Light guide for a communication unit

[0002] The invention relates to communication units having a light guide for guiding light from a light source to illuminate a display. Light guides are also used to transfer light from a light source to illuminating the keyboard/keys. In mobile phones the light guide is placed between a printed circuit board and the display and/or the keyboard to transfer the light from a light source, e.g. a light emitting diode (LED), to illuminate the display or/and the keyboard.

[0003] This is e.g. shown in U.S. Pat. No. 5,746,493, where a light guide is described having a plurality of light coupling recesses. Some of the light coupling recesses are placed between keyholes on the light guide, where the LEDs mounted on a printed circuit board sticks up, and transfer through the light guide light for illuminating mainly the keyboard and partly the display. On one side of the light guide are the light coupling recesses arcuately shaped to transmit light from the LED uniformly into the light guide.

[0004] Another approach of illuminating a keyboard is shown is U.S. Pat. No. 5,711,588, where the light is reflected on a cover, mounted over the keys of a keyboard assembly, into the keys. In this case a light guide is not needed, nor is there a need for a light source for each key on the keyboard. Yet another approach is shown in U.S. Pat. No. 5,847,336, with one LED for each key to illuminate the keys directly. The LEDs are mounted on a flexible film, which is placed directly under the keyboard. Between this flexible film and the printed circuit board there is a dome sheet with domes that short-circuit a pair of electrical contacts on the printed circuit board, when pressing the keys. This approach is not used to illuminate the display, just the keyboard.

[0005] Still another approach is described in U.S. Pat. No. 5,708,428, where LEDs are embedded, by insert moulding, directly into the light guide. The light guide is placed between the keyboard and printed circuit board, having aperture for permitting the conductor on the bottom of each of the keys to contact respectively positioned contacts on the printed circuit board.

[0006] Furthermore, JP 9287981 describes a device for guiding the light from a substantially linear light-emitting element into a photo-conducting plate, without increasing the thickness of the plate. To manage to transmit the light without having a thicker plate a lens is used more exactly a Fresnel lens.

[0007] The invention provides a light guide for illuminating a display or a keyboard. The light guide is a substantially transparent plate-formed element with reception means for receiving light from light sources and for guiding the light into the transparent plate-formed element of the light guide. The reception means includes light in-coupling surfaces facing towards the light sources. The reception means is disposed in a plane that is in a substantially parallel relationship with the main surface of the light guide. The reception means includes a lens and a diffuser, for dispersing the light substantially parallel with the main surface of the light guide. The advantage provided by the light guide and associated lens and diffuser is that it allows for dispersing light in a light guide from LED's in a printed circuit board (PCB) that is coupled to the light guide. The light can therefore be transferred efficiently without making the light guide too thick or too large.

[0008] The invention also provides a light guide for illuminating a display or a keyboard incorporated in a communication unit. This enables the communication unit to have an efficient transferring of light from a light source to a display or a keyboard without becoming too thick.

[0009] In another approach of the invention there is provided a plastic dome sheet placed on one side of the light guide. On the side, which is closest to the printed circuit board. The dome sheet includes a reflector sheet, which covers a part of the light guide that could be the back screen of the display.

[0010] The invention will be explained more fully below, by way of example, in connection with preferred embodiments and with reference to drawing, in which:

[0011] FIGS. 1-2 shows in a perspective view a preferred embodiment of the communication unit according to the invention.

[0012] FIG. 3 schematically shows the essential parts of a telephone for communication with a cellular network.

[0013] FIGS. 4-5 shows in a perspective view a light guide.

[0014] FIG. 6 shows a front view of the light guide, where several cross-sections has been indicated.

[0015] FIG. 7 shows cross section A A of the light guide of FIG. 6.

[0016] FIG. 8 shows cross section B B of the light guide of FIG. 6.

[0017] FIG. 9 shows cross section C C of the light guide of FIG. 6.

[0018] FIG. 10 shows a front view of the light guide, where cross section D D has been indicated.

[0019] FIG. 11 shows cross section D D of the light guide of FIG. 10.

[0020] FIG. 12 shows in a perspective view the front side of the light guide with a plastic dome sheet applied to the backside.

[0021] FIG. 13 shows in a perspective view the back side of the light guide with a plastic dome sheet applied thereto.

[0022] FIG. 14 shows in a perspective view the plastic dome sheet with a reflector sheet applied thereto.

[0023] FIG. 15 is a perspective view of a light guide and plastic dome sheet positioned above a PCB having LED's and electrical contacts shown schematically thereon.

[0024] FIG. 16 is a cross-section of a typical keypad contact arrangement on a PCB.

[0025] According to a first aspect the communication unit according to the invention will be described with reference to a hand portable phone, preferably a cellular phone. A preferred embodiment of this phone is shown in FIG. 1 and 2. The phone is shown in perspective with the front in FIG. 1 and with the back FIG. 2. As will be seen, the phone is provided with a front cover 2 having a window frame 3 encircling the protection window of the liquid crystal display LCD assembly 1. The phone comprises a user interface having an on/off button 4, a keyboard/keypad 7, a battery 11, a display/LCD 1, an earpiece 21 and a microphone 22FIG. 3 (not shown in FIG. 1 or 2).

[0026] FIG. 3 schematically shows the most important parts of a preferred embodiment of the phone, said parts being essential to the understanding of the invention. The microphone 22 records the user's speech, and the analogue signals formed thereby are ND converted in an ND converter (not shown) before the speech is encoded in an audio part 20. The encoded speech signal is transferred to the controller 18 (physical layer processor), which e.g. supports the GSM terminal software. The controller 18 also forms the user interface to the peripheral units of the apparatus, including RAM and ROM memories 17aand 17b, a SIM card 16, the LCD display I and the keyboard 7 (as well as data, power supply, etc.). The controller 18 communicates with the transmitter/receiver circuit 19. The audiopart 20 speech-decodes the signal, which is transferred from the controller 18 to the earpiece 21 via a D/A converter (not shown).

[0027] The preferred embodiment of the phone of the invention is adapted for use in connection with the GSM network, but, of course, the invention may also be applied in connection with other phone networks. It could be cellular networks, various forms of cordless phone systems or in dual band phones accessing sets of these systems/networks.

[0028] The controller 18 is connected to the user interface. Thus, it is the controller 18, which monitors the activity in the phone and controls the LCD display I in response thereto.

[0029] Therefore, it is the controller 18, which detects the occurrence of a state change event and changes the state of the phone and thus the display text. The user may cause a state change event, when he activates the keyboard 7 including the navigation key 10, FIG. 1 and these type of events are called entry events or user events. However, the network communicating with the phone may also cause a state change event. These type of events and other events beyond the user's control are called non-user events. Non user events comprise status change during call set-up, change in battery voltage, change in antenna conditions, message on reception of SMS, etc.

[0030] Reference is now made to FIG. 4 which is a perspective view of the back side of a light guide 30 that embodies the invention. The light guide 30 provides illumination for the LCD display 1 or the keyboard 7 shown in FIG. 1. The light guide 30 is a substantially transparent plate-formed element. The transparent plate-formed element has reception means 35a, 35b, 35c, 35d, 35eand 35fthat receive light from respective light sources (not shown) and to guide the light into the transparent plate-formed element of the light guide 30. The light sources may be LED's which are shown in FIG. 15. The transparent plate formed element is comprised of a first part 32 of the light guide which constitutes being a back screen for a display and a second part 33 being a keyboard part. The light guide 30 could be made of a plastic material or other substantially transparent materials. The keyboard part includes a plurality of keyholes two of which 34a, 34bare referenced and reception means 35athrough 35f. Each of the reception means 35 includes a plurality of light in-coupling surfaces 35a′, 35b′c35c′, 35d′, 35e′, 35f′, which face towards respective light sources (see FIG. 15). The light in-coupling surfaces 35a′ through 35f′ are substantially parallel with a main surface of the light guide 30 and transfers the light from the light sources located under each light in-coupling surface 35a′-35f′ into the light guide 30. The light in-coupling surfaces 35a-35fhave means for dispersing the light substantially perpendicular to the direction of the light source to illuminate the display 1. The means for dispersing the light from the light source into the light guide 30 are lenses 37, 37′ and diffusers 38, 38′ (see FIG. 7). The lenses 37, 37′ are preferably concave and the light source (not shown) could be an LED that would be located to the left of the lenses 37, 37′.

[0031] In FIG. 7 is shown that the lenses 37, 37′ and the diffusers 38, 38′ are together almost not as thick as the light guide 30. A plane containing a line tangent of the central part of the lenses 37, 37′ is parallel with the surface 31 of the light guide 30, which is closest to the light source (not shown). This means that the thickness of the light guide 30 does not have to be thicker than the diffuser/lens, which enables having a thinner light guide, 30 and less material. This light guide 30 is also more efficient since the lenses 37, 37′ and the diffusers 38, 38′ transfer a very large portion of the light from the light source to the light guide 30. The diffuser provides for the diffusion of light by the distribution of incident rays of light by reflection on the inner surfaces of the light guide. The reflected rays are reflected in a multiplicity of directions. In earlier known light guides, like the one shown in U.S. Pat. No. 5,746,493, the light is transferred directly from the LED into the light guide, giving a larger energy loss. In this document LEDs are also used, which extends through the whole light guide increasing the possible lost of energy.

[0032] Attention is now directed to FIGS. 8 and 9 which depict sections of the light guide 30 that reveal the cross-section of key holes 45a, 45b, 45c, 45d, 45eand 45f. See FIG. 6, FIG. 8 and FIG. 9. The light guide 30 in the preferred embodiment is used to illuminate the keyboard 7. The light transferred from the diffuser travels substantially parallel to the surfaces of the light guide 30 and is reflected at the keyholes such as keyhole 46 by a chamfered surface 39 in the keyhole 46 (FIG. 9) and keyholes 45c, 45d, FIG. 8. The chamfered surface 39 reflects the light in the light guide 30 perpendicular to the surface of the light guide 30 onto the keyboard 7.

[0033] Attention is now directed to FIG. 10 which illustrates a front view of the light guide 30 with its first part 32 and second part 33 having disposed therebetween a row of light in-coupling surfaces 40a, 40b, 40d, 40d.

[0034] Each of the light in-coupling surfaces 40a, through 40dclosest to the first part 32 which is a back screen for a display I has means to ensure that a maximum of the light from the light sources, e.g. LED 41a, 41b, 41c, 41d(FIG. 15), is transferred into the first part 32 of the light guide 30. The light sources just noted are located under said light in-coupling surfaces 40a, 40b, 40c, 40d, mounted on a printed circuit board 48. In FIG. 11 the means to ensure that a maximum of light from the LED's, just noted, are transferred into the first part 32 of the light guide 30 include a lens 43 and a diffuser 42 that stretches from the lens 43 to the light guide 30.

[0035] The light guide 30 comprises a front side as seen in FIG. 10 turning towards the keyboard 7 of FIG. 1 and the display I and a back side turning towards a printed circuit board 48, FIG. 15.

[0036] In FIG. 12 and 13 is a light guide 30 shown having a plastic dome sheet 50 attached on to the back side of the light guide 30. The plastic dome sheet 50 is provided with metal domes 51, 51a, 51bon the side not attached to the light guide, which are affected by pressing the keys 8 of the keypad 7, to close circuit contacts 53, 54acircuit/switch, corresponding to each key 8, on printed circuit board 48. In FIG. 15 circuit contacts of the nature of 53, 54 are located on the PCB beneath each of the keys on the keypad 7, FIG. 1. FIG. 16 shows a cross-section of PCB 48 with circuit contacts 53, 54, plastic dome sheet 50, metal dome 51 and a key portion 7athat includes key portion extension 7bwhich extends through one of the keyholes in the light guide 30. The key portion extension 7bis secured to the metal dome 51 of the dome sheet 50 by way of the adhesive 52. All keypad keys are secured in the same manner to the dome sheet. A downward force keypad portion 7awill cause the metal domes 51 to flex as shown in dotted outline and complete a circuit across the contacts 53, 54. The dome sheet 50 is also provided with a plurality of holes 52 through which the light reaches the light in-coupling surfaces 35a-35fon the light guide, otherwise the light from the light sources would not pass through the plastic dome sheet 50. The part of the plastic dome sheet 50 that covers the first part 32, being the back screen for the display 1, includes a reflector sheet 53 as best seen in FIG. 14 for improving the illumination of the display.

[0037] The plastic dome sheet 50 is glued onto the light guide 30 with an adhesive 52 best seen if FIG. 16. This adhesive is also applied to the plastic dome sheet 50 surfaces that covers the keyholes 34 to flexibly attach the keyboard 7 via keypad 7aand keypad extension to the light guide 30. The keyboard 7 is therefore, when the phone is disassembled, attached to the light guide 30 and there are fewer loose parts. The keyboard 7 is also easily replaced if necessary.

[0038] FIG. 15 is a perspective view of the light guide 30 with plastic dome sheet 50 in place and positioned above PCB 48 to which it will be secured. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.