Abstract:
An adjustable-frequency oscillator, is formed by two looped systems, functioning at the same frequency but the signals are phase shifted by 90°. Each looped system includes a phase shift device, an active element providing the gain and a resonator having a fixed phase-frequency characteristic. As the phase shift in each loop is imperatively a whole multiple of 2π, the phase shift added in each loop by the phase shift device entails that each resonator introduces a complementary phase shift to comply with the oscillation criterion. This complementary phase shift is produced at a frequency defined by the resonator, this then defining the frequency of oscillation. The frequency is adjusted by two phase shift stages, which carry out the analogue multiplication of the signals coming from the two looped systems by control voltages and the summing of these products.

Description:
BACKGROUND 
     The present application relates to an oscillator making it possible to generate an adjustable-frequency electric signal. 
     The field of the invention is the field of electronic circuits and, in particular, of integrated electronic circuits used in the radiofrequency and microwave frequency fields, for example in communication systems. 
     In the radiofrequency and microwave frequency fields, the most used method for obtaining an adjustable-frequency oscillator consists of modifying the phase-frequency characteristic of the resonator. 
     In particular, oscillators can be mentioned which are designed around one or more varactors (or voltage-controlled variable capacitors). 
     This type of component does not however generally allow a frequency variation greater than one octave. Moreover, if it is desired to fully integrate the oscillator, the technology used during the design of the integrated circuit most often complies with choices which are not optimized, in order to obtain a maximum variation of the value of the capacitance of the varactor. The variable capacitor does not therefore make it possible to obtain a frequency variation over a wide frequency band or it must be located outside of the integrated circuit. 
     Moreover, the introduction of variable components in the resonator creates losses, which reduces the quality factor of the loaded resonator. 
     SUMMARY 
     A purpose of the present invention is to overcome the above-mentioned drawbacks. 
     Another purpose of the invention is to propose an oscillator making it possible to obtain a frequency variation range which is wider than that of currently existing oscillators. 
     Another purpose of the invention is to propose an oscillator which makes it possible to obtain a variable-frequency signal and which improves the noise characteristic. 
     Finally, another purpose of the invention is to propose an oscillator which can be fully integrated. 
     In order to achieve at least one of these objectives, the invention proposes an oscillator for generating an adjustable-frequency signal, said oscillator comprising a looped system, called principal, said principal looped system comprising:
         a phase shift device, called principal, comprising at least one phase shift stage, called principal, for shifting the phase of a signal, called principal, by an adjustable phase shift value, said principal signal being a cosine signal or a sine signal,   at least one means for adjusting the phase shift produced by said phase shift device, and   a resonator, called principal, the input of which is connected to the output of said principal phase shift device and the output of which is connected to the input of said principal phase shift device,
 
said principal looped system providing a signal the frequency of which depends on said phase shift value.
       

     In order for oscillations to be established in the oscillator, one of the criteria defined by theory entails the existence in the looped system of a phase shift which is a whole multiple of 2π. As the phase shift device imposes an adjustable phase shift in the looped system, the resonator therefore introduces a complementary phase shift such that the sum of these two phase shifts is a whole multiple of 2π. The complementary phase shift introduced by the resonator therefore defines the oscillation frequency, by the intermediary of the phase-frequency characteristic of that resonator. 
     Thus, the invention proposes an oscillator providing a signal the frequency of which is adjusted by a phase shift. The oscillator according to the invention therefore makes it possible to carry out an adjustment/variation of the frequency without modifying the phase-frequency characteristic of the resonator used, in particular without modifying the value of a component element of the oscillator, such as for example a capacitive element and or an inductive element. 
     The frequency of the signal provided/generated by the oscillator according to the invention is directly adjusted by the phase shift applied by the phase shift device. 
     The oscillator according to the invention can be capable of complete integration. 
     Moreover, the oscillator does not comprise any capacitive element the value of which can be modified. 
     Moreover, the range of variation of the frequency is directly dependent on the range of variation of the phase shift value. For example, a range of variation of the phase shift value of 180° or of 360° makes it possible to obtain, with the oscillator according to the invention, a range of variation of the frequency greater than that obtained with presently existing oscillators. 
     The use of a phase shift device combined with a resonator makes it possible to obtain a variable-frequency signal with less noise. 
     Advantageously, the principal phase shift device can comprise several phase shift stages, connected in series, each phase shift stage defining a level of phase shift. 
     The use of several phase shift stages makes it possible, by making use of phase shift stages having a small phase shift range or small phase shift ranges, to obtain a large “overall” phase shift range for the principal phase shift device and thus to have a large range of variation of the frequency of the output signal of the oscillator. 
     The use of several phase shift stages also makes it possible to obtain several independent means for adjusting the phase shift. 
     In the present application, the verb “connect” denotes a direct or indirect connection between two elements. 
     Advantageously, the at least one means of adjusting the phase shift produced by said phase shift device can comprise:
         at least one means of adjustment common to all the phase shift stages, each of said phase shift stages producing an identical phase shift, or   at least one means of adjustment associated with each phase shift stage and making it possible to adjust the phase shift produced by each phase shift stage independently, or   at least one means of adjustment common to several phase shift stages, producing an identical phase shift for these phase shift stages, the other phase shift stages being adjusted by other means of adjustment.       

     According to a particularly advantageous embodiment that is in no way limitative, the at least one phase shift means can be reduced to a line entering one or more phase shift stages and provided for conveying a phase shift control signal, generated by a means outside of the oscillator, this control signal causing the phase shift in the phase shift stage or stages to vary. In this case, the control signal can be a control voltage. 
     According to a particular embodiment, at least one phase shift stage can comprise:
         a first multiplier providing a first signal corresponding to the product of the principal signal and a first control voltage,   a second multiplier providing a second signal, corresponding to the product of a so-called secondary signal and:
           a second control voltage when said principal signal is a sine, said secondary signal corresponding to the principal signal advanced by a value of 90°, or   a third control voltage when said principal signal is a cosine, said secondary signal corresponding to the principal signal delayed by a value of 90°;   
           an adder for adding said first and second signals provided by said multipliers;
 
said first, second and third control voltages corresponding respectively to the cosine, sine and −sine of the adjustable phase shift value multiplied by the same constant.
       

     Such a phase shift stage makes it possible to phase-shift the principal signal by an adjustable phase shift value. 
     Thus, in this particularly advantageous embodiment of the oscillator according to the invention, the phase shift of a signal is produced by analogue multiplication of this signal by control voltages, according to the following trigonometric equations:
 
cos(ω t )*cos( a )+sin(ω t )*(−sin( a ))=cos(ω t+a ), when the signal the frequency of which is adjusted is a cosine and
 
sin(ω t )*cos( a )+cos(ω t )*sin( a )=sin(ω t+a ), when the signal the frequency of which is adjusted is a sine
 
where ω is the angular frequency of the signal generated.
 
     In this embodiment, the control voltages can be:
         identical for all the phase shift stages: in this case all the phase shift stages produce a phase shift of the same value, or   different for each phase shift stage: in this case, each phase shift stage produces a phase shift of a value different from that of the other phase shift stages.       

     In this embodiment, the control voltages directly modify the phase of the signal within the looped system. 
     When the principal looped system comprises several phase shift stages, as each of the phase shift stages defines a level of phase shift, each phase shift stage receives as input a principal signal and a secondary signal and provides the phase-shifted principal signal. This phase-shifted principal signal becomes the principal signal for the following stage. 
     In a particular embodiment, the secondary signal can be obtained from the incoming principal signal of each phase shift stage. In order to do this, the oscillator according to the invention comprises, upstream of each principal phase shift stage of a given level, a constant phase-shifter, the phase-frequency characteristic of which exhibits a phase shift which is constant with respect to frequency and generating the secondary signal for said principal phase shift stage from the principal signal. 
     When the principal signal is a cosine, the constant phase-shifter provides a sine of the same amplitude and of the same frequency as the principal signal. In the case where the principal signal is a sine, the constant phase-shifter provides a cosine of the same amplitude and of the same frequency as the principal signal. 
     In another embodiment, the secondary signal can be obtained from a second looped system, called secondary. Thus, the oscillator according to the invention can comprise a second looped system, called secondary, said secondary looped system comprising:
         a second phase shift device, called secondary, comprising as many so-called secondary phase shift stages, connected in series, as there are principal phase shift stages, the output of the principal resonator being connected to an input of said secondary phase shift device,   a second resonator, called secondary, the input of which is connected to the output of said secondary phase shift device and the output of which is connected to an input of said secondary phase shift device and to an input of said principal phase shift device;
 
a secondary phase shift stage of a given level producing the same phase shift as that of the principal phase shift stage of the same level and
 
the output of a phase shift stage of a given level being connected to an input of the principal phase shift stage of the following level, said secondary phase shift stage of said level providing the secondary signal to said principal phase shift stage of said following level.
       

     The function of the secondary looped system is to provide the secondary signal to each phase shift stage. In order to do this, the secondary looped system comprises as many phase shift stages as there are in the principal looped system, i.e. as many phase shift levels as there are in the principal looped system. Each secondary phase shift stage produces a phase shift of the same value as the phase shift produced by a principal phase shift stage of the same level and provides the secondary signal to the principal phase shift stage of the following level. The secondary signal used by the principal phase shift stage of the first level of phase shift is obtained at the output of the resonator of the secondary looped system. 
     In a particular embodiment of the secondary looped system:
         the output of a principal phase shift stage of a given level of phase shift is connected to an input of the secondary phase shift stage of the level following and   each secondary phase shift stage comprises:
           a third multiplier providing a signal corresponding to the product of the secondary signal and the first control voltage,   a fourth multiplier providing a signal corresponding to the product:
               of the principal signal and the second control voltage when said signal is a cosine,   of the principal signal and the third control voltage when said signal is a sine,   
               an adder for adding the signals provided by said third and fourth multipliers and for providing said secondary signal.   
               

     Thus, each secondary phase shift stage uses the principal signal in order to obtain the secondary signal by analogue multiplication with control voltages. The control voltages used by the principal and secondary phase shift stages of the same level produce a phase shift of the same value. The secondary signal is obtained according to the following trigonometric equations carried out by each of the secondary phase shift stages:
 
cos(ω t )*cos( a )+sin(ω t )*(−sin( a ))=cos(ω t+a ), when the signal the frequency of which is adjusted, i.e. the principal signal, is a sine and
 
sin(ω t )*cos( a )+cos(ω t )*sin( a )=sin(ω t+a ), when the signal the frequency of which is adjusted, i.e. the principal signal, is a cosine.
 
where ω is the angular frequency.
 
     In this embodiment, the output of each resonator (principal and secondary) is connected to an input of each first level phase shift stage (principal and secondary) and the output of each phase shift stage (principal and secondary) of a given level of phase shift is connected to an input of each phase shift stage (principal and secondary) of the level following. 
     According to an embodiment of a phase shift stage, at least one multiplier of a phase shift stage can comprise:
         a switching circuit comprising four transistors connected two by two as differential pairs and controlled by the control voltages,   an amplifier circuit comprising two transistors connected as a differential pair.       

     Moreover, two multipliers of two phase shift stages of the same level of phase shift and receiving the same signals can comprise:
         a switching circuit each, each switching circuit comprising four transistors connected two by two as differential pairs, and   an amplifier circuit common to the two multipliers and comprising two transistors connected as a differential pair.       

     Moreover, two multipliers of two phase shift stages of a same level of phase shift and receiving different signals can comprise:
         an amplifier circuit each, each amplifier circuit comprising four transistors connected two by two as differential pairs, and   a common switching circuit comprising two transistors connected as a differential pair.       

     The fact of placing an amplification circuit or a switching circuit in common for two multipliers makes it possible to reduce the number of components and therefore to reduce the manufacturing cost and the dimensions of the oscillator. 
     The oscillator according to the invention can also comprise a power divider, arranged upstream of each phase shift stage. 
     The oscillator according to the invention can also comprise at least one amplifier arranged in each looped system, more particularly at the input of each phase shift device. 
     In a particular embodiment, at least one resonator can be a transmission line, the phase-frequency characteristic of which is linear or non-linear. 
     Advantageously, the oscillator according to the invention can be produced using integrated circuit technology. 
     The oscillator according to the invention is particularly suitable for use in the radiofrequency or microwave frequency field or in the optical field in order to obtain an adjustable-frequency signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and characteristics of the invention will become apparent on examination of the detailed description of an embodiment which is in no way limitative, and the attached diagrams, in which: 
         FIG. 1  is a diagrammatic representation of a first embodiment of an oscillator according to the invention; 
         FIG. 2  is a diagrammatic representation of a second embodiment of an oscillator according to the invention; 
         FIG. 3  is a diagrammatic representation of a third embodiment of an oscillator according to the invention; 
         FIG. 4  is a diagrammatic representation of a fourth embodiment of an oscillator according to the invention; 
         FIG. 5  is a diagrammatic representation of a fifth embodiment of an oscillator according to the invention; 
         FIG. 6  is a diagrammatic representation of a sixth embodiment of an oscillator according to the invention; 
         FIG. 7  is a diagrammatic representation of a phase shift stage capable of use in the embodiments shown in  FIGS. 3 to 6 ; 
         FIGS. 8 and 9  are diagrammatic representations of two architectures of phase shift stages that are more compact, capable of use in the embodiments shown in  FIGS. 5 and 6 ; and 
         FIG. 10  is a diagrammatic representation of a preferred embodiment of an oscillator according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagrammatic representation of a first embodiment of an oscillator according to the invention. 
     The oscillator  100  shown in  FIG. 1  is a very simplified version of an oscillator according to the invention. In fact, the oscillator  100  is essentially a looped system comprising a phase shift device  102  consisting of an adjustable phase shifter  104 , a resonator  106  arranged downstream of the phase shifter  104  and an amplifier  108  arranged upstream of the phase shifter  104 . The output of the resonator  106  is connected directly to the input of the amplifier  108 . 
     The oscillator  100  comprises moreover means for adjusting the phase shift produced by the phase shifter  104 . In the example shown in  FIG. 1 , these means comprise a control line, represented by the arrow  110 . The control line  110  makes it possible to adjust the phase shift produced by the phase shifter  104  by a control voltage for example. 
     The resonator  106  can be, but is not limited to, a transmission line the phase-frequency characteristic of which is linear. 
       FIG. 2  is a diagrammatic representation of a second embodiment of an oscillator according to the invention. 
     The oscillator  200  is a looped system comprising a phase shift device  202  comprising a plurality of adjustable phase shifters  104   1 - 104   n  connected in series, a resonator  106  arranged downstream of the phase shift device  202  and an amplifier  108  arranged upstream of the phase shift device  202 . The output of the resonator  106  is connected directly to the input of the amplifier  108 . 
     The oscillator  200  comprises moreover means for adjusting the phase shift produced by each phase shifter  104 . In the example shown in  FIG. 2 , these means comprise a control line for each phase shifter, represented by the arrows  110   1 ,  110   n . The control lines  110   1 - 110   n  make it possible to adjust the phase shift produced by each phase shifter,  104   1 - 104   n  respectively, by a control voltage for example. The control voltage can either be identical for all or for a portion of the phase shifters  104   1 - 104   n  such that the phase shift applied by a portion or by all of the phase shifters  104   1 - 104   n  is identical, or different for each phase shifter  104   1 - 104   n  such that the phase shift applied by each phase shifter  104   1 - 104   n  can be different and can be adjusted individually and independently of the other phase shifters. 
     Each phase shifter  104   1 - 104   n  defines a level of phase shift. Thus, the phase shifter  104   1  corresponds to the first level of phase shift, the phase shifter  104   n  corresponds to the phase shift of level n. The looped system of the oscillator  200  therefore comprises n levels of phase shift, where n is a positive integer. 
       FIG. 3  is a diagrammatic representation of a third embodiment of an oscillator according to the invention. 
     The oscillator  300  comprises a looped system  302 . 
     The looped system  302  comprises a phase shift device  304  comprising a phase shift stage  306 , an amplifier  108  arranged upstream of the phase shift device  304  and a resonator  106  arranged downstream of the phase shift device  304 . 
     The phase shift stage  306  comprises a first multiplier  308  providing a first signal corresponding to the product of the signal to be phase-shifted, hereinafter called the “principal signal” and a first control voltage. The phase-shift stage  306  comprises a second multiplier  310  providing a second signal, corresponding to the product of a signal, called the secondary signal, and:
         a second control voltage when the principal signal is a sine, the secondary signal corresponding to the principal signal advanced by a value of 90°, or   a third control voltage when the principal signal is a cosine, the secondary signal corresponding to the principal signal delayed by a value of 90°;
 
the first, second and third control voltages corresponding respectively to the cosine, sine and −sine of the adjustable phase shift value multiplied by the same constant.
       

     The phase shift stage  306  comprises moreover an adder  312  arranged downstream of the multipliers  308  and  310  and adding the signals provided by the multipliers  308  and  310 . 
     The first control voltage is provided to the phase shift stage  306  and more particularly to the multiplier  308  by a control line represented by the arrow  314 . 
     The second or the third control voltage is provided to the phase shift stage  306  and more particularly to the multiplier  310  by a control line represented by the arrow  316 . 
     The oscillator  300  also comprises a constant phase shifter, the phase-frequency characteristic of which exhibits a phase shift which is constant with respect to frequency,  318 , arranged between the amplifier  108  and the phase shift stage  306  and providing the secondary signal from the principal signal. The phase shifter  318  is provided for:
         delaying the principal by 90° when the principal signal is a cosine and   advancing the principal signal by 90° when the principal signal is a sine.       

     The sum of the signals thus obtained at the output of the adder  312  corresponds to the principal signal shifted by the phase shift value according to the following equations:
 
cos(ω t )*cos( a )+sin(ω t )*(−sin( a ))=cos(ω t+a ), when the principal signal is a cosine and
 
sin(ω t )*cos( a )+cos(ω t )*sin( a )=sin(ω t+a ), when the principal signal is a sine
 
“a” being the adjustable phase shift value and ω being the angular frequency of the generated signal.
 
       FIG. 4  is a diagrammatic representation of a fourth embodiment of an oscillator according to the invention. 
     The oscillator  400  comprises a looped system  402 . 
     The looped system  402  comprises a phase shift device  404  comprising a plurality of phase shift stages  306   1 - 306   m  connected in series and each defining a level of phase shift, an amplifier  108  dispose upstream of the phase shift device  404  and a resonator  106  arranged downstream of the phase shift device  404 . 
     Each phase shift stage  306   1 - 306   m  of the phase shift device  404  is identical to the phase shift stage  306  of  FIG. 3 . Each phase shift stage  306   1 - 306   m  is provided for producing a phase shift on the principal signal provided by the preceding phase shift stage by analogue multiplication with control voltages. The control voltages can be:
         identical for all or a portion of the phase shift stages  306   1 - 306   m : in this case, these phase shift stages produce the same phase shift on the principal signal, or   different for each phase shift stage  306   1 - 306   m : in this case, each phase shift stage  306   1 - 306   m  produces a different phase shift of the principal signal.       

     According to the chosen configuration, the control voltages can be adjusted independently for each phase shift stage  306   1 - 306   m  or in a way which is common to all or a portion of the phase shift stages  306   1 - 306   m . 
     The oscillator  400  also comprises a constant phase shifter,  318   1 - 318   m  for each phase shift stage  306   1 - 306   m , arranged upstream of each phase shift stage  306   1 - 306   m  and providing the secondary signal to the phase shift stage  306  of a given phase shift level from the principal signal received from the phase shift stage of the preceding level of phase shift. Each constant phase shifter  318   1 - 318   m  is identical to the constant phase shifter  318  in  FIG. 3 . 
       FIG. 5  is a diagrammatic representation of a fifth embodiment of an oscillator according to the invention. 
     The oscillator  500  in  FIG. 5  comprises a first looped system  502 , called the principal looped system and a second looped system  504 , called the secondary looped system. 
     The principal looped system  502  comprises an amplifier  108 , a resonator  106  and a principal phase shift device  506  comprising a phase shift stage  306  identical to the phase shift stage  306  shown in  FIG. 3 . A power divider  508  is arranged between the amplifier  108  and the phase shift stage  306 . In the continuation of the description the phase shift stage or stages of the principal phase shift device  506  will be called principal phase shift stage(s). 
     The function of the secondary looped system  504  is to provide the secondary signal used by the principal phase shift stage  306  of the principal looped system  502 . In order to do this, the secondary looped system  504  comprises a phase shift device  510 , called secondary, comprising a phase shift stage  512 , called secondary, supplying the secondary signal by analogue multiplication with control voltages, an amplifier  514  arranged upstream of the secondary phase shift stage  512  and a resonator  516  arranged downstream of the secondary phase shift stage  512 . The output of the resonator  516  is connected to the input of the amplifier  514 . 
     A power divider  518  is arranged between the amplifier  514  and the secondary phase shift stage  512 . 
     The secondary phase shift stage  512  is identical to the principal phase shift stage  306  and comprises:
         a multiplier  520  providing a signal corresponding to the product of the secondary signal and the first control voltage,   a multiplier  522  providing a signal corresponding to the product:
           of the principal signal and the second control voltage when said signal is a cosine,   of the principal signal and the third control voltage when said signal is a sine,   
           an adder  524  for adding the signals provided by the multipliers  520  and  522  and providing the secondary signal.       

     The first control voltage is provided to the secondary phase shift stage  512  by a control line represented by the arrow  526 . The second or the third control voltage is provided to the secondary phase shift stage  512  by a control line represented by the arrow  528 . 
     The first, second and third control voltages used by the principal phase shift stage  306  and the secondary phase shift stage  512  are identical. Thus, the phase shift stages  306  and  512  apply the same phase shift to the principal signal and to the secondary signal respectively. 
     The sum of the signals thus obtained at the output of the adder  524  corresponds to the secondary signal shifted by the phase shift value applied to the principal signal by the principal phase shift stage  306 :
 
cos(ω t )*cos( a )+sin(ω t )*(−sin( a ))=cos(ω t+a ), when the principal signal is a sine and
 
sin(ω t )*cos( a )+cos(ω t )*sin( a )=sin(ω t+a ), when the principal signal is a cosine.
 
where “a” is the phase shift value and ω is the angular frequency of the generated signal.
 
     The principal signal and the secondary signal are each divided into two by the power dividers  508  and  518  respectively and provided to each of the principal  306  and secondary  512  phase shift stages. 
     The principal and secondary looped systems provide two signals in quadrature. 
       FIG. 6  is a diagrammatic representation of a sixth embodiment of an oscillator according to the invention. 
     The oscillator  600  shown in  FIG. 6  comprises a principal looped system  602  comprising an amplifier  108 , a resonator  106  and a principal phase shift device  604  comprising a plurality of principal phase shift stages  306   1 - 306   p , connected in series and identical to the phase shift stage  306  in  FIG. 3 . Each principal phase shift  306   1 - 306   p  defines a level of phase shift. 
     The oscillator  600  also comprises a secondary looped system  606  comprising an amplifier  514 , a resonator  516  and a secondary phase shift device  608  comprising as many secondary phase shift stages  512   1 - 512   p , connected in series and identical to the secondary phase shift stage  512  in  FIG. 5 , as there are principal phase shift stages  306   1 - 306   p , each phase shift stage  512   1 - 512   p  defining a level of phase shift. Each secondary phase shift stage  512   1 - 512   p  of a given phase shift level produces a phase shift of value identical to that of the phase shift produced by the principal phase shift stage  306   1 - 306   p  of the same level of phase shift. 
     Before each principal phase shift stage  306   1 - 306   p  is arranged a power divider  508   1 - 508   p , dividing the principal signal coming from the preceding level of phase shift in order to inject it into the principal phase shift stage and the secondary phase shift stage of the following level. 
     Before each secondary phase shift stage  512   1 - 512   p , is arranged a power divider  518   1 - 518   p , dividing the secondary signal coming from the preceding level of phase shift in order to inject it into the principal phase shift stage and the secondary phase shift stage of the following level. 
       FIG. 7  is a diagrammatic representation of a phase shift stage capable of use in the embodiments shown in  FIGS. 3 to 6  as a principal phase shift stage or as a secondary phase shift stage. 
     The phase shift stage  700  comprises, for each multiplier of the phase shift stage, a switching circuit  702  and  704 , each comprising four transistors connected two by two as differential pairs and controlled by the control voltages. Each multiplier also comprises an amplifier circuit  706  and  708  comprising two transistors connected as a differential pair and coupled with the switching circuits,  702  and  704  respectively. The resistors  710  and  712  inserted between the power supply line V cc  and the collectors of the transistors carry out the operation of summing the signals and more particularly the addition of the currents. 
     When two multipliers of two phase shift stages of the same level use the same signals, a more compact architecture can be proposed for producing these two multipliers. 
     Thus,  FIG. 8  is a diagrammatic representation of such an architecture capable of use in the embodiments shown in  FIGS. 5 and 6 . 
     Each of the two multipliers of two phase shift stages of the same level receiving the same signals comprise a switching circuit  802  and  804 , each switching circuit  802  and  804  comprising four transistors connected two by two as differential pairs and controlled by the control voltages. According to the architecture proposed in  FIG. 8 , a common amplifier circuit  806  is associated with the two switching circuits  802  and  804 , this amplifier circuit  806  comprising two transistors connected as a differential pair. The resistors  808  and  810  inserted between the power supply line V cc  and the collectors of the transistors carry out the operation of summing the signals and more particularly the addition of the currents. 
     In the architecture shown in  FIG. 8 , connections make it possible, on the one hand, to convey, in the resistors  808  and  810 , the currents coming from the other multiplier of the same phase shift stage and, on the other hand, to convey the voltages resulting from the summing of the signals in the resistors  808  and  810  either to the multipliers of the level of phase shift following, or to the resonator or resonators. 
     Thus, two transmission lines  812  and  814  each constitute a connection with the phase shift stages of the level of phase shift following or the resonator and convey either the principal signal or the secondary signal. 
     Two other transmission lines  816  and  818  each convey the signal obtained at the output of a multiplier and which is to be summed with the signal obtained at the output of the other multiplier of the same phase shift stage. 
     When two multipliers of two phase shift stages of the same level use different signals, a more compact architecture can also be proposed for producing these two multipliers. 
     Thus,  FIG. 9  is a diagrammatic representation of such an architecture capable of use in the embodiments in  FIGS. 5 and 6 . 
     Each of the two multipliers of two phase shift stages of the same level receiving different signals comprise an amplification circuit  902  and  904 , each amplification circuit  902  and  904  comprising four transistors connected two by two as differential pairs, the bases of which are connected to a resonator or to the outputs of the phase shift stages of the preceding level of phase shift. According to the architecture proposed in  FIG. 9 , a common switching circuit  906  is associated with the two amplification circuits  902  and  904 , this switching circuit  906  comprising two transistors connected as a differential pair. 
     The resistors  908  and  910  inserted between the power supply line V cc  and the collectors of the transistors carry out the operation of summing the signals and more particularly the addition of the currents. 
     In the architecture shown in  FIG. 9 , connections make it possible, on the one hand, to convey, in the resistors  908  and  910 , the currents coming from the other multiplier of the same phase shift stage and, on the other hand, to convey the voltages resulting from the summing of the signals in the resistors  908  and  910 , either to multipliers of the following level of phase shift, or to the resonator or resonators. 
     Thus, two transmission lines  912  and  914  each constitute a connection with the phase shift stages of the following level of phase shift or with the resonator and convey either the principal signal or the secondary signal. 
     Two other transmission lines  916  and  918  each convey the signal obtained at the output of a multiplier and which is to be summed with the signal obtained at the output of the other multiplier of the same phase shift stage. 
       FIG. 10  is a representation of a preferred embodiment of an oscillator according to the invention using the compact architecture described with reference to  FIG. 8 . 
     The oscillator  1000  shown in  FIG. 10  comprises a single level of phase shift comprising two phase shift stages, namely a principal phase shift stage and a secondary phase shift stage. 
     The resistors  808  and  810  of a phase shift stage are replaced by inductances. Thus, the oscillator  1000  comprises two inductances  1002  and  1004  for the principal shift stage and  1002 ′ and  1004 ′ for the secondary phase shift stage. 
     The oscillator  1000  comprises moreover two switching circuits per phase shift stage, namely the switching circuits  802  and  804  for the principal phase shift stage and the switching circuits  802 ′ and  804 ′ for the secondary phase shift stage. 
     Each phase shift stage comprises an amplifier circuit, namely the amplifier circuit  806  for the principal phase shift stage and the amplifier circuit  806 ′ for the secondary phase shift stage. The resistor of each amplifier circuit is also replaced by an inductance. 
     Resonators  1006  and  1008 , which are transmission lines, make it possible to loop back the signal coming from the principal phase shift stage to the input of the principal phase shift stage. 
     Similarly, resonators  1006 ′ and  1008 ′, which are transmission lines, make it possible to loop back the signal coming from the secondary phase shift stage to the input of the secondary phase shift stage. 
     In the examples described, it is also possible to replace at least one of the resistors  710 ,  712 ,  908  and  910 , by an impedance, having a non-zero imaginary part. These impedances can correspond at least partly to all or part of the resonator. 
     Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without exceeding the scope of the invention.