Abstract:
The invention relates to an input circuit for an electronic circuit, for receiving and assessing an input signal and for driving the input signal to a downstream circuit. The input circuit includes a first reception circuit which is configured to receive and drive the input signal and has a first current consumption characteristic, the current consumption of the first reception circuit depending on the input signal to be driven, a second reception circuit which is configured to receive and drive the input signal and has a second current consumption characteristic, the current consumption of the second reception circuit depending on the input signal to be driven, wherein the first reception circuit and the second reception circuit may be activated separately, and a control circuit configured to activate either the first reception circuit or the second reception circuit and to deactivate the respective other reception circuit on the basis of the driven input signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims foreign priority benefits under 35 U.S.C. §119 to co-pending German patent application number DE 10 2004 015 318.3-55, filed 30 Mar. 2004. This related patent application is herein incorporated by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to an input circuit for an electronic circuit, in particular to an input circuit for an integrated circuit such as, for example, an integrated memory circuit. 
   2. Description of the Related Art 
   Digital integrated circuits such as memory modules, for example, communicate with other integrated circuits using signals on lines, wherein the electrical potential of the signals contains the information. The signals are, for example, data, address, clock and/or other signals. To receive and assess the signals which have been externally applied to the integrated circuit, input circuits are provided in the integrated circuits. In general, the potential of the applied signal is compared with a second voltage (which, as a reference voltage, may be constant or may be in antiphase with the input signal) to assign a state level to the result of the comparison. Input circuits contribute, to a great extent, to the current consumption of an integrated circuit, and thus, it is desirable, particularly in the case of applications which are critical in terms of current consumption, to reduce the current consumption of the input circuits of an integrated circuit. In addition, in conventional input circuits, it is not possible to separately set the timing response for detecting the rising and falling edges of the input signal. 
   Therefore, there is a need to provide an input circuit which can be used to reduce the current consumption and additionally, to set the timing response in a more specific manner. 
   SUMMARY OF THE INVENTION 
   In accordance with a first aspect of the present invention, an input circuit for an electronic circuit is provided for receiving and assessing an input signal and for driving the input signal to a downstream circuit. The input circuit has a first reception circuit configured to receive and drive the input signal and has a first current consumption characteristic, the current consumption of the first reception circuit depending on the input signal to be driven. The input circuit furthermore has a second reception circuit configured to receive and drive the input signal and has a second current consumption characteristic, the current consumption of the second reception circuit depending on the input signal to be driven. The first and second reception circuits may be respectively activated, separately from one another. A control circuit activates either the first reception circuit or the second reception circuit on the basis of the current consumption of the first and second reception circuits in the case of the input signal to be driven. 
   As a result of the reception circuits having different current consumption characteristics, the reception circuit having the lower current consumption may be selected on the basis of the input signal, and the respective other reception circuit is deactivated. Since driving the applied input signal gives rise to a different current consumption of the reception circuit when driving a logic “1” and a logic “0”, one reception circuit may be selected for driving a low signal level, and another reception circuit may be selected for driving a high signal level, in order to optimize the current consumption. 
   In accordance with one preferred embodiment, the control circuit may have a first switch for switching the first reception circuit and a second switch for switching the second reception circuit. 
   The first and/or second reception circuit may respectively have a differential amplifier stage and a current mirror, the differential amplifier stage having a reference voltage connection and an input signal connection to assess the input signal with respect to an applied reference voltage. The differential amplifier stage of the first reception circuit may be formed with n-channel field effect transistors, and the current mirror circuit of the first reception circuit may be formed with p-channel field effect transistors. The differential amplifier stage of the second reception circuit may be formed with p-channel field effect transistors, and the current mirror circuit of the second reception circuit may be formed with n-channel field effect transistors. 
   In one embodiment, the differential amplifier stage of the first reception circuit is connected to a high supply potential, and the current mirror circuit of the first reception circuit is connected to a low supply potential. The differential amplifier stage of the second reception circuit may be connected to the low supply potential, and the current mirror circuit of the second reception circuit may be connected to the high supply potential. 
   In accordance with another embodiment, the first switch may be in the form of an n-channel field effect transistor which is arranged between the low supply potential and the differential amplifier stage of the first reception circuit. In a corresponding manner, the second switch may be in the form of a p-channel field effect transistor which is arranged between the high supply potential and the differential amplifier stage of the second reception circuit. 
   In particular, the non-inverted driven input signal which is taken from the output of the input circuit is utilized to control the n-channel field effect transistor designed as the first switch and the p-channel field effect transistor designed as the second switch. 
   The control circuit may have a delay element for activating either the first reception circuit or the second reception circuit, after a predetermined delay time, on the basis of the driven input signal. 
   In accordance with one embodiment of the invention, the first and/or the second reception circuit may have a driver circuit which can be switched to be inactive or active on the basis of the driven input signal. 
   The respective driver circuit may be switched to high impedance in the inactive state. 
   In accordance with another aspect of the present invention, a method is provided for receiving and assessing an input signal and for driving the input signal to a downstream circuit. In one embodiment, the input signal is received both by a first reception circuit having a first current consumption characteristic, the current consumption of the first reception circuit depending on the input signal to be driven, and by a second reception circuit having a second current consumption characteristic, the current consumption of the second reception circuit depending on the input signal to be driven. One of the first and the second reception circuit is activated on the basis of the driven input signal while the respective other reception circuit is deactivated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       FIG. 1   a  shows a reception circuit for an input circuit having a differential amplifier which has n-channel field effect transistors; 
       FIG. 1   b  shows another reception circuit for an input circuit which has a differential amplifier having p-channel field effect transistors; 
       FIG. 2  shows a graph of the current consumption of the reception circuit shown in  FIG. 1   a  for input voltages of between 0 and 1.8 V; 
       FIG. 3  shows a block diagram of an input circuit according to one embodiment of the invention; 
       FIG. 4   a  shows a reception circuit in accordance with  FIG. 1   a  having an activatable driver circuit for driving the input signal; 
       FIG. 4   b  shows a reception circuit in accordance with  FIG. 1   b  having an activatable driver circuit for driving the input signal; and 
       FIG. 5  shows a timing diagram illustrating the activation of the respective reception circuit in the input circuit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1   a  and  1   b  show reception circuits (in accordance with the prior art) which are usually used as an input circuit. The reception circuits shown are usually used in integrated circuits for receiving input signals and assessing the input signals. Both reception circuits may be used in an input circuit according to one embodiment of the invention which will be described further below with reference to  FIG. 3 . The design and operation of the input circuits will be described in more detail below with reference to the input circuits shown in  FIGS. 1   a  and  1   b.    
     FIG. 1   a  shows a first reception circuit  1  for receiving and assessing the input signal. The reception circuit  1  has a current mirror circuit  3  which mirrors a current in a reference current path  4  into a mirror current path  5 . The current mirror circuit  3  is coupled to a differential amplifier circuit  6  which has a first n-channel transistor  7  and a second n-channel transistor  8 . The first n-channel transistor  7  is arranged in the reference current path  4 . A control input of the first n-channel field effect transistor  7  is connected to a reference voltage V REF . The second n-channel field effect transistor  8  is arranged in the mirror current path  5 , and the input voltage is applied to the control input of the second n-channel field effect transistor  8 . The source connections of the first and second n-channel field effect transistors  7 ,  8  are connected to a low supply voltage potential VSS via a resistor  9 . 
   The current mirror circuit  3  may be designed in a known manner with a first and a second p-channel field effect transistors  10 ,  11 , the source connections of the first and second p-channel field effect transistors  10 ,  11  being connected to a high supply voltage potential VDD. The gate connections of the p-channel field effect transistors  10 ,  11  of the current mirror circuit  3  are connected to a drain connection of the first p-channel field effect transistor  10  and of the first n-channel transistor  7 . In this manner, the current in the reference current path  4  is mirrored into the mirror current path  5 . 
   On the basis of the input signal that is applied to the gate input of the second n-channel field effect transistor  8 , an intermediate signal (which is assessed in a corresponding manner) may be tapped off at the drain connections of the second n-channel field effect transistor  8  and of the second p-channel field effect transistor  11 . The intermediate signal is applied to an input of a driver circuit  12  which applies the input signal to be driven to an output of the input circuit  1 . 
     FIG. 1   b  shows an alternative design of a reception circuit. In an analogous manner to the reception circuit  1  shown in  FIG. 1   a , the reception circuit  21  comprises a current mirror circuit  23  having a reference current path  24  and a mirror current path  25 . A differential amplifier circuit  26  which has a first p-channel field effect transistor  27  and a second p-channel field effect transistor  28  is provided and may have a complementary design to the differential amplifier circuit of  FIG. 1   a . The source connections of the first and second p-channel field effect transistors  27 ,  28  are connected to the high supply voltage potential VDD via a resistor  29 . 
   The current mirror circuit  23  has a first n-channel field effect transistor  30  and a second n-channel field effect transistor  31 , the source connections of which being connected to the low supply voltage potential VSS. The gate connections of the first and second n-channel field effect transistors  30 ,  31  are connected to the drain connections of the first p-channel field effect transistor  27  and of the first n-channel field effect transistor  30 . The input signal which is applied to the second p-channel field effect transistor  28  is assessed in the differential amplifier circuit  26 , and the input signal which has been assessed is provided as an intermediate signal to the output of the reception circuit which is formed by the drain connections of the second p-channel field effect transistor  28  and of the second n-channel field effect transistor  31 . The intermediate signal is applied to an input of a driver circuit  32  which inverts the intermediate signal and applies the driven input signal to an output of the reception circuit  21 . The reference voltage V REF  is applied to the gate connection of the first p-channel field effect transistor  27 . 
   The reception circuits  1 ,  21  shown in  FIG. 1   a  and  FIG. 1   b  are generally of analogous design to one another and have respective complementary field effect transistors. The current consumption characteristics of the two reception circuits therefore differ from one another. 
     FIG. 2  shows the current consumption characteristic of the input circuit shown in  FIG. 1   a . The upper graph shows a voltage profile (which results from an input voltage that varies between 0 and 1.8 V) of the output voltage for an exemplary reception circuit which is designed in accordance with  FIG. 1   a  and to which a reference voltage of 0.9 V is applied. The lower graph correspondingly shows the current consumption at the supply voltage connections, which current consumption results from the applied input signal and from the output signal that is output. It is evident that different current consumption levels of the reception circuit result for different states of the output signal level. Whereas a current consumption of approximately 92 μA results when an input signal having a low state level is applied, the current consumption rises to approximately 133 μA when a high state level is to be output. In view of the fact that an integrated circuit generally has a large number of reception circuits of this type or of a comparable type, a considerable current consumption that depends on the applied/received signals results. In the further input circuit shown in  FIG. 1   b , the current profile as a function of the input voltage is correspondingly reversed, with the result that a high supply current flows when outputting a low state potential and a low supply current flows when outputting a high state potential. 
     FIG. 3  shows a block diagram of an input circuit  40  according to one embodiment of the invention. The input circuit  40  includes two reception circuits which are complementary to one another and have respectively different current consumption characteristics. By way of example, the reception circuit  1  shown in  FIG. 1   a  and the reception circuit  21  shown in  FIG. 1   b  may be utilized in the input circuit  40  since they have current consumption characteristics which are complementary to one another. The input circuit  40  shown in  FIG. 3  therefore has a first reception circuit  41  having a first current consumption characteristic and a second reception circuit  42  having a second current consumption characteristic. Both of the reception circuits  41 ,  42  receive the same reference voltage V REF , with respect to which the applied input signal is assessed. 
   The input signal is likewise applied to both reception circuits  41 ,  42 . The first and second reception circuits  41 ,  42  are respectively connected to the supply voltage, via a first switch  43  and a second switch  44 , respectively, in such a manner that they may be switched on or off. The first and second switches  43 ,  44  are driven in such a manner that only either the first reception circuit  41  or the second reception circuit  42  is connected to the supply voltage, so that connected reception circuit may respectively operate. The first and second switches  43 ,  44  may comprise field effect transistors which are complementary to one another. In one embodiment, the first switch is in the form of an n-channel field effect transistor, and the second switch  44  is in the form of a p-channel field effect transistor. A driven received signal which has been delayed and is taken from an output of the input circuit  40  is applied to the respective gate connections of the field effect transistors  43 ,  44 . As a result of the complementary configuration of the first and second switches  43 ,  44 , only one of the two switches  43 ,  44  (in the form of field effect transistors) is respectively turned on while the other is turned off. The current supply is thus interrupted by one of the reception circuits  41 ,  42 . 
   An inverted drive signal may also be used to drive the first and second switches  43 ,  44 . It is merely necessary to ensure that only one of the two switches  43 ,  44  is respectively turned on. The switch activates one of the reception circuits  41 ,  42  which requires the smaller supply current based on the input signal to be output. 
   For example, if the first reception circuit corresponds to the input circuit shown in  FIG. 1   a  and the second reception circuit  42  corresponds to the input circuit shown in  FIG. 1   b , the second reception circuit is activated and the first reception circuit is deactivated in the case of a state potential of the input signal that is greater than the reference voltage. If a state potential that is less than the reference voltage is applied to the input IN, the first reception circuit  41  is activated while the second reception circuit  42  is deactivated. The first and second switches  43 ,  44  are switched in a delayed manner. A delay element  45  is provided which receives the driven input signal at the output OUT of the input circuit  40  and provides this signal, in a delayed manner, as a drive signal for the first and second switches  43 ,  44 . The delay circuit  45  may provide the drive signal both in inverted form and in non-inverted form, with the result that it is respectively possible to implement the first and second switches  43 ,  44  using both n-channel field effect transistors and p-channel field effect transistors. Other components may be implemented or utilized as switches. 
   The reception circuits  41 ,  42  are connected to one another by their outputs, which constitutes the output of the input circuit  40 . To prevent current from draining through the respective deactivated reception circuit when driving the received input signal, the reception circuits  41 ,  42  respectively have driver circuits which can be deactivated in such a manner that the respective output of the reception circuit  41 ,  42  is switched to high impedance when being deactivated.  FIG. 4   a  shows, by way of example, such a driver circuit for the input circuit shown in  FIG. 1   a . The complementary driver circuit for the input circuit shown in  FIG. 1   b  may be implemented in an analogous manner as shown in  FIG. 4   b . Both the first and second reception circuits  41 ,  42  therefore may have driver circuits  51 ,  52 , respectively, which are, for example, in the form of a connected inverter. A connected inverter may have two p-channel field effect transistors and two n-channel field effect transistors which are connected in series between the high supply potential and the low supply potential. An inverted drive signal is used to drive one of the p-channel field effect transistors, and a non-inverted drive signal is used to drive one of the n-channel field effect transistors, with the result that the driver circuit is deactivated when the entire reception circuit is deactivated. Thus, the output of the respective reception circuit may be switched to high impedance when being deactivated without it being possible for a current path to the high or low supply potential to occur as a result of circuit parts which are not connected to a fixed potential (e.g., connected to a floating potential). 
     FIG. 5  shows the temporal sequence of activating the different reception circuits of the input circuit. Separating the input circuit into a part which detects the low-high edge of the input signal and a part which detects the high-low edge of the input signal makes it possible to set the timing properties of the input circuit separately from one another. As shown in  FIG. 5 , after the driven input signal has changed state, the reception circuit which interprets and assesses the applied input signal is also changed after a delay time, and the current consumption of the entire input circuit is thus reduced, by selecting the respective reception circuit which has the lower current consumption. 
   While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.