Abstract:
An electronic circuit with an improved current stabilization operating in an RF transceiver or receiver, e.g. in a wireless local area network system, and a corresponding method is provided for generating a supply current and supplying the generated supply current to at least two subunits of the electronic circuit. The at least two subunits are connected in parallel to each other. Each of the subunits receives an input voltage at an input transistor in the first one of at least two parallel current paths of the subunit. Each subunit stabilizes the current through the input transistor by means of a control circuit a second current path of the subunit and a common voltage output terminal is connected to each subunit for outputting a voltage. The provided technique may allow for detecting maximum values or generating absolute values.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention generally relates to electronic circuits for processing voltages that may be used in units or subunits of communication systems such as WLAN (Wireless Local Area Network) systems.  
           [0003]    2. Description of the Related Art  
           [0004]    A wireless local area network is a flexible data communication system implemented as an extension to, or as an alternative for, a wired LAN. Using radio frequency (RF) or infrared technology, WLAN systems transmit and receive data over the air, minimizing the need for wired connections. Thus, WLAN systems combine data connectivity with user mobility. Most WLAN systems use spread spectrum technology, a wide-band radio frequency technique developed for use in reliable and secure communication systems. The spread spectrum technology is designed to trade-off bandwidth efficiency for reliability, integrity and security.  
           [0005]    One element in wireless communication systems are RF transceivers. Today, RF transceivers are often provided as integrated circuits and the realization of RF transceivers in highly integrated circuits may be a requirement for applications such as those in wireless local area networks and in the cellular telephony to achieve very high dynamic range and very high frequency on the one hand and a low power consumption and a reduction in the passive components on the other hand.  
           [0006]    One possibility to satisfy these requirements may be to build RF transceivers in CMOS (Complementary Metal Oxide Semiconductor) technology. The CMOS technology may offer low power consumption and a high level of integration.  
           [0007]    The central device in such technologies is the MOSFET (Metal Oxide Semiconductor Field Effect Transistor) transistor. It is a three or four terminal device that draws no power from an input signal and allows for very fast switching. The fourth terminal is connected to the substrate and is called the bulk.  
           [0008]    [0008]FIG. 1 shows a typical electronic circuit that may act as an absolute value generator and comprises a current source  100  and two p-channel MOSFET transistors  110 ,  140 . The current source  100  is connected to the source terminals of the p-channel MOSFET transistors for supplying the current to the transistors. Further, the source terminal of each transistor is connected to its bulk terminal. The electronic circuit of FIG. 1 further comprises two input terminals  120 ,  130  wherein one is connected to the gate of the first transistor  110  and the other is connected to the gate of the second transistor  140  to provide respective input voltages. The drain terminals of the transistors  110 ,  140  are connected to a ground line to provide a common ground level. An output terminal  150  is provided at a point connecting the current source  100  with the source terminals of the transistors  110 ,  140 . It can further be seen that the transistors  110 ,  140  are connected in parallel to each other.  
           [0009]    The shown electronic circuit of FIG. 1 is disadvantageously affected by a poor accuracy in particular if small voltages, i.e., V peak &lt;V gs −V thr  and large voltages, i.e., V peak &gt;(V gs −V thr )*1.414 are processed. When for instance a large signal is delivered to one of the two input terminals  120 ,  130  and the other input terminal receives a small signal, one transistor turns off (V gs &lt;V thr ) while the other has to carry twice the current: V gs ≅1.414*V gs (0V). This situation may results in an additional level shift caused by nonlinear changes of a gate source voltage and may undesirably change the value of the voltage of the output terminal  150 .  
           [0010]    Therefore, the conventional electronic circuits do often not meet the requirements of accuracy, operating speed and precision.  
         SUMMARY OF THE INVENTION  
         [0011]    An improved electronic circuit, improved wireless LAN receiver and operation method are provided that may allow for high operating speed, high precision and high accuracy.  
           [0012]    In one embodiment, there is provided an electronic circuit that comprises a current supply unit adapted to generate a supply current, and at least two subunits that are connected in parallel to each other and are further connected to the current supply unit. Each of the subunits comprises at least two parallel current paths, wherein a first one of the at least two parallel current paths comprises an input transistor that is connected to receive an input voltage of the respective subunit. A second one of the at least two parallel current paths comprises a control circuit that is adapted to stabilize the current through the input transistor in the first current path. The subunits are further connected to a common voltage output terminal.  
           [0013]    In a further embodiment, there is provided a WLAN (Wireless Local Area Network) receiver that comprises a current supply unit adapted to generate a supply current, and at least two subunits that are connected in parallel to each other and are further connected to the current supply unit. Each of the subunits comprises at least two parallel current paths, wherein a first one of the at least two parallel current paths comprises an input transistor that is connected to receive an input voltage of the respective subunit. A second one of the at least two parallel current paths comprises a control circuit that is adapted to stabilize the current through the input transistor in the first current path. The subunits are further connected to a common voltage output terminal.  
           [0014]    In another embodiment, there is provided a method of operating an electronic circuit. The method comprises generating a supply current and supplying the generated supply current to at least two subunits of the electronic circuit. The at least two subunits are connected in parallel to each other. The method further comprises receiving in each of the subunits, an input voltage at an input transistor in a first one of at least two parallel current paths of the subunit. The method further comprises stabilizing in each of the subunits, the current through the input transistor by means of a control circuit in a second one of the at least two parallel current paths of the subunit. Moreover the method comprises outputting a voltage at a common voltage output terminal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The accompanying drawings are incorporated into and form a part of the specification for the purpose of explaining the principles of the invention. The drawings are not to be construed as limiting the invention to only the illustrated and described examples of how the invention can be made and used. Further features and advantages will become apparent from the following, and more particular description of the invention as illustrated in the accompanying drawings, wherein:  
         [0016]    [0016]FIG. 1 shows a conventional electronic circuit for processing voltages;  
         [0017]    [0017]FIG. 2 shows an electronic circuit according to an embodiment comprising two subunits;  
         [0018]    [0018]FIG. 3 shows the subunits of FIG. 2 in more detail;  
         [0019]    [0019]FIG. 4 shows the electronic circuit of FIG. 2 having inserted the subunit circuit of FIG. 3;  
         [0020]    [0020]FIG. 5 shows an electronic circuit according to another embodiment having more than two subunits; and  
         [0021]    [0021]FIG. 6 is a flowchart illustrating the process of a current stabilization according to an embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    The illustrative embodiments of the present invention will be described with reference to the figure drawings, wherein like elements and structures are indicated with like reference numbers.  
         [0023]    Referring now to the drawings, in particular to FIG. 2, an electronic circuit is depicted according to an embodiment. The electronic circuit comprises a current supply unit  100  that is adapted to generate a constant supply current, and two subunits  200 ,  210  each one depicted as a block. The first subunit  200  is connected to a first input terminal  220  and the second subunit  210  is connected to a second input terminal  230 , to receive respective input voltages V in1 , V in2 . The subunits  200 ,  210  are connected in parallel to each other wherein a current line  240  connects the subunits  200 ,  210  to the current supply unit  100  for distributing the current to the subunits  200 ,  210 . The current line  240  further connects the subunits  200 ,  210  to a common voltage output terminal  250 . A ground line  260  is connected to the subunits  200 ,  210  to provide a common ground level.  
         [0024]    The subunits  200 ,  210  depicted in FIG. 2 have the same structure. For this reason, the internal construction of only one of the subunits  200 ,  210  will be described in the following exemplarily in detail with reference to FIG. 3.  
         [0025]    The circuitry of the subunit depicted in FIG. 3 comprises two parallel current paths, wherein the first current path comprises a p-channel MOSFET transistor  310  operating as an input transistor, and a current source unit  330  generating a constant current. The second current path acts as a control circuit for controlling the current through the first current path, and comprises an n-channel MOSFET transistor  320  for this purpose. The transistor  320  will be referred to in the following as control transistor.  
         [0026]    The current source unit  330  is provided at a point  340  connecting the gate terminal of the control transistor  320  in the second current path and the drain terminal of the input transistor  310 .  
         [0027]    The gate terminal of the input transistor  310  is connected to the input terminal  220  to receive the respective input voltage V in . The bulk and the source terminals of the input transistor  310  are connected with each other (V bs =0V) and are further connected to the second current path formed by the control transistor  320 . The two current paths are further connected to the output terminal  250  to provide a subunit output voltage.  
         [0028]    The internal circuitry of the subunit of FIG. 3 is inserted into the above-mentioned subunit blocks  200 ,  210  of FIG. 2, and FIG. 4 shows the resulting detailed electronic circuit.  
         [0029]    Discussing now in more detail the circuit of FIG. 4, the gate terminals of the input transistors  310 ,  410  are connected, as explained above, to respective input terminals  220 ,  230  to receive respective input voltages, and the drain terminals of the input transistors  310 ,  410  are connected to points  340 ,  440  connecting the gates of the control transistors  320 ,  420  and the current source units  330 ,  430 .  
         [0030]    An applied input voltage at one of the input terminals  220 ,  230  has influence on the channel resistance of the respective input transistor  310 ,  410 , and a current flows through the transistor channel. The current source unit  330 ,  430  keeps the current through the input transistor  310 ,  410  constant at a level corresponding to the strength of the constant source current by the control transistor. Simultaneously, a resulting voltage at the gate terminal of the respective control transistor  320 ,  420  has influence on the resistance of the control transistor  320 ,  420 . Thus, the voltage drop in the first current path controls the current flow in the second current path. The control circuit  320 ,  420  can be seen as a control loop.  
         [0031]    The above-mentioned voltage at the gate of the control transistor  320 ,  420  varies the control transistor channel resistance and therefore, the current through the control transistor  320 ,  420  varies such that the current through the entire subunits  200 ,  210  can change although the current through the input transistor  310  is kept stable.  
         [0032]    The difference between that part of the current delivered by the current supply unit  100  that is distributed to the subunit  200 ,  210 , and the current flowing through the respective input transistor channel  310 ,  410  of this subunit  200 ,  210  is routed through the control transistor  320 ,  420  in the second current path of the subunit  200 ,  210 .  
         [0033]    Thus, an input voltage V in1 , V in2  at each input terminal  220 ,  230  of the respective subunits  200 ,  210  effects an adaptation of the related input transistor channel resistance of the respective input transistor  310 ,  410 , and current through the respective first current path can flow. The current through the respective first current path of each subunit  200 ,  210  effects a voltage at the gate terminal of the respective control transistor  320 ,  420 , which influences the channel resistance of the control transistor  320 ,  420  and, therefore, the current through the respective control transistor  320 ,  420  in the second current path assists in varying the subunit currents while keeping the current through the input transistor  310 ,  410  in the first current path stable.  
         [0034]    At the end, the sum of the current through the respective first and second current path of each subunit  200 ,  210  is equal to the current distributed to the respective subunits, and the sum of the current through the subunits  200 ,  210  is equal to the current generated by the current supply unit  100 .  
         [0035]    By means of the current line  240 , subunits are interrelated to provide a common output voltage of the electronic circuit at the circuit output terminal  250 .  
         [0036]    Turning now to FIG. 5 which illustrates another embodiment, the figure shows the detailed construction of an electronic circuit similar to that of FIG. 4, having an increased number n of subunits. Therefore, the electronic circuit of FIG. 5 differs from the electronic circuit of FIG. 4 by the number of input terminals of the electronic circuit.  
         [0037]    Because of the parallel construction of the electronic circuit, the number of the input terminals  310 ,  410 ,  510  can be adapted to any required number of input voltages, whereby only the value of the supply current of the supply current unit  100  has to be adapted. The number of input terminal may be only restricted by the current flow capability of the acting n-channel transistor, when a large input is applied.  
         [0038]    As mentioned before, the supply current unit  100  delivers a constant supply current I supply  to the subunits. Assuming, the electronic circuit of FIG. 5 comprises a number n of subunits. The current through the first current path of each subunit i may be specified as I i1  and the current through the associated second current path of the respective subunit is specified as I i2 . Further assuming, i is a variable that counts from  1  to n, then the calculation of the supply current delivered by the current supply unit  100  can be expressed as follows:  
         I   supply     =         ∑     i   =   1     n                     (       I   i1     +     I   i2       )       =   constant                           
 
         [0039]    [0039]FIG. 6 is a flowchart relating to the embodiment of FIG. 4 that comprises two subunits  200 ,  210 . The flowchart of FIG. 6 illustrates the process of operating the electronic circuit leading to an improved current stabilization. The process starts with step  610  wherein a constant supply current is generated and the generated supply current is distributed to the subunits  200 ,  210 .  
         [0040]    In step  620 , a first input voltage V in1  is received, and step  630  is provided for stabilizing the first input transistor  310  that receives the input voltage in step  620 . The next step of the illustrated flowchart is the step  640 , wherein a second input voltage V in2  is received. Similar to step  630 , step  650  stabilizes the second input transistor  410 .  
         [0041]    The last step of the sequence of operating the electronic circuit with an improved current stabilization is step  660  of generating and outputting an absolute value of the input voltages received in step  620  and  640 .  
         [0042]    In another embodiment, the sequence of operating the electronic circuit, may differ in the order of the above-described steps. In particular, step  640  and step  650  may be performed prior to the steps  620  and  630 .  
         [0043]    In a further embodiment, the sequence of operating the electronic circuit may be modified such that the steps  620  and  640  of receiving the input voltages and the steps  630  and  650  of stabilizing the respective input transistors may be performed simultaneously.  
         [0044]    In yet another embodiment, the process of FIG. 6 may be supplemented with further receiving and stabilizing steps to allow for operating more than two subunits.  
         [0045]    As apparent from the foregoing description, all of the embodiments, as described, may advantageously provide high accuracy, high precision and improved operating speed, because the input with the most significant input voltage is biased by a constant current and a modulation of gate source voltage is avoided.  
         [0046]    The arrangements may have the advantage to allow magnitude measurements of the applied signals, and the applied signals may be differential as well as single ended.  
         [0047]    The arrangements may further have the advantage that additional level shifts are avoided, because the p-channel transistors used as input transistors  310 ,  410 ,  510  have an enhanced input transconductance due to the control circuits.  
         [0048]    The above described embodiments may offer the advantage that the gate to source voltage drop V gs  of the input transistors  310 ,  410 ,  510  is constant because the source to substrate voltage drop V bs  remains unchanged by means of shorting the source and the substrate terminal (V bs =0V), also referred as bulk terminal.  
         [0049]    The provided techniques may further offer the advantage that the current through the input transistor  310 ,  410 ,  510  with applied peak voltage remains unchanged by the control loop.  
         [0050]    The arrangements may provide the advantage that the current of the input transistors  310 ,  410 ,  510  which are turned off when a large input signal is applied, can flow through the control transistor  320 ,  420 ,  520 .  
         [0051]    Moreover the manufacturing may be simplified because the electronic circuit uses a decreased number of component parts since additional circuitry for post processing the output signal can be avoided. Therefore, the above-described embodiments may, in effect, reduce the production costs.  
         [0052]    While the invention has been described with respect to the physical embodiments constructed in accordance therewith, it will be apparent to those skilled in the art that various modifications, variations and improvements of the present invention may be made in the light of the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention. For instance, while the above described embodiments use the current supply unit  100  for generating the constant supply current, other embodiments may be provided with a resistor that is connected to a voltage source for generating that constant supply current.  
         [0053]    In addition, those areas in which it is believed that those of ordinary skill in the art are familiar, have not been described herein in order not to unnecessarily obscure the invention described herein. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrative embodiments, but only by the scope of the appended claims.