Patent Publication Number: US-9425748-B2

Title: Amplifier circuit, bi-stage amplifier circuit, multi-stage amplifier circuit, RF-amplifier circuit, receiver section, RF-transceiver, and integrated circuit

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     The present application claims priority to International Patent Application No. PCT/IB2014/001215, entitled “AMPLIFIER CIRCUIT, BI-STAGE AMPLIFIER CIRCUIT, MULTI-STAGE AMPLIFIER CIRCUIT, RF-AMPLIFIER CIRCUIT, RECEIVER SECTION, RF-TRANSCEIVER, AND INTEGRATED CIRCUIT,” filed on May 20, 2014, the entirety of which is herein incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention pertains to an amplifier circuit, to a bi-stage amplifier circuit, to a multi-stage amplifier circuit, to a RF-transceiver, to a radio device, and to an integrated circuit. 
     BACKGROUND OF THE INVENTION 
     Automotive radar applications are becoming very popular. In order to increase available production capacity and products reliability, efforts are made to integrate more functions inside a single chip (towards a fully-integrated transceiver) and to simplify assembly and production by using a packaged solution. Next generation of automotive radar products may move from today&#39;s bare die solution to a fully integrated packaged solution. Use of a given packaging technology may impose new challenges in terms of thermal dissipation and overall power consumption. U.S. Pat. No. 3,383,613A describes an amplifier comprising four transistors of same type connected as full-bridge having four arms and junctions therebetween with a transistor in each arm of the bridge. Two of said junctions form terminals of a differential output. For coupling an output of a driver amplifier to the amplifier, a coupling transformer having four secondary windings is employed. Each of the secondary windings is prepared for feeding the base terminal of another one of the four transistors. 
     Although the structure of this known full-bridge power amplifier may help to fulfill the above object of reducing overall power consumption of an automotive radar product, today&#39;s standard production processes impose the challenge of avoiding a coupling transformer as employed in the known amplifier. 
     SUMMARY OF THE INVENTION 
     The present invention provides an amplifier circuit, a bi-stage amplifier circuit, a multi-stage amplifier circuit, a RF-transceiver (RF=radio frequency), a radio device, and an integrated circuit as described in the accompanying claims. 
     Specific embodiments of the invention are set forth in the dependent claims. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the Figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. 
         FIG. 1  schematically shows a circuit diagram of a first example of an amplifier circuit. 
         FIG. 2  schematically shows a circuit diagram of an example of an optional output filter circuit. 
         FIG. 3  schematically shows a circuit diagram of a second example of an amplifier circuit according to  FIG. 1 , wherein the common tail element circuit comprises a current source. 
         FIG. 4  schematically shows a circuit diagram of a third example of an amplifier circuit of an amplifier circuit according to  FIG. 1 , wherein the common tail element circuit comprises a resistor. 
         FIG. 5  schematically shows a circuit diagram of a fourth example of an amplifier circuit of an amplifier circuit according to  FIG. 1 , wherein the common tail element circuit is formed by an electrical connection from a negative supply terminal to ground. 
         FIG. 6  schematically shows example diagrams of simulated gain as a function of frequency and of input and output voltages as a function of time of an amplifier circuit in bipolar technology according to  FIG. 1  compared to gain as a function of frequency of a classical follower and compared to input and output voltages as a function of time of a classical follower. 
         FIG. 7  schematically shows example diagrams of simulated gain as a function of frequency and of input and output voltages as a function of time as with  FIG. 6 , wherein, however, each semiconductor amplifier is implemented as a MOSFET (MOSFET=metal-oxide semiconductor field-effect transistor). 
         FIG. 8  schematically shows a diagram of simulated gain as a function of frequency of an amplifier circuit according to  FIG. 1 , for different bias current values. 
         FIG. 9  schematically shows an example of a bi-stage amplifier circuit. 
         FIG. 10  schematically shows an example of a multi-stage amplifier circuit. 
         FIG. 11  schematically shows an example of a radio device comprising a transceiver, a transmitter antenna, and a receiver antenna, the transceiver connected to a microcomputer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Because the illustrated embodiments of the present invention may for the most part, be implemented using electronic components, software and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention. 
       FIG. 1  schematically shows a circuit diagram of a first example of an amplifier circuit AMP comprising an amplifier core AMP-CORE, a common tail circuit cTEC, and a bias voltage supply circuit BVS. 
     The amplifier core AMP-CORE may comprise a first branch BRa, a second branch BRb, a positive supply terminal STa, a negative supply terminal STb, a first output terminal OTa, a second output terminal OTb, a first input terminal ITa, and a second input terminal ITb. 
     The first branch BRa may have a first positive supply node SNap and a first negative supply node SNan. The first branch BRa may comprise a first semiconductor amplifier Q 1  and a second semiconductor amplifier Q 2 . A first main current path of the first semiconductor amplifier Q 1  may be connected by a first intermediate connection IMa in series to a second main current path of the second semiconductor amplifier Q 2 . A first tap TPa at the first intermediate connection IMa may be connected to the first output terminal OTa. 
     The second branch BRb may have a second positive supply node SNbp and a second negative supply node SNbn. The second branch BRb may comprise a third semiconductor amplifier Q 3  and a fourth semiconductor amplifier Q 4 . A third main current path of the third semiconductor amplifier Q 3  may be connected by a second intermediate connection IMb in series to a fourth main current path of the fourth semiconductor amplifier Q 4 . A second tap TPb at the second intermediate connection IMb may be connected to the second output terminal OTb. 
     The first SNap and second SNbp positive supply nodes may be connected to the positive supply terminal STa. The first SNan and second SNbn negative supply nodes may be connected to the negative supply terminal STb. 
     The first semiconductor amplifier Q 1  may be provided for controlling a first current I 1  on the first main current path between the first supply node STa and the first tap TPa. The second semiconductor amplifier Q 2  may be provided for controlling a second current I 2  on the second main current path between the first tap TPa and the second supply node STb. The third semiconductor amplifier Q 3  may be provided for controlling a third current I 3  on the third main current path between the first supply node STa and the second tap TPb. The fourth semiconductor amplifier Q 4  may be provided for controlling a fourth current I 4  on the fourth main current path between the second tap TPb and the second supply node STb. 
     As shown in the example, the amplifier circuit AMP may be a differential amplifier. The pair of first ITa and second input ITb terminals may form a differential input port of the amplifier circuit AMP. The pair of first OTa and second OTb output terminals may form a differential output port of the amplifier circuit AMP. Connecting the first input terminal ITa to both, a first control terminal CT 1  of the first semiconductor amplifier Q 1  and to a fourth control terminal CT 4  of the fourth semiconductor amplifier Q 4  may help to avoid a need of a coupling transformer employed in known full-bridge amplifiers. Same may apply to a connection of the second input terminal ITb to both, a second control terminal CT 2  of the second semiconductor amplifier Q 2  and to a third control terminal CT 3  of the third semiconductor amplifier Q 3 . 
     The amplifier circuit AMP may comprise a first DC-insulation C 1  (DC=direct current) between the first input terminal ITa and the first control terminal CT 1 , connected thereto. The first DC-insulation C 1  may comprise a first capacitor. The amplifier circuit AMP may comprise a second DC-insulation C 2  between the second input terminal ITb and the second control terminal CT 2 , connected thereto. The second DC-insulation C 2  may comprise a second capacitor. The amplifier circuit AMP may comprise a third DC-insulation C 3  between the second input terminal ITb and the third control terminal CT 3 , connected thereto. The third DC-insulation may comprise a third capacitor. The amplifier circuit AMP may comprise a fourth DC-insulation C 4  between the first input terminal ITa and the fourth control terminal CT 4 , connected thereto. The fourth DC-insulation C 4  may comprise a fourth capacitor. 
     The DC-decoupling capacitors C 1 , C 2 , C 3 , C 4  may be adjusted for setting a cutoff frequency of the RC high passes (RC=resistor plus capacitor). 
     At least one of the DC-insulations may comprise optocouplers for transferring the respective input signal VSa, VSb to the related pair of control terminals CT 1 , CT 4 , or CT 2 , CT 3 , respectively (not explicitly illustrated in the figures). Any of the optocouplers may have a photosensor. The photosensor may comprise at least one of a photoresistor, a photodiode, and a phototransistor, or of another type of photosensing device. At least one of the semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4  may comprise the photosensor. 
     Alternatively, or in addition, at least one of a transformer and a micro-mechanical coupler may be employed for DC-insulation. 
     For a differential operation, during the positive cycle of a differential input signal V Sin=VSa−VSb, the third semiconductor amplifier Q 3  may act as a classical follower (gain G=1) copying the first input voltage component VSa to the second output terminal OTb. At the same cycle, the first branch BRa comprising stacked semiconductor amplifiers Q 1  and Q 2  may operate as a gm 2 ×Zload buffer. Zload may be an impedance of a load of the semiconductor amplifier Q 2 . Zload may be 1/gm 1 . 
     gm 1  may be a transductance of the first semiconductor amplifier Q 1 , gm 2  may be a transductance of the second semiconductor amplifier Q 2 , gm 3  may be a transductance of the third semiconductor amplifier Q 3 , and gm 4  may be a transductance of the fourth semiconductor amplifier Q 4 . The term ‘transductance’ may generally be used for designating a ratio of a current change ΔIout at an output port SNap, TPa, SNbp, TPb of any of the semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4  to a voltage change ΔVin at an input port CT 1 , CT 2 , CT 3 , CT 4  of the respective semiconductor amplifier Q 1 , Q 2 , Q 3 , Q 4 . The transductance may be written as gm=ΔIout/ΔVin. Each of the transductances gm 1 , gm 2 , gm 3 , gm 4  may be a transistor transconductance of a bipolar transistor or of a MOSFET, respectively. 
     When the semiconductor amplifiers Q 1  and Q 2  may present a high gain G (beta), collector and emitter currents may be almost equivalent (Ic≈Ie or simply I 1 =I 2 ). Generally, the term ‘beta’ may be used for designating a common-emitter current gain, which may be approximately the ratio of a DC collector current to a DC base current in forward-active region of a bipolar transistor. 
     A gain of the left branch BRa (having Q 1  and Q 2 ) may be gm 2 ×1/gm 1 . Both semiconductor amplifiers Q 1  and Q 2  may present a same transconductance (gm 1 =gm 2 =gm). The gain G of the left branch BRa (having Q 1  and Q 2 ) may simply equal to 1, as with a classical follower, however with an opposite polarity (VSa″=−VSb). A gain of the right branch BRb (having Q 3  and Q 4 ) may be gm 4 ×1/gm 3 . Both semiconductor amplifiers Q 3  and Q 4  may present the same transconductance (gm 3 =gm 4 =gm). The gain G of the right branch BRb (having Q 3  and Q 4 ) may simply equal to 1, as with a classical follower, however with an opposite polarity (VSb″=−VSa). 
     The amplifier circuit AMP may comprise a respective bias circuit B 1 , B 2 , B 3 , B 4  for each or any of the control terminals CT 1 , CT 2 , CT 3 , CT 4 . Each or any of the bias circuits B 1 , B 2 , B 3 , B 4  may comprise a resistor R 1 , R 2 , R 3 , R 4  connecting the control terminal to a bias voltage supply circuit BVS for adjusting bias currents of each or any of the semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4 . 
     At least two of the bias circuits B 1 , B 2 , B 3 , B 4  may be connected to the same bias voltage supply circuit BVS. The use of the same bias supply circuit BVS may allow to reduce current consumption. The first Q 1  and third Q 3  semiconductor amplifiers may share a first bias supply voltage Vb_h (see  FIGS. 1 and 3 to 5 ). The second Q 2  and fourth Q 4  semiconductor amplifiers may share a second bias supply voltage Vb_l (see  FIGS. 1 and 3 to 5 ). The bias voltage supply circuit BVS may be configured to provide both, the first Vb_h and the second Vb_l bias supply voltages (see  FIGS. 1 and 3 to 5 ). 
     The amplifier circuit AMP may comprise a common tail element circuit cTEC connected to the second supply terminal STb (or to the first supply terminal STa). The common tail element circuit cTEC may be employed for equally biasing each branch BRa, BRb of the amplifier circuit AMP. The common tail element circuit cTEC may comprise a current source controlled by a bias supply voltage vb provided by the same bias supply voltage circuit BVS (or a further bias supply voltage circuit not illustrated in the figures). The common tail element circuit cTEC may provide a constant current Itail=I 2 +I 4 . Each or any of the four semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4  may be operated at a bias current I 1 , I 2 , I 3 , I 4 , respectively, of a same level Itail/2. 
     The common tail element circuit cTEC may be connected to the first STa or to the second STb supply terminal for enforcing an anti-synchronous amplifier operation of a second branch BRb of the amplifier circuit AMP in relation to an amplifier operation of a first branch BRa of the amplifier circuit AMP, the first branch BRa comprising the first Q 1  and second Q 2  semiconductor amplifiers, the second branch BRb comprising the third Q 3  and fourth Q 4  semiconductor amplifiers. 
     All four semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4  may be implemented as bipolar transistors, field-effect transistors (FET), MOSFETs, or transistors of another type. 
     The amplifier circuit AMP configuration of  FIG. 1  uses a first pair Q 1 , Q 2  of stacked NPN bipolar semiconductor amplifiers and a cross-coupling of a differential input signal V Sin=VSa−VSb of a first pair Q 1 , Q 2  of stacked NPN bipolar semiconductor amplifiers to a second pair Q 3 , Q 4  of stacked NPN bipolar semiconductor amplifiers to provide twice the gain G of a conventional emitter follower circuit. Generally, the terms PNP and NPN may be used for designating a type of a doping sequence of three main terminal regions of a bipolar transistor. An NPN transistor may comprise two n doped semiconductor junctions that may share a thin p doped anode region. A PNP transistor may comprise two p doped semiconductor junctions that may share a thin n doped cathode region. A 6 dB gain G (db=decibel) may be obtained thanks to the differential configuration and to the stacks of same type of semiconductor amplifiers (Q 1 , Q 2 ), (Q 3 , Q 4 ) with inverted input phases. 
     For low supply voltage applications, the common tail element circuit cTEC may be replaced or represented by a tail resistor RT 1  (see  FIG. 4 ), or replaced or represented by a wire (see  FIG. 5 ). The amplitude of the differential output voltage Vout=VSa″−VSb″ at the output port OTa, OTb of the amplifier circuit AMP may be twice the amplitude of a conventional single follower, as follows from Equation 1a (see Table 1). This is also valid for the negative cycle of the first input voltage component VSa, with now the second branch BRb of the amplifier circuit AMP of  FIG. 1  operating as a gm 4 ×Zload buffer, with Zload now equal to 1/gm 3 , as shows Equation 1b. 
     When the bias voltages of the first CT 1  and third CT 3  control terminals have a same voltage level vb_h, while the bias voltages of the second CT 2  and fourth CT 4  control terminals have a same voltage level vb_I, while all semiconductor amplifiers Q 1  to Q 4  are of a same built, the currents I 2  and I 4  through the second Q 2  and fourth Q 4  semiconductor amplifiers may have a same level. This topology may provide an increased amplitude (gain G=2 corresponding to 6 dB) compared to a conventional follower (Gain=1), as shows Equation 2. The configuration of the stacked and cascaded NPN semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4  and the cross-coupling of the differential input signal Vin=VSa−VSb may provide (with same bias current) twice the voltage gain of a conventional emitter follower circuit. The amplifier circuit AMP may provide (with a same total overall current consumption I 2 +I 4 ) a higher total gain G than that of a conventional amplifier circuit having only one branch BRa. For each cycle of the input signal V Sin=VSa−VSb, this topology may allow maintaining a low output impedance ZoutP, N as a classical follower has, see Equation 3. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Proof of concept of an amplifier circuit according 
               
               
                 to the present invention (for the bipolar case) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 VSb″ − VSa″ = VSb − VSa ≈ −2 VSa 
                 Equation 1a 
               
               
                   
                 VSa″ − VSb″ = VSa − VSb ≈ 2 VSa 
                 Equation 1b 
               
               
                   
                 high beta, gm2 = gm1 (lc ≈ le) 
                 Equation 2 
               
               
                   
                 G = (gm2 × 1/gm1) × 2 
               
               
                   
                 G = 2 = 6 dB 
               
               
                   
                 ZoutP, N = 1/gm 
                 Equation 3 
               
               
                   
                   
               
            
           
         
       
     
     The semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4  may be bipolar semiconductor amplifiers or MOS-based semiconductor amplifiers (MOS=metal-oxide semiconductor). The semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4  may be NMOS semiconductor amplifiers, PMOS semiconductor amplifiers, NPN bipolar semiconductor amplifiers, PNP bipolar semiconductor amplifiers, CMOS semiconductor amplifiers, or another type of semiconductor amplifiers (NMOS=n channel metal-oxide semiconductor; PMOS=p channel metal-oxide semiconductor; NPN=doping sequence of main terminal regions; CMOS=complementary-metal-oxide semiconductor). Also, mixed configurations are possible, which may provide a final gain G different from 6 dB, since a transductance of the first Q 1  and third Q 3  semiconductor amplifiers would be different to a transductance of the second Q 2  and fourth Q 4  semiconductor amplifiers (see Equation 2). 
     The example of an amplifier circuit AMP in a differential gain-boosted follower buffer amplifier may be suitable for an energy-saving application. Because more gain may be provided at the same current, the current can be reduced for a same gain. Thus, the power consumption of products using the amplifier circuit may be reduced, notably when the amplifier circuit is used in a buffer stage. The amplifier circuit AMP may allow a same output amplitude for half the current drain of a conventional amplifier circuit. The amplifier circuit AMP allows a reduction of power dissipation with respect to a conventional emitter follower. 
     The gain G of the amplifier circuit AMP may be programmable by selectively enabling/disabling at least one of the connection between the first input terminal ITa and the fourth control terminal CT 4  of the fourth semiconductor amplifier Q 4  (see switch Sa) and the connection between the second input terminal ITb and the second control terminal CT 2  of the second semiconductor amplifier Q 2  (see switch Sb). 
     The amplifier circuit AMP may comprise a first switch Sa between the first input terminal ITa and the fourth control terminal CT 4  for connecting the first input terminal ITa to the fourth control terminal CT 4 . The amplifier circuit AMP may comprise a second switch Sb between the second input terminal ITb and the second control terminal CT 2  for connecting the second input terminal ITb to the second control terminal CT 2 . 
     A gain control of the amplifier circuit AMP may be obtained by selectively closing ON and opening OFF each of the switches Sa, Sb, as shown in Table 2. It will be apparent that the gain G with closed switches Sa, Sb may deviate from 6 dB (in particular it may be lower than 6 db) depending on the specific implementation and technology. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Dependency of gain of amplifier circuit 
               
               
                 AMP on states of switches Sa, Sb 
               
            
           
           
               
               
            
               
                 G 
                 Sa, Sb 
               
               
                   
               
               
                  0 dB 
                 open 
               
               
                 +6 dB 
                 closed 
               
               
                   
               
            
           
         
       
     
     These switches may be implemented as MOS switches (or other kind of switches). The switches may present a low intrinsic ON resistance (Ron) in order to not attenuate the input signal V Sin=VSa−VSb. The programmability may be controlled as follows: for 0 dB gain G, both switches Sa, Sb may be opened. Then, no signal flows to the control terminals of the second Q 2  and fourth Q 4  semiconductor amplifiers. Then, the second Q 2  and fourth Q 4  semiconductor amplifiers operate as simple current sources. Under this condition, the first Q 1  and third Q 3  semiconductor amplifiers of the amplifier circuit AMP may operate as a classical emitter (or common drain) follower. Consequently a unitary gain G may be obtained (G=1 corresponding to 0 dB). For the 6 dB gain step, both switches Sa, Sb may be closed. The semiconductor amplifiers Q 2 , Q 4  may be active (input signal VSb and VSa may be present at the control terminals CT 2 , CT 4 , respectively); and the amplifier circuit AMP may operate as a boosted follower, as presented above. 
       FIG. 2  schematically shows a circuit diagram of an example of an optional output filter circuit OF. The optional output filter circuit OF may be connected to the differential output port OTa, OTb of the amplifier AMP. A first RC filter comprising a first resistor Ra′ and a first capacitor Ca′ may be connected to the first output terminal OTa. A second RC filter comprising a second resistor Rb′ and a second capacitor Cb′ may be connected to the second output terminal OTb. The output terminals OTa f , OTb f  may form a differential output port of the amplifier circuit AMP, used separately or in any of the example embodiments described in the following. 
     The  FIGS. 3 to 5  show examples of amplifier circuits AMP each comprising another example of common tail element circuit cTEC. Such a common tail element circuit cTEC may comprise one or more electrical components. The common tail element circuit cTEC may comprise at least one of a resistor and a current-source. 
       FIG. 3  schematically shows a circuit diagram of a second example of an amplifier circuit AMP comprising an amplifier core AMP-CORE, a common tail circuit cTEC, and a bias voltage supply circuit BVS. The amplifier circuit AMP may comprise a common tail element circuit cTEC connected to the second STb (or to the first STa supply terminal not illustrated in  FIG. 3 ). The common tail element circuit cTEC may comprise a current source controlled by a bias supply voltage vb provided by the bias supply voltage circuit BVS (or a further bias supply voltage circuit). 
     The bias voltage supply circuit BVS may comprise three current-to-voltage converters Q_h, Q_I, Qb connected in series to a reference current source Iref for providing the bias voltages vb_h, vb_I, and vb. At least one of the current-to-voltage converters Q_h, Q_I, Qb may comprise a bipolar transistor, wherein a base of the bipolar transistor is connected to a collector of the bipolar transistor, and wherein the base of the bipolar transistor serves as output terminal of the respective current-to-voltage converter Q_h, Q_I, Qb. The bias voltage vb_h may be a sum of base-to-emitter voltages of the three current-to-voltage converters Q_h, Q_I, Qb. The bias voltages vb_h, vb_I, vb may be calculable by following Equations:
 
 vb _ h=vbe ( Q _ h )+ vbe ( Q _ I )+ vbe ( Qb )  (Equation 4a);
 
 vb _ I=vbe ( Q _ I )+ vbe ( Qb )  (Equation 4b);
 
 vb=vbe ( Qb )  (Equation 4c).
 
     Generally, the term vbe (Q) may be used for designating a voltage between a base and an emitter of any bipolar transistor. 
       FIG. 4  schematically shows a circuit diagram of a third example of an amplifier circuit AMP comprising an amplifier core AMP-CORE, a common tail circuit cTEC, and a bias voltage supply circuit BVS. The amplifier circuit AMP may comprise a common tail element circuit cTEC connected to the second STb (or to the first STa supply terminal not illustrated in  FIG. 4 ). The common tail element circuit cTEC may comprise a first tail resistor RT 1 . 
     The bias voltage supply circuit BVS may comprise three current-to-voltage converters Q_h, Q_I, RT 2  connected in series to a reference current source Iref for providing the bias voltages vb_h, vb_I. The third current-to-voltage converter RT 2  may be a second resistor. The second tail resistor RT 2  may have the resistance value of RT 1 . At least one of the current-to-voltage converters Q_h, Q_I may comprise a bipolar transistor, wherein a base of the bipolar transistor is connected to a collector of the bipolar transistor, and wherein the base of the bipolar transistor serves as output terminal of the respective current-to-voltage converter Q_h, Q_I. The bias voltage vb_h may be a sum of base-to-emitter voltages of the current-to-voltage converters Q_h and Q_I, and the voltage drop across the second tail resistor RT 2 . The bias voltages vb_h and vb_I may be calculable by following Equations:
 
 vb _ h=vbe ( Q _ h )+ vbe ( Q _ I )+( RT 2)( I ref)  (Equation 5a);
 
 vb _ I=vbe ( Q _ I )+( RT 2)( I ref)  (Equation 5b).
 
       FIG. 5  schematically shows a circuit diagram of a fourth example of an amplifier circuit AMP comprising an amplifier core AMP-CORE, a common tail circuit cTEC, and a bias voltage supply circuit BVS. The amplifier circuit AMP may comprise a common tail element circuit cTEC connected to the second STb (or to the first STa supply terminal not illustrated in  FIG. 5 ). The common tail element circuit cTEC may be formed by an electrical connection from a negative supply terminal STb to ground GND. The common tail element circuit cTEC may not comprise any electrical or electronic component (apart from a wiring resistance of the electrical connection from the negative supply terminal STb to ground GND). 
     The bias voltage supply circuit BVS may comprise two current-to-voltage converters Q_h, Q_I, connected in series to a reference current source Iref for providing the bias voltages vb_h, vb_I. At least one of the current-to-voltage converters Q_h, Q_I may comprise a bipolar transistor, wherein a base of the bipolar transistor is connected to a collector of the bipolar transistor, and wherein the base of the bipolar transistor serves as output terminal of the respective current-to-voltage converter Q_h, Q_I. The bias voltage vb_h may be a sum of base-to-emitter voltages of the current-to-voltage converters Q_h and Q_I. The bias voltages vb_h and vb_I may be roughly calculable by following equation:
 
 vb _ h=vbe ( Q _ h )+ vbe ( Q _ I )  (Equation 6a);
 
 vb _ I=vbe ( Q _ I )  (Equation 6b).
 
     The diagram on the left side of  FIG. 6  shows gain G over frequency of an amplifier circuit AMP according to  FIG. 1  (see curve K 1 ) in comparison to gain G over frequency of a known follower circuit (see curve K 2 ). The diagram on the right side of  FIG. 6  shows input and output voltages over time of an amplifier circuit AMP according to  FIG. 1  (see curve K 3 ) in comparison to output voltages over time of a known follower circuit (see curve K 4 ). 
     The diagram on the left side of  FIG. 7  shows gain G over frequency of an amplifier circuit AMP according to  FIG. 1  (see curve K 5 ), when each of the four semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4  thereof is a MOSFET, in comparison to gain G over frequency of a known follower circuit (see curve K 6 ). The diagram on the right side of  FIG. 7  shows input and output voltages over time of an amplifier circuit AMP according to  FIG. 1 , when each of the semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4  thereof is a MOSFET (see curve K 7  for the input voltage and curve K 8  for the output voltage), in comparison to output voltage over time of a known follower circuit (see curve K 7  for the input voltage and curve K 9  for the output voltage). 
       FIG. 8  schematically shows an example diagram of gain G over frequency of an amplifier circuit AMP according to  FIG. 1 . The diagram shows that a gain of this topology at lower to mid frequencies (up to 10 GHz) may be not dependent on the bias current. Above 10 GHz, there may be some gain dependency (some drop) on bias current because of operating at the transfer frequency f T  (where the input transistor pair may offer only a low Beta). In this operation region the bias current may be increased for maintaining or achieving a gain G of about 6 dB (see Equation 2). 
     A domain of application of the amplifier circuit AMP may range from low/mid RF-frequencies &lt;1 GHz, high RF frequencies &lt;10 GHz, and up to millimeter-wave RF frequencies 10 GHz to 100 GHz. 
     The amplifier circuit AMP may only require adjusting values of capacitors C 1  to C 4  employed for DC-insulation. The high-pass cutoff frequency (dependent on pairs C 1 R 1 , C 2 R 2 , C 3 R 3 , C 4 R 4 ) may be set low enough compared to the transfer frequency f T , in order to avoid an attenuation of the desired signal. Some first order high-pass filtering may be implemented taking benefit from the intrinsic filtering function of the pairs C 1  R 1 , C 2 R 2 , C 3 R 3 , C 4 R 4 . The amplifier circuit AMP may comprise a first order high-pass filter, the filter comprising at least one resistor and at least one capacitor. 
     As shown in  FIG. 9 , the bi-stage amplifier circuit BSAMP may comprise a first amplifier circuit AMP and a second amplifier circuit AMP″, which may be implemented as described above. The second amplifier circuit AMP″ of  FIG. 9  may be built as the amplifier circuit AMP described before. It may be built as shown in  FIG. 1 . 
     As shown, the first input terminal ITa″ of the second amplifier circuit AMP″ may be connected to the first output terminal OTa of the first amplifier circuit AMP. The second input terminal ITb″ of the second amplifier circuit AMP″ may be connected to the second output terminal OTb of the first amplifier circuit AMP. 
     Both amplifier stages AMP, AMP″ may share a same bias voltage supply circuit BVS and same bias voltage levels Vb_h, Vb_l, Vb (see bias supply net illustrated by dashed lines: Vb_h: high bias level; Vb_l: low bias level; Vb: bias level). Employing a same bias voltage supply circuit BVS for both amplifier stages AMP, AMP″ may allow reducing current consumption. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Switch states of bi-stage amplifier circuit BSAMP of FIG. 9 
               
            
           
           
               
               
               
            
               
                 G 
                 Sa, Sb 
                 Sa″, Sb″ 
               
               
                   
               
               
                  0 dB 
                 open 
                 open 
               
               
                 +6 dB 
                 closed 
                 open 
               
               
                 +6 dB 
                 open 
                 closed 
               
               
                 +12 dB  
                 closed 
                 closed 
               
               
                   
               
            
           
         
       
     
     A common gain control logic circuit GCL may be used to select (close or open) internal gain control switches Sa“, Sb” of each stage AMP, AMP″, as shown in Table 3, which may be similar to switches Sa, Sb in the example of  FIG. 1 . The same concept may be applied to the multi-stage amplifier circuit MSAMP shown in  FIG. 10 . 
       FIG. 10  shows a multi-stage amplifier circuit MSAMP that may comprise n cascaded stages of amplifier circuits AMP, AMP″, AMP (n) . The multi-stage amplifier circuit MSAMP may comprise one of the amplifier circuits AMP as defined above and a second amplifier circuit AMP″ which may have the built of the same or any other of the amplifier circuits AMP as defined above. All or any subset of the amplifier circuit stages AMP, AMP″, AMP(n) of the multi-stage amplifier circuit MSAMP may have the built of the amplifier circuit AMP shown in  FIG. 1 . The multi-stage amplifier circuit MSAMP may be considered as a variable gain amplifier circuit (VGA circuit). 
     The multi-stage amplifier circuit MSAMP may avoid a trade-off of gain, bandwidth, accuracy, and bias current consumption features, wherein the trade-off may be intrinsic to conventional VGAs. This may offer an additional degree of freedom during design, allowing to reach fully optimized amplifier circuits with increased performance. 
     The amplifier circuits AMP, BSAMP, MSAMP may be used for replacing classical emitter follower stages in any place of a radar transceiver, or in any transceiver of a system, in any technology and for any application requiring low power consumption. 
       FIG. 11  schematically shows an example of a radio device RD that may comprise a transceiver TR, a transmitter antenna AT and a receiver antenna AR. The transceiver TR may comprise a transmitter section T, a receiver section R, and a frequency synthesizer section FS. The frequency synthesizer section FS may be connected to at least one of the transmitter section T and the receiver section R to provide a local oscillator frequency f LO  to at least one of the transmitter section T and the receiver section R, respectively. 
     The receiver section R may comprise a mixer MX, a first filter F 1 , a first amplifier circuit AMP 1 , a second filter F 2 , a second amplifier circuit AMP 2 , and an analog-to-digital converter ADC. Each or any of both amplifier circuits AMP 1 , AMP 2  may be any of the one-stage AMP, bi-stage BSAMP, or multi-stage MSAMP amplifier circuits described before. 
     A RF-amplifier circuit AMP 1 , AMP 2  may comprise at least one of following: at least one of the suggested amplifier circuits AMP, at least one of the suggested bi-stage amplifier circuits BSAMP, at least one of the suggested multi-stage amplifier circuits MSAMP. 
     The analog-to-digital converter ADC may have a data output for providing output data DO (e.g. radar information) to be supplied to a microcontroller MC. The first filter F 1  may comprise at least one of a high-pass filter, of a bandpass filter, and a low-pass filter. The transceiver TR may comprise more than one transmitter/receiver channels in parallel. The transceiver TR may comprise more than one pair of transmitter section T and receiver section R (although  FIG. 11  shows only one pair). For each transmitter section T an own transmitter antenna AT may be provided. For each receiver section R an own receiver antenna AR may be provided. 
     As an example, in a typical radar receiver chip (or receiver path inside a transceiver), several receiver channels may be placed in parallel. In each channel, two or more multi-stage amplifier circuits MSAMP may be commonly used for accurately amplifying an input signal (VSb−VSa) up to certain required level. 
     Modern automotive radar technology uses a continuous wave frequency modulation (FMCW). This type of application may require a very accurate gain G in the whole receiver chain, together with accurate multi-stage gain steps when an automatic gain control (AGC) is used. The concept based on the novel programmable multi-stage amplifier circuit MSAMP may allow addressing this requirement. 
     Furthermore, radar transceiver products (for example transmitter sections, receiver sections, frequency synthesizer sections) may require buffer stages with low total power consumption. The suggested amplifier circuits AMP, BSAMP, MSAMP may represent an important contribution for facilitating to integrate such a transceiver in a compact single integrated circuit package. 
     A RF-transceiver TR may comprise at least one of the suggested RF-amplifier circuits AMP 1 , AMP 2 . A radio device RD may comprise one of the suggested RF-transceivers TR, and at least one of a receiver antenna AR and a transmitter antenna AT. 
     An integrated circuit may comprise at least one of following: at least one of the suggested amplifier circuits AMP, at least one of the suggested bi-stage amplifier circuits BSAMP, at least one of the suggested multi-stage amplifier circuits MSAMP, at least one of the suggested RF-amplifier circuits, at least one of the suggested RF-transceivers, at least one of the suggested radio devices RD. 
     The suggested amplifier may be realized with a lower overall die size than comparable conventional amplifiers. A very good gain accuracy may be not anymore dependent on dimensions of resistors or ratios of resistors, as it is the case for most of conventional multi-stage amplifiers. 
     In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims, and that the claims are not limited to the examples described above. 
     Any of the DC-insulations may be provided by at least one of a transformer, of a capacitor, of an optocoupler, or of a micro-mechanical coupler. 
     At least one of the amplifier circuits AMP, BSAMP, and MSAMP may comprise PNP bipolar semiconductor amplifiers instead of all or a subset of the NPN bipolar semiconductor amplifiers Q 1 , Q 2 , Q 3 , Q 4 , Q_h, Q_I, Qb. 
     Moreover, the terms first, second, third, fourth, and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. 
     The connections as discussed herein may be any type of connection suitable to transfer signals and/or data from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise, the connections may for example be direct connections or indirect connections. The connections may be illustrated or described in reference to being a single connection, a plurality of connections, unidirectional connections, or bidirectional connections. However, different embodiments may vary the implementation of the connections. For example, separate unidirectional connections may be used rather than bidirectional connections and vice versa. Also, plurality of connections may be replaced with a single connection that transfers multiple signals serially or in a time multiplexed manner. Likewise, single connections carrying multiple signals may be separated out into various different connections carrying subsets of these signals. Therefore, many options exist for transferring signals. 
     Any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality. 
     Also for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within a same device. 
     Also for example, the examples, or portions thereof, may implemented as soft or code representations of physical circuitry or of logical representations convertible into physical circuitry, such as in a hardware description language of any appropriate type. 
     However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. 
     In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first”, “second”, “third”, and “fourth” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.