Infrared signal communication system and method including transmission means having automatic gain control

[0001] This application is a continuation of application Ser. No. 09/131,825, filed Aug. 10, 1998, now U.S. Pat. No. 6,590,682, which application is incorporated herein in its entirety by this reference.

[0002] 1. Field of the Invention

[0003] This invention relates generally to infrared communications systems and, more specifically, to an Improved Infrared Signal Communication System and Method Including Transmission Means Having Automatic Gain Control.

[0004] 2. Description of Related Art

[0005] As technology becomes continually more accessible to the “common man,” the ability to use, store, transfer and otherwise manipulate information has become the focus of most businesses as well as for the individual consumer. Access to the information resources is commonly by some sort of network system, including World Wide Web, “Intranets”, local area networks, wide area networks, as well as corporate databases.

[0006] While the conventional method for connecting to one of these information networks has been via cable and wire, as the reliance upon connectivity to information has deepened, the desire to gain such access from mobile or portable devices has strengthened. These portable devices, such as Personal Digital Assistants, hand-held computers, cellular telephones, and even digital cameras are now being connected to each other and to networks via Infrared Data Communications. In fact, it is virtually impossible to purchase a notebook computer today that does not include an Infrared Data Communications assembly resident within it.

[0007] One drawback of these portable devices or appliances is their inherent dependency upon portable power sources (i.e. batteries of some sort). As functionality is added to the device, so is demand upon the portable power source, therefore any way of reducing the demand upon the portable power source is extremely desirable. One particular system that can place a significant demand upon the portable power source is the Ir transmission subsystem. FIGS. 1A–1C provide pertinent details about this subsystem. FIGS. 1A, 1B and 1C depict Infrared communications between a pair of conventional Ir-enabled appliances. As shown in FIG. 1A, a first Ir-capable appliance 10 is in Ir-communication with a second Ir-capable appliance 12. Of crucial importance to reliable Ir communications is the requirement that the Ir signal transmissions 14 be strong enough to cross the separation distance 16 between the two appliances 10 and 12 (in addition to any other interferences with transmission and receipt).

[0008] FIG. 1B depicts one-half of the communications loop depicted by FIG. 1A. In FIG. 1B, the first appliance 10 is the transmitting appliance 11, and the second appliance 12 is the receiving appliance 13. Under the current IrDA (Infrared Data Association) standards, all Ir signal transmissions 14 must be adequate to cross a separation distance 16 of 1 (one) meter. Jn order to achieve this range consistently, devices have been designed with a constant, default transmit power setting (P_TXO) that will insure that the receiving appliance 13 receives a certain minimum receive power (P_RCVMIN). As mentioned earlier, P_TXO is of a constant, fixed magnitude that will result in a received power equal to P_RCVMIN when the separation distance 16 is 1 (one) meter.

[0009] While this system design does insure reliable Ir communications at the separation distance 16 specified by the IrDA, it is also very wasteful. Under common usage conditions, once a communications loop has been initialized, the transmitting appliance 11 and receiving appliance 13 are usually placed much closer to one another than one meter for the actual data transfer process. As depicted by FIG. 1C, where the separation distance 16 is 0.5 meter, the Ir transmissions “overshoot” the receiving appliance 13. This is a critical problem for a device class (i.e. portable electronic devices) where power efficiency is of primary importance.

[0010] FIG. 2 captures the magnitude of the inefficiency of the prior systems. FIG. 2 is a graph illuminating the effect of Ir transmit range on transmit power requirements. It should be understood that there is an inverse square relationship between the transmit distance and the power required to make such a transmission. Consequently, where all transmissions are made at the default power P_TXO, there is significant waste. For example, if P_TXO is assumed to be 500 mA (i.e. to reach a distance of one meter), then only approximately 25 mA would be required to reliably reach one-half that distance (i.e. 0.5 meter). This means that the transmissions are 80% overpowered at a 0.5 meter separation distance! What would be beneficial would be an Ir transmission system that adjusts its transmit range (and its P_TX) to the minimum level for reliable communications (P_TXMIN) “on the fly”, so that such power waste is minimized.

[0011] FIG. 3 gives additional enlightenment regarding this problem; it is a graph illuminating the effect of transmission distance 16 on received signal strength. It can be seen that at one meter, the magnitude of the received power P_RCV is at a level sufficient to support reliable communications P_RCVMIN. The problem is that as the separation distance goes to zero, the received power P_RCV goes up until it virtually equals the default transmit power P_TX0. In this example, at close distances the receiver signal overpower 20 (i.e. the difference between P_TX and P_RCVMIN) is relatively large compared to P_RCVMIN (the amplitude which would provide completely reliable communications). What is needed is a system and transmission method that automatically reduces the magnitude of the receiver signal overpower 20 to minimum levels.

[0012] In light of the aforementioned problems associated with the prior devices and methods, it is an object of the present invention to provide an Improved Infrared Signal Communication System and Method Including Transmission Means Having Automatic Gain Control. The preferred system and method should adjust signal transmission power in response to incident signal power amplitude. It is an object that the preferred system include a control signal loop within the signal receiving system, and that the signal transmitting system is responsive to this control signal loop. It is a further object that the system include manual, semi-automatic and automatic modes of operation. It is yet another object that the preferred method include at least two Ir-enabled appliances “stepping” each other “down” in transmit power in response to directives issued by the other Ir-enabled appliance.

[0021] The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide an Improved Infrared Signal Communication System and Method Including Transmission Means Having Automatic Gain Control.

[0022] The present invention can best be understood by initial consideration of FIGS. 4A and 4B. FIGS. 4A and 4B are circuit diagrams of preferred Ir receive and Ir transmit subsystems, 22 and 24 (or receive and transmit means), of the present invention. As can be seen, incident Ir signals 26 are detected by an Ir receive diode 28. The incident signal is amplified by an amplifier 29 so that the signal amplitude will be within some preferred range. The output of the amplifier 29 preferably enters a comparator 30, which compares the amplified signal to some desired amplitude. The comparator 30 sends a control signal back to the amplifier 29 via the Automatic Gain Control loop (AGC loop) to increase or decrease signal amplification exiting the amplifier 29. From the comparator 30, the received signal preferably enters the receive driver 32, where the signal is conditioned and sent on for translation and/or other use within the appliance. It is pointed out that conventional Ir receive subsystems already include an AGC feature to adjust the amplifier in response to changes in received signal power P_RCV. Conventionally, this AGC has been included in the Ir receive subsystem to prevent damage to the internal circuits of the electronic device due to excessively high P_RCV's.

[0023] Now turning to FIG. 4B, we might understand the unique functionality of the present invention; it is a schematic diagram of a preferred design for an Ir transmit subsystem 24 of the present invention. Data entering the subsystem 24 for Ir transmission typically enters a mode and power controller 34 wherein the signal/data is formatted for effective transmission. The signal then enters a transmit driver 36, which amplifies the signal for transmission by the Ir transmit diode 38. The unique feature of the present invention is the AGC signal cross-connect 40. Essentially, the AGC signal cross-connect 40 provides the transmit driver 36 with the same feedback signal created and used by the Ir receive subsystem 22. When the other electronic appliance (see FIGS. 1A–1C) is in close proximity to the appliance in which the subsystems of FIGS. 4A and 4B reside, the AGC signal will indicate that the amplitude of the incident Ir signals 26 is large. Subsequently, the AGC signal will direct the transmit driver 36 to reduce its power setting so that the amplitude of the transmitted Ir signals 42 is optimized.

[0024] It should be appreciated that the depicted circuit designs are simply functional examples of acceptable circuits; other components and circuit designs might be used, depending upon the particular application. What is unique is the automatic and/or manual amplitude control of the transmitted Ir signals.

[0025] The benefits of the improved circuit are best described by FIGS. 5 and 6. FIG. 5 is a graph depicting an optimum received signal power, P_RCVOPT, for all separation distances. P_TRCVOPT is the “target” power amplitude for the Ir signals incident upon the receiving appliance, this power level being achieved by the system and method described above in connection with FIGS. 4A and 4B. In this example, P_RCVOPT has been established at a level that is somewhat higher than P_RCVMIN in order to account for conditions that may have degraded the actual transmit and receive power efficiencies of the transmitting and receiving devices. No matter what the separation distance 16 between the communicating devices, P_RCVOPT will remain unchanged (at least as unchanged as conditions and system response will permit). Now turning to FIG. 6, we can see the benefit of reducing the target amplitude of the incident Ir signals. FIG. 6 depicts the new transmit power curve for the device of the present invention that incorporates Automatic Gain Control in the transmit subsystem. As can be seen, the AGC transmit power P_TXAGC ranges from a minimum level of P_RCVOPT where the separation distance 16 is small, to a maximum level of P_TXO where the separation distance 16 approaches one meter. The shaded section indicates the area between the P_TXAGC and P_TXO curves. This is the zone where power savings exist from implementation of the device and method of the present invention. It should be casually apparent that the savings are significant. As an added benefit, it is pointed out that since the transmission range has been optimized, there will be less “overshoot” by Ir signals. This will act to improve the security of the communications between devices, since it will be much more difficult for an unauthorized participant to “overhear” a “conversation.”

[0026] Finally, we will consider FIG. 7 to understand an example of a preferred “conversation” between two electronic appliances incorporating the automatic gain-controlled transmitter of the present invention. In this example, the transmitting device 11 will be adjusting its transmit power level; in reality, this process (oversimplified for discussion purposes) would be followed by both devices as they establish Ir communications.

[0027] At “discovery”, the receiving device 13 sends 44: “Hello”, to which the transmitting device 11 replies 46: “Hello Back to You,” followed by “Are My Transmissions Clear to You?”. In this case, where the separation distance 16 is less than one meter, the transmitting device's 11 transmit power (initially set to P_TX0) is higher than necessary. Consequently, the receiving device 13 replies 48: “Yes, your transmissions are clear, in fact, you can reduce your transmit power by 10%”. [This 10% number is arbitrary; other increments might be more appropriate under other circumstances.]

[0028] In response to this message, the transmitting device 11 adjusts P_TX to 0.9×P_TX, and queries 50: “How's That.” Should P_RCV at the receiving device 13 still be above P_RCVOPT, the receiving device 13 might respond 52: “That is still good, in fact, you can reduce your transmit power by another 10%.” In response, the transmitting device will probably adjust P_TX to 0.9×P_TX, and again query 54: “How's That?” If P_RCV is now acceptably close to P_RCVOPT, the receiving device 13 will respond 56: “That's good, because you are now close to P_RCVOPT,” after which data transfer will commence 56, 58.

[0029] A final point is that the adjustment of P_TX may be multi-modal, including the possibility for automatic, semi-automatic, and even manual adjustment of P_TX, depending upon the particular circumstances and environment.

[0030] Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.