Abstract:
A radio frequency (RF) transceiver having improved low power operating modes. The RF transceiver comprises: 1) a radio frequency (RF) modem section comprising: a) receive path circuitry for receiving and down-converting an incoming RF signal to thereby produce an incoming baseband signal; and b) transmit path circuitry for receiving and up-converting an outgoing baseband signal to thereby produce an outgoing RF signal; 2) a baseband section comprising baseband circuitry for receiving and processing the incoming baseband signal and for generating the outgoing baseband signal; and 3) a power-saving apparatus for determining that the baseband section is idle and, in response to the determination, reducing a power supply voltage providing power to the baseband section.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention is directed, in general, to radio frequency (RF) receivers and, more specifically, to an apparatus and related method for reducing power consumption in a portable wireless device. 
   BACKGROUND OF THE INVENTION 
   The field of wireless communications encompass a variety of products, including personal devices such as pagers, cellular phones, and PCS phones, and information systems, such as wireless LANs (local area networks) and smaller wireless office networks. These products are widely used due to their convenience and comparatively low cost. 
   To maximize usage of the available bandwidth, a number of multiple access technologies have been implemented to allow more than one subscriber to communicate simultaneously with each base transceiver station (BTS) in a wireless system. These multiple access technologies include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA). These technologies assign each system subscriber to a specific traffic channel that transmits and receives subscriber voice/data signals via a selected time slot, a selected frequency, a selected unique code, or a combination thereof. 
   FDMA systems include frequency-hopped communication systems, in which the frequency spectrum is broken into channels that are small sub-spectrums. A transmitter and receiver pair can establish a communication link over a channel while other transmitter-receiver (TX-RX) pairs can use other channels. The channels selected by the TX-RX pair are chosen pseudo-randomly, typically based on a common time reference and the address (i.e., telephone number) of the receiver. For subsequent messages, new channels may be selected. 
   Mobile stations, such as cellular telephones, PCS handset devices, portable computers, telemetry devices, and the like, frequently operate from an external power source connected to the mobile station, with an internal battery supply being available to provide a limited period of operation without the external power source. Mobile stations which provide more extended intervals of battery back-up operation offer increased value of service to users and competitive advantages for service providers. 
   A mobile station enters the idle state when the mobile station is turned ON, is synchronized with the system, and has no calls in progress. During the idle state, a mobile station actively listens to a paging channel for information which includes overhead messages, such as system parameter messages, as well as messages directly addressed to the mobile station from a base station. Unfortunately, a mobile station operating on battery when it is in the idle state continues to drain the battery, even though the user does not make any effective use of the device. 
   Therefore, there is a need in the art for improves wireless devices that consume less power. In particular, there is a need for portable wireless mobile stations that consume less battery power. More particularly, there is a need for portable wireless mobile stations that consume less battery power when operating in an idle mode. 
   SUMMARY OF THE INVENTION 
   The limitations inherent in the prior art described above are overcome by the present invention which provides a radio frequency (RF) transceiver having improved low power operating modes. According to an advantageous embodiment of the present invention, the RF transceiver comprises: 1) a radio frequency (RF) modem section comprising: a) receive path circuitry capable of receiving and down-converting an incoming RF signal to thereby produce an incoming baseband signal; and b) transmit path circuitry capable of receiving and up-converting an outgoing baseband signal to thereby produce an outgoing RF signal; 2) a baseband section comprising baseband circuitry capable of receiving and processing the incoming baseband signal and capable of generating the outgoing baseband signal; and 3) a power-saving apparatus capable of determining that the baseband section is idle and, in response to the determination, reducing a power supply voltage providing power to the baseband section. 
   According to one embodiment of the present invention, the power-saving apparatus is further capable of reducing a power supply voltage providing power to the receive path circuitry. 
   According to another embodiment of the present invention, the power-saving apparatus comprises a timer and a switch operable to switch the power supply voltage on and off to the receive path circuitry. 
   According to still another embodiment of the present invention, the power-saving apparatus is further capable of monitoring the incoming baseband signal during a time period when the power supply voltage is switched on to the receive path circuitry and determining if the incoming baseband signal is directed to the RF transceiver. 
   According to yet another embodiment of the present invention, the power-saving apparatus, in response to a determination that the incoming baseband signal is directed to the RF transceiver, increases the power supply voltage providing power to the baseband section. 
   According to a further embodiment of the present invention, the power-saving apparatus, in response to a determination that the incoming baseband signal is directed to the RF transceiver, increases the power supply voltage providing power to the receive path circuitry. 
   According to a still further embodiment of the present invention, the power-saving apparatus is further capable of reducing a power supply voltage providing power to the transmit path circuitry. 
   According to a yet further embodiment of the present invention, the power-saving apparatus, in response to a determination that the incoming baseband signal is directed to the RF transceiver, increases the power supply voltage providing power to the transmit path circuitry. 
   The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form. 
   Before undertaking the DETAILED DESCRIPTION OF THE INVENTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram illustrating a low power RF transceiver according to one embodiment of the present invention; and 
       FIG. 2  is a flow diagram illustrating the low power mode operation of the RF transceiver in  FIG. 1  according to an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged frequency-hopped radio frequency (RF) transceiver. 
     FIG. 1  is a block diagram illustrating low power radio frequency (RF) transceiver  100  according to one embodiment of the present invention. RF transceiver  100  may be any type of wireless communication device in which it is important to minimize power consumption, particularly battery-operated portable devices. Thus, RF transceiver  100  may be a mobile (i.e., cellular) phone, a two-way pager, a personal communication services (PCS) device, a laptop personal computer (PC) equipped with a wireless modem, and the like. 
   RF transceiver  100  comprises antenna  101 , timer  105 , battery  110 , radio frequency (RF) modem section  120 , and baseband section  150 . RF modem section  120  comprises transmit path circuitry  122 , receive path circuitry  124 , signal acquisition block  126 , memory  128 , paging mode controller  132 , and power switch  134 . Memory  128  may be, for example, a non-volatile memory, such as a low-power flash RAM that stores RF communication parameter data, such as frequency hopping (FH) data parameters  129 , used by RF transceiver  100  to transmit data to receive data. Baseband section  150  comprises RF modem controller  152 , baseband processing circuitry  154 , idle detection circuit  156 , and power switch  158 . 
   During normal operation, power switch  134  and power switch  158  are closed (ON) and supply voltage power from battery  110  is applied to the components of RF modem section  120  and baseband section  150 , thereby enabling RF transceiver  100  to send and receive data. However, as will be described below in greater detail, power switches  134  and  158  may be selectively opened (OFF) when RF transceiver  100  is not transmitting data to, or receiving data from, a remote base station or a wireless network. When power switches  134  and  158  are opened, the power supply voltage is cut off to the components of RF modem section  120  and baseband section  150 , thereby greatly reducing power consumption in RF transceiver  100 . When switches  134  and  158  are both open, only timer  105  continues to consume power. 
   Receive path circuitry  124  and signal acquisition block  126  in RF modem section  120  convert incoming RF signals from antenna  101  down to a baseband bit stream. Receive path circuitry  124  typically comprises signal amplifiers, down-conversion mixers, and demodulation circuitry. Signal acquisition block  126  receives the baseband bit stream and performs simile comparison operations to determine if the received data bits match a known pattern or address indicating that RF transceiver  100  is receiving a data transmission form an external transmitter. The receive path components are usually implemented with application specific integrated circuit (ASIC) chips, such as low noise amplifier (LNA) chips, filters, frequency discriminators, bit slices, and the like. 
   Once a signal is acquired by signal acquisition block  126 , the baseband bit stream is transferred to baseband processing circuitry  154  for subsequent processing. Generally speaking, baseband section  150  implements higher level functions, such as grouping received baseband bits into user data packets, parsing user data packets into a baseband bit stream suitable for transmission, establishing network layer links across the wireless link to other devices, and the like. These functions are typically implemented using a microprocessor and RAM. 
   Transmit path circuitry  122  receives outgoing baseband bit streams from baseband processing circuitry and converts it to an outgoing RF signal that is transmitted via antenna  101  to, for example, a base station in a cellular network. Transmit path circuitry  122  typically comprises modulation and encoding circuitry, up-conversion mixers, and RF power amplifiers. If RF transceiver  100  is idle (i.e., not actively transmitting and receiving data) paging mode controller  130  may generate intermittent paging messages (i.e., beacon signals) that are transmitted by transmit path circuitry  122  in order to notify the external wireless network that RF transceiver  100  is still active in the network. 
   Baseband section  150  controls the operation of RF modem section  120  via RF modem controller  152 . RF modem controller  152  provides selected RF operating parameters, signal parameters, ESN data, encoding or encryption data, and the like that enable transmit path circuitry  122  and receive path circuitry  124  to operate in a particular network according to a particular multiple access protocol, such as TDMA, FDMA, CDMA, or the like. For example, if RF transceiver  100  is a frequency-hopped system, RF modem controller  152  determines the sequence of hopping channels that the receiver components must search and stores the frequency-hopping (FH) parameters in memory  128 . RF modem controller  152  also provides paging information to paging mode controller  130 . 
   At times it is desired for the baseband processor to be powered down, or otherwise disassociated with the radio chip. During these times, the radio chip can listen for transmissions on its own, or enter a paging mode in which it alternately transmits and receives, waking up the baseband processor when it detects an incoming packet destined for it. These functions are performed by low power mode controller  132  and timer  105 . 
   Idle detection circuit  156  monitors baseband processing circuitry  154  and determines when an idle condition exists, such as when baseband processing circuitry  154  is not transmitting or receiving user data traffic. Idle detection circuit  156  notifies low-power mode controller  132  of the idle condition and low power mode controller  132  may respond by entering one of three low-power modes. In a first low-power mode, low power modem controller  132  opens power switch  158 , thereby turning off baseband section  150 . At this point, RF modem section  120  contains sufficient digital logic functionality to interpret the frequency hopping parameters and autonomously search for the transmitter without interaction by baseband section  150 . Likewise, during paging operations, paging mode controller  130  in RF modem section  120  can use the same parameters to hop to the predetermined frequencies while baseband section  150  is off. 
   In a second low-power mode, low power modem controller  132  again opens power switch  158 , turning off baseband section  150 , but also selectively turning off power to the transmission circuitry in RF modem section  120 . In particular, RF modem section  120  may close embedded power switches (not shown) that cut off power to transmit path circuitry  122  and paging mode controller  130 . This mode saves even more power, but still permits receive path circuitry  124  and signal acquisition block  126  to continually monitor for incoming RF signals directed to RF transceiver  100 . If an incoming RF signal directed to RF transceiver  100  is detected, signal acquisition block  126  sends a notification signal to low power mode controller  132 , which responds by reapplying power to the transmitter portion of RF modem section  120  and by closing power switch  158 , thereby reapplying power to baseband section  150 . 
   In a third low-power mode, low power modem controller  132  again opens power switch  158 , turning off baseband section  150 , but also selectively transmits a disable signal to timer  105 , which responds by opening power switch  134 , turning off power to all of RF modem section  120 , including low power mode controller  132 . However, data in non-volatile memory  128  is preserved. In this mode, only timer  105  receives power from battery  110 . This mode saves the most power. 
   Thereafter, timer  105  cycles power switch  134  on and off according to predefined parameters established for RF transceiver  100 . The on periods are sufficiently long so that receive path circuitry  124  and signal acquisition block  126  can detect an incoming RF signal directed to RF transceiver  100 . If such an incoming signal is detected, signal acquisition block  126  sends a notification signal to timer  105 , which stops cycling power and simply leaves power switch  134  closed. This reapplies power to the transmitter and receiver portions of RF modem section  120 . Lower power mode controller  132  then closes power switch  158 , which reapplies power to baseband section  150 . 
   The power reduction in RF modem section  120  is determined by the duty cycle of timer  105 . For example, if timer  105  closes power switch  134  for 0.25 seconds and opens power switch  134  for 0.75 seconds, once each second, then power consumption in RF modem section  120  is reduced 75% during idle periods. 
     FIG. 2  depicts flow diagram  200 , which illustrates the low power mode operation of RF transceiver  100  according to an exemplary embodiment of the present invention. During routine operations, RF modem controller  152  stores RF parameter data in memory  128  (process step  205 ). After a period of idleness in baseband processing circuitry  154 , low power mode controller  132  shuts off power to baseband section  150  (process step  210 ). Low power mode controller  132  then sets timer  105 , which uses switch  134  to cycle power on and off in RF modem section  120  (process step  215 ). 
   During the ON phase, receive path circuitry  124  and signal acquisition block  126  scan paging frequencies to detect signals from a base station or other remote transmitter. Transmit path circuitry  122  transmits Acknowledgment Response (ACK Back) messages, if required (process step  220 ). Optionally, during the ON phase, transmit path circuitry  122  may transmit paging signals to remote network base stations, and receive path circuitry  124  and signal acquisition block  126  may search for response signals from a base station or other remote transmitters (process step  225 ). If signal acquisition block  126  detects data traffic, timer  105  closes switch  134 . Low power mode controller  132  then closes switch  158 , turning on baseband section  150  (process step  230 ). 
   Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.