Abstract:
A tuner, for example, for a television receiver, includes a UHF and a VHF section and a mixer oscillator stage. It is known that the VHF frequency band has to be split in at least two parts to handle the VHF signals. To that end, the mixer oscillator stage uses two separate VHF oscillators and a detector to switch tuned parts of the VHF section. In this way, the performance of the tuner is improved.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a tuner for tuning an input signal, having an input for receiving the input signal, a UHF section coupled to the input for handling UHF signals, a VHF section coupled to the input for handling VHF signals, the UHF section and the VHF section being coupled, with outputs, to a mixer oscillator stage which comprises UHF oscillation means with a UHF tuning circuit, and VHF oscillation means with a VHF tuning circuit, said mixer oscillator stage being coupled to an output of the tuner. The invention further relates to a mixer oscillator stage. 
     The invention further relates to a receiver, more particularly, but not exclusively to a television receiver. 
     2. Description of the Related Art 
     Such a tuner is used in, for example television receivers. For such a tuner, different solutions are known. As is known, television signals comprise signals in the so-called UHF and VHF band, which are tuned with a UHF section and a VHF section. Tuning can, for example be accomplished by the change in capacitance with an applied dc voltage to varicap diodes. One diode is used in each tuned circuit. Tuning the signals of the UHF band can be covered by a single varicap diode, whereas the tuning of the signals of the VHF band has to be split into at least two ranges and at least two varicap diodes are necessary. The most straight forward solution is to use a so-called 3-band concept (UHF, VHFL and VHFH) having, for each band, its own path: a tuned input circuit, a so-called RF amplifier and a bandpass filter. The UHF, VHFL and VHFH sections are then followed by a mixer oscillator (and PLL) stage. 
     As the above solution is quite complex, nowadays, to reduce the costs of three separate bands, a switching between the low and high VHF signals (channels) is used. A solution to perform this is to simply short-circuit, with a switching diode, a part of the tuning coil in the relevant resonant circuit to change the tuning frequency range. To obtain the off state of the switching diode, it is well known in the art to supply a negative voltage to the anode of the switching diode. Further, it is known that when the negative voltage is not connected to the switching diode, the switching diode in the oscillator circuit operates as a detector and provides a negative voltage for the other tuned circuits. 
     See for example “Television and Audio Handbook, page 9.22, Figure. 9.15”. 
     One of the disadvantages of the use of a diode detector is that a good switching diode is a poor detector. Sometimes the switching diode for the oscillator circuit is selected using a so-called detector test. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a tuner, a mixer oscillator stage and a receiver that do not have the disadvantages of the prior art, and, further, to improve the performance and to lower the costs of a tuner. To this end a first aspect of the invention provides a tuner as described in the opening paragraph, characterized in that the VHF oscillation means comprises a first and a second VHF oscillator, with, respectively, a first and a second VHF tuning circuit for, respectively, a first and a second VHF frequency range, and the tuner comprises detecting means for detecting which VHF oscillator is operating, the detecting means being arranged to supply a switching signal to the switchable elements of the VHF section. A second aspect of the invention provides a mixer oscillator stage for use in such a tuner. A third aspect of the invention provides a receiver compromising such as a tuner. 
     The invention is based on the recognition that by using two separate oscillators for the VHF signals, less parallel capacitance on the lower band VHF oscillator circuit exists than with a biased switching diode in a combined VHF tuning circuit of one VHF oscillator. Further, the tuner is much less complex as the known 3-band concept and as the known switched version. By detecting the VHFL oscillator signal when this oscillator is switched on, the detecting means provides a negative voltage to switch-off the switching diodes of the other tuned circuits. 
     An embodiment of a tuner according to the invention characterized in that the VHF section comprises a series arrangement of a switchable tuned input circuit, an amplifier stage, a switchable primary high frequency band filter and a switchable secondary high frequency band filter, these switchable circuits being under switching control of the detecting means. 
     All tuned circuits of the VHF section are supplied with the switching signal of the detecting means. 
     An embodiment of a tuner according to the invention characterized in that the detecting means comprises a diode detector coupled to the first VHF tuning circuit, the detecting means being part of the mixer oscillator stage. 
     Normally, capacitance can be added to further improve tracking in the lower VHF band, but by adding a diode detector as detecting means instead, a negative voltage can be generated. This negative voltage can then be used as switching signal for the other switchable tuned circuits of the VHF section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention and additional features which may optionally be used to implement the invention to advantage will be apparent from and elucidated with reference to the examples described hereinafter and shown in the Figures, in which: 
     FIG. 1 shows a block schematic diagram of a tuner according to the invention; 
     FIG. 2 shows a block schematic diagram of a tuner according to the invention in more detail; 
     FIG. 3 shows a more detailed block schematic diagrams of a tuner of the invention; and 
     FIG. 4 shows part of a schematic diagram of a mixer oscillator stage according to the invention. 
     Throughout the description same elements will be indicated with corresponding reference signs. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a block schematic diagram of a tuner  1  according to the invention. The tuner has an input AI, for an antenna, or a cable input. Further the tuner comprises a UHF section US and a VHF section VS for handling, respectively, the UHF and VHF signals. The outputs of the UHF section and the VHF section are coupled to a mixer oscillator stage MIOS, which comprises a UHF oscillator OSU with a UHF tuned circuit UTC, and a first and a second VHF oscillator OSVL and OSVH with respective VHF tuned circuits VTCL and VTCH, whereby the tuned circuits normally will be located outside an integrated circuit whereas the other parts of the mixer oscillator stage MIOS can be located inside the integrated circuit. 
     An output of the mixer oscillator stage is coupled to an output MFO of the tuner  1  for supplying the MF signal. 
     The tuner further comprises detecting means DM which can be part of the mixer oscillator stage (dashed line in FIG. 1) for receiving a detecting signal D 1  from the mixer oscillator stage and for supplying a switching signal S 1 . 
     At the input AI, the tuner receives signals, for example, television signals being in different frequency bands (VHF and UHF). The VHF section and the UHF section select the relevant frequencies. Further, the mixer oscillator stage MIOS is programmed to receive the relevant frequency band by switching on the relevant oscillator that is, the UHF oscillator (OSU), or the first (OSVL) or second (OSVH) VHF oscillator, and a port to supply a relevant voltage or current as is known in the art. When the first (lower) VHF frequency band has to be received the first VHF oscillator is operating and the detecting means receive a detecting signal D 1  from the mixer oscillator stage and supply a switching signal S 1  (for example, negative voltage) to the switching diode&#39;s of the tuned circuits in the VHF section. 
     Below the operation of an example of the tuner according to the invention will be further described with reference to FIGS. 2,  3  and  4 . 
     FIG. 2 shows an embodiment of a tuner  1 ′ according to the invention in more detail. Herein, the UHF section and VHF section are shown in more detail. Normally both the UHF and the VHF section comprise a tuned input circuit UIC and VIC, respectively, a (RF) amplifier stage UAM and VAM, respectively a primary high frequency band filter UPF and a secondary high frequency band filter USF and USF, respectively. Except for the amplifier stage, all other parts of the UHF and VHF section contain tuned circuits which normally comprise so called varicaps and inductances, whereby the varicaps receive a tuning voltage (not shown in this figure, see FIG. 3 for more details). 
     The parts of the VHF section having tuned circuits also have to change over from the first (lower) VHF frequency band to the second (higher) VHF frequency band or vice versa. This changing over is achieved by switching on the relevant oscillator and port (see FIG. 4, Q 41 ). 
     Also in this example, the mixer oscillator stage MIOS 2  comprises a UHF oscillator OSU 2  with a UHF tuned circuit UTC 2 , and a first and second VHF oscillator OSVL 2  and OSVH 2  with a first and a second VHF tuned circuit VTCL 2 , and VTCH 2 , respectively. 
     When operating in the lower VHF frequency band, the oscillator OSVH 2  is switched off and the first VHF oscillator OSVL 2  is operating. The detecting signal D 2 , indicating that the first VHF oscillator is operating, is supplied to the detecting means DM 2 , the detecting means providing the switching signal S 2  as the negative voltage to switch off the switching diodes of the tuned circuits of the VHF section. 
     FIG. 3 shows a schematic block diagram of a tuner  1 ″ according to the invention in more detail. Herein the UHF section US 3  and the VHF section VS 3  are showed in more detail. The input AI 3  is coupled to the respective tuned input circuit UIC 3  and VIC 3 . These tuned input circuits comprise a varicap diode D 8  and D 7 , respectively, and an inductance L 8  and a series arrangement of a inductance L 7  and a parallel arrangement of an inductance L 12  and a capacitor C 10  in series with a switching diode D 12 , respectively. The varicap diodes D 8  and D 7  receive a (not shown) tuning voltage for tuning to the requested frequency. 
     The switching diode D 12  of the tuned input circuit VIC  3  is coupled to the detecting means DM 3  for receiving a switching signal S 3 . 
     The tuned input circuits UIC 3  and VIC 3 , respectively are coupled to the (RF) amplifier stage UAM 3  and VAM 3 , respectively. Each amplifier stage is coupled to a primary high frequency band filter UPF 3  and VPF 3 , respectively, whereby each filter comprises a varicap diode D 1  and D 3 , respectively, and an inductance L 1  and a series of arrangement of an inductance L 3  and a parallel arrangement of an inductance L 9  and a capacitor C 1  in series with a switching diode D 9 , respectively. 
     This switching diode D 9  of the primary high frequency band VPF 3  also receives the switching signal S 3  from the detecting means DM 3 . The varicap diode&#39;s D 1  and D 3 , respectively, also receive a (not shown) tuning voltage. 
     Each primary high frequency band filter is coupled to a secondary high frequency band filter USF 3  and VSF 3 , respectively, whereby each filter comprises a varicap diode D 2  and D 4 , respectively, and an inductance L 2  and a series arrangement of an inductance L 4  and a parallel arrangement of an inductance L 10  and a capacitance C 2  in series with a switching diode D 10 . Also the varicap diodes D 4  and D 2 , respectively, receive a (not shown) tuning voltage. 
     This switching diode D 10  of the secondary high frequency band filter VSF 3  also receives the switching signal S 3  from the detecting means DM 3 . 
     Each secondary high frequency filter USF 3 , respectively, is coupled to the mixer oscillator stage MIOS 3 . In the figure, the coupling is simplified with capacitances C 3 , C 4  and C 5 . As is known to the man skilled in the art, the practical coupling is more complex, but, as being not relevant to the invention concerned, not further explained here. 
     In this example, the mixer oscillator stage MIOS 3  comprises the UHF tuning circuit UTC 3 , a first VHF tuning circuit VTCL 3  and a second VHF tuning circuit VTCH 3 , coupling capacitances C 7 , C 8 , C 6 , and C 9  and a mixer oscillator integrated circuit MOIC comprising a UHF oscillator and a first VHF oscillator OSVL 3  and a second VHF oscillator OSVH 3 . The tuned circuits of the oscillators are normally placed outside the integrated circuit. As the mixer oscillator integrated circuit, for example, a Philips TDA 6404  can be used. Further, the mixer oscillator stage MIOS 3  can comprise the detecting means DM 3  (dash-point line). 
     The detecting means is coupled to the mixer oscillator stage MIOS for receiving a detecting signal D 3  which indicates that the first (lower) VHF oscillator OSVL 3  is operating. The detecting means DM 3  supplies on the basis of the detecting signal the switching signal S 3  to the switching diodes of the relevant parts of the VHF section VS 3 . The mixer oscillator integrated circuit MOIC is coupled to the output MFO 3  of the tuner for supplying the MF signal. 
     FIG. 4 shows, in more detail, part of a schematic diagram of a mixer oscillator stage. This diagram shows a first tuning circuit VTCL 4  for the first VHF frequency band (lower) and a second tuning circuit VTCH 4  for the second VHF frequency band (higher). The first tuning circuit VTCL 4  comprises an inductance L 41  and a series arrangement of a varicap diode D 41  and a capacitance C 45 . Between the varicap diode and the capacitance a tuning voltage VT is supplied via a resistor R 41 . This tuning circuit is coupled via capacitances C 41  and C 42  to the mixer oscillator integrated circuit MOIC 4  to a first VHF oscillator OSVL 4 . 
     A detecting means DM 4  is coupled in parallel to the inductance L 41  and comprises a diode D 43  operating as a detector and a parallel arrangement of a resistor R 44  and a capacitance C 47 . The cathode of the diode D 43  is coupled, via a resistor R 45 , to a transistor Q 41  of the mixer oscillator integrated circuit MOIC 4 . This transistor is the VHFH port that supplies a positive voltage when switched on. When the first VHF oscillator is operating, this transistor is switched off. The side of the resistor R 45  that is coupled to the transistor is also coupled to a resistor R 46  which is coupled with its other side to the (not shown) other tuned circuits of the VHF section VS 3  (see FIG. 3) for supplying a switching signal S 4 . 
     The other tuned circuit VTCH 4  of the mixer oscillator stage comprises an inductance L 42  and a series arrangement of a varicap diode D 42  and a capacitance C 46 , whereby a tuning voltage VT is supplied at the connection point of the varicap diode D 42  and the capacitance C 46 . The connection point of the varicap diode D 42  and the inductance L 42  is coupled via a resistance R 42  to ground. The tuned circuit VTCH 4  is coupled via capacitances C 43  and C 44  to a second VHF oscillator OSVH 4  of the mixer oscillator integrated circuit MOIC 4 . 
     In the above description, the idea of the invention has been described on the basis of some schematic diagrams. The man skilled in the art will be well aware of a lot of different solutions that fall within the scope of the invention concerned. 
     A tuner according to the invention can be used in a television receiver, a multi-media receiver, etc. 
     The detecting means can be incorporated in the mixer oscillator stage as is indicated in the schematic diagram of figure. 
     Further it is, for example, possible to integrate the detector means in the mixer oscillator integrated circuit MOIC. 
     The invention provides a tuner, a mixer oscillator stage and a receiver having such a tuner whereby by splitting the VHF oscillator in two separate VHF oscillators (so no switching diodes in the VHF tuned circuits of the oscillator). Further, detecting means are used to switch the tuned circuits of the VHF section. This results in an improved performance and lowered costs of the tuner.