Abstract:
An oscillator/mixer circuit having a reduced area requirement when producing it on a chip and where the circuit&#39;s mixer circuit is not based on the use of the nonlinear characteristic curve of an active component. The preferred embodiment of the oscillator/mixer circuit comprises an oscillator circuit; a mixer circuit, wherein the oscillator and mixer circuits have the same components to some extent and wherein the mixer circuit has at least a first switch element and a second switch element. An output of the first switch element is coupled to a control input of the second switch element via a first feedback element. An output of the second switch element is coupled to a control input of the first switch element via a second feedback element. The feedback elements are set up allow oscillator operation of the oscillator/mixer circuit.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to an oscillator/mixer circuit. 
   2. Description of the Related Prior Art 
   Such an oscillator/mixer circuit for processing analog signals is known in the form of a series circuit for an oscillator circuit with a mixer circuit. 
   In analog circuit technology, a voltage-controlled oscillator is used for producing a signal of a frequency prescribed by setting the dimensions of the oscillator circuit. Using a mixer circuit, particularly a switching mixer, such as a Gilbert cell, a signal to be mixed is mixed with a local oscillator signal, as explained in more detail below, i.e. frequency conversion is performed for the signal which is to be mixed. 
   Both a voltage-controlled oscillator and a switching mixer in a microelectronic circuit are currently used in a large number of appliances and systems, for example for wireless radio transmission of information, such as in a mobile radio system, a GPS receiver and a television satellite receiver. 
     FIG. 2  shows the basic design of a normal oscillator  200 , as used in microelectronics. 
   The oscillator  200  has a differential multivibrator  201  having two MOS field-effect transistors  202 ,  203 . In addition, the oscillator  200  shown in  FIG. 2  has a resonator element  204 ,  205  and also at least one voltage-controlled tuning element  206 ,  207 . The voltage-controlled tuning element  206 ,  207  is also simply called a tuning element. 
     FIG. 3  shows a basic circuit for an oscillator based on the prior art. 
   The oscillator  300  is in the form of an RC oscillator and has two MOS field-effect transistors  304 ,  305  coupled to an input  301  via their respective gate connection  302 ,  303 . The source connection and the drain connection of the first MOS field-effect transistor  304  are connected together and are coupled to a first output  306 . The drain connection and the source connection of the second MOS field-effect transistor  305  are likewise coupled to one another and to a second output  307  of the oscillator  300 . 
   The first output  306  is coupled to the gate connection  309  of a third transistor  310  via a first capacitor C  308 . 
   The second output  307  is coupled to the gate connection  312  of a fourth transistor  313  via a second capacitor C  311 . 
   The gate connection  309  of the third transistor  310  is also coupled to the supply connection  315 , to which the operating voltage V DD  for the oscillator circuit  300  can be applied, via a first electrical resistor R 1   314 . In addition, the gate connection  309  of the third transistor  310  is coupled to the ground potential via a second electrical resistor R 2   316 , which allows the operating point of the oscillator circuit  300  to be set. 
   The gate connection  312  of the fourth transistor  313  is connected to the supply connection  315  via a third electrical resistor R 1   317  and also likewise to the ground potential via a fourth electrical resistor  318 . 
   In addition, the drain connection of the third transistor  310  is coupled to the supply connection  315  via a fifth electrical resistor  319 , and the drain connection of the fourth transistor  313  is coupled to the supply connection  315  via a sixth electrical resistor  320 . The fifth electrical resistor  319  and the sixth electrical resistor  320  are load resistors. 
   In addition, the source connections of the third transistor  310  and of the fourth transistor  313  are coupled to the ground potential. 
     FIG. 4  shows the design of a normal Gilbert cell  400 , which is an example of a switching mixer, i.e. of a mixer circuit which, as described below, has two transistors, in general terms two switch elements, which are each operated by virtue of the transistors being turned on and off. In addition, the normal Gilbert cell  400  has an analog input transistor. 
   The Gilbert cell  400  has a first switching transistor  401  and a second switching transistor  402 . 
   The gate connection  403  of the first switching transistor is coupled to a first local oscillator input  404 . The first local oscillator input  404  has a first local oscillator signal LO+ applied to it which is thus applied to the gate connection  403  of the first switching transistor  401 , in order to control it by means of the local oscillator signal LO+, i.e. to turn it on and off. 
   The drain connection  405  of the first switching transistor  401  is coupled to a first output  406 . In addition, the drain connection  405  of the first switching transistor  401  is coupled to a supply connection  408  via a first electrical resistor  407  as a mixer load resistor. The supply connection  408  can have the operating voltage V DD  for operating the mixer circuit  400  applied to it. 
   Connected to the gate connection  409  of the second switching transistor  402  is a second local oscillator connection  410  to which a second local oscillator signal LO− can be applied for controlling the second switching transistor  402 . The second local oscillator signal LO− is shifted through 180° with respect to the first local oscillator signal LO+. 
   The drain connection  411  of the second switching transistor  409  is coupled to a second output  412  and also to the supply connection  408  via a second electrical resistor  413  as a mixer load resistor. 
   The source connections  414 ,  415  of the first switching transistor  401  and of the second switching transistor  402  are coupled to the drain connection  417  of an analog input transistor  418 . The gate connection  419  of the input transistor  418  is coupled to a mixing signal input  420  to which the analog input signal ZE to be mixed can be applied. The source connection  421  of the input transistor  418  is coupled to the ground potential. 
   In order to form an oscillator/mixer circuit from the known circuits described above, i.e. the oscillator circuit  300  and the mixer circuit  400 , it is known practice to connect these circuits in series, i.e. a known oscillator/mixer circuit  500  (cf.  FIG. 5 ) has the oscillator circuit  300  described in FIG.  3  and the mixer circuit  400  described in  FIG. 4 , which are connected to one another in series such that the first output  306  of the oscillator  300  is coupled to the first local oscillator input  404  of the mixer circuit  400  via a first electrical connection  501 . The second output  307  of the oscillator circuit  300  is coupled to the second local oscillator input  410  of the mixer circuit  400  via a second electrical coupling  502 . The local oscillator signals are shifted through 180° with respect to one another. 
   The known oscillator/mixer circuit  500  has several drawbacks.
         Connecting two complete, essentially mutually independent circuits, i.e. the oscillator circuit  300  and the mixer circuit  400 , in series requires a relatively large number of electrical components, i.e. a relatively large number of electrical resistors and transistors, normally MOS field-effect transistors. Integration of the known oscillator/mixer circuit  500  on a chip thus has a considerable requirement in terms of chip area in order to implement it.   Another considerable drawback of the oscillator/mixer circuit  500  can be seen in that two electrical connections  501 ,  502  are required between the circuit components, i.e. the oscillator circuit  300  and the mixer circuit  400 . Particularly in the area of very high-frequency applications, the electrical connections  501 ,  502  represent a considerable restriction in terms of their usability on account of the very high attenuation to which the output signal produced at the outputs  306 ,  307  of the oscillator circuit is subject before it reaches the inputs  404 ,  410  of the mixer circuit  400 . In the case of a very high-frequency application in which a signal frequency in a range of approximately 1 GHz to several tens of GHz, preferably up to 77 GHz and above, is required, this results in such an oscillator/mixer circuit  500  barely being able to be used, since no signal with sufficient signal amplitude is applied to, i.e. arrives at, the local oscillator inputs  404 ,  410  of the mixer circuit  400 .   In addition, particularly within the scope of implementing the oscillator/mixer circuit  500  as an integrated circuit, the “matching” problem is of great significance on account of the physical distances between the individual components of the circuit, since it is a considerable problem, technologically, to produce the components which are to be used with sufficient similarity over a relatively long distance from one another on a chip or on a wafer. This means that the components are frequently matched to one another only with great difficulty and sometimes not at all, resulting in an oscillator/mixer circuit  500  which works only poorly or not at all.       

   It is also known practice to use a diode or an electrical circuit containing a diode as a mixer circuit or as an oscillator circuit, where, in such a case in which a mixer circuit&#39;s mixing is based on an active component, mixing of the signals which are to be mixed is based on the nonlinear characteristic curve of an active component, in the specific case of the diode. 
   The invention is thus based on the problem of specifying an oscillator/mixer circuit which has a reduced area requirement, when producing it on a chip, as compared with the known oscillator/mixer circuit and where the oscillator/mixer circuit&#39;s mixer circuit is not based on the use of the nonlinear characteristic curve of an active component. 
   The problem is solved by the oscillator/mixer circuit having the features of the independent patent claim. 
   The oscillator/mixer circuit has an oscillator circuit and a mixer circuit. The oscillator circuit and the mixer circuit have the same components to some extent. 
   Expressed in other words, this means that the same components in the oscillator/mixer circuit are used both for frequency generation and for the mixing operation. 
   In addition, the mixer circuit has at least a first switch element and a second switch element, where an output of the first switch element is coupled to a control input of the second switch element via a first feedback element. An output of the second switch element is coupled to a control input of the first switch element via a second feedback element. The feedback elements are set up such that oscillator operation of the oscillator/mixer circuit is made possible. 
   Oscillator operation of the oscillator/mixer circuit is ensured, by way of example, by virtue of oscillation buildup being ensured in the oscillator circuit in the oscillator/mixer circuit, which can be achieved, by way of example, by virtue of the feedback elements ensuring that the control signals applied to the control inputs of the switch elements are certain to have a phase angle which is suitable for the oscillator circuit&#39;s respective circuit type, and also a loop gain of greater than 1. 
   Expressed clearly, this means that the oscillator/mixer circuit has an oscillator circuit and a mixer circuit which have common components and where the mixer elements are in the form of a switching mixer, i.e. in the form of a circuit which normally has at least two transistors operated in turn-on mode and turn-off mode. 
   This ensures that the mixing of signals in the oscillator/mixer circuit is not based on a nonlinear characteristic curve of an active component. 
   The oscillator circuit can also be set up as an LC oscillator circuit. 
   In this case, in one refinement of the invention, a respective inductor is coupled to the output of the first switch element and to the output of the second switch element, and the input of the first switch element is coupled to the input of the second switch element and to a mixing signal input to which a signal to be mixed can be applied. 
   Clearly, the oscillator/mixer circuit can thus be regarded as an oscillator circuit in which the ground connection and the source connections of the oscillator transistors in the oscillator circuit have an input transistor connected between them whose gate connection is coupled to the mixing signal input. In general terms, the drain connections of the oscillator transistors and the ground connection have an input transistor connected between them whose control input is coupled to the mixing signal input. 
   Thus, an oscillator/mixer circuit has been provided which has a significantly reduced number of required components and can simultaneously be operated as an oscillator circuit and as a mixer circuit. 
   The compact design and the, to some extent, common use of some components both by the oscillator circuit and by the mixer circuit in the oscillator/mixer circuit result in a significant reduction in required chip area for integrating the oscillator/mixer circuit. 
   In addition, the compact design of the oscillator/mixer circuit means that it is very well suited to a radio-frequency application, in particular, since the signals to be processed need to cover significantly reduced distances over electrical lines as compared with the known oscillator/mixer circuit described above, and are thus subject to significantly reduced attenuation. 
   In addition, the matching problem for the components used is avoided. 
   In one refinement of the invention, an analog input transistor is connected between the inputs of the switch elements and the mixing signal input, with the mixing signal input being coupled to the control input of the input transistor. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with an alternative refinement of the invention, provision is also made for the oscillator circuit to be in the form of an RC oscillator circuit. 
   In this refinement, there is also a first electrical resistor which is connected between the control input of the first switch element and a supply connection, to which supply connection an operating voltage V DD  for the oscillator/mixer circuit can be applied. A second electrical resistor is connected between the control input of the first switch element and the input of the first switch element, and a third electrical resistor is connected between the control input of the second switch element and the supply connection. A fourth electrical resistor is connected between the control input of the second switch element and the input of the second switch element. In addition, in this refinement of the invention, the input of the first switch element is coupled to the input of the second switch element and also to a mixing signal input to which a signal which is to be mixed can be applied. 
   In accordance with this refinement of the invention, provision is preferably made for the first electrical resistor and the third electrical resistor to be dimensioned in the same way, and for the second electrical resistor and the fourth electrical resistor to be given the same dimensions. 
   A further switch element can be connected between the inputs of the switch elements and the mixing signal input, with the mixing signal input being coupled to a control input of the input transistor. 
   In another refinement of the invention, the feedback elements are set up such that the phase angle of the signals applied to the respective control input can be set. 
   In addition, the feedback elements can be set up as frequency-determining elements of the oscillator/mixer circuit. 
   Within the context of this description, the expression “frequency-determining element” is to be understood to mean that such an element can be used to set the oscillation frequency of the oscillator circuit. 
   The first feedback element and the second feedback element can each have a capacitor, preferably a capacitor whose capacitance can be respectively varied, preferably using a control voltage. 
   The first switch elements and/or the second switch element can each have a transistor or can be formed by a transistor. 
   In another refinement of the invention, at least some of the components are produced using CMOS technology. 
   Exemplary embodiments of the invention are illustrated in the figures and are explained in more detail below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, 
       FIG. 1  shows an oscillator/mixer circuit according to a first exemplary embodiment of the invention; 
       FIG. 2  shows a basic illustration of a radio-frequency oscillator; 
       FIG. 3  shows an oscillator circuit according to the prior art; 
       FIG. 4  shows a basic circuit for a Gilbert cell according to the prior art; 
       FIG. 5  shows an oscillator/mixer circuit according to the prior art; 
       FIG. 6  shows an oscillator/mixer circuit according to a second exemplary embodiment of the invention; and 
       FIG. 7  shows an oscillator/mixer circuit according to a third exemplary embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows an oscillator/mixer circuit  100  according to a first exemplary embodiment of the invention. 
   The oscillator/mixer circuit  100  has an oscillator circuit  101  (symbolized using dashed lines in  FIG. 1 ) and a mixer circuit  102  (symbolized using dashes and dots in FIG.  1 ). 
   As  FIG. 1  shows, some components in the oscillator/mixer circuit  100  are contained both in the oscillator circuit  101  and in the mixer circuit  102 . 
   The oscillator/mixer circuit  100  has a first switching transistor  103  and a second switching transistor  104 . 
   The drain connection  105  of the first switching transistor  103  is coupled to a first output  106  of the oscillator/mixer circuit  100 . When the oscillator/mixer circuit  100  is in mixing mode, the first output  106  provides a first output signal OUT+, which is also referred to as a first intermediate frequency signal OUT+ in downward mixing mode. 
   In addition, the first output  106  and the drain connection  105  of the first switching transistor  103 , as switch output for the first switch element, are coupled to a first connection  107  of a first capacitor  108  as a first feedback element. A second connection  109  of the first capacitor  108  is coupled to the gate connection  110  of the second switching transistor  104 . 
   The drain connection  111  of the second switching transistor  104 , as switch output for the second switch element, is coupled to a second output  112  of the oscillator/mixer circuit  100 . When the oscillator/mixer circuit  100  is in mixer mode, the second output  112  provides a second output signal, which is also referred to as second intermediate frequency signal OUT− in downward mixing mode. 
   The phase angle of the second output signal is shifted through 180° with respect to that of the first output signal. 
   In addition, the drain connection  111  of the second switching transistor  104  is coupled to a first connection  113  of a second capacitor  114  as a second feedback element. A second connection  115  of the second capacitor  114  is coupled to the gate connection  116  of the first switching transistor  103 . 
   The source connection  117  of the first switching transistor  103 , as switch input for the first switch element, is coupled to the source connection  118  of the second switching transistor  104 , as switch input for the second switch element, and also to the drain connection  119  of an input transistor  120 , which is no longer a functional element of the oscillator circuit  101 , but is a functional element of the mixer circuit  102 . 
   The gate connection  121  of the input transistor  120  is coupled to a mixing signal input  122  to which a normally analog input signal ZE which is to be mixed can be applied. 
   The source connection  123  of the input transistor  120  is coupled to the ground connection  124 . 
   Expressed another way, this means that the drain connections, i.e. clearly the outputs of the two switching transistors  103 ,  104 , are fed back crosswise via a respective capacitor  108  or  114  to the gate connections  110 ,  116  of the respective other switching transistor  103 ,  104 . 
   This clearly means that the mixer circuit  102 , in comparison with the mixer circuit according to the prior art, which has a diode as mixing element, inventively uses a switching mixer which involves the respective switching transistors  103 ,  104  respectively turning one another on and off in antiphase. 
   Expressed another way, this means that, if the first switching transistor  103  is on, the second switching transistor  104  is in a deactivated state on account of the feedback via the first capacitor  108  to the gate connection  110  of the second switching transistor  104 . If the second switching transistor  104  is in an activated state, the first switching transistor  103  is in a deactivated state on account of the feedback via the second capacitor  114  to the gate connection  116  of the first switching transistor. 
   The drain connection  105  of the first switching transistor  103  is also coupled to a supply connection  126 , to which the operating voltage V DD  for the oscillator/mixer circuit  100  can be applied, via a first electrical resistor  125 . 
   The supply connection  126  likewise has the drain connection  111  of the second switching transistor  104  coupled to it via a second electrical resistor  127 . 
   In addition, the gate connection  116  of the first switching transistor and the second connection  115  of the second capacitor  114  are coupled to a first connection  128  of a third electrical resistor  129  and via the latter to the supply connection  126 . 
   In addition, the gate connection  116  of the first switching transistor and the second connection  115  of the second capacitor  114  are coupled to the ground connection  124  via a first connection  130  of a fourth electrical resistor  131  and via the latter. 
   The gate connection  110  of the second switching transistor  104  and the second connection  109  of the first capacitor  108  are coupled to a first connection  132  of a fifth electrical resistor  133  and via the latter to the supply connection  126 . 
   In addition, the gate connection  110  of the second switching transistor  104  and the second connection  109  of the first capacitor  108  are coupled to a first connection  134  of a sixth electrical resistor  135  and via the latter to the ground connection  124 . 
     FIG. 6  shows an oscillator/mixer circuit  600  according to a second exemplary embodiment of the invention. 
   In accordance with the second exemplary embodiment of the invention, the oscillator circuit is set up as an LC oscillator circuit. 
   The oscillator/mixer circuit  600  has a first switching transistor  601  and a second switching transistor  602 . 
   The drain connection  603  of the first switching transistor  601  is coupled to a first output  604  of the oscillator/mixer circuit  600 , and the drain connection  605  of the second switching transistor  602  is coupled to a second output  606  of the oscillator/mixer circuit  600 . 
   In addition, the drain connection  603  of the first switching transistor  601  is coupled to the gate connection  608  of the second switching transistor  602  via a first capacitor  607  as a first feedback element, and the drain connection  605  of the second switching transistor  602  is coupled to the gate connection  609  of the first switching transistor  601  via a second capacitor  608  as a second feedback element. 
   This again achieves crosswise feedback of the respective outputs of the switching transistors, as switch elements of the oscillator/mixer circuit  600 , to the respective control inputs, i.e. the gate connections of the respective other switching transistor. 
   In addition, the drain connection  603  of the first switching transistor  601  is coupled to a first connection  610  of a first inductor  611  and via the latter to a supply connection  612  of the oscillator/mixer circuit  600 . 
   The drain connection  605  of the second switching transistor  602  is additionally coupled to a first connection  613  of a second inductor  614  and via the latter likewise to the supply connection  612 . 
   In addition, the source connection  615  of the first switching transistor  601  and the source connection  616  of the second switching transistor  602  are coupled to one another and to a drain connection  617  of an input transistor  618 , whose source connection  619  is coupled to the ground connection  620 . 
   The source connection  621  of the input transistor  619  is coupled to a mixing signal input  622  of the oscillator/mixer circuit  600 . 
   The capacitors for the feedback elements described above both in the oscillator/mixer circuit  100  based on the first exemplary embodiment and in the oscillator/mixer circuit  600  based on the second exemplary embodiment are set up such that a respective phase shift of 180° is ensured for the respective electrical analog signals applied to the gate connections of the switching transistors. 
     FIG. 7  shows, as a third exemplary embodiment, two series-connected mixer/oscillator circuits according to the first exemplary embodiment or according to the second exemplary embodiment, which are coupled to each other via a phase shifter element  701  which is set up such that the phase of an output signal  702  produced at an output of the first oscillator/mixer circuit is shifted through 90° with respect to the input signal  703  applied to the input of the second oscillator/mixer circuit. 
   In this way, an oscillator/mixer circuit  700  providing a total of four output signals is specified whose output signals are each shifted through 90° with respect to one another. 
   In the two exemplary embodiments described above, the components are produced using CMOS technology, i.e. the transistors used, in particular, are CMOS field-effect transistors. 
   The implementations described above thus mean that the mixer circuit and the oscillator circuit are clearly no longer circuits which are physically separate from one another; instead, the same components are largely used both for the mixer circuit and for the oscillator circuit. 
   Hence, if component tolerances are produced in the oscillator/mixer circuit, these affect both the operation of the mixer circuit and that of the oscillator circuit in the same way, and the mixer circuit and the oscillator circuit thus remain ideally matched to one another. 
   On account of the saving on the connecting lines, required in an oscillator/mixer circuit according to the prior art, between the oscillator circuit and the mixer circuit (cf.  FIG. 5 , connecting lines  501 ,  502 ), the inventive oscillator/mixer circuit is particularly suitable for use in very high-frequency technology, particularly as a transmitter and/or receiver. A suitable frequency range for operating the inventive oscillator/mixer circuit is preferably in the order of magnitude of one to several 10 GHz, which means that the oscillator/mixer circuit can be used suitably for wireless radio transmission, for example as a mobile radio transmitter or mobile radio receiver, as a radar transmitter or radar receiver or as a receiver for a global positioning system (GPS). 
   The invention can clearly be seen as being that an oscillator circuit unit and a mixer circuit unit have, to some extent, the same components in order to perform their respective function. The mixer circuit has at least two switch elements. The latter&#39;s outputs are is respectively coupled crosswise to the control inputs of the respective other switch element via a respective feedback element. The feedback element is respectively set up such that oscillator operation of the oscillator/mixer circuit is additionally made possible. 
   It should be noted in this context that the oscillator/mixer circuit can be set up as an upward mixer or else as a downward mixer.