Wireless communication set having backlighted display

Abstract: A digital wireless communication set with a backlighted display (6, 8) wherein a power amplifier (12) ON/OFF-controlled (40) in a time division fashion for communication, a backlight source (8) is driven by backlight driving circuit (16) in synchronously with the ON/OFF control (40) of the power amplifier (12) so that the backlight source (8) is turned on and off during the power amplifier (12) is in the OFF condition and the ON condition, respectively, so as to reduce power consumption as well as variation of power supply voltage.

Description: This invention relates to a wireless communication set with a backlighted display and, in particular, to a driving of a backlight source in such a wireless communication set. A wireless communication set such as a wireless telephone set is known in the art which has a transmitter including a power amplifier. In a certain communication network, for example, a digital communication network such as a TDMA (Time Division Multiple Access) network system, the power amplifier is repeatedly turned on and off in a time division fashion to send out an information signal as a burst signal in a time slot allotted thereto. That is, the power amplifier is cyclically and alternatingly brought into an ON condition and an OFF condition. Thus, repetition of increase and decrease is caused in an electric current used in the power amplifier. This results in undesired variation of a power supply voltage for various other circuit portions in the wireless telephone set. This problem is severe in the wireless telephone set of a battery-powered portable type having an electric cell or battery. For example, in a cellular phone for use in the Cellular Communications System, an output power for transmission is usually several tens milliwatts to several watts, and an electric current of several tens milliamperes to several hundreds milliamperes is consumed therefor in the power amplifier. This results in voltage drop due to presence of internal resistance in the electric cell and/or impedance in a printed circuit board used therein. The voltage drop is varied according to the ON/OFF control of the power amplifier to thereby cause variation of the power supply voltage. On the other hand, the wireless communication set of a type described above often has a backlighted display for displaying information such as a telephone number, a time, and others which is lighted behind by a backlight source. For the display, there is known a liquid crystal display (LCD), and the display is backlighted by a light emission diode or an electric luminescent (EL) device as a backlight source. The wireless communication set having the backlighted display has a problem that a relatively large electric current is consumed for backlighting the display. Thus, the power supply voltage is lowered by the backlighting in addition to the power supply voltage variation due to ON/OFF operation of the power amplifier. This accelerates to reduce the life time of the electric cell. Therefore, it is a general object of this invention to provide a wireless communication set having a backlighted display with a reduced power consumption. It is a specific object of this invention to provide a battery-powered digital telephone set of a portable type having a backlighted display with a reduced power consumption of a battery. These objects are achieved with the features of the claims. This invention is applicable to a wireless communication set which has a backlighted display and with a power amplifier on/off controlled in a time division fashion for communication, for example, a digital portable telephone set for use in a TDMA telephone network system. Fig. 1 shows a circuit block diagram of a portable digital telephone set for use in the TDMA telephone network system according to one embodiment of this invention; and Fig. 2 shows voltage and current variations at various points in the circuit block diagram in Fig. 1. This invention will be described in connection with an embodiment applied to a digital portable telephone set for use in TDMA telephone network system, that is, so called a cellular phone set used in the Cellular Communications System. Referring to Fig. 1, the cellular phone set shown therein comprises a pack of electric cells or batteries 1, and a telephone circuit 2 powered by the cells 1 through power supply terminals 3. The telephone circuit 2 includes transmitter/receiver portion 4, control portion 5, display portion 6, and keyboard portion 7. The display portion 6 is provided with backlight device 8 having light emitting elements 8a such as light emission diodes. The transmitter/receiver portion 4 is supplied with an electric power from the cells 1 through a power switch 9 and a voltage regulator 10, and the control portion 5 and the display portion 6 are supplied with an electric power from the cells 1 through the power switch 9 and another voltage regulator 11. The transmitter/receiver portion 4 includes a power amplifier 12 which is cyclically supplied with the electric power through a switching circuit 13 comprising switching transistors 13a and 13b. The switching circuit 13 is controlled by an ON/OFF control signal 40 to bring the power amplifier 12 into an ON condition or a power-on condition and an OFF condition or power-off condition alternatingly to send out an information signal as burst signals into time slots allotted to the telephone set in the TDMA telephone network system. On the other hand, the backlight device 8 is supplied with the electric power from the voltage regulator 11 through a switching circuit 14 comprising switching transistors 14a and 14b. The switching circuit 14 is controlled by a light control signal 41 from a light control signal generator 15 and switched on and off so that the light emission diodes 8a are turned on and off in synchronization of the OFF and ON conditions of the power amplifier 12, respectively. The light control signal 41 is generated from the ON/OFF control signal 40 and a light-on signal 42 at a light control signal generator 15 which comprises an inverter 15a for inverting the ON/OFF control signal to produce an inverted signal and an AND gate 15b receiving the inverted signal and the light-on signal 42 to produce the light control signal 41. Thus, the display 6 is backlighted by the backlight device 8 during continuation of the light-on signal 42. Therefore, the switching circuit 14 and the light control signal generator 15 serve a driving circuit 16 for the backlight device 8. The control portion 5 includes a central processor unit (CPU) 20, a memory 21, a display control circuit 22, a power amplifier controller 23, a backlight controller 24, a key controller 25, and a transmitter/receiver controller (T/R controller) 26. The power amplifier controller 23 generates the ON/OFF control signal 40 under control by the CPU 20 and the T/R controller 26 so as to send out the burst signals to the allotted time slots. The backlight controller 24 generates the light-on signal 42 under control by the CPU 20 so as to turn on the backlight device 8 for a time duration in response to key operation in the keyboard 7 and/or reception of a calling signal at the transmitter/receiver portion 4. In operation, when the power switch 9 is turned on, the transmitter/receiver portion 4 and the control portion 5 are energized through the voltage regulators 10 and 11, respectively, and the transmitter/receiver portion 4 is controlled by the T/R controller 26 to perform transmission/reception of information signals for a communication. In detail, the power amplifier controller 23 generates the ON/OFF control signal 40 under control by the T/R controller 26. Therefore, the power amplifier 12 is alternatingly powered on and off by the ON/OFF control signal 40. Then, a transmission signal is power-amplified by the power amplifier 12 and sent out in a time division fashion, as burst signals, into the allotted time slots. Referring to Fig. 2, the ON/OFF control signal 40 is shown at (A). Synchronizing to the ON/OFF control signal 40, the transmission signal is sent out as the burst signals at time intervals as shown at (B) in Fig. 2. Therefore, a current flows as a transmitting current from the cells 1 to the transmitter/receiver portion 4 at the same intervals, as shown at (C) in the figure. Referring to Fig. 1 in addition to Fig. 2, the backlight controller 24 generates the light-on signal 42 under the control by CPU 20 as shown at (D) in Fig. 2 so as to turn on the backlight device 8. The light-on signal 42 is applied to one input of the AND gate 15b to open the AND gate. While, the ON/OFF control signal 40 from the power amplifier controller 23 is inverted at the inverter 15a to produce the inverted signal. The inverted signal is applied to the other input of the AND gate 15b. Therefore, the inverted signal is passes through the AND gate 15b to produce the light control signal 41 as shown at (E) in Fig. 2. Comparing the (A), (D) and (E) in Fig. 2, the ON/OFF control signal 40 comprises time serial and alternating first and second signal levels corresponding to the ON and OFF conditions, respectively, and the light control signal 41 comprises switched-off and switched-on signal levels which are corresponding to the first and second signal levels of the ON/OFF control signal 40, respectively, and are alternatingly repeated during continuation of the light-on signal 42. The switching transistor 14 as in the switching circuit 14 is applied with the light control signal 41 and is switched off and on by the switching off and on signal levels of the light control signal 41. Accordingly, the switching transistor 14b is also switched off and on in response to the switching operation of the switching transistor 14a and cyclically energizes or drives the light emission diodes 8a, as shown at (F) in Fig. 2. Thus, the light emission diodes 8a illuminate the display behind. Data read out from the memory 21 and/or inputted from the keyboard 7 are displayed on the display 6 under control of the display controller 22. The displayed images of the data are backlighted and can be clearly viewed. Turning on/off operation of the backlight device 8 is repeated at a rate of sending out of the burst signals, for example, at 50Hz in the PDC (Personal Digital Cellular) which is based on the RCR (Research & Development Center for Radio System) Standard 27. Therefore, the images on the backlighted display can be viewed without any flicker. In turning on/off operation of the backlight device 8, a current also flows, as a backlight current as shown at (G) in Fig. 2, from the cells 1 to the light emission diodes 8a through the voltage regulator 11 and switching transistor 14b. However, as will be clearly understood from Fig. 2, the backlight current (G) does not overlap with the transmission current (C). Therefore, the maximum of the total current of the backlight current (G) and the transmission current (C) is the larger one of them as shown at (H) and is not increased by use of the backlighted display. Accordingly, although the power amplifier and the backlight device are employed in combination thereof, the terminal voltage of the cells 1 is equal to that in operation of the power amplifier or operation of the backlight device alone, and is not lowered by the combination use, as shown at (I) in Fig. 2. Therefore, according to the present invention, voltage variation of the power supply for circuit portions other than the power amplifier and the backlight device is suppressed, and power consumption is also reduced so that the life time of the cells are prolonged. For comparison with this invention, it is provided that the light control signal generator 15 is not used but that the switching circuit 14 is directly controlled by the light-on signal 42. In the case, the backlight device 8 is energized and driven as shown at (J) in Fig. 2 over the time duration during the light-on signal 41 is continued as shown at (D) in Fig. 2. Therefore, the backlight current also continues to flow as shown at (K) in Fig. 2 over the time duration during the light-on signal 41 is continued. As a result, the maximum of the total current of the backlight current (K) and the transmission current (C) is a sum of them as shown at (L) and considerably varies in the level. Therefore, the terminal voltage of the cells is also significantly varied in the level as shown at (M) in Fig. 2. This results in erroneous operation of the telephone set and reduction of the life time of the cells.

Claims: A wireless communication set with a backlighted display (6, 8) and with a power amplifier (12) ON/OFF-controlled in a time division fashion for communication, characterized by backlight driving means (16) for driving a backlight source (8) synchronously with the ON/OFF-control of said power amplifier (12) so that said backlight source (8) is turned on and off during the power amplifier (12). is in the ON condition and the OFF condition, respectively. A wireless communication set as claimed in claim 1, which is a battery-powered wireless communication set. A wireless communication set as claimed in any one of claims 1 and 2, which is a portable wireless communication set. A wireless communication set as claimed in any one of claims 1-3, which is a digital telephone set for use in a TDMA telephone network system. A wireless communication set as claimed in any one of claims 1-4, comprising power amplifier control means (23) for producing an ON/OFF control signal (40) to control the ON/OFF condition of said power amplifier (12), wherein said backlight driving means (16) comprises: light control signal generating means (15) receiving said ON/OFF control signal for producing a light control signal (41); and switching means (14) receiving said light control signal (41) for switching on and off an electric power supply to said backlight source (8). A wireless communication set as claimed in claim 5, wherein: said ON/OFF control signal (40) has time serial and alternating first and second signal levels, each of said first signal levels and each of said second signal levels are corresponding to said ON and OFF conditions of said power amplifier (12); said light control signal (41) has time serial and alternating switch-off signal levels and switch-on signal levels corresponding to said first and said second signal levels, respectively; and said switching means (14) switches on and off the power supply to said backlight source corresponding to said switch-on and switch-off signal levels, respectively. A wireless communication set as claimed in any one of claims 5 and 6, further comprising light-on signal generating means (24) for generating a light-on signal (42), wherein said light control signal (15) generating means produces said light control signal (41) during a time when said light-on signal (40) is maintained. A wireless communication set as claimed in claimed in claim 7, wherein said light control signal generating means (15) comprises: an inverter (15a) responsive to said ON/OFF control signal (40) to produce an inverted signal: and an AND gate circuit (15b) having two input terminals for receiving said light-on signal (42) and said inverted signal, and an output terminal for producing said light control signal (41). A wireless communication set as claimed in claimed in any one of claims 1-8, wherein said backlighted display is a liquid crystal display (6) and said backlight source is a light emission diode (8a).

Inventors: TOMIYORI YUTAKA, TOMIYORI, YUTAKA
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1997
Main classification: H04B1
IPC codes: G02F1, H04B1, H04M1, G09G3, H04N5, H04Q7, H04B7