BACKGROUND 
     The invention relates to a mixer-system comprising gain-blocks and switches, and also relates to a gain-block-system for use in a mixer-system, and to a mixer for use in a mixer-system, and to a gain-block for use in a mixer-system and comprising at least a first, a second, a third, a fourth and a fifth gain-block-transistor, and to an apparatus which comprises a mixer-system, and to a method for mixing data input signals and oscillation signals. 
     Such an apparatus for example corresponds with a receiver for receiving modulated signals to be mixed (to be frequency translated or frequency converted) downwardly via a mixer-system or corresponds with a transmitter for transmitting modulated signals to be mixed (to be frequency translated or frequency converted) upwardly by a mixer-system etc. 
     DESCRIPTION OF THE RELATED ART 
     A prior art mixer-system is known from EP 0 316 999 A1, which discloses, in its  FIG. 1 , a mixer circuit comprising gain-blocks (transistors T 5 ,T 6 ) and mixers (transistors T 1 ,T 2 ,T 3 ,T 4 ). 
     The known mixer-system is disadvantageous, inter alia, due to being flexible insufficiently. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention, inter alia, of providing a more flexible mixer-system. 
     Further objects of the invention are, inter alia, providing a gain-block-system for use in a more flexible mixer-system, and a mixer for use in a more flexible mixer-system, and a gain-block for use in a more flexible mixer-system, and an apparatus which comprises a more flexible mixer-system, and a more flexible method for mixing data input signals and oscillation signals. 
     The mixer-system according to the invention comprises gain-blocks and switches, wherein control electrodes of a first, a second, a third and a fourth gain-block constitute data inputs for guiding data input signals, with first main electrodes of the first and third gain-block being coupled to each other and to a first impedance and with first main electrodes of the second and fourth gain-block being coupled to each other and to a second impedance for constituting outputs for guiding output signals, and with second main electrodes of the first and second gain-block being coupled to each other via a first switch and with second main electrodes of the third and fourth gain-block being coupled to each other via a second switch, with control electrodes of the switches constituting oscillation inputs for guiding oscillation signals. 
     By using the first main electrodes of the four gain-blocks as outputs and by using the control electrodes of the four gain-blocks as data inputs, with the second main electrodes of the first and second gain-block being coupled via the first switch and with the second main electrodes of the third and fourth gain-block being coupled via the second switch, and by using the control electrodes of the switches as oscillation inputs, a new type of flexible mixer-system has been designed. Due to certain parts of this mixer-system being responsible for certain parameters (for certain parts of the performance) and other parts of the mixer-system being responsible for other parameters (for other parts of the performance), several parameters (several parts of the performance) can now be improved flexibly. 
     For example the linearity of the mixer-system will be solely determined by the linearity of the gain-blocks as long as the switches will have a sufficiently low on-resistance. 
     The data input signals for example comprise Radio Frequency (RF) signals like for example RF voltages or RF currents to be converted into RF voltages via resistors, etc. The output signals for example comprise Intermediate Frequency (IF) signals like for example IF currents, etc. The oscillation signals for example originate from an oscillator and for example comprise square wave signals like for example square wave voltages or square wave currents to be converted into square wave voltages via resistors, etc. 
     An input guiding a signal may correspond with a positive signal arriving at or being present at this input or with a negative signal leaving or being present at this input, and vice versa. And an output guiding a signal may correspond with a positive signal leaving or being present at this output or with a negative signal arriving at or being present at this output, and vice versa. 
     An embodiment of the mixer-system according to the invention is defined by each switch comprising at least one switch-transistor, with each gain-block comprising at least one gain-block-transistor. 
     By providing each switch with one switch-transistor and by providing each gain-block with one gain-block-transistor, a simple embodiment has been created requiring little chip surface. 
     An embodiment of the mixer-system according to the invention is defined by a third, fourth, fifth, sixth and seventh impedance. 
     By providing the mixer-system with the third, fourth, fifth, sixth and seventh impedance, a mixer-system has been created which, when driven by a balanced data input source, will have a good performance (low noise, low distorsion) due to parasitic capacitances of the switch-transistors carrying no or little differential data input signal. 
     An embodiment of the mixer-system according to the invention is defined by a third and fifth impedance. 
     By providing the mixer-system with the third and fifth impedance and leaving out the fourth, sixth and seventh impedance, the mixer-system can be driven in a single ended mode (by a single ended data input source). 
     An embodiment of the mixer-system according to the invention is defined by a third and fourth switch. 
     By providing the mixer-system with the third switch parallel to the first switch and with the fourth switch parallel to the second switch, with control electrodes of the third and fourth switch guiding the further oscillation signals, which further oscillation signals for example originate from a further oscillator and for example comprise further square wave signals at for example three or five or seven times etc. the frequency of the oscillation signals comprising for example the square wave signals, the third of fifth or seventh harmonic etc. is suppressed. Of course, dependently upon the gain of the mixer-system related to this third or fifth or seventh harmonic etc., values for the (further) oscillator and/or values for the (further) impedances will need to be chosen properly. 
     An embodiment of the mixer-system according to the invention is defined by an eighth, nineth, tenth, eleventh and seventh impedance. 
     By providing the mixer-system with the eighth, nineth, tenth, eleventh and seventh impedance, a mixer-system has been created which, when driven by a balanced data input source, will have a good performance (low noise, low distorsion) due to parasitic capacitances of the switch-transistors carrying no or little differential data input signal. 
     An embodiment of the mixer-system according to the invention is defined by an eighth and tenth impedance. 
     By providing the mixer-system with the eighth and tenth impedance and leaving out the nineth, eleventh and seventh impedance, the mixer-system can be driven in a single ended mode (by a single ended data input source). Of course, the fifth and sixth embodiment respectively can be combined with the second and third embodiment respectively. 
     An embodiment of the mixer-system according to the invention is defined by a first, second, third, fourth and fifth gain-block-transistor. 
     By providing each switch with one switch-transistor and by providing each gain-block with the first, second, third, fourth and fifth gain-block-transistor, a highly linear mixer-system has been created, due to this gain-block applying negative feedback over several stages. This mixer-system will have an excellent performance (low noise, low distorsion) due to parasitic capacitances of the switch-transistors carrying no differential data input signal (a consequence of the fully balanced situation). 
     A current guiding terminal may supply a positive current leaving the terminal and flowing to the load or may supply a negative current arriving at the terminal via the load, or vice versa. A voltage guiding terminal may supply a positive voltage or a negative voltage. And of course, one or more of the second to sixth embodiments can be combined with this seventh embodiment. 
     Embodiments of the gain-block-system according to the invention and of the mixer according to the invention and of the gain-block according to the invention and of the apparatus according to the invention and of the method according to the invention correspond with the embodiments of the mixer-system according to the invention. 
     The invention is based upon an insight, inter alia, that the flexibility of a mixer-system depends upon its configuration, and is based upon a basic idea, inter alia, that for a more flexible configuration data input signals are to be supplied to the gain-blocks and that oscillation signals are to be supplied to switches for switching couplings between gain-blocks. 
     The invention solves the problem, inter alia, of providing a more flexible mixer-system, and is advantageous, inter alia, in that its performance is improved and can be further improved easily. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments(s) described hereinafter. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates in block diagram form a basic mixer-system according to the invention, 
         FIG. 2  illustrates in block diagram form a gain-block according to the invention for improving the basic mixer-system, 
         FIG. 3  illustrates in block diagram form an improved mixer-system according to the invention which suppresses a higher harmonic, and 
         FIG. 4  illustrates in block diagram form an apparatus according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The basic mixer-system according to the invention shown in  FIG. 1  comprises four gain-blocks  1 - 4  for example each comprising one transistor, like a bipolar transistor or a Field Effect Transistor (FET). Control electrodes (B) of gain-blocks  1  and  4  are coupled to each other and via a resistor  22  to a voltage source  41  (for biasing purposes) and to one side of current sources  30  and  31  which generate data input signals. The other side of current sources  30  and  31  is coupled to control electrodes (B) of gain-blocks  2  and  3 , which are coupled to each other and via a seventh impedance  17  (like for example a resistor etc.) to voltage source  41  (for biasing purposes). 
     First main electrodes (C) of gain-blocks  1  and  3  are coupled to each other and constitute a first output  32  coupled via a first impedance  11  (like for example a resistor etc.) to a voltage source  40  (main supply). First main electrodes (C) of gain-blocks  2  and  4  are coupled to each other and constitute a second output  33  coupled via a second impedance  12  (like for example a resistor etc.) to voltage source  40 . Voltage sources  40  and  41  are further coupled to ground. 
     Second main electrode (E) of gain-block  1  is coupled via a current source  42  (for biasing purposes) to ground and is coupled via a third impedance  13  (like for example a resistor etc.) to a first main electrode of a first switch  5  (for example comprising one or more switch-transistors, like a MOSFET). Second main electrode (E) of gain-block  2  is coupled via a current source  43  (for biasing purposes) to ground and is coupled via a fourth impedance  14  (like for example a resistor etc.) to a second main electrode of first switch  5 . A control electrode of switch  5  is coupled to a first output of an oscillator  34  for receiving a first oscillation signal. 
     Second main electrode (E) of gain-block  4  is coupled via a current source  45  (for biasing purposes) to ground and is coupled via a fifth impedance  15  (like for example a resistor etc.) to a first main electrode of a second switch  6  (for example comprising one or more switch-transistor, like a MOSFET). Second main electrode (E) of gain-block  3  is coupled via a current source  44  (for biasing purposes) to ground and is coupled via a sixth impedance  16  (like for example a resistor etc.) to a second main electrode of second switch  6 . A control electrode of switch  6  is coupled to a second output of oscillator  34  for receiving a second oscillation signal. 
     The mixer-system according to the invention has the advantage that the mixer (switches  5  and  6 ) are embedded in gain-blocks  1 - 4  which can be optimised for linearity and noise. The first and second oscillation signals are inverse signals like for example square wave signals etc., which drive one of the switches  5  and  6  in an on-state (low on-resistance) and the other one in an off-state (high off-resistance). Of a pair of gain-blocks  1 , 2  or  3 , 4 , one of the gain-blocks will provide gain, where at that time the other one will not provide any output current. Of course, more than four gain-blocks may be implemented. Further, one may define the combination of two gain-blocks and one or two resistors as one voltage-to-current converter. 
     The mixer-system according to the invention will reject at its outputs  32 , 33  both the oscillation signals and the Radio Frequency (RF) components of the data input signals. For the switches  5 , 6  having a sufficiently low on-resistance, the linearity will be solely determined by the linearity of the gain-blocks  1 - 4 . 
     The basic mixer-system shown in  FIG. 1  will be driven with a balanced (RF) data input source. In case of needing to be driven with a single ended (RF) data input source, impedances  14 ,  16  and  17  are to be left out, due to both switch-transistors of switches  5 , 6  then needing to be located at those sides where the RF voltages are virtually zero. 
     The gain-block  10  according to the invention shown in  FIG. 2  improves the basic mixer-system shown in  FIG. 1  due to having an improved linearity. Gain-block  10  for example corresponds with one or more of the gain-blocks  1 - 4  shown in  FIG. 1  and comprises a first  51 , a second  52 , a third  53 , a fourth  54  and a fifth  55  gain-block-transistor for example each comprising one transistor, like a bipolar transistor or a Field Effect Transistor (FET). A control electrode of the first gain-block-transistor  51  (for example npn) constitutes the control input (B) of the gain-block  10 , with a first main electrode of the first gain-block-transistor  51  being coupled to a first main electrode and to a control electrode of the second gain-block-transistor  52  (for example pnp) and to a control electrode of the third gain-block-transistor  53  (for example pnp), with a second main electrode of the second gain-block-transistor  52  being coupled to a second main electrode of the third gain-block-transistor  53  and to a voltage guiding terminal coupled to a voltage source  57  which is further coupled to ground. A second main electrode of the first gain-block-transistor  51  is coupled to a second main electrode of the fourth gain-block-transistor  54  (for example npn) and to a current guiding terminal coupled to a current source  56  which is further coupled to ground, with a control electrode of the fourth gain-block-transistor  54  constituting the second main electrode (E) of the gain-block  10  and being coupled to a second main electrode of the fifth gain-block-transistor  55  (for example npn), with a first main electrode of the fourth gain-block-transistor  54  being coupled to a control electrode of the fifth gain-block-transistor  55  and to a first main electrode of the third gain-block-transistor  53 , and with a first main electrode of the fifth gain-block-transistor  55  constituting a first main electrode of the gain-block (C). 
     When applying the gain-block  10  shown in  FIG. 2  in each gain-block  1 - 4  shown in  FIG. 1 , due to the fully balanced nature of this mixer-system, parasitic capacitances of the switch-transistors of switches  5 , 6  will not carry any differential RF signal. This results in an excellent performance. Of course, other alternative gain-blocks are not to be excluded and may be used instead. 
     The improved mixer-system according to the invention shown in  FIG. 3  suppresses a higher harmonic. This improved mixer-system corresponds with the basic mixer-system according to the invention shown in  FIG. 1 , with the following addition. 
     Second main electrode (E) of gain-block  1  is coupled via an eighth impedance  18  (like for example a resistor etc.) to a first main electrode of a third switch  7  (for example comprising one or more switch-transistors, like a MOSFET). Second main electrode (E) of gain-block  2  is coupled via a nineth impedance  19  (like for example a resistor etc.) to a second main electrode of third switch  7 . A control electrode of switch  7  is coupled to a first output of a further oscillator  35  for receiving a further first oscillation signal. 
     Second main electrode (E) of gain-block  4  is coupled via a tenth impedance  20  (like for example a resistor etc.) to a first main electrode of a fourth switch  8  (for example comprising one or more switch-transistors, like a MOSFET). Second main electrode (E) of gain-block  3  is coupled via an eleventh impedance  21  (like for example a resistor etc.) to a second main electrode of fourth switch  8 . A control electrode of switch  8  is coupled to a second output of further oscillator  35  for receiving a further second oscillation signal. 
     By providing the mixer-system with the third and fourth switches  7  and  8  and with further oscillator  35 , which further oscillator  35  for example generates further oscillation signals for example comprising further square wave signals at for example three or five or seven times etc. the frequency of the (basic) oscillation signals comprising for example the (basic) square wave signals (as discussed for  FIG. 1 ), the third of fifth or seventh harmonic etc. is suppressed. So, for each harmonic to be suppressed, two switches (a mixer) and an oscillator need to be added. Dependently upon the gain of the mixer-system related to this third or fifth or seventh harmonic etc., values for the (further) oscillator and/or values for the (further) impedances will need to be chosen properly. 
     Oscillators  34  and  35  for example each comprise a sine generator of which outputs are coupled to inputs of a limiter (for converting the sines into square waves). Outputs of the limiter for the outputs of the oscillator, with the first output further being coupled via a resistor to voltage source  41  (for biasing purposes) and with the second output further being coupled via a resistor to voltage source  41  (for biasing purposes). Alternatively, oscillator signals may be derived via one or more dividers from a single oscillator. 
     The apparatus  60  according to the invention shown in  FIG. 4  for example corresponds with a receiver for receiving modulated signals to be mixed (to be frequency translated or frequency converted) downwardly and then comprises for example an input stage  61  (like for example an antenna and/or one or more pre-amplifiers and/or one or more filters etc.) and a mixer-system  62  as shown in  FIGS. 1 and 3  and as described above and a processing stage  63  (like for example one or more processors and/or one or more gain-blocks etc.) and an output stage  64  (like for example one or more man-machine-interfaces etc.) etc. 
     Or the apparatus  60  according to the invention shown in  FIG. 4  for example corresponds with a transmitter for transmitting modulated signals to be mixed (to be frequency translated or frequency converted) upwardly etc. and comprises an input stage  61  (like for example one or more man-machine-interfaces etc.) and a processing stage  62  (like for example one or more processors and/or one or more gain-blocks etc.) and a mixer-system  63  as shown in  FIGS. 1 and 3  and as described above and an output stage  64  (like for example an antenna and/or one or more power-amplifiers and/or one or more filters etc.) etc. 
     Generally, but not exclusively, a first main electrode will correspond with a collector or a drain, a second main electrode will correspond with an emitter or a source, and a control electrode will correspond with a basis or a gate. 
     The expression “for” in for example “for A” and “for B” does not exclude that one or more other functions like “for C” etc. are performed as well, simultaneously or not. The expressions “X coupled to Y” and “a coupling between X and Y” and “coupling/couples X and Y” etc. do not exclude that an element Z is in between X and Y. The expressions “P comprises Q” and “P comprising Q” etc. do not exclude that an element R is comprised/included as well. 
     It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 
     The invention is based upon an insight, inter alia, that the flexibility of a mixer-system depends upon its configuration, and is based upon a basic idea, inter alia, that for a more flexible configuration data input signals are to be supplied to the gain-blocks and that oscillation signals are to be supplied to switches for switching couplings between gain-blocks. 
     The invention solves the problem, inter alia, of providing a more flexible mixer-system, and is advantageous, inter alia, in that its performance is improved and can be further improved easily.
Mixer-systems comprising gain-blocks ( 1 - 4) and switches ( 5 - 8) have a flexibility depending upon their configuration (insight) and are made more flexible (basic idea) by supplying data input signals to the gain-blocks ( 1 - 4) and oscillation signals to the switches ( 5 - 6) for switching couplings between the gain-blocks ( 1 - 4). A switch ( 5 - 6) comprises a switch-transistor and a gain-block ( 1 - 4) either comprises a gain-block-transistor or comprises five gain-block-transistors for increasing the linearity of the mixer-system. The switches ( 5 - 6) have main electrodes which in the balanced situation are all coupled via four impedances ( 13 - 16) to the gain-blocks ( 1 - 4). In the single ended situation two main electrodes are coupled via two impedances ( 13,15,18,20) to the gain-blocks ( 1 - 4) and two others are coupled directly to the gain-blocks ( 1 - 4). By introducing further switches ( 7 - 8) parallel to the switches ( 5 - 6), harmonics can be suppressed. The basic mixer-system has an improved performance which can be further improved easily.