  104  must meet a specific phase noise requirement, typically 84 dBC/Hz, a plurality of VCOs having smaller frequency ranges, and therefore lower phase noise, must be used. Additionally, the television tuner  100  is not capable of processing satellite TV signals. If a device needs to process both digital TV signals and satellite TV signals, a first television tuner for digital TV signals must be used in addition to a second television tuner for satellite TV signals. This increases the overall cost of the device. Accordingly, a need exists for a television tuner having reduced cost and being capable of processing both digital TV signals and satellite TV signals.  
         SUMMARY OF INVENTION  
         [0009]    It is therefore a primary objective of the claimed invention to provide a dual mode television tuner, to solve the above-mentioned problems and process both digital TV signals and satellite TV signals.  
           [0010]    According to the claimed invention, a first preamp stage for amplifying and filtering a received RF signal within a first frequency range, a second preamp stage for amplifying and filtering the received RF signal within a second frequency range, a first mixer being selectively coupled to either the first preamp stage or the second preamp stage according to a mode selection signal for generating a first intermediate-frequency signal, a first band-pass filter being selectively coupled to the first mixer according to the mode selection signal for filtering the first intermediate-frequency signal, a second band-pass filter being selectively coupled to the first mixer according to the mode selection signal for filtering the first intermediate-frequency signal, and a second stage being coupled to the first band-pass filter and the second band-pass filter for generating an output signal.  
           [0011]    Also according to the present invention, a method is disclosed for processing a received RF signal by a TV tuner, wherein the received RF signal is in at least one of a first frequency range and a second frequency range, the method comprising the following steps:pre-amplifying and filtering the received RF signal to form a pre-amplified signal;selectively mixing the pre-amplified signal with a first local oscillating signal to produce a first intermediate frequency signal, wherein the frequency of the first local oscillating signal is variable and is determined according to the frequency range of the received RF signal;filtering the first intermediate frequency to form a filtered intermediate signal; and selectively mixing the filtered intermediate signal with a second local oscillating signal to produce an output signal, wherein the frequency of the second local oscillating signal is fixed and is determined according to the frequency range of the received RF signal.  
           [0012]    These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is an integrated television tuner according to the prior art.  
         [0014]    [0014]FIG. 2 is a first dual mode television tuner capable of processing both digital and satellite television signals according to a first embodiment of the present invention.  
         [0015]    [0015]FIG. 3 is a second dual mode television tuner capable of processing both digital and satellite television signals according to a second embodiment of the present invention.  
         [0016]    [0016]FIG. 4 is a flowchart illustrating a method of processing a received RF signal according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]    [0017]FIG. 2 shows a first dual mode television tuner  200  capable of processing both digital and satellite television signals according to the first embodiment of the present invention. The dual mode television tuner  200  includes a digital TV preamp stage  202  and a satellite TV preamp stage  204 . The digital TV preamp stage  202  comprises a digital TV low-noise amplifier  232  and a first digital TV bandpass filter  230 . The satellite TV preamp stage  204  comprises a satellite TV low-noise amplifier  236  and a first satellite TV band-pass filter  234 . The dual mode television tuner  200  further comprises a first switch  206 , a first mixer  208 , a first local oscillator  210 , a second switch  212 , a digital TV band-pass filter  214 , a satellite TV band-pass filter  216 , a processor  228 , and a second stage  238 . The first digital TV band-pass filter  230  has a frequency range of 50 MHz to 860 MHz and the second digital TV band-pass filter  214  has a center frequency of 1220 MHz. The first satellite TV band-pass filter  234  has a frequency range of 950 MHz to 1800 MHz and the second satellite band-pass filter  216  has a center frequency of 480 MHz. In the first embodiment of the present invention, the second stage  238  includes a second mixer  218 , a second local oscillator  220 , an output amplifier  222 , a band-pass filter  224 , and a variable amplifier  226 .  
         [0018]    In the preferred embodiment of the present invention, the mixers  208 ,  218  are implemented as harmonic mixers as shown in FIG. 2. The operation and implementation of the harmonic mixer is explained in application Ser. No. 10/604,018, filed on Jun. 22, 2003, entitled “Passive Harmonic Mixer” and assigned to the same assignee. Because harmonic mixers  208 ,  218  are used, the first local oscillator  210  and the second local oscillator  220  run at half the frequency that would otherwise be required if non-harmonic mixers were used. The first local oscillator  210  operates at a variable frequency range between 635 MHz to 1140 MHz and provides a 0° phase signal and a 90° phase signal. The second local oscillator  210  operates at a first fixed frequency or a second fixed frequency depending on a mode selection signal and provides a 0° phase signal and a 90° phase signal.  
         [0019]    It should also be noted that, although the preferred embodiment of the present invention uses harmonic mixers, non-harmonic mixers can also be used with the present invention. If non-harmonic mixers are used, the operating frequency of the first local oscillator  210  and the second local oscillator  220  will be twice that of the frequencies described for the preferred embodiment of the present invention. Additionally, the local oscillators  210 ,  220  only need to provide a 0° phase signal.  
         [0020]    The operation of the first dual mode TV tuner  200  shown in FIG. 2 is as follows. When the source of the TV signals (RF_IN) is determined (usually by the user), the processor  228  sets the mode selection signal to configure the dual mode TV tuner  200  for the proper operation. If digital TV mode is selected by the processor  228  using the mode selection signal MODE, the digital TV low-noise amplifier  232  is turned on, the satellite TV low-noise amplifier  236  is turned off, the first switch  206  couples the output of the first digital TV preamp stage  202  to the input of the first mixer  208 , and the second switch  212  couples the output of the first mixer  208  to the input of the second digital TV band-pass filter  214 . In this way, a received radio frequency signal RF_IN is amplified by the digital TV low-noise amplifier  232  and is filtered by the first digital TV band-pass filter  230 . The output of the first mixer  208  is a first intermediate signal and has a desired channel in the received RF signal positioned at 1220 MHz, which is the center frequency of the bandwidth of the second digital TV band-pass filter  214 . The output of the second digital TV band pass filter  214  is coupled to the input of the second mixer  218 . The second local oscillator  220  operates at a constant frequency of 588 MHz and the output of the second mixer  218  is a second intermediate frequency centered at 44 MHz. The second intermediate frequency signal is amplified, filtered, and amplified again by the output amplifier  222 , the band-pass filter  224 , and the variable amplifier  226 , respectively.  
         [0021]    Alternatively, if satellite TV mode is selected by the processor  228  using the mode selection signal MODE, the satellite TV low-noise amplifier  236  is turned on, the digital TV low-noise amplifier  232  is turned off, the first switch  206  couples the output of the first satellite TV preamp stage  204  to the input of the first mixer  208 , and the second switch  212  couples the output of the first mixer  208  to the input of the second satellite TV band-pass filter  216 . In this way, the received radio frequency signal RF_IN is amplified by the satellite TV low-noise amplifier  236  and is filtered by the first satellite TV band-pass filter  234 . The output of the first mixer  208  is a first intermediate signal and has a desired channel in the received RF signal positioned at 480 MHz, which is the center frequency of the bandwidth of the second satellite TV band-pass filter  216 . The output of the second satellite TV band pass filter  216  is coupled to the input of the second mixer  218 . The first local oscillator operates at a constant frequency of 218 MHz and the output of the second mixer  218  is a second intermediate frequency centered at 44 MHz. The second intermediate frequency signal is amplified, filtered, and amplified again by the output amplifier  222 , the band-pass filter  224 , and the variable amplifier  226 , respectively.  
         [0022]    [0022]FIG. 3 is a second dual mode television tuner  300  capable of processing both digital and satellite television signals according to the second embodiment of the present invention. The second dual mode television tuner  300  comprises similar components and structure as the first dual mode television tuner  200  shown in FIG. 2. Components having the same operation as already described for FIG. 2 have been shown in FIG. 3 having the same numerical label and a repeated description of these components is hereby omitted. The difference between the first dual mode television tuner  200  shown in FIG. 2 and the second dual mode television tuner  300  shown in FIG. 3 is that the second dual mode television tuner  300  comprises a modified second stage  302 . The second stage  302  acts as a direct conversion receiver (DCR) and includes a second local oscillator  304 , a second mixer  306 , a third mixer  314 , an in-phage output amplifier  308 , an in-phase low-pass filter  310 , an in-phase variable amplifier  312 , a quadrature output amplifier  316 , a quadrature low-pass filter  318 , and a quadrature variable amplifier  320 . The operation and implementation of the DCR are explained in application Ser. No. 10/707,319, filed on Dec. 4, 2003, entitled “Harmonic Mixer Based Television Tuner And Method of Processing a Received RF Signal” and assigned to the same assignee If digital TV mode is selected by the processor  228  using the mode selection signal MODE, the second local oscillator  304  operates at a constant second frequency of 610 MHz and provides a 0° phase-delayed reference signal, a 45° phase-delayed reference signal, a 90° phase-delayed reference signal, and a 135° phase-delayed reference signal. The second harmonic mixer  306  mixes the 0° phase-delayed reference signal, the 90° phase-delayed reference signal, and the output of the second digital TV band-pass filter  214  to form an in-phase baseband signal. The in-phase baseband amplifier  308 , the in-phase low-pass filter  310 , and the in-phase variable amplifier  312  filter and amplify the in-phase baseband signal to produce an in-phase baseband output signal I for processing in later stages in the TV receiver. The third harmonic mixer  314  mixes the 45° phase-delayed reference signal, the 135° phase-delayed reference signal, and the output of the second digital TV band-pass filter  214  to form a quadrature baseband signal. Likewise, the quadrature baseband amplifier  316 , the quadrature low-pass filter  318 , and the quadrature variable amplifier  320  filter and amplify the quadrature baseband signal to produce an quadrature baseband output signal Q for processing in later stages in the TV receiver. Together, the output I of the in-phase variable amplifier  312  and the output Q of the quadrature variable amplifier  320  form a baseband video signal, which can then passed on to other video processing elements.  
         [0023]    If satellite TV mode is selected by the processor  228  using the mode selection signal MODE, the operation of the second mixer stage  302  is the same as for digital TV mode with the exception that the second local oscillator  304  operates at a constant second frequency of 240 MHz and the filtered first intermediate frequency signal is received from the output of the second satellite band-pass filter  216 .  
         [0024]    [0024]FIG. 4 is a flowchart illustrating a method of processing a received RF signal according to the embodiment of the present invention. The received RF signal can be a digital TV signal or a satellite TV signal. The flowchart includes the following steps:  
         [0025]    Step  400 : Pre-amplify and filter the received RF signal for a first frequency range or a second frequency range depending on the type of the received RF signal. For digital TV signals, the first frequency range is from 50 MHz to 860 MHz, and for satellite TV signal, the second frequency range is from 950 MHz to 1800 MHz.  
         [0026]    Step  402 : Mix the output of step  400  with a first reference signal to a particular channel selected from an incoming RF signal and produce a first intermediate signal. When using a harmonic mixer to perform step  402 , the first reference signal is variable between 635 MHz to 1140 MHz.  
         [0027]    Step  404 : Band-pass filter the first intermediate signal centered at a first center frequency or a second center frequency depending on the type of the received RF signal. For digital TV signals, the center frequency is 1220 MHz, and for satellite TV signals, the center frequency is 480 MHz.  
         [0028]    Step  406 : Mix the output of step  404  with a second reference signal to produce an output signal. As previously mentioned, step  406  may involve a single mixer wherein the output signal is a second intermediate signal. Alternatively, step  406  may involve an in-phase mixer and a quadrature mixer wherein the output signal is a baseband signal. The frequency of the second reference signal depends on the type of the received RF signal. In a first embodiment having a second intermediate frequency output signal using a harmonic mixer, the second reference signal is 588 MHz for digital TV signals and 218 MHz for satellite TV signals. In another embodiment having a baseband output signal using dual harmonic mixers, the second reference signal is 610 MHz for digital TV signals and 240 MHz for satellite TV signals.  
         [0029]    Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.