Abstract:
Apparatus, systems, and methods are disclosed that operate to trigger a reference voltage generator from a supply voltage detector, compare an output voltage level from the reference voltage generator with the a supply voltage, and to generate an enable signal when the supply voltage is greater than the output voltage level. Additional apparatus, systems, and methods are disclosed.

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to electrical power supplies, particularly to a power-on sequence of a power supply. 
       BACKGROUND ART  
       [0002]    Many devices in widespread use today incorporate low-power circuits. In contrast, certain portions of the circuitry within these low-power devices have a requirement for high-voltage functionality. For example, non-volatile memories require voltage levels for reading and programming operations that far exceed a voltage level available from the power supply. Additional circuitry, such as a charge pump, is able to boost electrical charge to a voltage level exceeding that provided by the power supply. In order to perform the voltage boosting function, the charge pump must be supplied with a correct voltage level to operate properly. 
         [0003]    Most circuits require a minimum voltage supply level before proper operation may be realized. Without at least a proper minimum power supply voltage level being available, circuitry may perform incorrectly or produce unexpected results. Power-on control circuits have typically used a voltage supply level detector and have compared that level with an internal reference. The internal reference typically has a dependence on internal device thresholds, an ability of accurately tracking electrical characteristics in the device, and on temperature and processing variation. 
         [0004]      FIG. 1  is a prior art system block diagram of a device incorporating threshold detection power-on sequencing  100 . An output of a VCC detector  110  is connected through a VCC status line  115  to the respective inputs of a bandgap voltage reference  140 , a read charge pump,  150 , and a circuit block  160 . Each one of the bandgap voltage reference  140 , the read charge pump,  150 , and the circuit block  160 , for example, are connected to a VCC power supply terminal to receive power-on voltage according to the comparison power-on sequencing apparatus  100 . 
         [0005]    An output of the band gap voltage reference  140  is connected through a voltage reference status line  145  to a control logic block  170 . An output of the read charge pump  150  is connected through a charge pump status line  155  to the control logic block  170 . An output of the circuit block  160  is connected through a circuit block status line  165  to the control logic  170 . An output of the control logic block  170  is a control logic status line  175 . 
         [0006]    At power-on, a ramping-up of the supply voltage level from a VCC power supply exceeds the magnitude of a voltage reference V 1  being compared to within the VCC detector  110 . The ramping-up supply voltage level triggers production of an enable signal (not shown) on the VCC status line  115  at an output of the VCC detector  110 . The enable signal on the VCC status line  115  is provided to the bandgap voltage reference  140 , the read charge pump  150 , and the circuit block  160 . After receipt of the enable signal, the bandgap voltage reference  140 , the read charge pump  150 , and the circuit block  160  commence operation with a level of VCC being supplied on the VCC terminal that exceeds the voltage reference V 1 . By appropriate selection of the magnitude of the voltage reference V 1 , a sufficient level is reached by the ramping-up VCC supply voltage being reached by the ramping-up VCC supply voltage being supplied to the associated circuits so that proper operation is ensured. The bandgap voltage reference  140 , the read charge pump  150 , and the circuit block  160  are able to successfully carry out their respective processes given enough voltage from the VCC power supply. Each circuit produces an affirmative status signal (not shown) on the bandgap status line  145 , the charge pump status line  155 , and the circuit block status line  165  respectively. 
         [0007]      FIG. 2  is a circuit diagram of a prior art supply voltage detector  200  corresponding to the VCC detector  110  of  FIG. 1 . An output of a PMOS pull-up transistor  210  is connected through a voltage detection trigger line  215  to a voltage level detector  230 . An input of the PMOS pull-up transistor  210  is connected to VCC. A gate input of the PMOS pull-up transistor  210  is connected to ground. An input of the bias resistor  220  is connected to the output of the PMOS pull-up transistor  210  and is connected through the voltage detection trigger line  215  to the voltage level detector  230 . An output of the bias resistor  220  is connected to ground. An output of the voltage level detector  230  is connected to a voltage level detection status line  235 . 
         [0008]    The ramping-up VCC supply voltage level is provided to an input of the PMOS pull-up transistor  210 . A full and unqualified level of conduction is possible through the PMOS pull-up transistor  210  with the gate input connected to ground. The ramping-up VCC supply voltage level produces a resultant increasing channel current through the PMOS pull-up transistor  210  which is provided to an input of the bias resistor  220 . The increasing current through the bias resistor produces an increasing VCC trigger voltage VCC T  (not shown) on the voltage detection trigger line  215 . The increasing VCC trigger voltage VCC T  is compared with the magnitude of the voltage reference V 1  within the voltage level detector  230 . As the ramping-up VCC supply voltage level exceeds the magnitude of the voltage reference V 1 , a detection signal (not shown) is asserted on a voltage level detection status line  235  which corresponds to the VCC status line  115  ( FIG. 1 ). When it is determined by comparison within the supply voltage detector  200  that the ramping-up VCC supply voltage level exceeds the magnitude of the voltage reference V 1 , an enable signal is produced on the voltage level detection status line  235  as an output signal from the voltage level detector  230 . Correspondingly, the enable signal is present on the VCC status line  115  of  FIG. 1 . 
         [0009]    With reference to  FIG. 3 , a voltage vs. temperature diagram of a prior art operational region  305  corresponding to  FIGS. 1 and 2 . An abscissa (T) of the diagram is a potential temperature range of the device. The device&#39;s operational temperature ranges from −40° Celsius (C.) to 125° C. along the abscissa. A left-hand ordinate of the diagram corresponds to the VCC power supply voltage applied to the device. An operational portion of the VCC power supply voltage for the device spans a range from 2.7 volts (V) to 3.6 V. A right-hand ordinate of the diagram is a range of the VCC trigger voltage VCC T . An operational range of the VCC trigger voltage VCC T  is from 2 V to 2.5 V. The area defined by the device&#39;s operational temperature range and operational range of the VCC trigger voltage VCC T  is the device&#39;s operational region  305 . 
         [0010]    The VCC trigger voltage VCC T  is highly dependent upon a device threshold voltage of the PMOS pull-up transistor  210  and the precision and linear tracking of electrical characteristics of the bias resistor  220 . Variations in fabrication processes and temperature fluctuations affect these device characteristics. These result in variations in device characteristics produce a VCC trigger voltage variation zone  310 . 
         [0011]    In order to ensure that proper operation occurs within the circuitry being supplied by the VCC power supply, a designer of a system incorporating power-on sequencing  100  crafts the supply voltage detector  200  such that a maximum value of the VCC trigger voltage variation zone  310  is less than the minimum value of VCC in the operational region  305 . Unfortunately, with a possible wide span of fluctuation in the VCC trigger voltage variation zone  310 , a minimum value for the VCC trigger voltage VCC T  may be too low to supply sufficient voltage and power to properly operate the circuits being supplied by the ramping-up VCC supply. 
         [0012]    In the case of a memory cell, the minimum VCC trigger voltage VCC T  may be about 2 volts (i.e., the lower boundary of the VCC trigger voltage variation zone  310 ). This magnitude of voltage is insufficient to source the read charge pump  130  and the bandgap voltage reference  140  with sufficient power to produce proper operation of these circuits even though affirmative status signals may be produced (but incorrectly) on the charge pump status line  155  and the bandgap status line  145  respectively. As a result, these incorrect status signals are provided to the control logic block  170  and are likely to produce an unpredictable condition in the system due to an incorrect production of the status signaling (not shown) on the control logic status line  175  at the conclusion of the power-on sequence. 
         [0013]    It would be desirable to have a capability of producing a stable voltage reference during the ramping-on power sequence that could be used as a basis for determining a sufficient level of the ramping-on VCC voltage. Such a capability would ensure that sufficient power is available to sustain proper operation of the circuitry being supplied and thus eliminate any incorrect status signaling from these devices which would produce erroneous conditions for the system. 
       SUMMARY  
       [0014]    In the present invention, the ramping-up of a supply voltage triggers the generation of a reference voltage, the reference is compared with a continued ramping level of the power supply, and operation of internal circuitry is enabled after the power supply voltage exceeds the reference voltage. The present invention incorporates a supply voltage detector to trigger a reference voltage generator. The reference voltage generator is a temperature and process independent voltage supply capable of operating at low power supply levels. In addition, the reference voltage generator is designed incorporating electrical components with values that accurately track expected electrical characteristics during operation. 
         [0015]    An output voltage level from the reference voltage generator is compared with the ramping-up supply voltage. When the ramping-up supply voltage has attained a level greater than he reference voltage generator output voltage level an enable signal is produced. The enable signal is propagated to various system elements and circuitry. The enable signal signifies to the system circuitry that a supply voltage level great enough to support nominal operation is present. Processes undertaken by system circuitry after receipt of the enable signal are assured receipt of sufficient supply voltage to attain a correct completion of their processes. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS  
         [0016]      FIG. 1  is a block diagram of a prior art system incorporating power-on sequencing. 
           [0017]      FIG. 2  is a circuit diagram of a prior art supply voltage detector corresponding to  FIG. 1 . 
           [0018]      FIG. 3  is a voltage vs. temperature diagram of an operational region corresponding to  FIG. 1 . 
           [0019]      FIG. 4  is a block diagram of a system incorporating a reference comparison power-on sequence controller of the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0020]    With reference to  FIG. 4 , an exemplary reference comparison power-on sequencing apparatus  400  is seen. An output of a VCC detector  410  is connected through a VCC status line  415  to a reference voltage generator  420 . An output of the reference voltage generator  420  is connected through a voltage generator status line  425  to a first input of a voltage comparator  430 . A VCC power supply terminal connects to a second input of the voltage comparator  430 . An output of the voltage comparator  430  is connected through a voltage comparator status line  435  to the respective inputs of a bandgap voltage reference  440 , a read charge pump,  450 , and a circuit block  460 . Each one of the bandgap voltage reference  440 , the read charge pump,  450 , and the circuit block  460 , for example, are connected to a VCC power supply terminal to receive power-on voltage according to the reference comparison power-on sequencing apparatus  400 . 
         [0021]    A voltage reference has been described as being a bandgap voltage reference source. One skilled in the art would readily conceive of many alternate sources of reference voltage. For instance, a voltage reference may be a buried zener diode, a device incorporating pnp base-emitter temperature coefficient cancellation of differential-diode temperature coefficient, or a collection of shunt or series reference sources to capture a similar cancellation of complementary temperature coefficients, and still readily incorporate the essential characteristics of a stable voltage across temperature and process variation. 
         [0022]    An output of the band gap voltage reference  440  is connected through a voltage reference status line  445  to a control logic block  470 . An output of the read charge pump  450  is connected through a charge pump status line  455  to the control logic block  470 . An output of the circuit block  460  is connected through a circuit block status line  465  to the control logic  470 . An output of the control logic block  470  is a control logic status line  475 . 
         [0023]    At power-on, a ramping-up of the voltage level from a VCC supply voltage exceeds a voltage reference V 1  magnitude being compared to within the VCC detector  410 . The ramping-up supply voltage level triggers production of an enable signal on the VCC status line  415  at an output of the VCC detector  410 . The enable signal on the VCC status line  415  triggers the reference voltage generator  420 . A reference voltage (not shown) is produced within the reference voltage generator  420  which is highly stable versus temperature variation and is capable of operation at low levels of VCC power supply voltage. The reference voltage generator  420  is stable versus internal device electrical characteristics such as device thresholds. The reference voltage may be, for example, a bandgap voltage reference source which inherently takes advantage of complementary thermal coefficients of materials generating the current and voltage of the device so that variations in temperature are compensated for and a stable reference voltage is produced. 
         [0024]    The reference voltage is provided through the voltage generator status line  425  to the voltage comparator  430  where the reference voltage level is compared with the ramping-up VCC supply voltage level. The voltage comparator  430  may be, for example, a differential analog voltage comparator capable of receiving two analog voltages and producing an output voltage level corresponding to a difference between the levels of the two input voltages. The voltage comparator  430  is capable of operating at low levels of VCC power supply voltage. 
         [0025]    While voltage comparison capabilities have been portrayed as an analog voltage comparator, one skilled in the art recognizes that a current sense amplifier incorporated with precision resistors may, due to an ability to accurately amplify small voltages in the presence of large common-mode voltage, for instance, be used for similar functionality. One skilled in the art would readily understand the use of an analog to digital converter with a microcontroller for comparing converted magnitudes of voltages as being the source of an equivalent voltage comparison capability. 
         [0026]    After the ramping-up VCC supply voltage level has exceeded the reference voltage, an enable signal is produced by the voltage comparator  430  on the voltage comparator status line  435 . The enable signal on the voltage comparator status line  415  is provided to the bandgap voltage reference  440 , the read charge pump  450 , and the circuit block  460 . After receipt of the enable signal, the bandgap voltage reference  440 , the read charge pump  450 , and the circuit block  460  commence operation with a level of VCC being supplied on the VCC terminal that exceeds the reference voltage generator output level. 
         [0027]    By appropriate selection of the magnitude of the reference voltage produced by the reference voltage generator  420 , a sufficient level is reached by the ramping-up VCC supply voltage such that proper operation of a plurality circuits being supplied is ensured. The magnitude of the reference voltage is selected to be equal to or greater than the greatest magnitude of VCC power supply voltage necessary to produce proper operation of any of the circuits being supplied. With a sufficient VCC power supply voltage level being supplied, the bandgap voltage reference  440 , the read charge pump  450 , and the circuit block  460  successfully carry out their respective processes. In turn, each circuit produces respectively, an affirmative status signal on the bandgap status line  445 , the charge pump status line  455 , and the circuit block status line  465 . The affirmative status signals are only produced after a sufficient VCC power supply voltage level has been assured in a manner independent of temperature and process variation. 
         [0028]    Each of the respective affirmative status signals is provided to the control logic block  470 , which in turn produces an affirmative system status signal on the control logic status line  475 . The affirmative system status signal indicates that all internal circuit blocks, supplied with a level of VCC derived from the reference comparison power-on sequence power supply, are working properly. 
         [0029]    By only commencing operation in circuit elements drive by the ramping-up VCC supply voltage after this assured level of voltage is attained, will production of correct results produce status signaling indicating a correct result for the power-on sequence. In this way, a system incorporating the power-on sequencing apparatus of the present invention produces a correct status signals from the internal circuit blocks to the control logic block  470 . The control logic block  470  in turn produces a valid affirmative system status signal on the control logic status line  475 .