Abstract:
An integrated circuit comprising an adjustable voltage source to allow a plurality of voltage values to be selected; means for measuring a voltage value derived from the adjustable voltage source; and means for configuring the adjustable voltage source to provide a selected voltage value, wherein the selected voltage value is selected based upon a voltage value measured by the means for measuring and a voltage selected by a controller.

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates to an integrated circuit and a method for selecting a voltage in a integrated circuit. 
       BACKGROUND OF THE INVENTION  
       [0002]    To allow faster operation, reduce cost and improve the power consumption of electronic devices, and in particular mobile electronic devices, integrated circuits are continuiglu being designed to operate on lower and lower voltages. 
         [0003]    To minimise cost and avoid the need to redesign all elements within an electronic device integrated circuits are sometimes designed to include a regulator. This is to allow an integrated circuit that is arranged to operate on a first voltage to be coupled to a power supply operating at a higher second voltage. Consequently, this allows electronic devices to be upgraded with new integrated circuits without the need to replace the electronis devices existing power supply. 
         [0004]    However, with the large range of different silicon technologies and associated operating voltages it can still be costly to have to design a range of different regulators, where different regulators are used with different integrated circuits and power supplies. 
         [0005]    One way to avoid this problem has been via the use of programmable voltage supplies, where supply voltages are adjusted to provide a required voltage, one example of this technique is described in U.S. Pat. No. 5,790,469. However, this technique requires the use of an external voltage reference to allow the programmable voltage supply to determine an appropriate voltage, which yet again will typically result in an increase in complexity and cost of a device. 
         [0006]    Further, as the operating voltage of integrated circuits continue to reduce it also becomes increasingly difficult to achieve the required voltage tolerances, for example a three percent tolerance on a one volt signal is a factor of ten less than a three percent tolerance on a ten volt signal. 
         [0007]    For proper operation of an integrated circuit the voltage supply should ideally be monitored for variations of voltage outside the operating voltage range of the integrated circuit. Additionally, to avoid incorrect operation and possibly damage to an electronic module the monitoring circuit typically resets the integrated circuit on occations when voltage excursions occur outside the operating voltage range of the integrated circuit. However, for an electronic device with a new integrated circuit a monitoring circuit associated with the power supply will typically be unaware of the operating voltage range of the newly incorporated integrated circuit. 
         [0008]    Further, as the testing of an integrated circuit will typically require operating the integrated circuit outside its normal operating voltage range any monitorint circuits will need to be disabled prior to testing to avoid the resetting of the integrated circuit. However, for safety related systems to include a mechanism to disable supply monitoring can be hazardous as it would be possible for the supply monitoring to be disable undesirably during normal operation. 
         [0009]    Accordingly, it is desirable to improve this situation. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with an aspect of the present invention there is provided an integrated circuit and method for selecting a voltage in an integrated circuit according to the accompanying claims. 
         [0011]    This provides the advantage of allowing a integrated circuit to be designed for use with a variety of different power supplies without different regulators being required. Further, this allows the voltage for an integrated circuit to be monitored during testing of the integrated circuit without the resetting of the integrated circuit occurring for excursions of voltage outside the integrated circuits operating voltage range while also maintaining a default initial status of correct supply monitoring. This also allows voltage tolerances supplied to an integrated circuit to be improved and consequently could allow an increase in yield of integrated circuits, and fine tuning of operating voltage as best suits the integrated circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    An embodiment of the invention will now be described, by way of example, with reference to the drawings, of which: 
           [0013]      FIG. 1  illustrates an integrated circuit according to a first embodiment of the present invention; 
           [0014]      FIG. 2  illustrates an integrated circuit according to a second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    A first embodiment of the present invention is described with reference to  FIG. 1 , where a control loop  101  on an integrated circuit  100  is arranged to select a voltage for regulating the voltage supply for the integrated circuit  100 . 
         [0016]    As shown in  FIG. 1  the integrated circuit  100  includes the control loop  101 , where the control loop  101  is coupled between an output from a regulator  102  and a control input of a selectable voltage source  103 . The control loop  101  is arranged to select a voltage for the integrated circuit  100  using the selectable voltage source  103 . 
         [0017]    The selectable voltage source  103  comprises a series of resistors  104  couple between a reference voltage, for example ground, and a second reference voltage, for example from a supply power line. Accordingly, the series of resistors act as voltage dividers between the two reference voltages. However, as would be appreciated by a person skilled in the art other techniques for providing a selectable voltage source can be provided. Further, while the power supply will be external to the integrated circuit the second reference voltage may be derived on the integrated circuit from the power supply voltage, for example from the collector of a transistor (not shown). 
         [0018]    Coupled between the series of resistors  104  are electrical taps  105 , where each electrical tap  105  includes a switch to allow selection of a voltage associated with the coupling position of the electrical tap  105  with respect to the series of resistors  104 . As such, a different voltage point along the voltage gradient formed by the series of resistors  104  is selectable by the respective electrical taps. Accordingly, a required voltage is selected using the selectable voltage source  103 . In the embodiment shown in  FIG. 1  the voltage selected is the target output voltage of regulator  102 . 
         [0019]    The voltage selected using the selectable voltage source  103  will depend upon the reference voltages and the configuration of resistors formed in the series of resistors  104  and the number and configuration of electrical taps  105 . A voltage selected by an electric tap switch is provided to an output of the selectable voltage source (i.e. the electric tap switch couples the selectable voltage source output to the appropriate voltage point on the series of resisters  104 ). 
         [0020]    Although,  FIG. 1  shows four resistors  104  in series and three electrical taps  105 , as would be appreciated by a person skilled in the art the selectable voltage source  103  could be configured with any number of resistors and/or electrical taps. Additionally, alternative mechanisms of providing a selectable voltage might also be used, such as the use of voltage not current reference, or the use of a variable element such as resistance of a transistor, or variable voltage gain with a fixed primary reference. 
         [0021]    The regulator  102  is for regulating the voltage supply to the integrated circuit  100 , as is well known to a person skilled in the art. 
         [0022]    Although any suitable form of regulator  102  could be used, for the purposes of the present embodiment the regulator  102  includes a differential amplifier  106  and an NPN transistor  107 . Although the NPN transistor  107  is shown to be part of the integrated circuit  100 , sometimes the NPN transistor will be instantiated externally to the integrated circuit  100 . Further, any suitable transistor could be used, for example a PNP transistor or FET. 
         [0023]    An output from the selectable voltage source  103  is coupled to a non-inverting input of the differential amplifier  106 , an output from the differential amplifier  106  is coupled to the base of the NPN transistor  107  and an inverting input of the differential amplifier  106  is coupled to the emitter of the NPN transistor  107 , where the emitter output of the NPN transistor  107  acts as the regulated voltage source for the integrated circuit  100 . The collector of the NPN transistor  107  is coupled to the supply power line. 
         [0024]    As is well known to a person skilled in the art the regulator  102  is arranged to maintain a constant voltage based on the input voltage applied at the non-inverting input of the differential amplifier  106 . 
         [0025]    The control loop  101  is arranged to measure the regulated voltage at the output of the regulator  102 , which for the purposes of the present embodiment is the output from the emitter of the NPN transistor  107 , and, based upon a required predetermined voltage, is arranged to set an appropriate electric tap  105  switch to select an appropriate voltage for outputting from the selectable voltage source  103  to the non-inverting input of the differential amplifier  106 . 
         [0026]    The control loop  101  includes an analogue to digital converter  108  ADC and a controller  109 . The ADC  108  is arranged to sample the regulated voltage at the output of the regulator  102  and provide the sampled digital representation of the regulated voltage to the controller  109 . Ideally the ADC  108  will have a resolution and accuracy equal to or greater than that of the selectable voltage source  103 . 
         [0027]    Based upon the measured voltage-information received by the controller  109  from the ADC  108  and predetermined voltage information stored in memory (not shown) of the controller  109 , the controller  109  determines whether the regulated voltage at the output of the regulator  102  needs to be modified. If the regulated voltage at the output of the regulator  102  does not correspond with the predetermined voltage information stored in the controller  109 , the controller  109  makes a determination as to the voltage that should be provided to the non-inverting input of the differential amplifier  106  and sets the appropriate electric tap switch of the selectable voltage source  103  to allow the appropriate voltage to be provided from the selectable voltage source  103  to the non-inverting input of the differential amplifier  106 . 
         [0028]    The operation of the controller  109  may be programmable. Examples of the type of actions that the controller  109  may be configured to perform include:
   1) determining that the regulated voltage is too low for optimum operation of the integrated circuit and cause the selected voltage to increase, for example using predetermined information relating to voltage taps, alternatively performing iterative increases in voltage;   2) determining, based on other information received by the integrated circuit, that the voltage should be reduced to reduce power consumption;   3) determining, based on other information, that the integrated circuit is in a test mode and that a voltage monitoring threshold should be reduced;   4) based on known characteristics of the regulator the controller  109  could be arranged to raise voltage supply to provide increased supply voltage margin for correct operation of the integrated circuit;   5) determine, based on information in memory, that the integrated circuit is used in a safety critical application and that a voltage monitor threshold should be adjusted closer to the operational limits of the integrated circuit;   6) determine, based on a previous measurement stored in non-volatile memory, that the regulator voltage should be adjusted.   
 
         [0035]    The controller  109  could be any suitable form of processing device, for example a microcontroller, logic element or a digital signal processor DSP. It will also be appreciated by a person skilled in the art that the entire feedback path, which includes the ADC  108 , the controller  109  and voltage adjustment, can be replaced by dedicated circuitry. The advantage of an ADC  108  and a microprocessor core, which acts as the controller  109 , is that such features typically exist in combination on many existing integrated circuits. 
         [0036]    As the ADC  108  samples the regulated voltage supply on the integrated circuit this allows an increase in accuracy of voltage measurement and consequently allows a more accurate selection of voltage to be provided to the regulator  102  from the selectable voltage source  103 . 
         [0037]    Although, as described above, the voltage information is stored in controller memory, equally the voltage information could be stored in memory external to the controller  109 . Typically the voltage information will be stored in memory in binary form. 
         [0038]    As such, when supply power voltage is provided to the integrated circuit  100  the controller  109  identifies the presence of regulated voltage at the output of the regulator  102  and based upon the predetermined voltage information stored in the controller  109 , the controller  109  will cause the regulated voltage provided by the regulator  102  to self adjust dynamically to the required regulated voltage by the controller  109  selecting an appropriate electric tap switch of the selectable voltage source  103  to allow the desired voltage to be provided to the non-inverting input of the differential amplifier  106 . Consequently, the control loop  101  will allow the regulated voltage provided by the regulator  102  to self adjust as predetermined by the instructions or operation of the controller  109 . 
         [0039]    A second embodiment of the present invention is described with reference to  FIG. 2 , where the same features as shown in  FIG. 1  have the same reference numerals. The second embodiment of the present invention is based on a control loop  101  that is configured to select a voltage for controlling the supply voltage range over which an integrate circuit  200  is arranged to operate. 
         [0040]    As shown in  FIG. 2  the integrated circuit  200  includes the control loop  101 , where the control loop  101  is coupled to a first input of a comparator  201  and a control input of the selectable voltage source  103 . The control loop  101  and first input of the comparator are also coupled to an output from a selectable voltage source  103 . 
         [0041]    A second input of the comparator  201  is coupled to the integrated circuits voltage supply, which will typically be regulated. An output of the comparator  201  is coupled to a reset line for the integrated circuit, which when set high will place the integrated circuit in a reset condition. 
         [0042]    The comparator  201  is arranged to compare the voltage output from the selectable voltage source  103 , which is received at the comparators first input, with the integrated circuits voltage supply, which is received at the comparators second input. Upon the comparator  201  detecting that the integrated circuits voltage supply is below the output voltage from the selectable voltage source  103  the comparator  201  is arranged to set its output high and consequently place the integrated circuit  200  in a reset condition. 
         [0043]    As the control loop  101  is able to select an appropriate output voltage from the selectable voltage source  103  it is possible for the control loop to dynamically define the operating voltage range for the integrated circuit  200 . Further, by allowing the control loop  101  to select different output voltages from the selectable voltage source  103  the control loop  101  can be configured, as described below, to select an appropriate operating range for the integrated circuit  200  during normal operation of the integrated circuit  200  to minimise risk of erroneous operation while also allowing the possibility of extending the operating voltage range of the integrated circuit  200  to allow testing of the integrated circuit  200  with an extended. operating voltage range, while still providing protection to the integrated circuit should large fluctuations in the integrated circuit voltage supply occur. 
         [0044]    As with the previous embodiment the selectable voltage source  103  comprises a series of resistors  104  couple between a first reference voltage, for example ground, and a second reference voltage, for example a supply power line. Accordingly, the series of resistors  104  act as voltage dividers between the two reference voltages. 
         [0045]    Coupled between the series of resistors  104  are electrical taps  105 , where each electrical tap  105  includes a switch to allow selection of a voltage associated with the coupling position of the electrical tap  105  with respect to the series of resistors  104 . As such, a different voltage point along the voltage gradient formed by the series of resistors  104  is selected by the respective electrical taps. Accordingly, a voltage is selected using the selectable voltage source  103  by closing an appropriate electrical tap switch at the voltage point along the voltage gradient formed by the series of resistors  104  corresponding to the voltage required. The voltages selectable using the selectable voltage source  103  will depend upon the difference in voltage between the first reference voltage and the second reference voltage and the configuration of resistors formed in the series of resistors  104  and the number and configuration of electrical taps  105 . 
         [0046]    Although,  FIG. 2  only shows four resistors  104  in series and three electrical taps  105 , as would be appreciated by a person skilled in the art the selectable voltage source  103  could be configured with any number of resistors and/or electrical taps. 
         [0047]    The control loop  101  includes an ADC  108  and a controller  109 . The ADC  108  is arranged to sample the output voltage from the selectable voltage source  103 , which is provided to the first input of the comparator  201 . The ADC  108  is arranged to provide the sampled digital representation of the voltage from the selectable voltage source  103  to the controller  109 , where as described above the controller  109  can control the output voltage of the selectable voltage source  103  as required. 
         [0048]    For the purpose of the present embodiment the controller  109  is programmed to allow one of two voltages to be output from the selectable voltage source. The first allowable output voltage from the selectable voltage source  103  corresponds to the minimum operating voltage of the integrated circuit  200  during normal operation. The second allowable output voltage from the selectable voltage source  103  corresponds to the minimum operating voltage of the integrated circuit during testing of the integrated circuit, where the second allowable output voltage is lower than the first allowable output voltage. 
         [0049]    If the controller  109  is configured to allow the integrated circuit  200  to operate under normal operating conditions the controller  109  sets the appropriate electric tap switch for allowing the first allowable output voltage to be output from the selectable voltage source  103  to the first input of the comparator  201 . As such, if the integrated circuits supply voltage goes below the first allowable voltage the comparator  201  will set is output high and place the integrated circuit  200  in a reset condition until the integrated circuits supply voltage increases above the first allowable voltage. To avoid the integrated circuit oscillating between an operational condition and a reset condition some form of hysterisis could be adopted. 
         [0050]    If testing of the integrated circuit  200  is required the controller  109  can be placed in a test mode that causes the controller  109  to set the appropriate electric tap switch for allowing the second allowable output voltage to be output from the selectable voltage source  103  to the first input of the comparator  201 . Consequently, this allows the operating voltage range of the integrated circuit  200  to be lowered to the second allowable voltage, thereby allowing extended testing of the integrated circuit  200 . This permits testing at below normal operating voltage and ensures highly reliable operation of the integrated circuit over its normal operating voltage range. Through use of the invention, the reset monitor is never fully disabled, which is advantageous to a safety critical system. As such, if the integrated circuits supply voltage goes below the second allowable voltage the comparator  201  will set is output high and place the integrated circuit  200  in a reset condition until the integrated circuits supply voltage increases above the second allowable voltage. To avoid the integrated circuit oscillating between an operational condition and a reset condition some form of hysteresis could be adopted. 
         [0051]    Although the controller  109  has been described as allowing the generation of two output voltages from the selectable voltage source  103 , the controller  109  can be configured to select any number of voltages from the selectable voltage source  103 . For example, in addition to the controller  109  being programmed with two operating modes, the controller  109  could be programmed with a safety critical mode, which allows the controller  109  to be configured to control the selectable voltage source  103  to output a third allowable output voltage that is higher than the first allowable output voltage, thereby narrowing the operating voltage range of the integrated circuit  200  which may be appropriate for safety critical devices, where the comparator would cause the integrated circuit  200  to reset if the integrated circuits voltage supply went below the third allowable output voltage. In operation the third allowable output voltage might be approached iteratively, whereby the current reset voltage is stored in a non-volatile manner that persists over a reset condition. The reset threshold might be increased fractionally, and if no reset occurs the new threshold would again be stored as a known good operating voltage. In this way the actual operating voltage range of the integrated circuit and supply can be established, and the controller could then set a suitable threshold for continuous operation as suits a safety critical system. It would be appreciated by a person skilled in the art that such an embodiment of the invention would use a multitude of voltage taps. 
         [0052]    In addition to the adjustable setting of the lower allowable operating voltage for the integrated circuit  200 , equally the same approach could be used to alternatively or additionally set the higher allowable operating voltage for the integrated circuit  200 . Whereas operating voltages lower than required are always encountered when the power supply to the integrated circuit is switched off, operating voltages higher than allowable are often indicative of a fault condition. Consequently, safety critical systems should monitor for such conditions. 
         [0053]    As such, the control loop for selecting a voltage for an integrated circuit can be used for selecting a voltage for an integrated circuit for a variety of different purposes. 
         [0054]    It will be apparent to those skilled in the art that the disclosed subject matter may be modified in numerous ways and may assume embodiments other than the preferred forms specifically set out as described above, for example the control loop  101  could be configured to provide the functionality described in the first and second embodiments within the same integrated circuit and/or the comparator  201  in the second embodiment could be configured to reset the integrated circuit  200  by setting its output low.