Abstract:
A power circuit in a battery powered portable communication terminal, having a battery and a transmission power amplifier for TDMA (Time Division Multiple Access) or TDD (Time Division Duplex) signals includes a power accumulator, a battery output current limiter, and a control circuit to control the current limiter and to connect the power accumulator to the battery and to the transmission power amplifier depending on whether the transmission power amplifier is transmitting a signal burst. The control circuit controls the battery to charge the power accumulator during a non-burst period. During burst periods, when the transmission power amplifier requires higher power, the control circuit connects the power accumulator to the transmission power amplifier, to supplement the current-limited current provided by the battery and provide a total current to the power amplifier that is higher than the battery output current.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power circuit and a communication device provided with the power circuit and more particularly to the power circuit being suitably used in portable cellular phones or a like employing a TDMA (Time Division Multiple Access) or TDD (Time Division Duplex) communication method and to the communication device provided with the power circuit. 
     The present application claims priorities of Japanese Patent Application No. 2003-030454 filed on Feb. 7, 2003 and No. 2003-183617 filed on Jun. 26, 2003, which are hereby incorporated by reference. 
     2. Description of the Related Art 
     In a conventional portable communication device (for example, a portable cellular phone) employing a TDMA or TDD communication method, a transmission signal having a burst period and non-burst period occurring alternately in a repeated manner, after having been amplified by a transmission power amplifier, is transmitted as a transmission radio wave. During the burst period, since the transmission power amplifier transmits a radio wave, power consumption is large and, during the non-burst period, since a radio wave receiving section of the portable cellular phone receives a radio wave, power consumption is small. Therefore, a load current increases or decreases in a burst manner. Moreover, power for the transmission power amplifier is ordinarily supplied from a battery. The battery discharges in synchronization with a repeating cycle of the burst period and non-burst period. 
     The battery supplies power also to internal circuits such as a CPU (Central Processing Unit) or a like in the portable cellular phone, however, if a voltage of the battery becomes below a lower limit value of an operating voltage of the CPU or a like even momentarily, the CPU or a like is put in a frozen state, causing the portable cellular phone to be inoperable. Therefore, whether or not a residual capacity of the battery exists is judged by detecting a lowest voltage value occurring in various operating states and, by setting a somewhat high terminating voltage obtained by providing a margin based on prediction of a momentary heavy loaded state. Under such conditions, research and development are being conducted to use the portable cellular phone for a longer period of time by expanding a capacity of a battery or by utilizing a DC-DC (Direct Current-Direct Current) converter circuit. Moreover, the TDMA communication method includes a PDC (Personal Digital Cellular) method being used domestically in Japan, a GSM (Global System for Mobile Communications) and/or GPRS (General Packet Radio Service) methods being used in Europe or a like. 
     Such the conventional portable cellular phone, as shown in  FIG. 15 , includes a transmission power amplifier  1 , a circuit block  2 , and a power circuit  3 . The transmission power amplifier  1  is made up of an amplifier (AMP)  11 , a capacitor  12 , an amplifier (AMP)  13 , a capacitor  14 , an amplifier (AMP)  15 , and a bias circuit  16 . Each of the amplifiers  11 ,  13 , and  15  is constructed of a bipolar transistor, a MOS (Metal Oxide Semiconductor) transistor, or a like. The bias circuit  16  generates a bias voltage to normally operate these amplifiers  11 ,  13 , and  15 . Moreover, each of the transmission power amplifier  1  and circuit block  2  has a lower limit value of an operating voltage required to be operated normally. In the transmission power amplifier  1 , a transmission signal RFIN having a burst period and a non-burst period occurring alternately in a repeated manner, which correspond to the GSM communication method, is input to the amplifier  11 . The transmission signal RFIN is amplified by the amplifier  11  and an output signal K is then output from the amplifier  11 . The output signal K, after its DC (Direct Current) component has been intercepted by the capacitor  12 , is input to the amplifier  13  where it is amplified and is output as an output signal M from the amplifier  13 . The output signal M, after its DC component has been intercepted by the capacitor  14 , is input to the amplifier  15  where it is amplified and a radio wave signal RFOUT as a transmission radio wave from the amplifier  15  is output. 
     The circuit block  2  includes various circuits each performing specified operations other than amplifying operations to be performed by the transmission power amplifier  1  using almost constant power to be consumed. The various circuits include, for example, a DC-DC converter  21 , loads  22  other than the transmission power amplifier  1 , or a like, and a lower limit value of a voltage for the specified operations to be performed by each of the various loads  22  is set to be higher than a lower limit value of the voltage for operations to be performed by the transmission power amplifier  1 . The DC-DC converter  21  boosts or lowers an output voltage of the power circuit  3 . The loads  22  other than the transmission power amplifier  1  includes, for example, a power source for a microcomputer, a power source for a DSP (Digital Signal Processor), a power source for a SIM (Subscriber Identity Module) card, a power source for a memory, a power source for human interface devices (for example, a voice device, an input/output device, an image pick-up device, or a like) and each of the loads  22  is so configured that an output voltage of the power circuit  3  is directly applied to the loads  22  which can operate at the output voltage of the power circuit  3  and the output voltage of the power circuit  3 , after being boosted or lowered by the DC-DC converter  21 , is applied to the loads  22  which cannot operate at the output voltage of the power circuit  3  and require conversion of the output voltage. 
     The power circuit  3  is made up of a battery  31 , a power management circuit  32 , a battery charging circuit  33 , and a power bypass condenser  34 . The battery  31  is a lithium ion battery and is made up of a single cell  35 , an internal resistor  36 , and a protective circuit  37 . The power management circuit  32  monitors an output voltage of the battery  31  so as to detect a residual capacity and, when the residual capacity of the battery  31  becomes low and when the output voltage reaches a specified reference level having been set to be more than a lower limit value of an operating voltage of the circuit block  2 , produces a control signal to display, for example, an alarm indicating a need for charging to notify a fact that the output voltage of the battery  31  has dropped. The battery charging circuit  33  is connected to an outer power source (not shown) charges the battery  31  under specified charging conditions according to a control signal fed from the power management circuit  32 . The power bypass condenser  34  delays increasing or decreasing of an output current of the battery  31  occurring at the start time or end time of the burst period. 
       FIG. 16  is a time chart explaining operations of the conventional portable cellular phone shown in  FIG. 15 .  FIG. 17  is a diagram showing a tolerance of a discharging voltage of the battery  31  shown in  FIG. 15 , reference for detection of a residual capacity of the battery  31  having been set to the management circuit shown in  FIG. 15 , a tolerance of an operating voltage of a transmission power amplifier  1  shown in  FIG. 15 , and a tolerance of an operating voltage of the circuit block  2  shown in  FIG. 15 . 
     Next, operations of the portable cellular phone shown in  FIG. 15  are described below by referring to  FIGS. 16 and 17 . As shown in  FIG. 15 , since the transmission power amplifier  1  is connected to the power circuit  3 , an output voltage of the battery  31  becomes equal to an operating voltage of the transmission power amplifier  1 . First, at time tα, when a signal transmitting operation is started and the transmission burst period begins, a current to be consumed by the transmission power amplifier  1  sharply increases from a current value 0 A to a current value IPA. An output current of the battery  31  also increases from a current value IB0 to a current value IBmax in synchronization with starting of the transmission burst period, however, increasing of the current is delayed due to a surge absorbing action caused by discharging of the power bypass condenser  34 . This serves to suppress a fluctuation of an output voltage of the battery  31  caused by starting of the transmission burst period. An output voltage of the battery  31 , due to an increase of its output current occurring at the start time of the transmission burst period and due to existence of a resistance component by serial connection between the internal resistor  36  and the protective circuit  37 , drops by a voltage value ΔVBRx (=VB0) from a voltage value VB0 (being equal to an operating voltage VPA0 of the transmission power amplifier  1 ). 
     During a period Tβ, that is, during the transmission burst period, since the transmission power amplifier  1  is continuing transmission operations, a current to be consumed remains constant at a level of the current value IPA. The output current of the battery  31 , since the delay caused by the power bypass condenser  34  has disappeared, becomes stable at a level of the current value IBmax being a sum of a current consumed by the transmission power amplifier  1  to a current (almost being constant and being equal to the current value IB0) consumed by the circuit block  2 . The output voltage of the battery  31 , due to a voltage drop corresponding to an electrostatic capacity component of the battery  31  induced by an output current with the value of IBmax, is lowered by a voltage value ΔVBCx (=ΔVCX). Therefore, an amount of change in the output voltage of the battery  31  at an end of the period Tβ, since an amount of voltage drop of ΔVBCx is added to a voltage value ΔVBRx occurring at the time tα, becomes ΔVBx (=ΔVPAx=ΔVBRx+ΔVBCx) and the output voltage of the battery  31  drops from the voltage value VB0 to a voltage value VB1 (=VPA1). 
     At the time tβ, when the transmission operation is terminated and the transmission burst period ends, the current consumed by the transmission power amplifier  1  sharply lowers from the current value IPA to almost 0A. The output current of the battery  31  decreases to a level of a current (with a value of IB0) consumed by the circuit block  2  in synchronization with ending of the transmission burst period, however, decreasing of the output current is delayed by the surge absorbing action caused by charging of the power bypass condenser  34 . This suppresses a fluctuation of the output voltage of the battery  31  caused by ending of the transmission burst period. The output voltage VB1 of the battery  31 , since the voltage drop caused by existence of a resistance component by serial connection between the internal resistor  36  and protective circuit  37  decreases in synchronization with ending of the transmission burst period, is boosted by a voltage value ΔVBRx (=ΔVRx). 
     During a period Tα, that is, during the receiving non-burst period, since the radio wave receiving section of the portable cellular phone is continuing receiving operations and the transmission power amplifier  1  does not operate, a current consumed by the transmission power amplifier  1  is almost 0A. The output current of the battery  31 , since the delay caused by the power bypass condenser  34  has disappeared, is stable at a level of the current value IB0 which is a current to be consumed by the circuit block  2 . The output of the battery  31 , since its output current has sharply decreased from the current value IBmax to the current value IB0, is boosted, based on a time constant, due to existence of a resistance component by serial connection between the internal resistor  36  and protective circuit  37  and due to an electrostatic capacity component of the battery  31 . 
     Then, these voltages and currents are again put into the state that has occurred at the time tα and, thereafter, same operations are repeated in order of the time tα, period Tβ, time tβ, period Tα, time tα, . . . . Thus, by a current consumed by the transmission power amplifier  1  during the transmission burst period, an amount of change in the output voltage of the battery  31  becomes a voltage value ΔVBx and the output voltage of the battery  31  drops from the voltage value VB0 occurring during the receiving non-burst period to the voltage value VB1 which is a lowest level during the transmission burst period. If this voltage value VB1 becomes below a lower limit value of an operating voltage of the internal circuit such as the CPU in the portable cellular phone even momentarily, since the portable cellular phone becomes inoperable, a residual life of the battery  31  is judged based on this voltage value VB1. 
     When a telephone speech is made using the portable cellular phone, for example, of the GSM type being typical of the TDMA-type portable cellular phone, a voltage value ΔVBx that can be obtained by simulation using following conditions becomes about 300 mV. 
     Simulation conditions; 
     Resistance of the internal resistor  36 ; 150 mΩ 
     Transmission burst period; 0.5 msec 
     Receiving non-burst period; 4.5 msec 
     Output current of the battery  31 ; 
     IBmax; 2.1 A, 
     IB0; 0.1 A. 
     ΔVBRx=0.15·(2.1−0.1)=0.3 V 
     ΔVBCx=(0.0005·2.1)/C&gt;0 
     where “C” is electrostatic capacity of the battery  31 . 
     ∴ΔVBx=ΔVBRx+ΔVBCx&gt;300 mV 
     That is, when the output of the battery  31  is, for example, 3.5V during the receiving non-burst period, it becomes 3.2V or less during the transmission burst period and, since it reaches the level that an alarm indicating a need for charging is issued according to the reference for detection of a residual capacity of the battery  31  shown in  FIG. 17 , a notification is provided by the power management circuit  32  informing that the output of the battery  31  has dropped. 
     As shown in  FIG. 17 , a tolerance of an operating voltage of the transmission power amplifier  1  is 4.2V to 2.7V, a tolerance of an operating voltage of the circuit block  2  is 4.2V to 3.0V and there is a difference of about 0.3V (ΔVM) in the lower limit values in the operating voltage between the transmission power amplifier  1  and the circuit block  2 . A reason for this is that the transmission power amplifier  1 , since it is constructed of analog circuits, is operable even at a comparatively low voltage, while the circuit block  2 , since it is constructed of a CPU and/or digital circuits, is inoperable at a low voltage. 
     Moreover, in addition to the portable cellular phone described above, a radio communication device as one of examples of the technology described above is disclosed in Japanese Patent Application Laid-open No. Hei 04-315320, in which a capacitor is charged by a battery to have a voltage of 10V using a voltage boosting device and, during a transmission burst period, a switching unit is closed to allow power to be applied by the capacitor to a power amplifier. At this point, a burst signal is amplified by the power amplifier and is transmitted and, during a non-burst period, a switching unit is opened to allow the capacitor to be charged. 
     However, such the conventional technologies as described above have following problems. That is, even if an output voltage of the battery  31  is, for example, 3.5V during the receiving non-burst period, it becomes 3.2V or less (terminating voltage) during a transmission burst period and, therefore, it reaches a level that an alarm indicating a need for charging is issued and, as a result, a notification is provided by the power management circuit  32  informing that the output voltage has dropped and, before the output voltage of the battery  31  reaches an actual terminating voltage, the conventional portable cellular phone becomes inoperable. To solve this problem, an idea is proposed that a capacity of the battery  31  is increased. However, if the capacity of the battery  31  is increased, it is made impossible to make the portable cellular phone smaller in size and lightweight, which further makes it difficult to meet market needs for the portable cellular phone which enables long-time speech and is compact and lightweight. 
     Moreover, in the burst radio communication device disclosed in the Japanese Patent Application Laid-open No. Hei 04-315320, power is applied to the power amplifier by the capacitor charged by the battery using the voltage boosting device. However, in many power amplifiers being presently a mainstream, a battery voltage (in the case of the lithium ion battery, it is about 3.7V on average) of the portable cellular phone is applied. Therefore, if a voltage of about 10V is applied by the capacitor, it exceeds a withstand voltage (about 5V) of a power amplifier of the portable cellular phone, which produces a fear that elements within the power amplifier may be broken. Moreover, even when a voltage fed from the capacitor is stepped down by a regulator, since DC/DC converters are used in two stages, another problem arises that power efficiency is remarkably lowered. 
     Also, in the disclosed burst radio communication device, the switching unit is closed during the transmission burst period and is opened during the non-burst period, however, such the method in which the capacitor is charged at an idle slot time during the non-transmission period (non-burst period) can be employed only in a device in which transmission time is comparatively short (its duty ratio being about ⅛). That is, as a ratio of transmission time becomes larger, the capacitor has to be charged in a shorter time and, when this ratio exceeds 50%, the switching unit produces an adverse effect. In recent years, functions of the portable cellular phone tend to be expanded, that is, although the conventional function is to perform only voice speech, a recent function includes transmission of data. In the portable cellular phone of the TDMA type, such the expansion of the functions causes transmission slots to increase and the ratio of transmission time to rise and, therefore, the switching unit is not effective in achieving long-time speech in the portable cellular phone. 
     Furthermore, one of the most important performance capabilities of portable communication devices such as portable cellular phones is to be able to provide a satisfactory size and weight that would not hinder a user from carrying them. In recent years in particular, since a folding body of a portable cellular phone is the main stream, it is requested that portable cellular phones are thin and lightweight. However, in the disclosed burst radio communication device, the voltage boosting device is a DC-DC converter made up of a coil, resistor, semiconductor, or a like, the switching unit is made up of a mechanical switching element or a semiconductor switching element, and the capacitor is about 100 mm 3  in size. If all these components are housed in the portable cellular phone, the portable cellular phone becomes very large and heavy, thus impairing a portability characteristic of the portable cellular phone. 
     SUMMARY OF THE INVENTION 
     In view of the above, it is an object of the present invention to provide a power circuit enabling long-time speech in portable communication devices and making them compact and lightweight and communication devices provided with the power circuit. 
     According to a first aspect of the present invention, there is provided a power circuit to be used in a communication device including a transmission power amplifier to amplify a transmission signal having a burst period and a non-burst period occurring alternately in a repeated manner, the power circuit including: 
     a power supplying unit to supply a first power to the transmission power amplifier, and 
     a power storing section to accumulate as a second power redundancy of the first power to be supplied from the power supplying unit to the transmission power amplifier during the non-burst period, and to feed the accumulated second power to the transmission power amplifier in addition to the first power being supplied from the power supplying unit to the transmission power amplifier during the burst period. 
     According to a second aspect of the present invention, there is provided a communication device including: 
     a transmission power amplifier to amplify a transmission signal having a burst period and a non-burst period occurring alternately in a repeated manner; and 
     a power circuit including: 
     a power supplying unit to supply a first power to the transmission power amplifier, and 
     a power storing section to accumulate as a second power redundancy of the first power to be supplied from the power supplying unit to the transmission power amplifier during the non-burst period, and to feed the accumulated second power to the transmission power amplifier in addition to the first power being supplied from the power supplying unit to the transmission power amplifier during the burst period. 
     According to a third aspect of the present invention, there is provided a power circuit to be used in a communication device including a transmission power amplifier to amplify a transmission signal having a burst period and a non-burst period occurring alternately in a repeated manner and with a load circuit to consume power required for performing operations, the power circuit including: 
     a power supplying unit to supply a first power to the transmission power amplifier and the load circuit; 
     a voltage monitoring section to monitor an output voltage of the power supplying unit and to inform a user of a drop of the output voltage, when the output voltage lowers to a specified reference level; and 
     a power storing section to accumulate as a second power redundancy of the first power to be supplied from the power supplying unit to the transmission power amplifier during the non-burst period, and to feed the accumulated second power to the transmission power amplifier in addition to the first power being supplied from the power supplying unit to the transmission power amplifier during the burst period. 
     According to a fourth aspect of the present invention, there is provided a communication device including: 
     a transmission power amplifier to amplify a transmission signal having a burst period and a non-burst period occurring alternately in a repeated manner; 
     a load circuit to consume power required for performing operations, and 
     a power circuit including: 
     a power supplying unit to supply a first power to the transmission power amplifier and the load circuit; 
     a voltage monitoring section to monitor an output voltage of the power supplying unit and to inform a user of a drop of the output voltage, when the output voltage lowers to a specified reference level; and 
     a power storing section to accumulate as a second power redundancy of the first power to be supplied from the power supplying unit to the transmission power amplifier during the non-burst period, and to feed the accumulated second power to the transmission power amplifier in addition to the first power being supplied from the power supplying unit to the transmission power amplifier during the burst period. 
     In the foregoing third aspect, a preferable mode is one wherein the transmission power amplifier has a lower limit value of a first operating voltage to normally operate the transmission power amplifier, the load circuit has a lower limit value of a second operating voltage to normally operate the load circuit, the lower limit value of the second operating voltage is set to be higher than the lower limit value of the first operating voltage, the reference level is set to be not less than the lower limit value of the second operating voltage, and the power supplying unit is made up of a battery or a direct current power source in which in which an upper limit value is imposed on a current to be output therefrom. 
     In the foregoing first and third aspects, a preferable mode is one wherein the power storing section is so configured as to be charged, when a voltage of the power storing section becomes lower than that of the power supplying unit during the burst period, until a voltage of the power storing section becomes almost equal to a voltage of the power supplying unit during the non-burst period occurring subsequent to the burst period. 
     Another preferable mode is one that wherein further includes: 
     a control circuit to control the first power to be fed from the power supplying unit to the transmission power amplifier, 
     wherein the power storing section accumulates as the second power redundancy of the first power to be supplied from the power supplying unit to the transmission power amplifier under control of the control circuit during the non-burst period. 
     Still another preferable mode is one wherein the control circuit controls the first power to be fed from the power supplying unit to the transmission power amplifier, by controlling an output current of the control circuit, the output current being fed from the power supplying unit to the transmission power amplifier. 
     A further preferable mode is one wherein the output current of the control circuit is set to have a current value such that almost all amount of power needed to be consumed by the transmission power amplifier during one frame period being made up of one burst period and one non-burst period may be supplied to the transmission power amplifier. 
     An additional preferable mode is one wherein the power storing unit supplies the second power to the transmission power amplifier by discharging when power needed to be consumed by the transmission power amplifier during the burst period is larger than the first power being supplied under control of the control circuit, and 
     wherein the control circuit exerts control so that the power storing section having discharged during the burst period is charged to accumulate redundancy of the first power as the second power when power to be consumed by the transmission power amplifier during the non-burst period is smaller than the first power being supplied under control of the control circuit. 
     still additional preferable mode is one wherein the delay device delays a rising and falling of an output current of the power supplying unit at time of start and end of the burst period. 
     A further preferable mode is one wherein the power storing section is made up of an electrical double layer capacitor. 
     Still further preferable mode is one wherein the electrical double layer capacitor has unit cells constructed as a capacitor of sheet-shaped electrical double layer structure which make up stacked cells in which arbitrary numbers of the unit cells are stacked in layer so as to be able to provide a specified withstand voltage and electrostatic capacity. 
     Another preferable mode is one wherein the transmission signal is transmitted by a TDMA (Time Division Multiple Access) or TDD (Time Division Duplex) communication method. 
     With the above configurations, since, by functions of the control circuit, an output current is supplied from the power supplying unit to the transmission power amplifier and the power storing section is charged so that power is accumulated therein and since power is applied from the power storing section to both the control circuit and the transmission power amplifier, even if power consumption of the transmission power amplifier increases during a burst period, a drop of an output voltage from the power supplying unit is small. Therefore, time required for the output voltage to reach a terminating voltage in the power supplying unit is made longer and a life of the power supplying unit can be lengthened. Also, even if the power supplying unit is put under a low-temperature circumstance and its internal resistance increases, shortening of the life of the power supplying unit can be avoided. Since the electrical double layer capacitor serving as the power storing section is made up of thin-sheet-shaped unit cells and is so constructed in a manner that a plurality of the unit cells are stacked in layer, the power circuit can be made thin, which enables mounting of the power circuit of the present invention suitably on a folding-type portable cellular phone without causing an increase in a thickness of a case of the portable cellular phone. 
     Also, the power circuit of the present invention does not use such the voltage boosting unit as disclosed in Japanese Patent Application Laid-open No. Hei 4-315320 and, therefore, no case occurs in which an operating voltage of the transmission power amplifier is higher than a voltage to be supplied by the power supplying unit. Moreover, the power circuit of the present invention is equipped with the control circuit to limit an output current fed from the power supplying unit to a pre-set upper limit current value, irrespective of transmitting and receiving timing in the TDMA-type or TDD-type communication system and, therefore, no effects decrease due to an increase in a ratio of transmission time. 
     Furthermore, the power circuit of the present invention includes the control circuit, the delay device made up of a capacitor, and power storing section having an electrical double layer capacitor, in which the capacitor and control circuit are constructed so as to be of surface mounting type and the electrical double layer capacitor is formed to be of a thin shape and, therefore, mounting of the power circuit on the folding-type portable cellular phone can be can be achieved without an increase in thickness of the folding-type portable cellular phone being presently a mainstream. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, advantages, and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a schematic block diagram showing electrical configurations of a communication device being equipped with a power circuit of a first embodiment of the present invention; 
       FIG. 2  is a diagram showing the antenna, antenna switch, local oscillator, transmitter, radio section interface, and human interface section, which are all taken from  FIG. 1 ; 
       FIG. 3  is a circuit diagram showing electrical configurations of main components of the power circuit, transmission power amplifier, and circuit block shown in  FIG. 1 ; 
       FIG. 4  is a diagram showing configurations of a circuit mounting section  65  shown in  FIG. 3 ; 
       FIG. 5  is a diagram showing configurations of an electrical double layer capacitor shown in  FIG. 4 ; 
       FIG. 6  is a diagram showing configurations of a unit cell shown in  FIG. 5 ; 
       FIG. 7  is a time chart explaining operations of the power circuit and the transmission power amplifier shown in  FIG. 3 ; 
       FIG. 8  is a diagram explaining an effect of lengthening a life of a battery according to the first embodiment of the present invention; 
       FIG. 9  is also a diagram explaining the effect of lengthening the life of the battery according to the first embodiment of the present invention; 
       FIG. 10  is a schematic block diagram showing electrical configurations of a portable cellular phone according to a second embodiment of the present invention; 
       FIG. 11  is a schematic block diagram showing electrical configurations of a portable cellular phone according to a third embodiment of the present invention; 
       FIG. 12  is a diagram illustrating configurations of a circuit mounting section in a power circuit according to a fourth embodiment of the present invention; 
       FIG. 13  is a diagram illustrating configurations of a circuit mounting section in a power circuit according to a fifth embodiment of the present invention; 
       FIG. 14  is a diagram illustrating configurations of the electrical double layer capacitor of  FIG. 13 ; 
       FIG. 15  is a schematic block diagram showing configurations of a conventional portable cellular phone; 
       FIG. 16  is a time chart explaining operations of the conventional portable cellular phone of  FIG. 15 ; and 
       FIG. 17  is a diagram showing a range of a discharging voltage of a battery shown in  FIG. 15 , reference for detection of a residual capacity of the battery connected to a power management circuit shown in  FIG. 15 , tolerance of an operating voltage of the transmission power amplifier shown in  FIG. 15 , and tolerance of an operating voltage of the circuit block shown in  FIG. 15 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Best modes of carrying out the present invention will be described in further detail using various embodiments with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a schematic block diagram showing electrical configurations of a communication device being equipped with a power circuit of a first embodiment of the present invention. The communication device of the first embodiment, as shown in  FIG. 1 , is a portable cellular phone and includes an antenna  41 , an antenna switch  42 , a receiver  43 , a local oscillator  44 , a transmitter  45 , a radio section interface  46 , a human interface section  47 , and a power circuit  48 . The antenna  41  is used to transmit and receive a radio wave to and from a radio base station (not shown) and its length is set based on a wavelength of a radio wave to be used for communication. The antenna switch  42  selects either the receiver  43  or the transmitter  45  to establish connection to the antenna  41 . 
     The receiver  43  performs amplification and/or frequency conversion of a received signal, or a like. The local oscillator  44  generates a signal having a reference frequency required for frequency conversion of a received signal or a transmitting signal by a control signal of the radio section interface  46 . The transmitter  45  makes a frequency conversion of and/or performs amplification on a transmitting signal. The radio section interface  46  encodes a received signal or a transmitting signal, transmits encoded signals to the human interface section  47 , and controls the local oscillator  44  all the time. The human interface section  47  is connected to analog input/output devices including a voice device such as a speaker, microphone, or a like (not shown), an input/output device such as a keyboard, display, or a like (not shown), an image pick-up device such as a camera (not shown), and serves as a mediator between a user and the portable cellular phone. The power circuit  48  supplies power to each of the above components. 
     In the portable cellular phone of the embodiment, during a period of receiving a radio wave, the antenna  41  is connected to the receiver  43  through the antenna switch  42 . The radio wave received by the antenna  41  is amplified by the receiver  43 , and its frequencies is further down-converted by a signal fed from the local oscillator  44 . The received wave of which frequency were down-converted is then transmitted to the radio section interface  46 . The received wave is demodulated and decoded by the radio section interface  46  and is further transmitted to a user through the human interface section  47 . Also, during a period of transmitting a radio wave, the antenna  41  is connected to the transmitter  45  through the antenna switch  42 . The user inputs information that the user wants to transfer to a destination as a voice, character, or image using a microphone, keyboard, camera, or a like being connected to the human interface section  47 . The input information is transmitted to the radio section interface  46  where encoding and/or modulation are performed and is then transmitted to the transmitter  45 . In the transmitter  45 , a transmitting signal is up-converted to become a high-frequency wave by a signal fed from the local oscillator  44  and is then amplified and transmitted as a radio wave through the antenna switch  42  from the antenna  41 . 
       FIG. 2  is a diagram showing the antenna  41 , antenna switch  42 , local oscillator  44 , transmitter  45 , radio section interface  46 , and human interface section  47 , which are all taken from  FIG. 1 , and illustrates electrical configurations of main components of the transmitter  45  and radio section interface  46 . The radio section interface  46 , as shown in  FIG. 2 , is made up of a signal processing section  51  and an intermediate frequency (IF) wave section  52 . The signal processing section  51  is made up of a DSP (Digital Signal Processor) or a like and performs digital signal processing such as filtering on data to be transmitted (voice signal, image signal, or a like) output from the human interface section  47 . The intermediate frequency wave section  52  performs modulation and intermediate frequency wave amplification on a signal output from the signal processing section  51 . 
     The transmitter  45  includes a band-pass filter  53 , a mixer (MIX)  54 , a band-pass filter  55 , a buffer (BUFF)  56 , and a transmission power amplifier  57 . The band-pass filter  53  eliminates noises contained in a transmitting signal fed from the intermediate frequency wave section  52 . The mixer  54  up-converts a frequency of the transmitting signal to become a high frequency wave by using a reference frequency fed from the local oscillator  44 . The band-pass filter  55  eliminates noises contained in the transmitting signal fed from the mixer  54 . The buffer  56  receives the signal having been up-converted to be a high frequency wave at high input impedance and transmits the signal at low output impedance to the transmission power amplifier  57 . The transmission power amplifier  57  performs power amplification on the signal fed from the buffer  56  to use the signal as a transmission radio wave. 
     In the radio section interface  46 , “data to be transmitted” output from the human interface section  47  is input to the signal processing section  51  in which digital signal processing is performed on the “data to be transmitted” and is then modulated by the intermediate frequency wave section  52  in which amplification is performed on an intermediate frequency wave and is output as a transmitting signal. Noises contained in the transmitting signal, which have occurred at the time of the amplification performed on the intermediate frequency wave, are removed by the band-pass filter  53  in the transmitter  45 . The transmitting signal output from the band-pass filter  53  receives a reference frequency fed from the local oscillator  44  in the mixer  54  and its frequency is up-converted to become a high frequency wave. Noises contained in the transmitting signal output from the mixer  54 , which have occurred by high-frequency conversion, are removed by the band-pass filter  55 . The transmitting signal fed from the band-pass filter  55  is output through the buffer  56  to the transmission power amplifier  57 . The signal sent out from the buffer  56  is power-amplified by the transmission power amplifier  57  and is transmitted through the antenna switch  42  from the antenna  41  as a radio wave. 
       FIG. 3  is a circuit diagram for showing electrical configurations of main components of the power circuit  48  shown in  FIG. 1 , the transmission power amplifier  57  shown in  FIG. 3 , and a circuit block  58 . The transmission power amplifier  57 , as shown in  FIG. 3 , includes an amplifier (AMP)  71 , a capacitor  72 , an amplifier (AMP)  73 , a capacitor  74 , an amplifier (AMP)  75 , and a bias circuit  76 . Each of the amplifiers  71 ,  73 , and  75  is made up of a bipolar transistor, MOS transistor, or a like. The bias circuit  76  generates a bias voltage used to normally operate these amplifiers  71 ,  73 , and  75 . Each of the transmission power amplifier  57  and the circuit block  58  has a lower limit value of an operating voltage for its normal operations. In the transmission power amplifier  57 , a transmission signal RFIN to be employed in the TDMA communication method (for example, GSM method) in which a burst period and a non-burst period occur alternately in a repeated manner or to the TDD communication method is input to the amplifier  71 . The transmission signal RFIN is amplified by the amplifier  71  from which an output signal K is output. The output signal K fed from the amplifier  71 , after its DC (Direct Current) component has been intercepted by the capacitor  72 , is input to the amplifier  73  where it is amplified and is then output as an output signal M from the amplifier  73 . The output signal M, after its DC component has been intercepted by the capacitor  74 , is input to the amplifier  75  where it is amplified and a radio signal RFOUT as a transmission radio wave is output from the amplifier  75 . 
     The circuit block  58  includes various circuits other than the transmission power amplifier  57  shown in  FIG. 2  and is made up of, for example, a DC-DC converter circuit  81  and loads  82  other than the transmission power amplifier  57  and provides a tolerance of an operating voltage having a lowest limit value being higher than that of an operating voltage of the transmission power amplifier  57  and consumes power required for operational processing. The DC-DC converter circuit  81  boosts or lowers an output voltage of the power circuit  48 . The loads  82  other than the transmission power amplifier  57  are made up of, for example, power sources for a microcomputer, DSP, SIM card, memory, human interface devices (for example, a voice device, input/output device, image pick-up device or a like) in which the output voltage of the power circuit  48  is directly applied to loads  82  other than the transmission power amplifier  57  that operate at the output voltage of the power circuit  48  and a voltage obtained by boosting or lowering the output voltage of the power circuit  48  using the DC-DC converter circuit  81  is applied to those that do not operate at the output voltage of the power circuit  48  and require conversion of voltages. 
     The power circuit  48  is made up of a battery  59 , a power management circuit  60 , a battery charging circuit  61 , and a circuit mounting section  65 . The circuit mounting section  65  includes a control circuit  63 , an input capacitor  62  as a delay device, and an electrical double layer capacitor  64 . The battery  59  is, for example, a lithium ion battery and its discharging voltage range is generally from about 4.2V to about 2.5V. The battery  59  includes a single cell  91 , an internal resistor  92 , and a protective circuit  93  and a resistance of the internal resistor  92  is produced by an electrolyte and a combined resistance including electrode connecting resistance and/or charge movement resistance, or a like. The protective circuit  93  is made up of a transistor, thermistor, or a like and detects occurrence of overcharge, over-discharge, over-current, heating, or a like and insulates the battery  59  from loads. 
     The power management circuit  60  monitors an output voltage of the battery  59  and detects a residual capacity according to a reference for detection employed in the conventional technology shown in  FIG. 17  and, when the residual capacity becomes small and the output voltage becomes a specified level of reference having been set to be more than a lower limit value of an operating voltage of the circuit block  58 , a notification informing that the output voltage has dropped is provided by producing a control signal, for example, to display an alarm for charging. As shown in  FIG. 17 , when the output voltage of the battery  59  is, for example, about 4.2V, a residual capacity is at a full charge level and the battery  59  has a voltage enough to drive the transmission power amplifier  57  and the circuit block  58 . Also, when the output voltage of the battery  59  is, for example, about 3.7V, the residual capacity is at an intermediate level and the battery  59  has a voltage enough to drive the transmission power amplifier  57  and the circuit block  58 . Moreover, when the output voltage of the battery  59  is, for example, about 3.2V, the residual capacity is at a level that an alarm indicates a need for charging. At this point, though the battery  59  has a voltage enough to drive the transmission power amplifier  57 , since the output voltage of the circuit block  58  has reached a lower limit value (3.0V) of tolerance of the output voltage of the circuit block  58 , a state in which an operating voltage is in short supply occurs. The voltage of 3.2V is set as a terminating voltage for the battery  59 . 
     The battery charging circuit  61 , by being connected to an outside power source not shown, charges the battery  59  at a specified voltage and at a specified current based on a control signal fed from the power management circuit  60 . The input capacitor  62  is charged or discharged when a current to be consumed by the transmission power amplifier  57  rapidly increases (rises up) or decreases (falls down), and delays a rising edge or a falling edge of an output current of the battery  59  occurring at a rise time or a fall time of the burst period. 
     The control circuit  63  is made up of a p-channel MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) (hereafter called simply as a “pMOS”)  101 , a gate control block  102 , and a current control block  103 . The current control block  103  detects a drain current based on a voltage between a drain and a source of the pMOS  101  and transmits a control signal C to the gate control block  102  so that the drain current becomes a pre-set value. The gate control block  102 , based on the control signal C, produces a gate control voltage G used to control a resistance value between the drain and source of the pMOS  101 . In the pMOS  101 , a resistance between the drain and source is controlled based on the gate control voltage G and a drain current based on the resistance flows. 
     The control circuit  63  feeds an output current being limited to a pre-set current value from the battery  59  to the transmission power amplifier  57  and, when a voltage of the electrical double layer capacitor  64  becomes below a voltage of the battery  59  during the burst period, charges the electrical double layer capacitor  64  during the subsequent non-burst period until a voltage of the electrical double layer capacitor  64  becomes almost equal to a voltage of the battery  59 . Moreover, an output current (drain current of the pMOS  101 ) of the control circuit  63  is set to be a current value that can supply almost all power being able to be consumed in one frame cycle made up of one burst period and one non-burst period to the transmission power amplifier  57 . In the case of the GSM-type portable cellular phone, the one frame cycle is several milliseconds. Furthermore, the control circuit  63 , when power to be consumed in the transmission power amplifier  57  during the non-burst period is smaller than power that the control circuit  63  can supply, charges the electrical double layer capacitor  64  that has discharged during the burst period. 
     The electrical double layer capacitor  64  is made up of, for example, an electrostatic capacitor  111  and an internal resistor  112  and is charged by an output current of the control circuit  63  and accumulates power to feed it to the control circuit  63  and the transmission power amplifier  57 . The electrostatic capacitor  111  has capacitance of a few tens of mF or more and the internal resistor  112  has resistance of 500 mΩ or less. Also, the electrical double layer capacitor  64 , when power to be consumed by the transmission power amplifier  57  during the burst period is larger than power that can be supplied by the control circuit  63 , feeds power for replenishing by discharging. 
     The circuit mounting section  65  includes the input capacitor  62 , control circuit  63 , and electrical double layer capacitor  64 , in which a power source terminal  313  and a ground terminal  314  are mounted on an input side and a power source terminal  311  and a ground terminal  312  are mounted on an output side. 
       FIG. 4  is a diagram showing configurations of a circuit mounting section  65  shown in  FIG. 3 . The circuit mounting section  65 , as shown in  FIG. 4 , is made of a flexible printed circuit board (FPC board) for example in which the input capacitor  62  constructed so as to be of surface mounting type and the control circuit  63  are mounted and, since the electrical double layer capacitor  64  is mounted to one terminal of the circuit mounting section  65 , its thickness is 2 mm or less and a product of a length and a width is about 200 mm 2 . Moreover, to one terminal of the circuit mounting section  65  are mounted the power source terminal  313  and the ground terminal  314  and to another terminal of the circuit mounting section  65  are mounted the power source terminal  311  and the ground terminal  312 . 
       FIG. 5  is a diagram showing configurations of the electrical double layer capacitor  64  shown in  FIG. 4 . The electrical double layer capacitor  64 , as shown in  FIG. 5 , includes six pieces of unit cells  121  having a structure of double-layers made of thin sheets in which these units cells  121  are stacked in layer which make up a stacked cell  122  that can provide a withstand voltage and electrostatic capacity required as a power source for the transmission power amplifier  57 . Also, at an end portion of the unit cell  121  placed on an uppermost portion is mounted a positive electrode  123  and at an end of the unit cell  121  placed on a lowermost portion is mounted a negative electrode  124 . The stacked cell  122  is sandwiched between the insulating films  125  in a manner that the positive electrode  123  and the negative electrode  124  are exposed. 
       FIG. 6  is a diagram showing configurations of the unit cell  121  shown in  FIG. 5 . The unit cell  121 , as shown in  FIG. 6 , is made up of a current collector  131 , a separator  132 , an activated carbon layer  133 , and a gasket  134 . The current collector  131  serves as a positive pole or a negative pole and the separator  132  separates the positive pole from the negative pole. The activated carbon layer  133  accumulates a charge and is held by the gasket  134 . By forming a layer-like unit cell  121 , a capacitor is constructed based on a principle of a thin-sheet-shaped electrical double layer. The electrical double layer capacitor  64  has an electrostatic capacity being larger than that of a ceramic capacitor, aluminum electrolytic capacitor, tantalum electrolytic capacitor, or a like, and its electrostatic capacitor has for example a product of a length and a width being about 1000 mm 2 , a thickness being about 2 mm, capacity of 30 mF or more (withstand voltage: for example, 5V). On the other hand, an effective dimension of a clearance between an outer case and a component mounting portion in presently-available portable cellular phones is 2 mm or so in height and about 1500 mm 2  in area and, since a clearance that can be formed by the circuit mounting section  65  and electrical double layer capacitor  64  of the embodiment can fall within the above effective dimension employed in the presently-available portable cellular phones, mounting of a power circuit in the portable cellular phone can be achieved, without impairing portability of portable cellular phones, by using the circuit mounting section  65  and electrical double layer capacitor  64  of the embodiment of the present invention. 
       FIG. 7  is a time chart explaining operations of the power circuit  48  and the transmission power amplifier  57  shown in  FIG. 3 .  FIG. 8  is a diagram explaining an effect of lengthening a life of the battery  59  according to the first embodiment of the present invention.  FIG. 9  is also a diagram explaining the effect of lengthening the life of the battery  59  according to the first embodiment of the present invention. Operations of the portable cellular phone of the first embodiment are described by referring to  FIGS. 7 ,  8 , and  9 . 
     First, at the time t0, when a transmission burst period begins by a start of transmitting operations, a current consumed by the transmission power amplifier  57  rapidly increases from 0A to a current value IPA. A discharging current IDCG is fed from the electrical double layer capacitor  64  to the transmission power amplifier  57 . A current output from the battery  59  increases, in synchronization with starting of the transmission burst period, up to a current value IBmax being an upper limit value set by the control circuit  63 , however, there is a delay in the increase of the output current of the battery  59  by an action of absorbing a surge caused by discharging of the input capacitor  62 . This serves to suppress a fluctuation of the output voltage of the battery  59  due to the start of the transmission burst period. Then, the current with the value IDCG of the electrical double layer capacitor  64  is combined with the current with the value IBmax of the battery  59  and the combined current is fed as a current value IPA to the transmission power amplifier  57 . A voltage being applied from the electrical double layer capacitor  64  to the transmission power amplifier  57  drops by a voltage value ΔVRy from a voltage value VPA0 induced by a voltage drop determined by resistance of the internal resistor  112  and an amount of a discharged current of the electrical double layer capacitor  64 , in synchronization with starting of the transmission burst period. An output voltage of the battery  59  drops due to existence of a resistance component in series between the internal resistor  92  and the protective circuit  93  and lowers from a voltage value VB0 by a voltage value ΔVBRy. 
     During a period T1, that is, during the transmission burst period, since the transmission power amplifier  57  is continuing transmission operations, a consumed current remains constant at a level of the current value IPA. A discharging current (current with a value of IDCG) fed from the electrical double layer capacitor  64  is continuously fed to the transmission power amplifier  57 . The output current of the battery  59 , after the delay caused by the input capacitor  62  has disappeared, remains at a level of the current value IBmax set by the control circuit  63 . A current (IPA=IBmax+IDCG) obtained by combining a discharged current (current value IDCG) fed from the electrical double layer capacitor  64  with a discharged current (current with the value of IBmax) of the battery  59  is continuously fed as a current with the value of IPA to the transmission power amplifier  57 . A voltage being applied to the transmission power amplifier  57  from the electrical double layer capacitor  64  is lowered by a voltage value ΔVCy due to a voltage drop caused by discharging of the electrical double layer capacitor  64 . Therefore, a voltage being applied to the transmission power amplifier  57  at a terminating time of a period T1, since a decrease of a voltage with a value of ΔVRy occurring at the time t0 is added to a decrease of a voltage with the value ΔVCy, lowers by a voltage value ΔVPAy (=ΔVRy+ΔVCy) and therefore changes from a voltage value VPA0 to a voltage value VPA1. The output voltage of the battery  59 , due to a voltage drop corresponding to an electrostatic capacity component of the battery  59  induced by an output current with the value of IBmax, lowers by a voltage value obtained by adding a voltage value ΔVBCy to a decrease ΔVBRy of a voltage value at the time t0. 
     At the time t1, when the transmission burst period ends after termination of the transmitting operation, a current consumed by the transmission power amplifier  57  rapidly lowers from the current value IPA to almost 0A. In the electrical double layer capacitor  64 , a discharging state is switched to a state in which charging begins at a current having a current value ICHG. At this point, an output current of the battery  59  remains at a level of the current value IBmax having been set by the control circuit  63  and the electrical double layer capacitor  64  is charged at a current with the value of ICHG and a current with the value of IB0 is supplied to the circuit block  58 . In this case, a following relational equation holds:
 
 IBmax=ICHG+IB 0.
 
A voltage being applied from the electrical double layer capacitor  64  to the transmission power amplifier  57  is boosted by a voltage value ΔVRy from a voltage with a value of VPA1 in synchronization with ending (falling edge) of the transmission burst period in response to an increase in voltage determined by a resistance of the internal resistor  112  in the electrical double layer capacitor  64  and by an amount of a charged current of the electrical double layer capacitor  64 . Due to a voltage drop being equivalent to a voltage value ΔVBRy occurring at the time t0 and due to an additional voltage drop corresponding to an electrostatic capacity component of the battery  59  induced by an output current with the value of IBmax, the output voltage of the battery  59  has further lowered.
 
     During the period T2, that is, during the receiving non-burst period, since the radio wave receiving section of the portable cellular phone is continuing signal receiving operations and the transmission power amplifier  57  does not operate, currents consumed by the transmission power amplifier  57  are almost 0A. The electrical double layer capacitor  64  is still in a state where it is being charged at a current with the value ICHG. The output current of the battery  59  remains at a level of the current value IBmax. The voltage to be fed from the electrical double layer capacitor  64  to the transmission power amplifier  57  is boosted exponentially since it is charged at a current with the value ICHG. The output voltage of the battery  59  lowers by a voltage value ΔVBCy due to a voltage drop corresponding to an electrostatic capacity component of the battery  59  induced by an output current with the value IBmax. Therefore, an output voltage of the battery  59  occurring at the end time of the period T2 lowers, due to a voltage drop of ΔVBCy in addition to a voltage drop of ΔVBRy occurring at the time t0, by a voltage value ΔVBy (=ΔVBRy+ΔVBCy) and from a voltage value VB0 to a voltage value VB1. 
     At the time t2, that is, during the receiving non-burst period, since the receiver  43  is continuing radio wave receiving operations and the transmission power amplifier  57  does not operate, currents consumed by the transmission power amplifier  57  are almost 0A. In the electrical double layer capacitor  64 , a charging current begins to decrease from a level of the current value ICHG. The output current of the battery  59  begins to decrease from a level of the current value IBmax in synchronization with decreasing of the charging current of the electrical double layer capacitor  64 . At this point, there is a delay in the decrease (falling time) of the output current of the battery  59  caused by an action of absorbing a surge induced by charging of the input capacitor  62 . A voltage being applied from the electrical double layer capacitor  64  to the transmission power amplifier  57  is gradually boosted since the electrical double layer capacitor  64  is charged at a current being smaller than the current value ICHG. The output voltage of the battery  59  is gradually boosted since the output current of the battery  59  is limited due to existence of a resistance component by serial connection between the internal resistor  92  and the protective circuit  93 . 
     During the period T3, that is, during the receiving non-burst period, since the receiver  43  is continuing radio wave receiving operations and the transmission power amplifier  57  does not operate, currents consumed by the transmission power amplifier  57  are almost 0A. The voltage of the electrical double layer capacitor  64  is approaching the output voltage of the battery  59  and charging is being completed. This causes the charging current to come near 0A. The output current of the battery  59  decreases, in synchronization with lowering of the charging current of the electrostatic double layer capacitor  64 , from a level of the current value IBmax and comes near to the load current (current with the value of IB0) of the circuit block  58 . A voltage being applied from the electrical double layer capacitor  64  to the transmission power amplifier  57 , since the electrical double layer capacitor  64  is charged, gradually comes near to an output voltage of the battery  59 . The output voltage of the battery  59 , as its output current decreases, is boosted exponentially based on a time constant of an electrostatic capacity and a resistance component of the battery  59 . 
     At the time t3, that is, during the receiving non-burst period, since the radio wave receiving section is continuing radio wave receiving operations and the transmission power amplifier  57  does not operate, currents consumed by the transmission power amplifier  57  are almost 0A. In the electrical double layer capacitor  64 , the charging has been completed and a charging current has become 0A. The battery  59 , since charging of the electrical double layer  64  has been completed, feeds a current with the value of IB0 to the circuit block  58 . A voltage being applied from the electrical double layer capacitor  64  to the transmission power amplifier  57 , since charging of the electrical double layer capacitor  64  has been completed, becomes almost equal to an output voltage of the battery  59 . The output voltage of the battery  59  becomes commensurate in voltage with a current with the value of IB0 to be fed to the circuit block  58 . 
     During the period T0, that is, during the receiving non-burst period, since the radio wave receiving section is continuing radio wave receiving operations and the transmission power amplifier  57  does not operate, currents consumed by the transmission power amplifier  57  are almost 0A. In the electrical double layer capacitor  64 , charging has been completed and its charging current still remains 0A. The output voltage of the battery  59 , since charging of the electrical double layer capacitor  64  has been completed, remains at a level of a current with the value of IB0 to be fed to the circuit block  58 . The voltage being applied from the electrical double layer capacitor  64  to the transmission power amplifier  57 , since charging of the electrical double layer capacitor  64  has been completed, remains almost equal to the output voltage of the battery  59 . The output voltage of the battery  59  remains commensurate in voltage with a current with the value of IB0 to be fed to the circuit block  58 . Then, these voltages and currents are again put into the state that has occurred at the time t0 and, thereafter, same operations are repeated in order of the time t0, period T1, time t1, period T2, time t2, period T3, time t3, period T0, time t0,. . . . 
     In the portable cellular phone of the embodiment, a life of the battery  59  is judged based on a lowest voltage value VB1 occurring during the transmission burst period. A simulation value of the voltage value ΔVBy used to obtain the above voltage value VB1, if the following simulation conditions are used, becomes about 90 mV being one third or less of a conventional value of 300 mV. 
     Simulation conditions; 
     Resistance of the internal resistor  92 ; 150 mΩ 
     Transmission burst period; 0.5 msec 
     Receiving non-burst period; 4.5 msec 
     Output current of the battery  59 ; 
     Ibmax; 0.7 A. 
     IB0; 0.1 A. 
     Discharging current of electrical double layer capacitor  64 ; 
     IDCG=1.4A 
     ΔVBRy=0.15·(0.7−0.1)=0.09V 
     ΔVBCy=(0.0005·0.7)/electrostatic capacity of the battery  59 &gt;0 
     ΔVBy=ΔVBRy+ΔVBCy&gt;9 mV 
     ∴ΔVBy&lt;&lt;ΔVBx 
     That is, in the portable cellular phone of the embodiment, the output of the battery  59  does not become 3.2V or less (terminating voltage) during the transmission burst period until it becomes 3.3V during the receiving non-burst period, the battery  59  is usable until its output voltage becomes lower than that in the conventional case and its life can be lengthened. 
     Next, a life of the battery  59  being put at ambient temperature being at room temperature of about 20° C. is described by referring to  FIG. 8 . In  FIG. 8 , a curve “A” shows movement of the voltage value VB0 (=VPA0) of the battery  31  occurring at the time tα employed in the conventional case shown in  FIG. 16  and movement of the voltage value VB0 of the battery  59  occurring at the time t0 shown in  FIG. 7 . The curve “B” shows movement of the voltage value VB1 of the battery  59  occurring at the time t2 shown in  FIG. 7 . The broken-line curve C shows movement of the voltage value VB1 (=VPA1) of the battery  31  occurring at the time tα shown in  FIG. 16 . The dotted-line curve D shows movement of an operating voltage VPA1 of the transmission power amplifier  57  occurring at the time t1 shown in  FIG. 7 . 
     In the conventional case, the output voltage of the battery  31  occurring during the transmission burst period moves as shown by the broken-line curve C and, at the time L1, the life of the battery  31  is judged to have been over. In the embodiment, the output voltage of the battery  59  occurring during the transmission burst period moves as shown in the curve B and, at the time of L2, the life of the battery  59  is judged to have been over and the life of the battery  59  being longer than that of the battery  31  can be provided. Moreover, by properly setting the current value IBmax, resistance of the internal resistor  112  of the electrical double layer capacitor  64 , and electrostatic capacity of the electrostatic capacitor  111 , a time point at which an operating voltage VPA1 reaches a lower limit value of the operating voltage of the transmission power amplifier  57  comes after the time L2, as shown in the dotted-line curve D. This makes it possible to provide the power circuit for the transmission power amplifier being well matched in terms of outer size and manufacturing cost. 
     Next, a life of the battery  59  being put at ambient temperature being below 0° C. is described by referring to  FIG. 9 . Generally, in the case of a battery operating by an electrochemical reaction, its internal resistance increases with a decrease of ambient temperatures. Therefore, an output voltage of the battery is lowered with an increase in internal resistance. On the other hand, a terminating voltage of a battery  31  being set in the power management circuit  60 , as shown in  FIG. 9 , is set to be constant irrespective of ambient temperatures and, therefore, in a low-temperature environment, a life of the battery  31  is remarkably shortened. Conventionally, an output voltage of the battery  31  being put in a low-temperature occurring during the transmission burst period moves as shown in the broken-line curve C and, at the time L1LT, the life of the battery  31  is judged to have been over and is remarkably shortened compared with a case where the battery is put at room temperature. In the embodiment of the present invention, however, an output voltage of the battery  59  occurring during the transmission burst period, as shown by the curve B, since a voltage drop is small during the transmission burst period, at the time L2LT, the life of the battery  59  is judged to have been over and the life is not shortened extremely unlike in the case of the battery  31 . 
     Thus, in the first embodiment, since a output current having been limited to become a current value set in advance is supplied from the battery  59  to the transmission power amplifier  57  and the electrical double layer capacitor  64  is charged and power is accumulated under control of the control circuit  63  and, since power is fed from the electrical double layer capacitor  64  to the control circuit  63  and the transmission power amplifier  57 , even if power consumed by the transmission power amplifier  57  increases during the burst period, a drop in the output voltage of the battery  59  is small. As a result, time required for the output voltage to reach a terminating voltage of the battery  59  is made longer and a life of the battery  59  is lengthened. Moreover, even if the battery  59  is put under a low-temperature environment and its internal resistance increases, shortening of the life of the battery  59  can be avoided. Furthermore, since the electrical double layer capacitor  64  is so constructed as to have thin-sheet shaped unit cells  121  and so that these unit cells  121  are stacked in layer, it can be mounted on a folding-type portable cellular phone without causing an increase in thickness. 
     Second Embodiment 
       FIG. 10  is a schematic block diagram showing electrical configurations of a portable cellular phone according to a second embodiment of the present invention. In  FIG. 10 , same reference numbers are assigned to corresponding parts having same functions as the first embodiment shown in  FIG. 1 . The portable cellular phone of the embodiment has, instead of a radio section interface  46  and a human interface section  47  employed in the first embodiment shown in  FIG. 1 , a radio section interface  46 A and human interface section  47 A to each of which new functions are added and further newly includes a PDA (Personal Digital Assistance) functional block  141 . In the PDA functional block  141 , an operating system (OS) is mounted and software is installed. Each of the radio section interface  46 A and human interface section  47 A, in addition of the functions of the radio section interface  46  and the human interface section  47 A employed in the first embodiment, has a function of swapping specified data with the PDA functional block  141 . Other components shown in  FIG. 10  have the same functions as the first embodiment shown in  FIG. 1 . 
     The portable cellular phone of the second embodiment performs, in addition to operations performed by the portable cellular phone of the first embodiment, operations of, for example, scheduling management and computation. 
     Third Embodiment 
       FIG. 11  is a schematic block diagram showing electrical configurations of a portable cellular phone according to a third embodiment of the present invention. The portable cellular phone of the third embodiment has, instead of a human interface  47  shown in  FIG. 1 , a digital interface  142 . The digital interface  142  is connected through, for example, a USB (Universal Serial Bus) port or a PC (Personal Computer) card slot to a personal computer  143 . The PC card slot adheres to the PCMCIA (Personal Computer Memorycard International Association). 
     In the portable cellular phone of the third embodiment, in ordinary cases, power is supplied from the personal computer  143  and, if the personal computer  143  is, for example, a battery-driven notebook PC, by using a power circuit  48 , communications time according to the TDMA-system can be extended. Moreover, when a power source such as a USB-type bus power source in which a limitation is imposed on an output current is employed as a power source for a transmitter  45 , in some cases, a power source current exceeds the limited power source current during a transmission burst period at the time of communications which impairs normal communications. In this case, by using the power circuit  48  of the invention, an amount of the power source current during the transmission burst period is reduced, thus enabling smooth communications. 
     Fourth Embodiment 
       FIG. 12  is a diagram illustrating configurations of a circuit mounting section  65 A of a power circuit according to a fourth embodiment of the present invention. In  FIG. 12 , same reference numbers are assigned to corresponding parts having same functions as the first embodiment shown in  FIG. 1 . The circuit mounting section  65 A is placed instead of the circuit mounting section  65  shown in  FIG. 3  and has electrical double layer capacitors  64 A and  64 B on its both sides. To obtain specified electrical characteristics, these electrical double layer capacitors  64 A and  64 B are connected to each other serially or in parallel. 
     Fifth Embodiment 
       FIG. 13  is a diagram illustrating configurations of a circuit mounting section  65 B in a power circuit according to a fifth embodiment of the present invention. In the circuit mounting section  65 B of the fifth embodiment, as in the case of a circuit mounting section  65  shown in  FIG. 4 , an electrical double layer capacitor  64 C is mounted on one end of the circuit mounting section  65 B. 
       FIG. 14  is a diagram illustrating configurations of the electrical double layer capacitor  64 C of  FIG. 13 . In  FIG. 14 , same reference numbers are assigned to corresponding parts having same functions as the first embodiment shown in  FIG. 5 . The electrical double layer capacitor  64 C, as shown in  FIG. 14 , includes, for example, three pieces of unit cells  121  in which these units cells  121  are stacked in layer which make up stacked cells  122 A. The stacked cells  122 A are placed on a cell-to-cell coupling plate  126  for connection among them. By configuring as above, the electrical double layer capacitor  64 C can be made thinner than an electrical double layer capacitor  64  shown in  FIG. 5 . 
     It is apparent that the present invention is not limited to the above embodiments but may be changed and modified without departing from the scope and spirit of the invention. For example, if a primary cell is used as the battery  59  in the configurations shown in  FIG. 3 , the battery charging circuit  60  is removed. Also, the circuit block  58  in  FIG. 3  may be any type of the circuit block so long as it can perform specified operations with specified power consumption. Moreover, in the above embodiments, examples in which the present invention is applied to portable cellular phones are described, however, the present invention may be applied to portable communication device of all types such as a transceiver or a like.