Abstract:
A circuit, an adjusting method, and use of a control loop for adjusting a data retention voltage and/or a leakage current of a CMOS circuit for a sleep mode, wherein the CMOS circuit is operated to control in a measuring mode, whereby in the measuring mode a leakage current exclusively flows through the CMOS circuit, the control loop in the measuring mode adjusts the data retention voltage and/or the leakage current, and the adjustments of the control loop for the sleep mode are stored.

Description:
[0001]    This nonprovisional application claims priority to German Patent Application No. DE 10 2008 053 535.4, which was filed in Germany on Oct. 28, 2008, and to U.S. Provisional Application No. 61/117,414, which was filed on Nov. 24, 2008, and which are both herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a circuit, an adjusting method, and a use of a control loop. 
         [0004]    2. Description of the Background Art 
         [0005]    If a digital CMOS circuit is placed in a sleep mode, the gate capacitances of the CMOS circuit should no longer be recharged. The current consumption of the CMOS circuit is therefore significantly reduced in the sleep mode. Only a leakage current flows in the sleep mode, when the supply voltage continues to be present in the CMOS circuit in the sleep mode. 
       SUMMARY OF THE INVENTION 
       [0006]    The object of the invention is to improve a circuit as much as possible. 
         [0007]    Accordingly, a circuit is provided that can be integrated monolithically on a semiconductor chip. The integrated circuit has a digital CMOS circuit with NMOS field-effect transistors and with PMOS field-effect transistors. NMOS field-effect transistors in this case are of the n-conducting type, whereas PMOS field-effect transistors are of the p-conducting type. In the digital CMOS circuit, the NMOS field-effect transistors and PMOS field-effect transistors are used as complementary types. In this case, in a basic logic function, such as, for example, a gate, each NMOS field-effect transistor is assigned at least one PMOS field-effect transistor and each PMOS field-effect transistor is assigned at least one NMOS field-effect transistor. 
         [0008]    The circuit can have a first load device and a second load device. The first load device is connected to a first supply voltage and to the source terminals of the NMOS field-effect transistors of the digital CMOS circuit. The first supply voltage, for example, can be ground or a negative voltage. The second load device is connected to a second supply voltage and to the source terminals of the PMOS field-effect transistors of the digital CMOS circuit. The second supply voltage is preferably a positive supply voltage. A load device in this case is taken to mean a circuit component that represents a load for a current flowing through said component and causes a voltage drop across the load. Preferably, the load device has a current voltage characteristic, which is assigned to a linear or preferably nonlinear course. The first load device and the second load device are preferably connected in series to the source terminals of the CMOS circuit. 
         [0009]    The circuit can have an evaluation circuit, which is formed to evaluate a first source voltage at the source terminals of the NMOS field-effect transistors and is connected to the source terminals of the NMOS field-effect transistors. The first source voltage can be applied at the source terminals of the NMOS field-effect transistors, for example, as a reference potential, such as ground. 
         [0010]    The evaluation circuit can be formed to evaluate a second source voltage at the source terminals of the PMOS field-effect transistors and is connected to the source terminals of the PMOS field-effect transistors. 
         [0011]    The evaluation circuit for the evaluation can have a measuring circuit with an analog-to-digital converter or a number of comparators. The measuring circuit advantageously has analog subcircuits, such as amplifiers or subtractors or the like for the evaluation. Preferably, the evaluation circuit has in addition an arithmetic logic unit, for example, a microcontroller core. 
         [0012]    The evaluation circuit can be formed for adjusting a first voltage drop across the first load device and for the adjustment is connected to a first control input of the first load device. The first control input can be an analog control input for the continuous adjustment of the first voltage drop. Preferably, the first control input however is a digital control input, which enables the adjustment of the first voltage drop in steps. For the adjustment, the first voltage drop depends on a control signal at the first control input. In addition, the first voltage drop can depend on a leakage current through the digital CMOS circuit and/or on a temperature. 
         [0013]    The evaluation circuit can be formed for adjusting a second voltage drop across the second load device and for the adjustment is connected to a second control input of the second load device. The second control input can be an analog control input for the continuous adjustment of the second voltage drop. Preferably, the second control input, however, is a digital control input, which enables the adjustment of the second voltage drop in steps. For the adjustment, the second voltage drop depends on a control signal at the second control input. In addition, the second voltage drop can depend on a leakage current through the digital CMOS circuit and/or on a temperature. 
         [0014]    The object of the invention furthermore is to provide as improved an adjustment method as possible. 
         [0015]    Accordingly, a method is provided for adjusting a data retention voltage, applied across a CMOS circuit, and/or a leakage current through the CMOS circuit for a sleep mode of the CMOS circuit. 
         [0016]    In the method, a first source voltage applied at the source terminals of NMOS field-effect transistors of the CMOS circuit is evaluated. For the evaluation, advantageously a first voltage difference between a first supply voltage and the first source voltage is determined. 
         [0017]    In the method, a second source voltage applied at the source terminals of PMOS field-effect transistors of the CMOS circuit is evaluated. For the evaluation, advantageously a second voltage difference between a second supply voltage and the second source voltage is determined. 
         [0018]    In the method, a first voltage drop across a first load device, connected to the source terminals of the NMOS field-effect transistors, is adjusted as a function of the first source voltage and/or the second source voltage. 
         [0019]    Alternatively or in combination, in the method, a second voltage drop of a second load device, connected to the source terminals of the PMOS field-effect transistors, is adjusted as a function of the first source voltage and/or the second source voltage. 
         [0020]    The object of the invention furthermore is to provide a use of a control loop. 
         [0021]    Accordingly, a use of a control loop is provided for adjusting a data retention voltage, applied across a CMOS circuit, and/or a leakage current through the CMOS circuit for a sleep mode. The control loop preferably has an evaluation circuit for evaluating a first source voltage, applied at the source terminals of NMOS field-effect transistors of the CMOS circuit, and/or for evaluating a second source voltage, applied at the source terminals of PMOS field-effect transistors of the CMOS circuit. Preferably, the control loop has a first adjustable load device connected to the source terminals of the NMOS field-effect transistors. Preferably, the control loop has a second adjustable load device connected to the source terminals of the PMOS field-effect transistors. 
         [0022]    The CMOS circuit is operated for control in a measuring mode. In the measuring mode, a leakage current exclusively flows through the CMOS circuit. 
         [0023]    The control loop in the measuring mode adjusts the data retention voltage and/or the leakage current. The adjustments of the control loop for the sleep mode are stored. 
         [0024]    The refinements described hereinafter relate to the circuit, as well as to the use of the control loop and to the adjusting method. Methods features emerge from the functions of the circuit. Functional features of the circuit emerge from the corresponding methods steps. 
         [0025]    In an embodiment, the circuit is formed for an operating mode and a sleep mode with a current consumption that is reduced compared with the operating mode. In this regard, multiple sleep modes and/or multiple operating modes may also be provided. In the operating mode, the digital CMOS circuit is formed to perform various operating functions. For example, in this case, the digital CMOS circuit performs calculations, writes information in the memory or the register, or reads the appropriate information out of memory cells. In the operating mode, a clock signal can be applied to the digital CMOS circuit. In contrast, the digital CMOS circuit preferably performs no operations in the sleep mode. 
         [0026]    In an operating mode, at least one of the load devices can be controlled to a low-resistance state. In the low-resistance state, a voltage drop across the load device can be disregarded in regard to circuit function. For example, the control of the low-resistance state can be effected by a switching on of a switching transistor. Preferably, in the sleep mode, the load device can be controlled to a state with a higher resistance value compared with the operating mode. The load device, in this case, is controlled in such a way that a leakage current, flowing through the MOS field-effect transistors and through the load device in the sleep mode, produces a voltage drop across the load device. It is preferably provided that in the sleep mode all digital elements of the CMOS circuit, such as gates or memory elements and the like, have a defined state. A defined state of this type is a logic one or logic zero at the output of the respective element. 
         [0027]    The body-source voltage can be produced in a sleep mode of the circuit. A leakage current, flowing through the CMOS circuit and through the (first and/or second) load device, causes a voltage drop at the load device. The voltage drop of the load device can be caused by the leakage current only. Because of the connections of the load device to the source terminals of the CMOS circuit, this voltage drop produces a body-source voltage at the source terminals and body terminals of the field-effect transistors of the CMOS circuit. 
         [0028]    According to a first embodiment, it is provided that the evaluation circuit or the first load device can have a first memory for storing the adjustment for the first voltage drop. The memory, for example, is a register or a nonvolatile memory cell. 
         [0029]    According to a second embodiment, which can also be combined with the first embodiment, it is provided that the evaluation circuit or the second load device has a second memory for storing the adjustment for the second voltage drop. The memory, for example, is a register or a nonvolatile memory cell. 
         [0030]    In an embodiment, the evaluation circuit can have a device for measuring a temperature. For example, a temperature sensor element together with the CMOS circuit can be integrated monolithically on a semiconductor chip. The evaluation circuit can be formed to evaluate a measuring signal corresponding to the temperature. Advantageously, the evaluation circuit can be formed to adjust the first voltage drop and/or to adjust the second voltage drop as a function of the measurement. Preferably, the evaluation circuit can be formed to map the adjustment of the first load device and/or to map the adjustment of the second load device to a measured temperature. Advantageously, the evaluation circuit has a mapping table. 
         [0031]    It is provided in an embodiment that the first load device has an adjustable load, which acts between the source terminals of the NMOS field-effect transistors and the first supply voltage. The acting load can be adjustable. Advantageously, the load is formed by a number of transistors. Multiple connectable NMOS field-effect transistors with a different geometry, particularly gate width and/or gate length, are providing for adjusting the acting load. 
         [0032]    It is provided in another embodiment that the second load device can have an adjustable load, which acts between the source terminals of the PMOS field-effect transistors and the second supply voltage. The acting load is preferably formed by a number of transistors and is adjustable by connection or disconnection of individual transistors. The adjustment occurs preferably automatically by the evaluation circuit, advantageously by the running of an adjustment program. 
         [0033]    In another embodiment, an adjustable load has a number of switchable resistors, which can be connected and disconnected by means of switching transistors. Alternatively, a variable (active) resistor in the form of a field-effect transistor may also be used as a switchable resistor. For example, its drain-source path can be varied between resistance values. In the sleep mode, the adjustable load acts in series to the source terminals of the digital CMOS circuit, so that a leakage current through the digital CMOS circuit causes a voltage drop across the adjustable load. 
         [0034]    The body terminals of the NMOS field-effect transistors of the digital CMOS circuit are preferably connected directly to the first supply voltage (conductively). Accordingly, no component, particularly no component with a resistance, is provided between the body terminals of the NMOS field-effect transistors and the first supply voltage. This also applies preferably to the body terminals of the PMOS transistors of the digital CMOS circuit, which are connected directly to the second supply voltage. 
         [0035]    In an embodiment, it is provided that for adjusting the data retention voltage and/or of the leakage current, a leakage current due to the PMOS field-effect transistors and a leakage current due to the NMOS field-effect transistors are made more similar by adjustment process steps. It is provided that the leakage current due to the PMOS field-effect transistors and leakage current due to the NMOS field-effect transistors are compared by a first voltage drop across the first load device and by a second voltage drop across the second load device. If transistors with known properties, such as a known characteristic, are used, they can be used for a quantitative differentiation between the leakage current due to the. PMOS field-effect transistors and the leakage current due to the NMOS field-effect transistor. Knowing the temperature of the CMOS circuit is helpful in this case but not absolutely necessary. If a number of field-effect transistors connected as MOS diodes are used as the load device, a temperature effect is relatively small. 
         [0036]    In an embodiment, it is provided that in a leakage current predominantly due to the PMOS field-effect transistors, the first load device can be adjusted to the lowest voltage drop. In a second embodiment variant, it is provided that in a leakage current predominantly due to the NMOS field-effect transistors, the second load device is adjusted to the lowest voltage drop. In a third embodiment variant, the first load device and the second load device are adjusted to a maximum and/or an average voltage drop. These embodiment variants can also be combined with one another, for example, as a function of temperature. 
         [0037]    For the evaluation, preferably reset values are set for a first resistance value of the first load device and for a second resistance value of the second load device. In addition, the temperature can be measured by means of an electrical temperature sensing element. Using a mapping table, a higher resistance value for the first and/or second load device is mapped to a more rapid CMOS circuit and a low resistance value to a slower CMOS circuit preferably as a function of the measured temperature. Alternatively, this is also possible without the temperature evaluation. To measure the process variation, the circuit preferably has a ring oscillator. The speed of the CMOS circuit, or the maximum operating frequency of the CMOS circuit, can be determined by the ring oscillator. As a rule, more rapid CMOS circuits have a higher leakage current. In the case of a high leakage current, it should be reduced as much as possible, so that the voltage drop at the load device should be maximized. In addition, however, the opposite requirement should also be fulfilled that the voltage drop across the CMOS circuit does not fall below a minimum voltage (for example, of 0.8 V). 
         [0038]    In another embodiment, it is provided that the first voltage drop across the first load device and/or the second voltage drop across the second load device are increased preferably in steps until the data retention voltage has achieved a predefined or predefinable minimum voltage range. 
         [0039]    In another embodiment, it is provided that the source voltage at the PMOS field-effect transistors and/or the source voltage at the NMOS field-effect transistors are evaluated in a measuring mode. Advantageously, moreover, the temperature of the CMOS circuit is evaluated. The decision is made from the measurement results by an arithmetic logic unit whether the first voltage drop across the first load device has increased or decreased and/or whether the second voltage drop across the second load device has increased or decreased. Preferably, by a separate adjustment of the first voltage drop and of the second voltage drop, the leakage current sum of both leakage currents is minimized. Preferably, in this case, a characteristic of the load device is known. Preferably, the load device has a number of field-effect transistors with a known characteristic. Measuring the actual temperature is advantageous to be able to estimate the exponential leakage current behavior of the PMOS field-effect transistors and/or the NMOS field-effect transistors of the CMOS circuit. 
         [0040]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
           [0042]      FIG. 1  shows a schematic block diagram of a circuit of an exemplary embodiment; 
           [0043]      FIG. 2  shows a schematic illustration of a first load device of an exemplary embodiment; 
           [0044]      FIG. 3  shows a schematic illustration of a second load device of an exemplary embodiment; 
           [0045]      FIG. 4  shows a schematic illustration of an evaluation circuit of an exemplary embodiment; and 
           [0046]      FIG. 5  shows a basic schematic circuit diagram to describe the mode of action. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    A first exemplary embodiment of a circuit is shown schematically in  FIG. 1  by a block diagram. A CMOS circuit  20  with a plurality of NMOS field-effect transistors and a plurality of PMOS field-effect transistors is depicted schematically as a block. The source terminals S P  of the PMOS field-effect transistors are connected to one another. The source terminals S N  of the NMOS field-effect transistors are connected to one another. 
         [0048]    A first load device  40  is connected to the source terminals S N  of the NMOS field-effect transistors. First load device  40  is in turn connected to a first supply voltage VSS, for example, ground. A second load device  30  is connected to the source terminals S P  of the PMOS field-effect transistors. Second load device  30  is in turn connected to a second supply voltage VDD, for example, a positive voltage relative to ground, for example, a battery. First load device  40 , second load device  30 , and digital CMOS circuit  20  are connected in series. 
         [0049]    In an operating mode, an operating current flows through the series connection comprising first load device  40 , second load device  30 , and digital CMOS circuit  20 . The operating current is determined by the CMOS circuit, particularly by the recharging of the gate capacitances of the NMOS field-effect transistors and PMOS field-effect transistors. In the operating mode, CMOS circuit  20  should operate as rapidly as possible, so that first load device  40  and second load device  30  are controlled to a low-resistance state by an evaluation circuit  100  connected to a first control input  41  of first load device  40  and to a second control input  31  of second load device  30 . In the operating mode, therefore, a first voltage drop U 40  across first load device  40  and a second voltage drop U 30  across second load device  30  are small. In the operating mode, in addition, a data exchange between CMOS circuit  20  and evaluation circuit  100  is possible, which is indicated in  FIG. 1  by a double arrow. 
         [0050]    In a sleep mode, a leakage current flows through the series connection comprising first load device  40 , second load device  30 , and digital CMOS circuit  20 .  FIG. 5  shows highly simplified a CMOS circuit  20  with two PMOS field-effect transistors MP 21  and MP 22  and two NMOS field-effect transistors MN 21  and MN 22 . 
         [0051]    The leakage current is caused partly by the blocking PMOS field-effect transistors MP 21  and MP 22  and partly by the blocking NMOS field-effect transistors MN 21  and MN 22 . The value of the leakage current and the portions due to the NMOS and PMOS field-effect transistors MN 21  and MN 22 , MP 21  and MP 22  in this case depend on the circuit, the logic states, and a manufacturing process for the NMOS and PMOS field-effect transistors MN 21  and MN 22 , MP 21  and MP 22 . Because of first load device  40 , the source potential at the source terminals S N  of the NMOS field-effect transistors MN 21  and MN 22  is increased compared with the body potential at the body terminals B N . The body effect in this regard causes a reduction of the leakage current by means of the blocking NMOS field-effect transistors MN 21  and MN 22 . This also applies to PMOS field-effect transistors MP 21  and MP 22 . Because of second load device  30 , the source potential at the source terminals S P  of PMOS field-effect transistors MP 21  and MP 22  is increased compared with the body potential at the body terminals B P . The body effect causes a reduction of the leakage current by means of the blocking PMOS field-effect transistors MP 21  and MP 22 . 
         [0052]    In the exemplary embodiment of  FIG. 1 , to reduce the leakage current, a voltage drop U 40  across the first load device  40  can be adjusted by evaluation circuit  100 . Accordingly, to reduce the leakage current, a voltage drop U 30  across the second load device  30  can be adjusted by evaluation circuit  100 . Evaluation circuit  100  and first load device  40  in this case can form a first control loop. Evaluation circuit  100  and second load device  30  in this case can form a second control loop. To this end, evaluation circuit  100  is connected to digital control inputs  41  and  31  of first load device  40  and second load device  30 . Alternatively, analog control inputs  41  and  31  can also be provided, when as in the exemplary embodiment of  FIG. 5  continuously adjustable load elements  49  or  39  are provided. In this case as well, a body-source voltage because of the body effect causes a reduction of the leakage current I LP  or I LN . 
         [0053]    CMOS circuit  20  of the exemplary embodiment of  FIG. 5  shows as an example of a memory element a latch with field-effect transistors MP 21 , MP 22 , MN 21 , and MN 22 . An H level would be present, for example, at the inputs of field-effect transistors MP 21  and MN 21 . Therefore, an L level would be present at the inputs of field-effect transistors MP 22  and MN 22 . In this example, transistors MN 21  and MP 22  are conductive, whereas transistors MN 22  and MP 21  block. The leakage current in this regard is the sum I LP +I LN  of the leakage current I LP  through the blocking PMOS field-effect transistor MP 21  and of the leakage current I LN  through the blocking NMOS field-effect transistor MN 22 . 
         [0054]    Digital circuit  20  and first load device  40  and second load device  30  are connected in series. In this case, the leakage current I LP +I LN  flows across first load device  40  and produces a first voltage drop U 40  at first load device  40 . The leakage current I LP +I LN  flows further through digital circuit  20  and finally through second load device  30  and there also produces correspondingly a second voltage drop U 30 . First voltage drop U 40  and second voltage drop U 30  may be different. First load device  40  and second load device  30  and memory elements MN 21 , MN 22 , MP 21 , and MP 22  in this case must be formed in such a way that the available supply voltages VDD, VSS less the voltage drop U 40  across first load device  40  and the voltage drop U 30  across second load device  30  produce a sufficient holding voltage (VDD-U 30 -U 40 -VSS) across digital circuit  20 , whereby the holding voltage (VDD-U 30 -U 40 -VSS) is sufficiently high so that memory elements MN 21 , MN 22 , MP 21 , and MP 22  retain a defined state, therefore a logic one or a logic zero. 
         [0055]    An exemplary embodiment for a first load device  40  is shown in  FIG. 2 .  FIG. 3  shows an exemplary embodiment for a second load device  30 . First load device  40  has a digital control input  41 , which is connected via a 2-bit-wide connection to the evaluation circuit. Evaluation circuit  100  via control input  41  can control a multiplexer  42 , which connects the gate terminals of NMOS switching transistors MN 41 , MN 42 , MN 43 , and MN 44  optionally to the positive supply voltage VDD for turning on. NMOS switching transistors MN 41 , MN 42 , MN 43 , and MN 44  are all connected to the source terminals S N  of the NMOS transistors of CMOS circuit  20 . Load transistors MN 45 , MN 46 , and MN 47  are NMOS field-effect transistors with different geometries (gate width, gate length), so that with the same drain current they cause different drain-source voltages and thereby differences in the first voltage drop U 40 . By means of transistors MN 41  to MN 47  and multiplexer  42 , in the exemplary embodiment of  FIG. 2 , switching between a lowest resistance value, when transistor MN 41  conducts, and three other resistance values of the transistors MN 45 , MN 46 , and MN 47  can occur in steps as a function of the control of multiplexer  42 . 
         [0056]    This also applies to second load device  30  according to the exemplary embodiment of  FIG. 3 . Here, as well, a multiplexer  32  can be controlled by means of a digital signal at control input  31 , which connects switching transistor MP 31 , MP 32 , MP 33 , and MP 34  optionally to the first supply voltage potential VSS. Load transistors MP 35 , MP 36 , and MP 37  are PMOS field-effect transistors with different geometries (gate width, gate length), so that they cause different drain-source voltages with the same drain current. 
         [0057]    An exemplary embodiment of an evaluation circuit  100  is shown schematically in  FIG. 4 . Evaluation circuit  100  has an arithmetic logic unit  150 , which is formed, for example, as a core of a microcontroller. Furthermore, evaluation circuit  100  has an analog-to-digital converter  120 , whose input signal can be switched by means of analog multiplexer  110  between a plurality of analog sources, such as analog inputs  101 ,  102 ,  103 ,  104 , and sensors  160 . For example, sensor  160  is a temperature sensor, such as a PTAT source [PTAT=proportional to absolute temperature], which together with CMOS circuit  20  is integrated monolithically on a semiconductor chip. Evaluation circuit  100  has memory elements  130 ,  140 . For example, a first register  140  is connected to control input  41  of first load device  40  via digital control output  105  of evaluation circuit  100 . For example, a second register  130  is connected to control input  31  of second load device  30  via digital control output  106  of evaluation circuit  100 . Evaluation circuit  100  in the exemplary embodiment of  FIG. 4  is formed to evaluate the first supply voltage VDD, the second supply voltage VSS, the source voltage U SP  applied at the source terminals S P  of the PMOS transistors, and the source voltage U SN  applied at the source terminals S N  of the NMOS transistors. 
         [0058]    The invention is not limited to the shown embodiment variants in  FIGS. 1 through 5 . For example, it is possible to provide more or fewer transistors as the adjustable load in the load device in order to be able to adjust, for example, the body-source voltage in finer or coarser increments. The functionality of the circuit according to  FIG. 1  can be used especially advantageously for a radio network, in particular according to the industry standard ZigBee. 
         [0059]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.