Battery capacity detector

Abstract: In a communication equipment which uses a battery as the power supply, when a controller increases the transmission power at a transmitter corresponding to a drop in the electric field intensity, the controller lowers, accompanying that operation, a reference voltage from a reference voltage source which is used for comparison with the battery voltage for the purpose of detecting a drop in the battery capacity. Therefore, even when the battery voltage is dropped due to an increase in the transmission output, the reference voltage is also lowered correspondingly, so that there will not occur an erroneous detection of drop in the battery capacity due to the drop in the battery voltage.

Description: The present invention relates to a communication device comprising a battery capacity detector, and more particularly to a device for accurately detecting a capacity drop in the power supply batteries used for communication equipment. In a portable equipment for mobile communication such as a portable telephone, batteries are generally used for its power supply. Therefore, the normal operation of the equipment cannot be secured if the battery power is deteriorated. For that reason, there have been proposed devices which urge the user the replacement or recharging of the batteries by issuing an alarm when the battery power, for example, the battery voltage, dropped to below a specified voltage level. A cordless telephone system having such an alarm function is disclosed in, for example, Japanese Patent Laid-Open Application No. 354230/1992 (JP-A-H04-354230). This cordless telephone system includes a master set and a slave set which is carried for use. In the slave set, a battery capacity detector detects the voltage of the batteries which supply power to a communication part which includes a radio part, a modem, a control part, and the like. When the detected battery voltage drops to below a value prescribed in advance, the control part displays in a display part a signal that indicates the drop of the remaining capacity, and notifies the information to the master set via a communication part. Upon receipt of this signal the master set issues an alarm. Now, a radio data transmitter, such as a teleterminal, has a function of controlling the voltage of transmission signals in response to the communication circumstances. For example, the radio data transmitter has a function of monitoring the electric field intensity of a received radio signal. When the electric field intensity is dropped, the transmission voltage is increased successively in accordance with the electric field intensity in order to perform all the time a suitable data transmission corresponding to the electric field intensity. However, when the detector for detecting the drop of the battery voltage as described in the above is installed in the radio data transmitter, the load in the circuit supplied with the power is increased with the increase in the transmission power, causing a drop in the battery voltage. Because of this, in a type of device which detects the battery capacity based on the battery voltage, a drop in the battery voltage is detected when the transmission power is increased, and an alarm is issued sometimes in spite of the fact that a sufficient battery capacity is remaining. Similarly, if one attempts to equip the above-mentioned cordless telephone system with a function which, for example, controls the transmission power in response to the electric field intensity of the received signal, the battery voltage is dropped temporarily due to the increase in the transmission power. Therefore, the system judges the situation as a drop in the battery capacity, which results in a problem of erroneous display or alarm issuance. Furthermore, when the battery voltage is dropped temporarily due not only to a change in the transmission power, but also to a variation in the battery load during communication, a similar erroneous detection of the battery capacity may happen. From EP-A-0 423 918 a battery voltage discriminator circuit is known. The battery voltage discriminator circuit for an apparatus having a battery and a plurality of loads which are driven by the battery and operate under various kinds of load conditions is disclosed. When the output voltage of said battery means drops under a predetermined reference voltage, the circuit generates a signal indicative of the voltage drop. The circuit has a reference voltage setting circuit for setting the reference voltage to one of predetermined values, which corresponds to the kind of the current load condition, and a reference voltage change circuit for activating the reference voltage setting circuit for a period of time in response to the change in the kind of current load condition. EP-A-0 416 589 relates to a computer having a function of detecting a low-battery state. A battery is used as a power source for a computer apparatus. A reference voltage for determining a low-battery state of the battery is set in consideration of not only the current value of a current output from the battery but also the temperature of the battery. An output voltage from the battery is compared with the reference voltage, thereby determining whether or not the battery is in the low-battery state. DE-A-25 11 681 discloses a device for indicating the charge state of a battery with changing loads, in particular, for a transmitter/receiver device. During transmitting the output voltage of the battery is compared with the voltage during the receiving. When the difference between the voltage during receiving and during transmitting is higher than a characteristic value the decharged state of the battery is indicated. EP-A-0 512 711 relates to a device for measuring the quantity of electricity stored in a battery of a transceiver comprising a voltage detection circuit for detecting the battery voltage, an A/D converter for converting the detected battery voltage into data, and a calculation circuit for calculating the quantity of battery electricity from the voltage data. The A/D converter operates to sample the battery voltage during the period when transmission and receiption are off and thus when the battery voltage does not pulsate, whereby the battery electricity can be evaluated accurately. It is therefore an object of this invention to provide a communication device and method capable of detecting the drop in a battery capacity more accurately irrespective of the variations in the battery load. Another object of this invention is to provide a communication device and method capable of detecting accurately the drop in the battery capacity irrespective of the changes in the transmission power of a transmitter. The objects are achieved by the features of the claims. In a communication device, it is desirable to have a function of detecting the battery capacity based on the battery voltage, and of urging the user to replace or recharge the battery when the battery voltage dropped to below a voltage where the communication device begins to fail to perform the normal operation. Therefore, it is desirable to designate a voltage value at which the communication device no longer performs its normal operation as the reference value, and compare the detected battery voltage with this reference value. However, the battery voltage drops temporarily due to changes in the communication circumstances, for example, an increase in the transmission power or the battery load. Therefore, the comparison of the battery voltage with the reference value results in the indication of a drop of the battery voltage to below the reference value, giving rise to the notification of this information to the user. In view of such problems, the battery capacity detector according to the present invention includes a detector which detects the battery voltage, a comparator which compares a detected battery voltage with a predetermined reference, and a controller which varies the predetermined reference value in response to a battery load. In a communication equipment in which the transmission power is controlled according to the communication circumstances, it is preferable to provide the communication equipment with a means of detecting the transmission power and a means of varying the reference voltage value in response to the detected transmission power. For example, a change in the transmission power may be detected by a change in the electric field intensity of the received signal. Or, the transmission power may be controlled based on the AGC signal in the receiving system of the communication equipment. According to this invention, when the battery voltage drops due to an increase in the battery load, the reference voltage is arranged to drop also in response to the drop in the battery voltage, so that there will not occur an erroneous detection of the battery capacity drop. Moreover, even when the battery voltage drops due to an increase in the transmission power at the time of drop in the electric field intensity of the received signal, the drop in the battery voltage is arranged not to be detected as a voltage drop, by lowering the reference voltage accompanying the increase in the transmission power. Therefore, the erroneous detection of the battery capacity drop can be prevented. The above and other objects, features and advantages of this invention will become more apparent from the following detailed description taken with the accompanying drawings in which: FIG. 1 is a block diagram of a communication device which is a preferred embodiment of a battery capacity detector according to the present invention; FIG. 2 is a block diagram of a preferred embodiment of the controller shown in FIG. 1; FIG. 3 is a block diagram of another preferred embodiment of the controller shown in FIG. 1; FIG. 4 is a block diagram of another embodiment of the present invention; and FIG. 5 is a block diagram of yet another embodiment of the present invention. In the drawings, the same reference numerals denote the same structural elements. FIG. 1 is a block diagram of a communication device, preferably a portable telephone, which has a first preferred embodiment of a battery capacity detector according to the present invention. During reception, a receiver 2 converts a radio signal received by an antenna 1 to a received intermediate frequency (IF) signal. An automatic gain controller (AGC) 3 controls the level of the received IF signal to a predetermined level and supplies a level-controlled IF signal to an amplifier 4. The amplifier 4 amplifies the level-controlled IF signal to obtain an amplified received IF signal, and outputs the amplified received IF signal to an IF part (not shown). On the other hand, during transmission, an amplifier 5 amplifies a transmitting IF signal which is input from the IF part. A transmitter 6 transmits a transmitting radio frequency (RF) signal, obtained by converting an amplified transmitting IF signal, via the antenna 1. The transmitter 6 has the function of varying the transmission power of the transmitting RF signal. A controller 7 is supplied from the AGC 3 with an AGC signal which is closely related to the electric field of the received signal, and outputs a transmission power control signal which varies the transmission power at the transmitter 6. A battery 8 is a power supply for driving the various parts within the telephone set. The voltage of the battery 8 is converted in an A/D converter 9 to a digital signal that corresponds to the voltage. This digital signal is input to a controller 18. The controller 18 compares the input battery voltage with a reference voltage. When the battery voltage dropped to below the reference voltage, the controller 18 causes a battery capacity display 10 to display the drop of the battery capacity, or an alarm 11 to issue an alarm. As will be described later, the reference voltage is made variable corresponding to the level of the AGC signal. FIG. 2 is a block diagram of a preferred embodiment of the controller 18 shown in FIG. 1. A reference voltage source 12 is connected in series with a plurality of resistors R1 to Rn. A plurality of voltages V1 to Vn obtained by dividing the reference voltage are taken out from the junctions of the resistors R1 to Rn, and the plurality of voltages V1 to Vn are input to a selector 13. A decision circuit 19 inputs an AGC signal from the AGC 3, and outputs a select signal which selects one out of the plurality of voltages in response to the level of the AGC signal. The selector 13 selects one out of the plurality of different voltages V1 to Vn in response to the select signal as described later. One of the voltages selected by the selector 13 is converted to a digital signal in an A/D converter 14, and is supplied to one of the input nodes of a comparator 15. To the other input node of the comparator 15 is input the output of the A/D converter 9 connected to the battery 8. The comparison output of the comparator 15 is supplied to a driving circuit 16 which drives the battery capacity display 10 and the alarm 11. In the portable telephone shown in FIG. 1, when the communication state is deteriorated by, for example, the drop of the electric field intensity of the received signal, the reception level at the receiver 2 goes down, so that the level of the AGC signal from the AGC 3 goes up. Therefore, upon receipt of the AGC signal, the controller 7 sends the transmission power control signal to the transmitter 6 to execute the control of the increase in the transmission power of the transmitting RF signal from the transmitter 6. Then, the load of the battery 8 is raised due to the increase in the transmission power, and the voltage of the battery 8 goes down. On the other hand, in the controller 18, the selector 13 selects one of the plurality of divided voltages V1 to Vn of the reference voltage source 12 based on the level of the AGC signal. In other words, the selection is carried out, based on the electric field intensity, or on the transmission power which is closely related to the electric field intensity. Preferably, a voltage, which is roughly inversely proportional to the transmission power, is selected in the selector 13 and is output as a reference voltage. The selected reference voltage, i.e., one of the divided voltages, is input to the comparator 15 after being converted to the digital signal by the A/D converter 14. This signal is compared in the comparator 15 with the voltage of the battery 8 which is converted to a digital signal by the A/D converter 9. As a result, if the voltage of the battery 8 is found to be lower than the selected reference voltage, a driving signal which drives the battery capacity display 10 and the alarm 11 is supplied to the driving circuit 16 to display and issue an alarm that the battery capacity has dropped. Since, the battery load is raised accompanying the increase in the transmission power, the voltage of the battery 8 gces down temporarily. However, at the same time, a voltage lower than the original reference voltage is also selected as the selected reference voltage, as a result of the increase in the transmission power. Therefore, even when the battery voltage drops due to the increase in the transmission power, the battery voltage in the comparator 15 does not go to a level below the selected reference voltage, avoiding the erroneous detection of the drop in the battery capacity. Moreover, the selector 13 selects a voltage which corresponds to the extent of increase in the transmission power as the selected reference voltage so that it is possible to vary the reference voltage by following the change in the transmission power. Therefore, a temporary drop in the battery voltage will not be judged as a drop in the battery capacity, and it is possible to accurately detect the battery capacity and issue a correct alarm all the time. FIG. 3 is a block diagram of another embodiment of the controller 18. In FIG. 3, a plurality of values TH1 to THn of the reference voltage corresponding to a plurality of different transmission powers are stored in advance in a memory 17. Either one of these stored reference values TH1 to THn is selected based on the level of the AGC signal in the selector 13, and supplied to one of the input nodes of the comparator 15. The value of the digital signal obtained in a manner similar to the above embodiment by converting the voltage of the battery 8 with the A/D converter 9 is supplied to the other input node of the comparator 15. Therefore, also in this embodiment, the controller 7 recognizes the electric field intensity based on the AGC signal, and accordingly controls the transmission power. At the same time, the selector 13 in the controller 18 reads from the memory one of the reference values corresponding to the transmission power based on the AGC signal, and uses the selected reference voltage as the reference voltage in the comparator 15. Consequently, even when the battery voltage drops temporarily due to an increase in the transmission power, the reference voltage value is reduced simultaneous with the drop, so that erroneous detection of this state as a drop in the battery capacity and an erroneous issuance of alarm will not take place. In the first embodiment of the controller 18, the reference voltage is selected by the selector in a stepwise manner. However, a constitution may be adopted by which a continuously varying reference voltage is output, and supplied to the comparator. For example, the plurality of resistors R1 to Rn may be replaced by a variable resistor, and may control the resistance of the variable resistor in response to the select signal which is based on the AGC signal. Moreover, in the above embodiments, the transmission power is controlled in response to the electric field intensity, so that the reference voltage is varied by utilizing the AGC signal which is closely related to the transmission power. However, when the transmission power is controlled by some other factor, for example, in a device whose transmission power is controlled based on the error rate or the like, the system may be constituted so as to change and control the reference voltage by directly utilizing the transmission power information. For example, as shown in FIG. 4, the reference voltage may be controlled based on a transmission power control signal from the controller 7. In that case, the transmission power control signal instead of the AGC signal is supplied to the decision circuit 19 shown in FIG. 2 or 3. Since the remaining configuration and operation of the device shown in FIG. 4 are the same as those of the device shown in FIG. 1, a further description will be omitted. Here, the controller 7 controls the transmitter 6 in response to the AGC signal, but the controller 7 may independently control the transmitter 6 without responding to the AGC signal. Furthermore, when the battery load is varied by some other factor regardless of the transmission power, this invention may be provided with a detector for detecting the load, and the device may be constructed so as to vary and control the reference voltage in response to the extent of the load. For example, as shown in FIG. 5, a resistor R is inserted between the battery 8 and the A/D converter 9, and the current flowing in the resistor R is detected by an ammeter 20, a current value detector, or the like. The detected current value is supplied to the decision circuit 19 shown in FIG. 2 or 3. The decision circuit 19 stores in advance several threshold values, and the detected current value is compared with these threshold values. According to the result of the comparison, the decision circuit 19 sends a select signal to the selector 13 indicating to select an adequate reference voltage. As in the above, by varying the reference voltage in response to the load on the battery, in a receiver having the battery saving function, it is possible to prevent an erroneous battery capacity detection. As described in the above, according to the present invention, in detecting the battery capacity by comparing the voltage of the battery used as a power supply with a reference voltage, the reference voltage with which the detected battery voltage is compared is made to vary in response to the battery load. Since the communication device is so arranged as to lower the reference voltage in response to a drop in the battery voltage caused by an increase in the battery load, the comparison of these voltages will not lead to the judgment of a drop in the battery capacity, and hence an erroneous detection of the battery capacity can be prevented. In addition, in a communication equipment whose transmission power is varied and controlled in response to the communication circumstances, according to the present invention in which the reference voltage is varied in response to the transmission power, even when the battery voltage is dropped due to an increase in the transmission power, the reference voltage is lowered accompanying the increase in the transmission power. Therefore, a detection result indicating that the battery capacity is dropped will not be output, and an erroneous detection of the drop in the battery capacity can be prevented. In this way, erroneous detection of the battery capacity due to variations in the load, operating conditions, or the like can be avoided, so that an accurate grasping of the remaining capacity of the battery is made possible, giving rise to an effect which ensures an accurate issuance of the battery alarm.

Claims: A communication device comprising: power supply means (8); detection means (9) for detecting a supply voltage of said power supply means (8); comparison means (15) for comparing said supply voltage with a reference value; varying means (18) for varying said reference value in response to a load on said power supply means (8); characterized in that said varying means (18) is adapted for varying said reference value in response to an AGC-signal which is generated by an AGC circuit (3) connected to a receiver (2) of said communication device and is supplied to a transmitter (6) of said communication device for controlling a transmission output power in response to said AGC-signal. The communication device as claimed in claim 1, wherein said varying means (18) continuously increases and decreases said reference value in response to an increase or a decrease in said load. The communication device as claimed in claim 1, wherein said varying means (18) comprises: generating means (12) for generating a plurality of reference values; and selection means (13) for selecting one of said plurality of reference values as said reference value in response to said load. The communication device as claimed in claim 1, 2 or 3, further comprising: a first control means (7) for controlling an output level of a transmitting signal of said transmitter (6). The communication device as claimed in any one of claims 1 to 4, further comprising: informing means (10, 11); and driving means (16) for driving said informing means (10, 11) when said power supply voltage is lower than said reference value. A method for controlling a detection of a remaining capacity of a battery (8) in a communication device, the method comprising the steps of: detecting a battery voltage of said battery (8); selecting a reference value in response to a load on said battery (8); comparing said battery voltage with a selected reference value; characterized by selecting said reference value in response to an AGC-signal which is generated by an AGC circuit (3) connected to a receiver (2) of said communication device and is supplied to a transmitter (6) of said communication device for controlling a transmission output power in response to said AGC-signal. The method as claimed in claim 6, the method further comprising the step of: informing a user about status when said battery voltage is lower than said selected reference value. Method as claimed in claims 6 and 7, the method comprising the steps of: supplying a plurality of reference values; and selecting one of said plurality of reference values.

Inventors: KANNO YUKIHIRO, YOSHIDA TOSHIO, KANNO, YUKIHIRO, YOSHIDA, TOSHIO, KANNO, YUKIHIRO, C/O NEC CORPORATION, YOSHIDA, TOSHIO, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1995
Main classification: G01R31
IPC codes: G01R19, H04M1, H04B7, H02J7, G01R31