Abstract:
A circuit disposes of a power supply terminal dedicated to the power supply V IO  of the input/output terminals in order that these terminals may be used by a customer in a voltage range of their choice. The input/output terminals produced according to the invention include transposition means that allow the voltage of the signal flowing through them to be adapted from a first voltage range to a second voltage range.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an integrated circuit having an input/output terminal configurable within a voltage range. The invention is applicable to all types of integrated circuit.  
         [0003]     2. Description of the Related Art  
         [0004]     Integrated circuits are circuits generally fabricated on silicon and include a circuit core communicating with the outside by means of a plurality of terminals.  
         [0005]     The terminals of an integrated circuit can be of several categories. There are power supply terminals, such as a ground terminal and one or more terminals for a supply voltage VDD, or possibly V DD1 , V DD2 , etc., that deliver the voltages powering the integrated circuit. There are also input/output terminals allowing data to be exchanged between the integrated circuit and its external environment, in one direction and/or in the other. The input/output terminals include a conducting pad that is used to interconnect the integrated circuit with the outside, either by means of a bonding wire connected to a connecting pin of a housing, or directly by soldering onto a printed circuit board receiving the integrated circuit, or else for being connected by another method. The terminals also include protection means generally used to avoid voltage surges (electrostatic protection of the ESD type or other). In the case of an input and/or output terminal, the terminal includes, in addition, adaptive means designed to adapt the internal signals of the circuit to the external signals of the circuit.  
         [0006]     Currently, a known solution is to have circuits operating according to one or more supply voltages, and whose input/output terminals communicate with other circuits that can also operate according to one or more voltage ranges.  
         [0007]      FIG. 1  shows an example of an integrated circuit according to the state of the art. This integrated circuit includes a first circuit core  10  and a second circuit core  20 . Each circuit core  10  and  20  operates with its own separate supply voltage.  
         [0008]     The supply voltages are delivered to the integrated circuit via a first power supply terminal  30 , via a second power supply terminal  31  via a ground terminal  32 . The ground terminal  32  is connected to ground circuit  40 . The first power supply terminal  30  and the ground terminal  32  are used, for example, to supply the first circuit core  10 . The second power supply terminal  31  and the ground terminal  32  are used, for example, to supply the second circuit core  20 .  
         [0009]     In addition to these power supply terminals, the circuit also includes input/output terminals, here divided into two categories. The first category corresponds to first input/output terminals  33  connected to a power supply network  41  coupled to the first power supply terminal  30 . Second input/output terminals  34  are connected to a second power supply network  42  that is coupled to the second power supply terminal  31 . When an input/output terminal is supplied by a power supply voltage, this input/output terminal can receive signals, coming from the outside, that are in a voltage range between zero volts and the supply voltage at which this terminal is supplied. Thus, the first input/output terminals  33  can exchange signals with the outside at a voltage level in the range between zero volts and the supply voltage of the first power supply terminal  30 . The second input/output terminals  34  can exchange signals with the outside whose voltage range extends from zero volts up to the supply voltage of the second power supply terminal  31 . In the design of the integrated circuit, the choices regarding the supply of the first and second input/output terminals  33  and  34  are made depending on the constraints imposed by the circuits to be connected to them.  
         [0010]     However, the evolution of the art can lead to circuits generally operating in a first range of voltages being, for reasons of cost, speed, operation and size, transferred into another technology that uses a different voltage range.  
         [0011]     When a circuit is dedicated for operation, for example, with memories operating in the range from 0 to 3.3 V, it can never control memory circuits operating in a range from 0 to 1.8 V.  
         [0012]     However, the evolution of the art shows that memories currently operating under a voltage regime of 3.3 V could disappear in the future and be completely replaced by memories operating at 1.8 V. What is true for memories is also true for many other circuits, which do not necessarily depend on a same manufacturer. In the case of an evolution of the art, it is necessary to produce a new integrated circuit modified accordingly.  
         [0013]     Now, a change in the power supply voltage that supplies an input/output terminal requires that the power supply circuit be redesigned. Indeed, if an input/output must change its operating range, this is not necessarily the case for all the elements connected to the same power supply circuit. However, redesigning the power supply circuit amounts to designing a new integrated circuit, and the fabrication of a new integrated circuit is a source of relatively high costs.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     The invention solves the aforementioned problem of redesign. In order to avoid having to redesign the whole of the circuit, it is proposed that a power supply terminal be dedicated to the supply of certain of the input/output terminals in order that these terminals may be used by a customer in a voltage range of their choice. The input/output terminals produced according to the invention include voltage transposition means that allow the voltage of the signal flowing through them to be adapted from a first voltage range to a second voltage range.  
         [0015]     More particularly, the subject of the invention is an integrated circuit having a circuit core powered by at least one power supply voltage received via a first power supply terminal, and including at least one input and/or output terminal serving as a link between the circuit core and the exterior of the integrated circuit. A second power supply terminal receives a terminal supply voltage within a given voltage range, the terminal supply voltage determining an operating voltage range of the input and/or output terminal with respect to the exterior of the integrated circuit. The input and/or output terminal includes at least one adaptor circuit supplied, on the one hand, with the terminal supply voltage and, on the other hand, with the power supply voltage. The adaptor circuit performs the transposition, of a signal flowing through the input and/or output terminal, from a first voltage range between zero volts and the power supply voltage to a second voltage range between zero volts and the terminal supply voltage, or vice versa.  
         [0016]     The second power supply terminal, preferentially, only supplies the input and/or output terminals. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0017]     The invention will be better understood and other features and advantages will become apparent upon reading the description that follows, this description making reference to the appended figures in which:  
         [0018]      FIG. 1  shows an integrated circuit according to the state of the art,  
         [0019]      FIG. 2  shows an integrated circuit according to the invention,  
         [0020]     FIGS.  3  to  5  show logic input/output terminals according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     For the sake of consistency, the same reference will be used to denote the same element in all the figures and in the description. Furthermore, in order to avoid needlessly cluttering the drawings, certain elements have been purposely omitted. Some of these elements not shown are mentioned in the description or completely omitted if they are only of a very secondary nature with respect to the invention.  
         [0022]     The integrated circuit shown in  FIG. 2  includes a first circuit core  10  powered according to a first power supply voltage V DD1  and a second circuit core  20  powered according to a second power supply voltage V DD2 . The first circuit core  10  is connected to a first power supply terminal  30  by means of a first power supply circuit  41 . The first circuit core  10  is also connected to a ground circuit  40 , itself connected to the ground terminals  32 . The second circuit core  20  is connected to a second power supply circuit  42 , itself connected to a second power supply terminal  31 . The second circuit core  20  is also connected to the ground circuit  40 . In order to exchange data with the exterior of the integrated circuit, the first and second circuit cores  10  and  20  are connected to a plurality of input/output terminals  33 ,  34  and  36 . These links between the circuit cores  10  and  20  and the input/output terminals  33 ,  34  and  36  are not shown in order to simplify the drawing. The first input/output terminals  33  are connected to the first power supply circuit  41  in order to operate in a first voltage range 0V-V DD1  corresponding to the first power supply voltage V DD1  delivered by the first power supply terminal and the first circuit  10 . The second input/output terminals  34  are connected to the second power supply circuit  42 , in order to operate in a second voltage range 0V-V DD2 , corresponding to the second power supply voltage V DD2  delivered by the second power supply terminal  31 . Third input/output terminals  36  are connected to a third power supply circuit  43  corresponding to a power supply dedicated to the configuration of an operating voltage range of the third input/output terminals  36 . A third power supply terminal  35  is connected to this third power supply circuit  43  in order to allow a customer user of the circuit to fix a third power supply voltage V IO  defining a voltage range 0V-V IO .  
         [0023]     Thus, the first input/output terminals  33  operate according to a first power supply voltage V DD1 , the second input/output terminals  34  operate according to the second power supply voltage V DD2 , and the third input/output terminals  36  operate according to a third voltage referred to as terminal supply voltage V IO  that is fixed by means of the power supply terminal  35 , and independently of the other voltages used within the integrated circuit. Although independent, the terminal supply voltage V IO  must be in a voltage range that is compatible with the rest of the circuit. Preferentially, this terminal supply voltage V IO  is in the range between the minimum power supply voltage, for example V DD1 , and the maximum power supply voltage, for example V DD2 , when the integrated circuit has at least two power supply voltages.  
         [0024]     The input/output terminals  33 ,  34  and  36 , and especially the third input/output terminals  36 , may be terminals of the input type, of the output type, or else of the input/output type, but also of the “digital” or of the “analogue” type.  
         [0025]      FIG. 3  shows a digital input/output terminal  36  configured according to the invention. This input/output terminal  36  includes a metal pad  100  connected to an input of an input adaptor circuit  101 . An output of the input adaptor circuit  101  is connected to an input of an input signal conditioning circuit  102 . An output of the input signal conditioning circuit  102  delivers the input signal I to one of the circuit cores  10  or  20 . The pad  100  is also connected to an output of an output signal conditioning circuit  103 , an input of the signal conditioning circuit  103  is connected to an output of an output adaptor circuit  104 . An input of the output adaptor circuit  104  receives an output signal  0  corresponding to a signal delivered by one of the circuit cores  10  or  20 . In addition, the pad  100  is also connected to protection means  105 . The input adaptor circuit  101  and the output adaptor circuit  104  can be the same kind of circuit. Indeed, these two circuits can be formed either by using a threshold circuit or by using amplifiers operating according to two power supply voltages. The ratio of the thresholds or the amplification coefficient, depending on the type of circuit used, is defined by the ratio of its two power supply voltages V IO  and V DDi , V DDi  corresponding to the power supply voltage V DD1  or V DD2  of the circuit core  10  or  20 , to which the terminal  36  is connected. Such adaptor circuits are known, notably for the transfer of data or other signals between two circuit cores operating at different voltages.  
         [0026]     The input signal conditioning circuit  102  is, for example, an inverter or any other type of logic circuit in the case of a logic input. This input signal conditioning circuit is powered by the power supply voltage V DDi  of the circuit core  10  or  20  to which it is connected.  
         [0027]     The output signal conditioning circuit  103  is powered by the third power supply voltage V IO . This output signal conditioning circuit  103  is, for example, a NAND gate (performing the operation AND-NOT) with output validation. In the case of an input/output gate, it is advantageous to include an output validation circuit, in this case a function that is also provided by the output signal conditioning circuit  103 . The purpose of the output validation circuit is to avoid configuring an output signal onto a bus to which the pad  100  might be connected while another bus element is imposing another state.  
         [0028]     A control signal OE is delivered by the circuit core to which the terminal is connected. Depending on the type of output signal conditioning circuit, it may be necessary to add an adaptor circuit in the link of the control signal OE. The protection means  105  here are represented by two diodes limiting negative and positive voltage surges. It will be noted that the voltage denoted V DDsup  corresponds to the higher of the power supply voltages V DD1  and V DD2  delivered by the first and second power supply terminals  30  and  31 .  
         [0029]     The choice of using an amplifier or a threshold circuit as adaptor circuit  101  or  102  may depend on the type of signal that is transmitted through the terminal. If the transmitted signal is of the analogue type, it follows that the adaptor circuit is preferentially an amplifier. In the case where the signals are of the digital type, namely level 0 and level 1, threshold circuits that are simpler than amplifiers may suffice.  
         [0030]     In addition, the digital input/output example shown here includes NAND gates. These NAND gates may be replaced by any other type of known gate, including known types of gates having an output validation for the output signal conditioning circuit  103 .  
         [0031]     In the case of an analogue input/output terminal, the function of the input signal conditioning circuit  102  and the output signal conditioning circuit  103  can also be provided by the adaptor circuits  101  and  104 . Indeed, in the case of analogue circuits, the signal conditioning circuits are generally amplifiers already present for the voltage adaptation carried out in the input adaptor circuit  101  and the output adaptor circuit  104 .  
         [0032]     The terminals  36  can be relatively simple terminals. Indeed, these terminals may be input-only terminals such as is shown in  FIG. 4 . The input terminal differs from the input/output terminal by the elimination of the output path, namely of the output adaptor circuit  104  and of the output signal conditioning circuit  103 .  
         [0033]     It can also be desirable to have only an output terminal, as shown in  FIG. 5 . In that case, the input/output terminal in  FIG. 3  is modified by the elimination of the path corresponding to the input path. The input adaptor circuit  101  and the input signal conditioning circuit  102  are therefore eliminated. It should be noted that, in the case of an output-only terminal, the output validation is not necessarily required. This remains in the circuit diagram, but could just as easily be eliminated in the case where this output is not designed to be set in a high impedance state in order to connect onto a bus.  
         [0034]     In the example described, the terminal supply voltage V IO  is only used for powering the input/output terminals. However, it is possible that this power supply voltage could also power a circuit that is internal to the integrated circuit if, by way of its structure or its function, this internal circuit must operate with the same voltage as the external voltage of the terminals.  
         [0035]     From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.