Abstract:
A circuit and method to decrease power consumption of fast infrared links. Reduced power consumption allows continuous infrared standby in battery-powered (and other power-consumption sensitive) devices. A low speed, low power-consumption infrared receiver preamplifier is used in conjunction with a higher speed, higher power-consumption infrared receiver preamplifier. While the battery-powered device awaits an infrared transmission, the low power-consumption receiver preamplifier operates in standby mode and the high power-consumption receiver preamplifier is in shutdown mode. Because the higher power consumption receiver preamplifier is in shutdown mode, standby power consumption is reduced and time between battery recharging is increased. When the low power receiver preamplifier detects an infrared transmission, the high power receiver preamplifier can be activated if high-speed communication is needed. An alternative discloses dual receivers rather than dual preamplifiers in one receiver.

Description:
FIELD OF THE INVENTION 
     This invention relates to infrared communications and, more particularly, to fast infrared transceivers having low standby power consumption. 
     BACKGROUND OF THE INVENTION 
     Electronic devices such as portable computers, electronic organizers, personal digital assistants, and cellular telephones, use infrared communications. The devices typically adhere to one of the Infrared Data Association (IrDA) infrared communication standards. The IrDA standards are based on the OSI seven-layer model. Presently, there are two generations of standards in the IrDA family: the 1.0 generation and the 1.1 generation. IrDA 1.0 sets a maximum data rate (aka signaling rate) of 115,000 bits per second (115 kbps) over a communications link. IrDA 1.1 sets a maximum data rate of 4,000,000 bits per second (4 Mbps) over the communications link. When using current technology, data rates over 200 kbps can be considered high-speed. 
     An infrared communications link usually incorporates a combination infrared transmitter and receiver, known as a transceiver. The transceiver transmits a modulated infrared signal and receives modulated infrared signals. An IR transceiver always operates in one of four modes: shutdown, standby, receive, or transmit. 
     In shutdown mode, the transceiver consumes almost no power. It is not capable of receiving or transmitting while in shutdown mode. Thus the transceiver cannot detect when another device attempts to establish an infrared communication link. The user generally must manually “wakeup” the transceiver from shutdown mode. 
     In standby mode, the transceiver consumes more power than when in shutdown mode but less than when in transmit or receive mode. The transceiver may detect infrared transmissions when in standby mode but may not receive or transmit. This ability to detect infrared transmissions is an important functional difference between standby mode and shutdown mode. 
     The “active” modes of a transceiver are receive mode and transmit mode. During reception, the transceiver operates in receive mode. During transmission it operates in transmit mode. Active modes consume more power than standby or shutdown modes. 
     High power consumption in transceivers for fast infrared links (for example the 4 Mbps IrDA 1.1 implementation) is at least partially due to the power required by the receiver stage. High-speed receivers generally consume more power than low-speed receivers do, even when operated in standby or shutdown mode. In active mode, a 4 Mbps capable receiver consumes more power than the slower 115 kbps receiver, regardless of the speed at which the 4 Mbps receiver is actually receiving data. In other words, even if both are operated at 115 kbps, a 4 Mbps receiver consumes much more power than a 115 kbps receiver. 
     Additional general background, which helps to show the knowledge of those skilled in the art regarding the system context, and of variations and options for implementations, may be found in the following from the IrDA 1.0 and 1.1 families of standards: IrDA Serial Infrared Physical Layer Link Specification; IrDA Serial Infrared Link Access Protocol (IrLAP); IrDA Serial Infrared Link Management Protocol (IrLMP); IrDA Tiny TP; IrDA Command and Control Ir Standard (formerly known as IrBus); IrDA Infrared Communications Protocol 1.0; IrDA Infrared Tiny Transport Protocol 1.1; IrDA Infrared LAN Access Extensions for Link Management Protocol 1.0; IrDA Object Exchange Protocol 1.2; IrDA Minimal IrDA Protocol Implementation; IrDA Plug and Play Extensions; IrDA Infrared Mobile Communications; and IrDA Infrared Transfer Picture Specifications; all of which are hereby incorporated by reference. IrDA standards and protocols are available over the internet from the Infrared Data Association at www.irda.org. 
     SUMMARY OF THE INVENTION 
     Disclosed is a circuit and method to dramatically reduce power consumption of fast infrared links without putting the link in shutdown mode. A low speed, low power-consumption infrared receiver preamplifier is used in conjunction with a higher speed, higher power-consumption infrared receiver preamplifier. While waiting for an IR link to be initiated, the low-power preamplifier operates in standby mode and the high-power preamplifier is shutdown to reduce power consumption. When the low power receiver preamplifier detects an infrared transmission, the high power receiver preamplifier can be activated if high-speed communication is needed. Unlike power-saving schemes that put the link in shutdown mode, infrared communications are continuously available by use of the disclosed innovations. Thus a user does not have to manually “wake up” the infrared receiver to receive a message. 
     At the system level in a disclosed embodiment, a communications link between two devices using IrDA standards is initiated with a simple 9.6 kbps modulation. After the communications link is initiated at 9.6 kbps, a communication speed for further communication over the link is negotiated between the two devices. Bit rate negotiations and link control are discussed in IrDA Serial Infrared Link Access Protocol. 
     A 115 kbps transceiver can receive and transmit the necessary 9.6 kbps modulation required to negotiate a communications link. Therefore, every time two IrDA systems (including the faster 4 Mbps IrDA 1.1 devices) establish a connection, they could initiate the connection with a low power 115 kbps receiver rather than a higher power consumption 4 Mbps receiver. 
     Disclosed is a transceiver with a single receiver having two preamplifiers. A low power consumption, low-speed infrared receiver preamplifier stage is used in combination with a higher power consumption, higher speed infrared receiver preamplifier stage. The higher speed preamplifier can be put in shutdown mode to conserve power while the lower power consumption preamplifier remains in standby. This allows a high-speed transceiver to remain in continuous standby while awaiting an infrared message, yet limit power consumption while waiting. In the presently preferred embodiment, a 115 kbps preamplifer is used in combination with a 4 Mbps preamplifier. In an alternate embodiment, dual receivers could be used instead of dual preamplifiers in one receiver. In other words the transceiver could have two receivers, perhaps one that operates at 115 kbps and one that operates at 4 Mbps. In another embodiment, the receiver(s) and transmitter could be physically separate, not together in a transceiver. 
     While waiting for a communication link to be initiated, the low power preamplifier stage is in standby and the fast preamplifier is in shutdown. After a high-speed connection is established, an IrDA-compliant controller switches the transceiver from the  115  kbps preamplifier stage to the 4 Mbps preamplifier stage. Compared to prior art 4 Mbps infrared transceivers, the innovative infrared transceiver consumes very little power when in standby mode because the fast preamplifier (which consumes the more power than the slower preamplifier) is in shutdown mode when it is not needed for communication. 
     The method and circuit allow a continuous infrared standby because power consumption is dramatically reduced. Low power consumption preamplifiers generally are considered to be those that have a standby current of less than 3 mA. For example, standby current in the presently preferred embodiment is reduced from over 3 mA to under 100 μA at a supply voltage of 2.7V. Thus continuous infrared standby is now a viable option for battery powered devices that incorporate the disclosed innovations for fast infrared communications. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The disclosed inventions will be described with reference to the accompanying drawings, which show important sample embodiments of the invention and which are incorporated in the specification hereof by reference, wherein: 
     FIG. 1 depicts an electronic device having an IrDA compliant controller and an IR transceiver. 
     FIG. 2 depicts an IR transceiver circuit with two receiver preamplifiers and dual comparators. 
     FIG. 3 depicts an IR transceiver circuit with two receiver preamplifiers and a single comparator. 
     FIG. 4 shows a table of possible mode relationships between the two receiver preamplifiers of FIGS. 2 and 3. 
     FIG. 5 depicts a dual transceiver embodiment. 
     FIG. 6 depicts a dual photodiode embodiment. 
     FIG. 7 depicts a dual receiver embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The numerous innovative teachings of the present application will be described with particular reference to the presently preferred embodiment. However, it should be understood that this class of embodiments provides only a few examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily delimit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others. 
     Definitions: 
     Passive Mode: Shutdown or standby mode. 
     Active Mode: Receive or transmit mode. 
     FIG. 1 is a block diagram of an electronic device  50  that uses an IrDA compliant controller  100  and an IR transceiver  200  for infrared communications. Through the transceiver  200 , the IrDA compliant controller  100  negotiates with a remote device to establish an IR communication link. When an IR signal from the remote device is received at IR transceiver  200 , it is passed via RxD to the controller  100 . The controller  100  may process the received signal or pass it on to an electronic device  50 . The controller  100  sends control signals via control line CONTROL to a control logic block (shown in FIGS. 2 and 3) in the transceiver  200 . Data to be transmitted passes from the controller  100  to the transceiver  200  along TxD (the transmit data line). 
     Power consumption in fast infrared links (for example the 4 Mbps IrDA 1.1 implementation) is affected by the power required by the receiver stage, particularly the receiver preamplifier. Generally, the higher the speed for which the preamplifier is designed, the greater its power consumption. A receiver preamplifier designed to operate at 4 Mbps consumes more power than a receiver preamplifier designed to operate at 115 kbps, regardless of the speed at which the 4 Mbps preamplifier is actually operating. In other words, even if both are operated at 115 kbps, a preamplifier designed for 4 Mbps operation consumes much more power than one designed for 115 kbps operation. 
     Referring to FIG. 2, the transceiver  200  is shown in an embodiment having two receiver preamplifiers and two comparators. To save power while waiting for an IR communication, control logic  250  initially holds a low-speed preamplifier  210  in standby mode and high-speed preamplifier  220  in shutdown mode. When an IR signal is received at a photodiode  280 , the low-speed preamplifier  210  wakes from standby to active mode and amplifies the received IR signal. A comparator  230  converts the amplified signal to an appropriate digital output level. Control logic  250  selects the appropriate input to a multiplexer (MUX)  240  depending on which receiver preamplifier ( 210  or  220 ) is active. When initially negotiating a communications link, control logic  250  is set to select the low-speed preamplifier input to MUX  240 . The digital signal then passes through the MUX  240  and RxD (the received data line) to an IrDA compliant controller  100  (shown in FIG.  1 ). 
     In response to the received signal, controller  100  (shown in FIG. 1) will negotiate a communications link with the signal&#39;s sender. During this negotiation, the controller  100  will transmit data along TxD, through the transmitter stage of the transceiver. The transceiver stage typically consists of an open collector driver  260  and an IR LED  270 . If a high-speed link is negotiated, the controller  100  signals the control logic  250  to wake the high-speed receiver preamplifier  220  from shutdown mode to standby or active mode and to put low-speed receiver preamplifier  210  in shutdown or standby mode. 
     Referring to FIG. 3, the transceiver  300  is shown in an embodiment having two receiver preamplifiers and a single comparator. The operation of the transceiver  300  shown in FIG. 3 is much like that of the transceiver  200  shown in FIG.  2 . The main difference between the two transceivers ( 200  and  300 ) is in the arrangement of comparator and multiplexer. Using a single comparator  320  that is placed after multiplexer  310  instead of before the multiplexer, as in transceiver  200 , reduces circuit complexity. This reduced complexity allows an optional driver  330  to be included in the receiver circuitry of transceiver  300 . In alternate embodiments, instead of being a separate circuit element, driver  330  could be implemented within the circuitry of MUX  240  or comparator  320 . In the embodiment shown, control logic  250  supplies an optional control signal to a driver  330 , placing the driver  330  in a reduced power mode for increased power savings. 
     At any given time, receiver preamplifiers  210  and  220  may be in receive, standby, or shutdown mode. FIG. 4 shows a table of the relationships possible in the disclosed embodiments. When low-speed preamplifier  210  is in receive mode, high-speed preamplifier  220  must be in shutdown mode. When low-speed preamplifier  210  is in standby or shutdown mode, high-speed preamplifier  220  may be in any of its three possible modes (shutdown, standby, or receive). A transceiver can reduce power consumption by putting high-speed preamplifier  220  in shutdown mode when low-speed preamplifier  210  is waiting in standby for a remote device to initiate communications. As shown in FIG. 4, the relative modes of the two preamplifiers ( 210  and  220 ) depend upon whether a particular embodiment of the invention has the capability to put low-speed preamplifier  210  in shutdown mode. In an embodiment of the invention that does not allow low-speed receiver preamplifier  210  to be put in shutdown mode, low-speed preamplifier  210  will be in standby mode when high-speed preamplifier  220  is receiving or in standby. In the embodiments disclosed, high-speed preamplifier  220  will only enter standby mode if a high-speed link has been established and its associated transceiver is transmitting or waiting to receive data. In an embodiment that does allow low-speed preamplifier  210  to be put in shutdown mode, low-speed preamplifier  210  will be in shutdown mode when high-speed preamplifier  220  is in receive mode or standby mode (which occurs if a high-speed link has been established). Optionally, low-speed preamplifier  210  and high-speed preamplifier  220  may be put in shutdown mode at the same time for increased power savings if the embodiment is one that allows low-speed preamplifier  210  to be put in shutdown mode. 
     FIG. 5 shows an alternate embodiment of the disclosed innovations. This embodiment mainly differs from the embodiment disclosed in FIG. 2 in that two transceivers are used, rather than one transceiver having two preamplifiers. An electronic device  5200  contains an IrDA compliant controller  5800 , a low power consumption transceiver  5000 , and a higher power consumption transceiver  5500 . When waiting for an IR link to be initiated, the controller  5800  places transceiver  5000  in standby and transceiver  5500  in shutdown via control signals communicated to control logic  5020  and  5520 , over control lines CTRL 1  and CTRL 2  respectively. IR signals are detected by photodiode  5050  and amplified by preamplifier  5060 . The detected signal then passes through the comparator  5010  to the controller  5800 . Note that, unlike the transceivers of FIGS. 2 and 3, a MUX is not required in the transceiver. When negotiating a communication link, controller  5800  will transmit data over line TxD 1  through open collector driver  5030  and LED  5040 . If a high-speed link is negotiated, controller  5800  will send a “wake” signal to control logic  5520  and transceiver  5500  will “wake” from shutdown mode. High-speed communications will take place through photodiode  5550 , preamplifier  5560 , comparator  5510 , open collector driver  5530 , and LED  5540  in the essentially the same way that they occur through the low speed transceiver  5000 . 
     FIG. 6 shows an alternate embodiment of the disclosed innovations having two photodiodes ( 610  and  690 ) instead of one photodiode as shown in the embodiment of FIG.  3 . Low-speed preamplifier  620  receives IR signals through photodiode  610  and high-speed preamplifier  630  receives IR signals through photodiode  690 . In response to control signals from an external controller, control logic  660  can change the modes of the preamplifiers ( 620  and  630 ) and select the appropriate input to MUX  640 . The output of MUX  640  then passes through comparator  650 . Transceiver  600  transmits data through open-collector driver  670  and LED  680 . 
     FIG. 7 shows an alternate embodiment of the disclosed innovations having a transceiver with two separate receivers (one slow, the other faster). The slow receiver has low speed, low power consumption preamplifier  720  and comparator  740 . The fast receiver has fast, high power consumption preamplifier  730  and comparator  750 . Both receivers share photodiode  710  in this embodiment. While waiting for a communications link to be initiated, control logic  760  holds preamplifier  720  in standby mode and preamplifier  730  in shutdown mode. If a high-speed link is negotiated, control logic  760  will wake fast preamplifier  730  in response to control signals from a controller external to transceiver  700 . Data is transmitted through open-collector driver  770  and LED  780 . 
     FIGS. 2,  3 , and  5 - 7  show block diagrams of transceivers  200 ,  300 ,  5000 ,  5500 ,  600 , and  700 . These block diagrams show the transceivers as a packaged integrated circuit (having pins such as RxD, TxD, etc.). However, each of these transceivers may be manufactured as an integrated circuit or from discrete components. 
     As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a tremendous range of applications, and accordingly the scope of patented subject matter is not limited by any of the specific exemplary teachings given. 
     For example, if additional power savings are needed, the ability to put the link in shutdown mode could be retained. This could be accomplished by optionally deactivating (putting in shutdown) the 115 Kpbs receiver stage in addition to deactivating the 4 Mbps receiver stage. 
     For example, there are many possible arrangements of receiver components that can be used with the disclosed innovations. Although FIGS. 2,  3 , and  5 - 7  show several such arrangements, other electrical arrangements of the multiplexers, comparators, and photodiodes are possible. In fact, components such as the multiplexers or comparators may be excluded entirely in some designs. 
     For example, there are many electronic circuit components that are freely substitutable for some of the components shown in FIGS. 2,  3 , and  5 - 7 . Any suitable IR detector may be substituted for photodiodes. Any suitable components such as an analog-to-digital (A/D) converter may be substituted for the comparators shown. The invention is not restricted to controlling the mode of preamplifiers. Any suitable receiver components may be substituted for the preamplifiers shown. 
     For example, although IrDA standards are discussed, the inventions disclosed may be practiced without adherence to the IrDA standards. The benefits of the inventions may be had without adherence to any standards or to standards other than the IrDA standards.