MIXER OSCILLATOR STAGE

Abstract: Until now, a switched 2-band concept of a mixer oscillator stage has been developed independently of a 3-band concept. The invention provides a mixer oscillator stage which can be used both with the switched 2-band concept and the 3-band concept without changing the architecture of the mixer oscillator stage. This is achieved by using a number of oscillators which exceeds the number of mixers and by coupling the mixer(s) and oscillators via switching means so as to switch between the different oscillators in dependence upon the part of the band converging the signal.

Description: Mixer oscillator stage. The invention relates to a mixer oscillator stage. The invention further relates to a mixer oscillator integrated circuit and to a tuner. The invention also relates to a receiver, more particularly but not exclusively a television receiver. Such a mixer oscillator stage is used in, for example, television receivers. Different solutions are known for such a mixer oscillator stage. As is known, television signals comprise signals in the bands historically referred to as UHF and NHF bands. In most cases, the VHF band is split into at least two ranges (NHFL and NHFH). For 3-band tuners, the different bands are often referred to as A, B and C, or Low, Mid and High. For 2-band tuners, it is customary to refer to the bands as NHF-Low, VHF -High and UHF, although the UHF band may be capable of receiving frequencies transmitted below the UHF band. The most straightforward solution is to use the 3-band concept with its own mixer and oscillator for each band. The above solution is quite complex. To reduce the costs of three different bands, a switching between the low and high NHF signals is performed. The range switching is normally performed with a switching diode which selects a different coil inductance for VHF-Low and NHF-High. Especially, if the mixer oscillator stage is implemented as an integrated circuit which also has a PLL function, referred to as MO-PLL Combi IC, a 3-band tuner is not possible without exceeding the 28-pin structure as the 2-band switched version has. The 28-pin package is one of the largest cost-effective packages available today. To reduce the number of necessary pins, it is proposed to pursue asymmetrical input / output functions. To achieve a good performance, a good isolation between the mixer/oscillator functions like oscillators, mixers, and the IF amplifier is necessary. It is hardly possible to achieve this good isolation by using asymmetrical input /output functions. Balanced signal pairs and balanced circuitry have so far provided the best performance. The performance must meet the more stringent requirements recently imposed by the European CEΝELEC directive EΝ55020. EN55020 is a European directive on EMC requirements for television and sound broadcast receivers and associated equipment. Special attention must be paid during tuner design to ensure that the requirements are met. One of the disadvantages of the known mixer oscillator stages (topologies) is that different mixer oscillator topologies are necessary for the 3-band concept and for the switched 2-band concept, making the development of at least two different topologies expensive and time-consuming. A further disadvantage is that the 3-band concept (especially MOPLL Combi) requires more input and oscillator pins necessary for the mixer oscillator integrated circuit. It is object of the invention to overcome the disadvantages of the prior art and further to provide a mixer oscillator stage, a mixer oscillator integrated circuit, a tuner and a television receiver having an improved performance. To this end, a first aspect of the invention provides a mixer oscillator stage as defined in claim 1. A second aspect of the invention provides a mixer oscillator integrated circuit as defined in claim 3. A third aspect of the invention provides a tuner as defined in claim 4. A fourth aspect of the invention provides a receiver as defined in claim 5. By choosing the number of oscillators to be larger than the number of mixers and by using switching means in between, the same mixer oscillator stage can be used for different applications. The cost of development are thereby largely decreased. An embodiment of a mixer oscillator stage according to the invention has the features of claim 2. By using three oscillators and switching means, it is possible to use the same mixer oscillator stage for a 2-band switched concept and for a genuine 3-band concept. 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 drawings. In these drawings: Figure 1 shows a first embodiment of a tuner according to the invention, Figure 2 shows a second embodiment of a tuner according to the invention, and Figure 3 shows an embodiment of an input circuit for use in a tuner according to the invention. Identical elements are denoted by the same reference numerals throughout the description. Figure 1 shows a first embodiment of a tuner TUN1 according to the invention, having an input II for receiving an antenna signal. The input II is coupled to a VHF tuned input circuit VIC1 and to a UHF tuned input circuit UICl . The tuned input circuits VIC1 and UICl are coupled to amplifier stages VAM1 and UAMl, respectively. Each amplifier stage is coupled to a bandpass filter VF1 and UFl, respectively. The bandpass filter VF1 is coupled via a varicap diode vdl to a first input ilO of a mixer oscillator integrated circuit MOIC 1. The bandpass filter UFl is coupled via a first and a second inductance indl 1 and indl 2 to a second and a third input il 1 and il2 of the mixer oscillator integrated circuit MOIC1. The first input ilO is coupled to a first mixer MIX11 of the mixer oscillator integrated circuit, and the second and third inputs il 1 and i 12 are coupled to a second mixer MIX 12 of the mixer oscillator integrated circuit. The tuner TUN1 further comprises a first, a second and a third oscillator OSCl 1, OSCl 2 and OSCl 3, which oscillators are part of the mixer oscillator stage MOSl and are coupled to one of the mixers MIX11 and MIX 12 via first and second switching means SW11 and SW12, respectively. The output of each mixer MIX11 and MIX12 is coupled to an output OI of the tuner TUN1 for supplying an IF signal. The mixer oscillator integrated circuit MOIC1 and the oscillators OSCl 1, OSCl 2 and OSCl 3 are part of the mixer oscillator stage. This embodiment of the tuner TUN1 operates as follows. After receiving the antenna signal at the input II, the signal in this embodiment is split into a VHF band and a UHF band, in which the tuned input circuit VIC1, the amplifier stage VAM1 and the filter VF1 will handle the VHF signals (as is known to those skilled in the art). The tuned input circuit UICl, the amplifier stage UAMl and the filter UFl will handle the UHF signals (as is also known to those skilled in the art). In this embodiment, the filtered signals are supplied to the mixer oscillator integrated circuit MOIC1 at inputs ilO, input il 1 and il2, respectively. The VHF signals are supplied to the mixer MIX11, the other input of which receives, via the switching means SW11, a signal from either the first oscillator OSCl 1 or the second oscillator OSCl 2, depending on the part of the VHF band the required signal belongs to. After mixing, the mixer supplies the IF signal at the output OI. Nowadays, UHF signals are handled symmetrically. The UHF filter UFl supplies the UHF signal symmetrically via the inductances indl 1 and indl 2 to the mixer MIX12, the other input of which receives a signal from either the second oscillator OSC12 or the third oscillator OSC13, depending on the part of the UHF band the required signal belongs to. In this way, the mixer oscillator stage can handle all the signals of a switched 2- band concept. Instead of an implementation as an integrated circuit, it is also possible to obtain a mixer oscillator stage with discrete components only. Figure 2 shows a second embodiment of a tuner TUN2 according to the invention, having an input 12 for receiving an antenna signal. The input is coupled to tuned input circuits IC21 , IC22 and IC23, respectively. Each tuned input circuit is coupled to an amplifying stage AM21, AM22 and AM23, respectively. Each amplifying stage is coupled to a filter F21, F22 and F23, respectively. The filter F21 is coupled via a varicap diode vd2 to a first input i20 of a mixer oscillator integrated circuit MOIC2. The filter F22 is coupled via a first and a second inductance ind21, ind22 to a second and a third input i21, i22, respectively, of the mixer oscillator integrated circuit. The filter F23 is coupled via a third and a fourth inductance ind23 and ind24 to the second and the third input i21, i22 respectively, of the mixer oscillator integrated circuit. The tuner TUN2 further comprises a first, a second and a third oscillator OSC21, OSC22 and OSC23, which oscillators are part of the mixer oscillator stage MOS2 and are coupled to one of the mixers MIX21 and MIX22 via first and second switching means SW21 and SW22, respectively. The output of each mixer MIX21, MIX22 is coupled to an output 02 of the tuner TUN2 for supplying an IF signal. This embodiment of the tuner TUN2 operates as follows. As will be noted in this embodiment of the tuner TUN2, this tuner is built up as a 3-band concept. Similarly as in Figure 1 the mixer oscillator integrated circuit MOIC2 receives the different filtered signals at either input i20 or, as symmetrical signal, at the inputs i21 and i22. Also in this embodiment, the mixer oscillator stage MOS2 comprises two mixers MIX21 and MIX22 and three oscillators OSC21, OSC22 and OSC23. The relevant mixer MIX21 (MIX22) receives the filtered signal at one input (symmetrical input) and the signal from either oscillator OSC21 or OSC22 (OSC22 or OSC23) at the other input. The mixer concerned supplies the obtained IF signal to the output of the tuner TUN2. As is shown in relation to Figures 1 and 2, the same mixer oscillator stage MOSl, MOS2 can be used for the switched 2-band concept (Figure 1) and the 3-band concept (Figure 2). As mentioned above, instead of an implementation as a mixer oscillator integrated circuit, it is also possible to implement the mixer oscillator stage with discrete components only. Figure 3 shows an embodiment of filter means for use in a tuner according to the invention. The input circuit IC3 receives an antenna signal at an input 13. A first tuned circuit Tl comprising diode D3 and inductance L3 is coupled to the input 13 via an inductance L6 and a capacitance Cl. A second tuned circuit T2 comprising diode Dl and inductance LI is coupled to the input 13 via inductance L4. A third tuned circuit T3 comprising diode D2 and inductance L2 is coupled to the input 13 via an inductance L5 and the capacitance Cl. The inductances L4, L5 and L6 are coupling coils which perform an impedance transformation from the antenna impedance to the varying frequency-dependent impedance of the tuned circuits Tl, T2 and T3. For signals intended for tuned circuit Tl, the filter can be considered as a highpass filter comprising of L4+L1, Cl and L5+L2. This input circuit has been described extensively in the United States Patent US-A-4,851 ,796 which patent is herein incorporated by reference. In the above description, the idea of the invention has been described on the basis of some examples. It is to be noted that those skilled in the art will be well aware of many different solutions within the scope of the invention concerned. The invention provides a mixer oscillator stage which can be used both with the switched 2-band concept and the 3-band concept without changing the architecture of the mixer oscillator stage.

Claims: CLAIMS: 1. A mixer oscillator stage comprising mixing means with at least one mixer, oscillator means with at least two oscillators and switching means coupled between the at least one mixer and the at least two oscillators, the number of oscillators exceeding the number of mixers. 2. A mixer oscillator stage as claimed in claim 1, characterized in that the oscillator means comprises a first, a second and a third oscillator, the mixing means comprises a first and a second mixer, and the switching means are coupled between the mixers and the oscillators. 3. A mixer oscillator integrated circuit comprising the mixing means and switching means as claimed in claim 1. 4. A tuner comprising a mixer oscillator stage as claimed in claim 1. 5. A receiver comprising a tuner as claimed in claim 4.

Inventors: BREKELMANS JOHANNES H A, BREKELMANS, JOHANNES, H., A.
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SVENSKA AB, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS AB
Application year: 1999
Main classification: H03J5
IPC codes: H03J5, H04B1