Abstract:
A power supply voltage regulator circuit including a power supply circuit which switches to a first through a fourth state; the first state being the state wherein voltage is supplied to neither a normal circuit nor a backup system circuit based on the combination of logic for the normal circuit power control signal, the second state being the state wherein a primary power supply voltage is supplied to the normal circuit and a secondary power supply voltage is supplied to the backup system circuit, the third state being the state wherein voltage is not supplied to the normal circuit and the secondary power supply voltage is supplied to the backup system circuit, the fourth state being the state wherein the primary power supply voltage is supplied to both the normal circuit and the backup system circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-55092 filed on Mar. 6, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a power supply voltage regulator circuit for supplying power supply voltage to a normal circuit and backup system circuit, and a microcomputer. 
         [0004]    2. Description of Related Art 
         [0005]    Recently, in order to reduce power consumption and improve battery lifetime, some mobile devices e.g. digital video cameras are being made so that no power is supplied to the microcomputers embedded therein when in a state (a standby state) in which CPU operation is not necessary. However, even when in the standby state, power must be provided to the microcomputer&#39;s clock function and to memory such as backup RAM. Therefore, power is separated between CPU side normal circuit power and backup system circuit power so that when in the standby state, the supply of power to the normal circuit is stopped and power is supplied to the backup circuit. 
         [0006]    In Japanese Laid-Open Unexamined Patent Application Publication No. S62-6315, a memory backup apparatus for microcomputers was set forth. For example, the microcomputer memory backup apparatus has a microcomputer that can back up memory at low power consumption, a reset circuit for sending reset signals when voltage is below a certain reference voltage, a backup power circuit for switching the power supply of the microcomputer to microcomputer backup power (such as lithium batteries) when voltage is below a certain reference voltage, and a power detection circuit for detecting whether or not there is power. Furthermore, the microcomputer is configured such that after a reset signal is detected from the reset circuit, the operation mode or low power consumption mode (standby mode) is executed by a signal from the power detection circuit. 
       SUMMARY 
       [0007]    According to one aspect of the present invention, the power supply voltage regulator circuit is a power supply voltage regulator circuit that supplies a primary power supply voltage or a secondary power supply voltage, which is lower than the primary, to a normal circuit and a backup system circuit, both of which have separate power supplies. The power supply voltage regulator circuit also has a power supply circuit that switches to a state between a first, a second, a third, and a fourth state. 
         [0008]    In the first state, based on the combination of logic for a normal circuit power control signal for controlling power to the normal circuit and a backup circuit power control signal for controlling power to the backup system circuit, voltage is supplied to neither the normal circuit nor the backup system circuit. 
         [0009]    In the second state, the primary power supply voltage is supplied to the normal circuit and the secondary power supply voltage is supplied to the backup system circuit. 
         [0010]    In the third state, voltage is not supplied to the normal circuit and the secondary power supply voltage is supplied to the backup system circuit. 
         [0011]    In the fourth state, the primary power supply voltage is supplied to both the normal circuit and the backup system circuit. 
         [0012]    According to another aspect of the present invention, a microcomputer has 
         [0013]    a normal circuit comprising a CPU, 
         [0014]    a backup system circuit having a separate power supply from the normal circuit, and 
         [0015]    a power supply circuit for switching to a first state wherein, based on the combination of logic for a normal circuit power control signal for controlling power to the normal circuit and a backup circuit power control signal for controlling power to the backup system circuit, voltage is supplied to neither the normal circuit nor the backup system circuit; to a second state wherein the primary power supply voltage is supplied to the normal circuit and the secondary power supply voltage, which is lower than the primary power supply voltage, is supplied to the backup system circuit; to a third state wherein voltage is not supplied to the normal circuit and the secondary power supply voltage is supplied to the backup system circuit; and to a fourth state wherein the primary power supply voltage is supplied to both the normal circuit and the backup system circuit. 
         [0016]    Additional advantages and novel features of aspects of the present invention will be set forth in part in the description that follows, and in part will become more apparent to those skilled in the art upon examination of the following or upon learning by practice thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a power supply voltage regulator circuit and microcomputer configuration according to Embodiment 1. 
           [0018]      FIG. 2  shows the configuration of a voltage selection circuit in the power supply voltage regulator circuit according to Embodiment 1. 
           [0019]      FIG. 3  is a table explaining the operation of the voltage selection circuit shown in  FIG. 2 . 
           [0020]      FIG. 4  shows a power supply voltage regulator circuit and microcomputer configuration according to Embodiment 2. 
           [0021]      FIG. 5  shows the configuration of a voltage selection circuit in the power supply voltage regulator circuit according to Embodiment 2. 
           [0022]      FIG. 6  is a table explaining the operation of the voltage selection circuit shown in  FIG. 5 . 
           [0023]      FIG. 7  shows the configuration of an auxiliary power source control signal generation circuit in the RAM address decoder. 
           [0024]      FIG. 8  shows the configuration of an automatic wait generation circuit. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Hereinafter, the attached drawings are used to explain the embodiments in detail. 
         [0026]    Note, in the following explanation, the same symbol is given to similar configurations to omit duplicate explanations. 
       Embodiment 1  
       [0027]      FIG. 1  shows a power supply voltage regulator circuit and microcomputer configuration according to Embodiment 1. As shown in  FIG. 1 , a microcomputer  11  has a normal circuit  12  and a backup circuit  13  with separate power sources. The normal circuit  12  has a CPU  14  and a RAM address decoder  15 . Also, the backup circuit  13  has RAM memory  16  as its backup memory. 
         [0028]    A power supply circuit  17  switches between the primary power supply voltage and the backup power supply voltage, providing power supply voltage to the normal circuit  12  and the backup circuit  13 , accordingly. The power supply circuit  17  comprises a regulator on-board voltage selection circuit (hereinafter “voltage selection circuit”)  18 . The voltage selection circuit  18  selects the power supply voltage to be supplied to the normal circuit  12  and the backup circuit  13  based on a normal circuit power control signal AE and a backup circuit power control signal BE. 
         [0029]    The primary power supply voltage here is the voltage at which data can be read from or written to RAM memory  16 , e.g. 3.3 V. On the other hand, the backup power supply voltage cannot be used for reading or writing data to/from RAM memory  16 , but is instead a voltage at which data can be retained in RAM memory  16 , e.g. 1.3 V. 
         [0030]    Normal circuit power control signal AE is a signal indicating the power source status during normal operation, and backup circuit power control signal BE is a signal indicating operation by a backup power source. For example, if the microcomputer  11  is embedded into a digital video camera, normal circuit power control signal AE indicates that the camera&#39;s main switch is “on”. Consequently, in this case, the main switch signal can be used as normal circuit power control signal AE in its current state. Also, backup circuit power control signal BE indicates that the high-capacity battery, the primary power source, is removed from the camera. Consequently, when backup circuit power control signal BE becomes active, the microcomputer switches to a state in which the clock function operates or a state in which RAM memory  16  stores data using a small button-type battery. 
         [0031]      FIG. 2  shows the configuration of the voltage selection circuit in the power supply voltage regulator circuit according to Embodiment  1 . As shown in  FIG. 2 , a first switch  25  is connected between a primary power supply voltage input pin  21  and a normal circuit supply voltage output pin  23  of the voltage selection circuit  18 . A second switch  26  is connected between a backup power supply voltage input pin  22  and a backup circuit supply voltage output pin  24 . A third switch  27  is connected between the second switch  26  and the backup circuit supply voltage output pin  24 . A fourth switch  28  is connected between the normal circuit supply voltage output pin  23  and the backup circuit supply voltage output pin  24 . A diode  33  for backflow prevention is inserted between the third switch  27  and the backup circuit supply voltage output pin  24 . 
         [0032]    A regulator  34  is connected between the primary power supply voltage input pin  21  and the backup power supply voltage input pin  22 . This regulator  34  outputs the same voltage as the backup power supply voltage (e.g. 1.3 V) when stepping the primary power supply voltage down. However, either the output voltage of the regulator  34  or the backup power supply voltage which was input to the backup power supply voltage input pin  22  is selected by the second switch  26 . Also, this is not shown in the diagram, but the regulator  34  outputs each voltage, which is required, by each part of the microcomputer  11 . 
         [0033]    The first switch  25  is controlled by normal circuit power control signal AE. For example, the first switch  25  closes when normal circuit power control signal AE is “1”, and opens when the control signal AE is “0”. The second switch  26  is controlled by the output signal of an AND gate  32 , which uses as its inputs the signal resulting when normal circuit power control signal AE is inverted by an inverter  31  and backup circuit power control signal BE. For example, the second switch  26  selects the backup power supply voltage input pin  22  side when the output signal of the AND gate  32  is “1”, and selects the regulator  34  side when the output signal is “0”. 
         [0034]    The third switch  27  is controlled by the output signal of an OR gate  30  which uses as its inputs normal circuit power control signal AE and backup circuit power control signal BE. For example, the third switch  27  closes when the output signal of the OR gate  30  is “1”, and opens when the output signal is “0”. The fourth switch  28  is controlled by an output signal of an AND gate  29  which uses as its inputs normal circuit power control signal AE and backup circuit power control signal BE. For example, the fourth switch  28  closes when the output signal of the AND gate  29  is “1”, and opens when the output signal is “0”. 
         [0035]      FIG. 3  is a table explaining the operation of the voltage selection circuit shown in  FIG. 2 . As shown in  FIG. 3 , the first switch  25  and the third switch  27  open when both normal circuit power control signal AE and backup circuit power control signal BE are “0”, so voltage VA of the normal circuit supply voltage output pin  23  and voltage VB of the backup circuit supply voltage output pin  24  are both 0 V At this time the microcomputer  11  is in a stop state, so both the CPU  14  and the RAM memory  16  have stopped. 
         [0036]    The first switch  25  closes when normal circuit power control signal AE is “1” and backup circuit power control signal BE is “0”, so voltage VA of the normal circuit supply voltage output pin  23  is the primary power supply voltage (e.g. 3.3 V). Also, the second switch  26  selects the regulator  34  side, the third switch  27  closes, and the fourth switch  28  opens, so voltage VB of the backup circuit supply voltage output pin  24  is the output voltage (e.g. 1.3 V) of the regulator  34 . At this time, the microcomputer  11  is in a run state, the CPU  14  runs, and RAM memory  16  retains data. Primary power supply voltage is supplied to the primary power supply voltage input pin  21  by a large-capacity battery such as a lithium ion battery. 
         [0037]    The first switch  25  opens when normal circuit power control signal AE is “0”, and backup circuit power control signal BE is “1”, so voltage VA of the normal circuit supply voltage output pin  23  is 0V Also, the second switch  26  selects the backup power supply voltage input pin  22 , the third switch  27  closes, and the fourth switch  28  opens, so voltage VB of the backup circuit supply voltage output pin  24  is the backup power supply voltage (e.g. 1.3 V). At this time, the microcomputer  11  is in a backup state, the CPU  14  has stopped, and RAM memory  16  retains data. Backup power supply voltage is supplied to the backup power supply voltage input pin  22  by a button-type battery, for example. 
         [0038]    The first switch  25  closes when normal circuit power control signal AE and backup circuit power control signal BE are both “1”, so voltage VA of the normal circuit supply voltage output pin  23  is the primary power supply voltage (e.g. 3.3 V). Also, the second switch  26  selects the regulator  34  side, and the third switch  27  and fourth switch  28  close, but because of the diode  33  for backflow prevention, voltage VB of the backup circuit supply voltage output pin  24  is the primary power supply voltage (e.g. 3.3 V). At this time the microcomputer  11  is in a normal operation state, so both the CPU  14  and RAM memory  16  operate. 
       Embodiment 2  
       [0039]      FIG. 4  shows a power supply voltage regulator circuit and microcomputer configuration according to Embodiment 2. As shown in  FIG. 4 , Embodiment 2 differs from Embodiment 1 in that the automatic wait generation circuit  19  is provided in the normal circuit  12  of the microcomputer  11  in Embodiment 1. In addition, the voltage selection circuit  18  switches the voltage depending on the combination of logic among normal circuit power control signal AE, backup circuit power control signal BE, and auxiliary power control signal CE. Auxiliary power control signal CE is a signal that becomes active when a RAM access signal is issued from the CPU  14 , e.g. when the RAM access signal is output from the RAM address decoder  15 . 
         [0040]      FIG. 5  shows the configuration of the voltage selection circuit in the power supply voltage regulator circuit according to Embodiment 2 . As shown in  FIG. 5 , in Embodiment 2 , the AND gate  35  and OR gate  36  are provided to the voltage selection circuit  18  in addition to the configuration explained in Embodiment 1 . The AND gate  35  uses as its inputs normal circuit power control signal AE and auxiliary power control signal CE. The OR gate  36  uses as its inputs the output signal of the AND gate  29 , which in turn uses as its inputs normal circuit power control signal AE and backup circuit power control signal BE, and the output signal of the AND gate  35 , which was added on. The fourth switch  28  is controlled by the output signal of this OR gate  36 , which was added on. 
         [0041]      FIG. 6  is a table explaining the operation of the voltage selection circuit shown in  FIG. 5 . As shown in  FIG. 6 , normal circuit power control signal AE is “0” when both normal circuit power control signal AE and backup circuit power control signal CE are “0” (stop state). Then, when backup circuit power control signal BE is “1” (backup state) and normal circuit power control signal AE and backup circuit power control signal BE are both “1” (normal state), the state is the same as that explained in Embodiment 1 regardless of auxiliary power control signal CE. 
         [0042]    Normal circuit power control signal AE is “1”, and backup circuit power control signal BE is “0”. The first switch  25  closes when auxiliary power control signal CE is “0”, so voltage VA of the normal circuit supply voltage output pin  23  is the primary power supply voltage (e.g. 3.3 V). Also, the second switch  26  selects the regulator  34  side, the third switch  27  closes, and the fourth switch  28  closes. Consequently, voltage VB of backup circuit supply voltage output pin  24  is the output voltage (e.g. 1.3 V) of the regulator  34 . The microcomputer  11  at this time is in a run state, but the microcomputer  11  is in a state where there has been no access to RAM memory  16  of the backup circuit  13 . 
         [0043]    If there has been access to RAM memory  16  of the backup circuit  13  when normal circuit power control signal AE is “1” and backup circuit power control signal BE is “0”, auxiliary power control signal CE becomes “1”. Then, the output signal of the AND gate  35 , which uses as its inputs normal circuit power control signal AE and auxiliary power control signal CE, transitions from “0” to “1”, and the output signal of the OR gate  36 , which uses this output signal as its input, also transitions from “0” to “1”. Thereby, the fourth switch  28  closes and voltage VB of the backup circuit supply voltage output pin  24  is the primary power voltage (e.g. 3.3 V), because the backflow prevention diode  33  exists. 
         [0044]    Therefore, the voltage at which data can be written to or read from RAM memory  16  in the microcomputer  11  is supplied, thereby making access to RAM memory  16  possible. In other words, the microcomputer  11  at this time is in a run state, and is in a state where there has been access to RAM memory  16  of the backup circuit  13 . When access to RAM memory  16  ends, auxiliary power control signal CE resets to “0”, so voltage VB of the backup circuit supply voltage output pin  24  returns to the output voltage (e.g. 1.3 V) of the regulator  34 . 
         [0045]      FIG. 7  shows a configuration of the auxiliary power source control signal generation circuit in the RAM address decoder. At this point, the address of RAM memory  16  in a 16-bit address space shall be from 0xF000 to 0xFFFF. In this case, as shown in  FIG. 7 , the auxiliary power source control signal generation circuit comprises the AND gate  41 , which uses as its inputs address signals A 15 , A 14 , A 13 , and A 12  which are the upper  4  bits. Decoding signal DEC, which is output from this AND gate  41 , is passed off to the voltage selection circuit  18  as auxiliary power control signal CE. Also, decoding signal DEC is passed off to the automatic wait generation circuit  19  as the RAM address access signal. Decoding signal DEC is output at the timing when the write signal or read signal are combined with a timing or other such signal and RAM memory  16  is accessed. 
         [0046]    Note, the portion of the conventional address decoder circuits used in the RAM address decoder  15  which decodes address signals A 15 , A 14 , A 13 , and A 12 , which are the upper 4 bits, then generates a chip enable signal can also be used as the auxiliary power source control signal generation circuit. In addition, providing the AND gate  41  as the auxiliary power source control signal generation circuit is acceptable. Also, if there is an area in RAM memory  16  that cannot read or write data at low voltage (e.g. 1.3 V) and an area that can read or write data, configuring the auxiliary power source control signal generation circuit to output the decoding signal DEC when accessing the area which cannot read or write data at low voltage (e.g. 1.3 V) is acceptable. 
         [0047]      FIG. 8  shows the configuration of an automatic wait generation circuit. As shown in  FIG. 8 , the automatic wait generation circuit  19 , without any particular limit on the number of stages therein, comprises two flip-flop stages  51  and  52 . When the RAM address access signal from the RAM address decoder  15  becomes active, the automatic wait generation circuit  19  uses flip-flops  51  and  52  to generate a signal that becomes active for a predetermined period of time then output the signal to the CPU  14  as an automatic wait signal. The time the CPU  14  accesses RAM memory  16  is thereby extended, allowing the supply voltage to RAM memory  16  to stabilize. The number of flip-flop stages is selected in accordance with the time required for the supply voltage to RAM memory  16  to stabilize. 
         [0048]    As described above, according to Embodiment 1 , low power supply voltage is supplied to the backup circuit  13  except when RAM memory  16  of the backup circuit  13  is being accessed. Also, the power supply voltage supplied to the normal circuit  12  and the backup circuit  13  is determined by the combination of logic for normal circuit power control signal AE and backup circuit power control signal BE, and is automatically switched. Consequently, high voltage can be supplied to the backup circuit  13  only when necessary, in order to reduce the power consumption of the microcomputer  11 . 
         [0049]    Also, according to Embodiment 2 , the power supply voltage of the backup circuit  13  is controlled by auxiliary power control signal CE, and the automatic wait generation circuit  19  extends the access time to RAM memory  16 . In addition, when RAM memory  16  is in a standby state, the CPU  14  can access RAM memory  16  without any waiting time. The power supply voltage regulator circuit and microcomputer is not limited to the above-mentioned aspects and a variety of modifications thereof are possible. In embodiment 2 for example, when the microcomputer  11  is in a run state and transitions from a state in which RAM memory  16  has not been accessed into a state in which RAM memory  16  has been accessed, it is also acceptable for the microcomputer  11  to control the regulator  34  of the voltage selection circuit  18  and change the output voltage of the regulator  34  from a low voltage to a high voltage. Also, the automatic wait generation circuit  19  is not limited to comprising flip-flops. 
         [0050]    Example embodiments of aspects of the present invention have now been described in accordance with the above advantages. It will be appreciated that these examples are merely illustrative of aspects of the present invention. Many variations and modifications will be apparent to those skilled in the art.