BATTERY-POWERED MOBILE COMMUNICATIONS APPARATUS HAVING TRANSMITTER RESET FUNCTION

Abstract: The voltage level b of a battery 18 supplying a transmitter 16 is sensed by a reset voltage detector 1 which switches a transmitter on/off controller 3 to the OFF state if the battery voltage b falls below a predetermined level within a predeter­ mined time interval T o measured, by a timer 4 and compared by a time decision circuit 5, starting at the beginning of a trans­ mitter turning-on signal a. If the detected voltage fall occurs af­ ter T o , the controller 3 keeps the transmitter 16 in operation unless the output d from an instantaneous voltage drop detec­ tor 2 determines that the detected voltage fall is not an instan­ taneous, i.e. short term, voltage fall.

Description: The present invention relates to a mobile communications apparatus comprising a load circuit to which a DC voltage is supplied from a DC power source; reset voltage detector means for generating a reset signal for turning off said load circuit when said DC voltage falls below a predetermined level and a reset release signal for turning on said load circuit when said DC voltage returns to or above said predetermined level; and means for detecting whether or not a change in said DC voltage is a sustained drop. Mobile communications apparatuses when battery-powered have a transmitter reset function because, when the battery output falls below a prescribed level, the transmitter is susceptible to such abnormalities as output interruption and radiation of radio waves at unlicensed frequencies. This reset function monitors the output level of the battery, and turns off the transmitter when the output falls below the prescribed level. As the battery deteriorates, its output level transiently falls off steeply when the transmitter is turned on, and the reset function is actuated to turn off the transmitter. As soon as the transmitter is turned off, the output level of the battery is restored relatively quickly. This restoration releases the reset function, and an instantaneous drop detector circuit in the apparatus judges the transient fall of the battery's output level to be an instantaneous drop. Consequently the transmitter is turned on again in response to the release of the reset function and the action of the instantaneous drop detector circuit. The reactuation of the transmitter causes a steep fall in the battery's output level again, and the aforementioned process is repeated. Thus the transmitter is turned on and off repeatedly, making normal communication impossible. US-A-4509201 describes a mobile wireless telephone apparatus comprising a load circuit to which a DC voltage is supplied from a DC power source, and reset voltage detector means for generating a reset signal for turning off the load circuit when the DC voltage falls below a first predetermined level and a reset release signal for turning on the load circuit when the DC voltage returns to or above the predetermined level. The apparatus also has means for detecting a fall sustained to below a lower second level and for turning off further load circuitry if such a fall is detected. The further load circuitry is turned on again if the DC voltage subsequently moves above the second predetermined level. GB-A-1424550 describes means for detecting a sustained voltage drop in a power supply circuit by comparing the duration of a voltage drop below a threshold with predetermined time periods. US-A-4471492 describes a radio transceiver with means for limiting the transmission time when the power supply voltage is below a threshold. An object of the present invention, therefore, is to provide a battery-powered mobile communications apparatus having a reset function such that its transmitter can correctly operate when its battery has deteriorated. Another object of the invention is to provide a DC-powered mobile communications apparatus free from the undesirable repetition of the transmitter's turning on and off when the DC power source has deteriorated. Still another object of the invention is to provide a DC-powered mobile communications apparatus capable of distinguishing between an instantaneous voltage drop occurring from the deterioration of the DC power source while the transmitter is on and any other instantaneous voltage drop, and thereby preventing faulty functioning when the DC power source has deteriorated. According to the invention, a mobile communications apparatus of the kind defined hereinbefore at the beginning is characterised by means for measuring the lapse of time from the actuation of said load circuit till the generation of said reset signal; and means for comparing, when said reset voltage detector means and said sustained drop detecting means indicate the occurence of an instantaneous drop, the measured lapse of time with a predetermined length of time, and restoring the actuated state of said load circuit if the measured time is longer than said predetermined time, and keeping said load circuit turned off if the former is shorter than the latter. The invention will now be described by way of example with reference to the accompanying drawings, in which:- FIG. 1 is a block diagram of a mobile communications apparatus according to the invention; FIG. 2 is a block diagram of the essential part of the logic circuit illustated in FIG. 1; FIGS. 3A to 3G and 4A to 4G are time charts for explaining the operation of the circuit shown in FIG. 2; FIG. 5 is a schematic circuit diagram illustrating a reset voltage detector circuit shown in FIG. 2; FIG. 6 is a schematic circuit diagram illustrating a sustained drop detector circuit shown in FIG. 2; FIG. 7 is a block diagram illustrating another preferred embodiment of the mobile communications apparatus according to the invention; and FIG. 8 is a flow chart for explaining the operation of the apparatus shown in FIG. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a mobile communications apparatus includes a transmitter 16 and a receiver 14. A synthesizer 15 supplies a local oscillation signal to the transmitter 16 and receiver 14, which are coupled to an antenna 12 through an antenna duplexer 13. The control of turning on and off the transmitter 16 and receiver 14, and that of the oscillation frequency of the synthesizer 15 are achieved by a control circuit 17. A dry battery 18 supplies DC voltage to the logic circuit 17, transmitter 16, receiver 14 and synthesizer 15. The control circuit 17, monitoring the DC output of the battery 18, has a reset function to turn off the transmitter 16 when the DC output falls below a prescribed level. It also has a function to detect an instantaneous drop in the DC output level. The control circuit 17 further has a function to distinguish an instantaneous voltage drop caused by the deterioration of the battery from any other instantaneous voltage drop. This last mentioned function eliminates the undesirable repeated interruption of transmitted radio waves that may otherwise be caused by the battery deterioration. Referring now to FIG. 2, a DC voltage from the battery 18 is supplied to a reset voltage detector circuit 1 and a sustained drop detector circuit 2 as well as to the transmitter 16. Initially, the transmitter 16 is still in a standby state and has not started transmission. When a transmitter "ON" signal a is given, a transmitter ON/OFF controller circuit 3 outputs a control signal g to let the transmitter 16 start transmission unless there is any abnormality in the battery voltage. Meanwhile, if there is any abnormality in the battery voltage, for instance if the battery has deteriorated, the controller circuit 3 disables the transmitter 16 so as to prevent the transmitter 16 starting transmission in response to the control signal g . Determination of the presence or absence of an abnormality in the battery voltage is achieved by the reset voltage detector circuit 1, the sustained drop detector circuit 2 and a reset decision circuit 6. The reset voltage detector circuit 1, monitoring the battery voltage, outputs a reset signal when the voltage falls below a prescribed level, and a reset release signal when it returns to the prescribed level or above. The sustained drop detector circuit 2, also monitoring the battery voltage, checks the duration for which the voltage lies below the prescribed level. Thus, the circuit 2, normally keeping its output at a high level of "1", which does not vary even if an instantaneous voltage drop occurs, changes its output to a low level of "0" when the voltage remains below the prescribed level for more than a prescribed length of time. The circuits 1 and 2 thereby determine whether or not fluctuation in the battery voltage is an instantaneous drop. The reset decision circuit 6, comprising a timer circuit 4 and a time decision circuit 5, determines whether or not an instantaneous voltage drop is due to the deterioration of the battery. The operation of the circuit illustrated in FIG. 2 will now be described in detail with reference to FIGS. 3A to 3G and 4A to 4G. FIGS. 3A to 3G show how the circuit of FIG. 2 operates when the battery has deteriorated. When the transmitter "ON" signal a is supplied at time t₁ in FIG. 3A, the output g of the transmitter ON/OFF controller circuit 3 rises to its high level as shown in FIG. 3G, and the transmitter 16 is turned on. Once the transmitter is turned on, a large amperage is consumed (for instance from 600 to 800 mA), so that, if the battery of 6 or 7.2 volts and 600 mAH capacity has already deteriorated, its voltage b will quickly fall off (see FIG. 3B). When the voltage b falls below a prescribed level V TH , at time t₂, the reset voltage detector circuit 1 changes its output from a high to low level as shown in FIG. 3C. Along with this change, the output g of the controller circuit 3 also changes to its low level to turn off the transmitter 16. The timer circuit 4 starts counting in response to the transmitter ON signal a , and discontinues counting in response to the reset signal c , as shown in FIG. 3E. The count T C1 at this time is written as an output e into and stored in the time decision circuit 5. The battery voltage is quickly restored by the turning-off of the transmitter 16 as shown in FIG. 3B. When this restoration brings the battery voltage to or above the prescribed level V TH at a time t₃, the reset voltage detector circuit 1 change its output from a low to high level as shown in FIG. 3C, and supplies the output c as a reset release signal to the time decision circuit 5 and the transmitter ON/OFF controller circuit 3. In response to the reset release signal, the time decision circuit 5 compares the earlier stored count T C1 with a prescribed length of time T₀. Since T₀ is greater than T C1 in FIGS. 3A to 3G, the time decision circuit 5 attributes the reset from time t₂ to time t₃ to battery deterioration, and keeps the output at its high level as shown in FIG. 3F. Although the reset release signal commands the controller circuit 3 to reactuate the transmitter 16, since an output f is supplied indicating that the deterioration of the battery has been detected by the time decision circuit 5, the circuit 3 continues to keep the transmitter 16 off, as shown in FIG. 3G. FIGS. 4A to 4G show how the circuit of FIG. 2 operates when the battery has not deteriorated. When the transmitter "ON" signal a rises to its high level at time t₄,, the transmitter 16 is turned on, as shown in FIG. 4G, and at the same time the timer circuit 4 starts counting, as shown in FIG. 4E. When the battery has not deteriorated and the transmitter 16 is turned on, there is scarcely any voltage drop. As shown in FIG. 4B, the battery voltage does not fall as far as to the prescribed level V TH . Therefore, the output c of the reset voltage detector circuit 1 (FIG. 4C) does not vary, and the timer circuit 4 continues counting. The output g of the transmitter ON/OFF controller circuit 3 does not vary, and so the transmitter 16 remains ON. If then the battery voltage drops instantaneously for some reason or other as shown in FIG. 4B at time t₅, the output g of the controller circuit 3 will temporarily fall to its low level in response to the output c of the reset detector circuit 1. The output c also causes the timer circuit 4 to stop counting and to provide a count T C2 . When the output c returns to its high level at time t₆, the time decision circuit 5 compares the count T C2 with the prescribed length of time T₀. Because T₀ is smaller than T C2 , the time decision circuit 5 judges the instantaneous drop between time t₅ and time t₆ to be a simple instantaneous drop, and the output f remains at its low level. Since the output f is at its low level at time t₆ when the reset releast signal is supplied, the transmitter ON/OFF controller circuit 3 brings back the output g to its high level, and turns the transmitter 16 on again. In the manner described above, it is possible to determine whether a given instantaneous voltage drop is a simple one or attributable to the turning-on of the transmitter when the battery is deteriorated. If the battery voltage remains at a low level for a relatively long period of time as from t₇ to t₉ in FIG. 4B and the sustained drop detector circuit 2 determines that the sustained drop is not an instantaneous drop, by comparison with a time τ to be explained below, the transmitter 16 will be kept turned off even if the voltage returns to its normal level at time t₉. FIG. 5 is a circuit diagram illustrating the reset voltage detector circuit 1. A voltage b from the battery 18 is divided by resistors R1 and R2, and the divided voltage is compared with a reference voltage (e.g., 2.5 V) by a comparator 19, which outputs the reset signal c when the battery voltage falls below 2.5 V. FIG. 6 illustrates the sustained drop detector circuit 2. When the battery voltage b falls off, a capacitor C1 discharges at a time constants τ (= C1R3), and as the terminal voltage of the capacitor C1 falls below the reference voltage (2.5 V), a comparator 20 senses that the drop is not an instantaneous drop and changes its output d from high to low level, as illustrated at time t₈ in FIG. 4D. If the battery voltage recovery within τ, the output d of the comparator 20 does not change, as illustrated by FIGS. 3B and 3D. In the embodiment FIG. 7, a central processing unit (CPU) 26 has the functions of the transmitter ON/OFF controller circuit 32 and the time decision circuit 5 of the first preferred embodiment illustrated in FIG. 2. A counter 21 corresponds to the timer circuit 4 in FIG. 2, and counts clock pulses supplied from a clock generator 23 through an AND gate 25. An input/output (I/O) port 22 serves to connect external circuits to the CPU 26, which controls the turning on and off of the transmitter 16 through a bus line 24 and the I/O port 22. A high level signal to turn on the transmitter 16 is supplied to the AND gate 25 as well as to the transmitter 16 from the I/O port 22. As shown in FIG. 8, when the CPU 26 generates a transmitter "ON" signal at Step S1, it clears the counter 21 at Step S2. The counter 21 starts counting in response to the transmitter "ON" signal (Step S3). At Step S4, the CPU 26 checks the output c of the reset voltage detector circuit 1 (FIG. 2) and, in the absence of a reset output, stores the count of the counter 21 into a memory within the CPU 26 at Step S5, followed by a return to Step S4. In the presence of a reset output, the process moves ahead to Step S6 to read the output d of the sustained drop detector circuit 2 (FIG. 2), and determines whether or not there is an instantaneous voltage drop at Step S7. If it is determined at Step S7 that there is a sustained voltage drop, i.e., the voltage drop lasts longer than the period of time τ, the CPU 26 will initialize the whole apparatus. Conversely, if the presence of an instantaneous voltage drop is detected, the count T C of the counter will be read out of the memory at Step S8, and compared with the prescribed value T₀ at Step S9. If T C is found greater than T₀, the battery will be judged normal as at Step S12, and the transmitter will be turned on again (Step S13), as at time t₆ in FIG. 4C. If the T C is smaller than T₀, as in FIG. 3E the battery will be judged at Step S10 to have deteriorated, and the process will move ahead to Step S11 to keep the transmitter 16 turned off.

Claims: A mobile communications apparatus comprising: a load circuit (16) to which a DC voltage (b) is supplied from a DC power source (18); reset voltage detector means (1) for generating a reset signal for turning off said load circuit (16) when said DC voltage (b) falls below a predetermined level (V TH ) and a reset release signal for turning on said load circuit (16) when said DC voltage (b) returns to or above said predetermined level (V TH ); and means (2) for detecting whether or not a change in said DC voltage is a sustained drop; characterised by means (4) for measuring the lapse of time from the actuation of said load circuit (16) till the generation of said reset signal; and means (5) for comparing, when said reset voltage detector means (1) and said sustained drop detecting means (2) indicate the occurence of an instantaneous drop, the measured lapse of time (T C ) with a predetermined length of time (T O ) and restoring the actuated state of said load circuit ( 16) if the measured time (T C ) is longer than said predetermined time (T O ), and keeping said load circuit (16) turned off if the former is shorter than the latter. A mobile communications apparatus according to claim 1, characterised in that the DC power source comprises a dry battery (18). A mobile communications apparatus according to claim 1, characterised in that the load circuit comprises a transmitter (16). A mobile communications apparatus according to claim 1, characterised in that the reset voltage detector means (1) comprises resistors (R₁, R₂) for dividing said DC voltage and a voltage comparator (19) for comparing the divided voltage with a reference voltage and supplying the result of comparison as the output (c) of said reset voltage detector means (1). A mobile communications apparatus according to claim 1, characterised in that the sustained drop detecting means (2) comprises an integrator circuit (R₃ C₁) coupled to said DC power source (18) and a voltage comparator (20) for comparing the output of said integrator circuit (R₃ C₁) with a reference voltage and suplying the result of comparison as the output (d) of the sustained drop detecting means. A mobile communications apparatus according to claim 5, characterised in that the integrator circuit comprises a resistor (R₃) connected between the DC power source (18) and the voltage comparator (20), and a capacitor (C₁) connected between a common voltage point and the connection point of the said resistor (R₃) and the voltage comparator (20). A mobile communications apparatus according to claim 1, characterised in that the said measuring means includes a counter which starts counting clock pulses in response to a signal for actuating the load circuit (16), and the said comparing means includes a central processing unit (26) for providing the said actuating signal. A method of detecting the deterioration of a DC power source, comprising the following steps: supplying a DC voltage (b) from the DC power source (18) to a load circuit (16); comparing (1) the DC voltage (b) with a predetermined level of voltage (V TH) ; providing a reset signal when the DC voltage (b) falls below the predetermined level (V TH ) and a reset release signal when the DC voltage (b) returns to or above the predetermined level (V TH ); and determining (2) whether or not a change in the DC voltage (b) is a sustained drop; characterised by measuring (4) the lapse of time from the actuation of the load circuit (16) till the generation of said reset signal; comparing (5), when a change in the DC voltage (b) has been determined to be an instantaneous drop, the measured lapse of time (T C ) with a predetermined length of time (T O ); restoring the actuated state of the load circuit (16) if the measured time (T C ) is longer than the predetermined time (T O ); and keeping the load circuit (16) turned off if the measured time (T C ) is shorter than the predetermined time (T O ).

Inventors: SAITO, AKIO
Applicants: NEC CORPORATION
Application year: 1986
Main classification: H04B1
IPC codes: H04B1, H02J7, H02J1