Abstract:
A low-current transceiver, powered by two small low-voltage batteries, for use in wireless headset/phoneset applications, such as hands-free headsets used with cellular telephones. Re-use of current from at least one circuit to provide power to at least one other power-consuming element of the transceiver, along with interrupt-driven control of the current made available to transmit and receive circuits, enables extended battery life (e.g., 120 hours). The headset/phoneset circuits incorporate a technique that draws an extremely low supply current from two low-voltage batteries while providing clear two-way communication over a range of about 3 meters.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Application Ser. No. 60/708,556, filed Aug. 16, 2005 (Aug. 16, 2005). 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       THE NAMES OR PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not applicable. 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0004]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Field of the Invention 
         [0006]    The present invention relates generally to radio-frequency (RF) transceivers, and more particularly to an improved battery-powered RF transceiver apparatus for use in wireless headsets, wireless computer keyboards and mice, and any other application that requires a battery-powered transceiver that communicates over a distance of a few meters. 
         [0007]    2. Discussion of Related Art Including Information Disclosed Under 37 CFR §§1.97, 1.98 
         [0008]    The use of wireless cell phones has become commonplace in the U.S. and throughout the world. The use of cell phones in an automobile and while doing other mobile activities is very common. Because of the distractions associated with cell phone use, many states in the United States require use of “hands free” devices. Most of these devices are wired headsets connected to the cell phone. Although functional, users have found them to be frustrating to use during everyday activities. Consequently, there is a need for a wireless headset that connects to the cell phone. Current wireless headset devices, however, are troubled with poor quality of sound and lack of a low-power solution enabling reasonable talk time for the headset or phoneset. As an example, Bluetooth-enabled headsets today only provide between 3-6 hrs of talk time on new rechargeable batteries. 
         [0009]    These same issues exist for other wireless transceiver applications, such as the wireless computer keyboard and mouse, the wireless headset/phoneset for a landline phone and the wireless remote control. 
         [0010]    In general, there is a need for a low-power transceiver that operates on commonly available low-voltage batteries, and extends transceiver battery life between recharge events. 
         [0011]    The foregoing discussion reflects the current state of the art of which the present inventors are aware. Reference to, and discussion of, this information is intended to aid in discharging Applicant&#39;s acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that no prior art patents or other references disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein. 
         [0012]    The foregoing patents reflect the current state of the art of which the present inventor is aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicant&#39;s acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    The present invention provides a low-current-drain RF transceiver for use in short-range communications, such as wireless headset/phoneset pairs for landline and cellular phones, wireless computer keyboards, and the like. The invention enables clear transmission and reception of radio signals by the transceiver using two small, commonly available, low-voltage batteries, while dramatically extending the transceiver&#39;s battery life between recharge events (e.g., 120 hours, versus the current art&#39;s typical 3 to 6 hours). 
         [0014]    The inventive transceiver circuits incorporate an arrangement that draws an extremely low supply current from two low-voltage batteries while providing clear two-way communication over a range of about 3 meters. The transmitted power is low enough to be permitted under current United States Federal Communications Commission rules without requiring special certifications or licensing. 
         [0015]    It is therefore an object of the present invention to provide a new and improved RF low-current-drain transceiver, powered by two commonly available low-voltage batteries, that is useful for clear wireless full-duplex communications over short distances. 
         [0016]    Another object or feature of the present invention is to significantly extend the transceiver&#39;s operational time before its batteries require recharging. 
         [0017]    A further object of the present invention is to provide a novel transceiver circuit arrangement for providing extended operational time on a single battery charge by reusing current from a portion of the transmitter circuitry to power a portion of the receiver circuitry. 
         [0018]    Yet another object or feature of the present invention is to provide a novel transceiver circuit arrangement for providing extended operational time on a single battery charge by reusing current from one portion of the receiver circuitry to power another portion of the receiver circuitry. 
         [0019]    It is an additional object or feature of the present invention is to provide a novel transceiver circuit arrangement for providing extended operational time on a single battery charge by reusing current from one portion of the power control circuitry to power a portion of the receiver circuitry. 
         [0020]    It is even further an object or feature of the present invention is to provide a novel transceiver circuit arrangement for providing extended operational time on a single battery charge by using the internal logic of an interrupt-driven microcontroller to turn power off to as many transceiver circuits as practical for as much time as is practical when insufficient RF signal is received. 
         [0021]    Other novel features which are characteristic of the invention, as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings, in which preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration and description only and not intended as a definition of the limits of the invention. The various features of novelty that characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. The invention resides not in any one of these features taken alone, but rather in the particular combination of all of its structures for the functions specified. 
         [0022]    There has thus been broadly outlined the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form additional subject matter of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based readily may be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
         [0023]    Further, the purpose of the Abstract is to enable the U.S. Patent and Trademark Office and the public generally, and especially the scientists, engineers and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The Abstract is neither intended to define the invention of this application, which is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way. 
         [0024]    Accordingly, before explaining the preferred embodiment of the disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the construction and the arrangements set forth in the following description or illustrated in the drawings. The inventive apparatus described herein is capable of other embodiments and of being practiced and carried out in various ways. 
         [0025]    Also, it is to be understood that the terminology and phraseology employed herein are for descriptive purposes only, and not limitation. Where specific dimensional and material specifications have been included or omitted from the specification or the claims, or both, it is to be understood that the same are not to be incorporated into the appended claims. 
         [0026]    As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based may readily be used as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims are regarded as including such equivalent constructions as far as they do not depart from the spirit and scope of the present invention. Rather, the fundamental aspects of the invention, along with the various features and structures that characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the present invention, its advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated the preferred embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0027]    The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
           [0028]      FIG. 1  is a schematic view of the power management section of a low-current RF transceiver incorporating the novel circuitry arrangement of this invention; 
           [0029]      FIG. 2  is a schematic view of the RF transmitter, RF receiver and battery sections of a low-current RF transceiver incorporating the novel circuitry arrangement of this invention. 
           [0030]      FIG. 3  is a schematic view of an alternate embodiment of the power management section of a low-current RF transceiver incorporating the novel circuitry arrangement of this invention; and 
           [0031]      FIG. 4  is a schematic view of an alternate embodiment of the RF transmitter, RF receiver and battery sections of a low-current RF transceiver incorporating the novel circuitry arrangement of this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Referring first to  FIGS. 1 and 2 , wherein like reference numerals refer to like components in the various views, there are illustrated therein, exemplary schematic views of a preferred embodiment of a new and improved low-current RF transceiver.  FIG. 1  is a schematic view of the power management section of a low-current RF transceiver incorporating the novel circuitry arrangement of this invention, and  FIG. 2  is a schematic view of the RF transmitter, RF receiver and battery sections of the low-current RF transceiver of  FIG. 1 . Note that  FIGS. 1 and 2  should be viewed as separate parts of a single schematic diagram. In each case where an electrical connection point in the schematic drawing is diagrammatically separated from another electrical connection point with which it has an electrical junction, both electrical connection points are labeled identically to indicate their shared electrical junction. 
         [0033]    Overview of Inventive Features: While  FIG. 1  and  FIG. 2  are used to describe these novel features, the transceiver schematic design shown in  FIG. 3  and  FIG. 4  represents an alternative embodiment of the invention that retains these same advantages, while having reasonable variations in specific component values and arrangements. It is also important to note that, while the schematics show a transceiver that transmits a carrier signal on a specific radio frequency, and receives a carrier signal of a specific frequency, the inventive features of the transceiver are not related to the operating frequencies of the RF circuits. 
         [0034]    In preview, the following are some of the unique aspects of the inventive circuit design that, in combination, permit the design to accomplish the aforementioned objectives. 
         [0035]    The use of a low-voltage, very-low-current, commercially available FM RF receiver chip reduces battery drain during receiver operation. In  FIG. 2 , it can be seen that the receiver chip is U 7 . 
         [0036]    The use of two batteries (with a center tap between the two) compensates for supply current variations from unit to unit in the receiver, without affecting the transmitter operation. BT 1  and BT 2  in  FIG. 2  are the batteries used by the transceiver. 
         [0037]    The use of a frequency multiplier chain in the transmitter circuit permits very low-current operation and takes advantage of the sufficiently wideband frequency modulation capability of a crystal oscillator. It can be seen that, in  FIG. 2 , oscillator Q 1  is the transmit oscillator; Q 2  and Q 3  are each X3 multiplier stages. 
         [0038]    The use of an operational amplifier-controlled current source provides the ability to stabilize the power output of the transmit frequency multiplier circuits. Operational amplifier U 11  (seen in  FIG. 1 ) performs this function. 
         [0039]    Directly modulating the transmitter&#39;s fundamental frequency oscillator Q 1  transistor, without the use of a varactor, avoids the undesirable variations in varactor capacitance from unit to unit, while providing a power-efficient modulation stage. In  FIG. 2 , Crystal Y 1  and oscillator Q 1  are frequency-modulated directly by the baseband signal impressed onto the base of oscillator Q 1 . 
         [0040]    By re-using the current from portions of the transmitter, receiver and power control circuits to provide power to low-current-drain receiver chip U 7  of the receiver (seen in  FIG. 2 ), the invention reduces battery drain during receiver operation. Referring to  FIG. 2 , it can be seen that current passing through transmitter components Q 1 , Q 2 , and Q 3  provides power to receiver chip U 7 . It can also be seen that current passing through receiver component LNA Q 4  provides additional power to receiver chip U 7 . It can finally be seen that current passing through power control components R 51  and R 52  (both seen in  FIG. 1 ) provides further power to receiver chip U 7 . Notably, when receiver chip U 7  is drawing less current, the voltage present at connection pint VBAT 1 _SW is higher, causing the voltage at the center-tap of the voltage divider network comprised of resistor R 51  and R 52  to be reduced, thereby reducing the output voltage at pin  4  of operational amplifier U 11 . Pin  4  of operational amplifier U 11  acts as a constant current source for all components drawing power from connection point TX_VCC. This has the effect of stabilizing the output power of the transmitter stages when there are changes in the current drawn by receiver chip U 7  from connection point VBAT 1 _SW (seen in  FIG. 2 ). 
         [0041]    These inventive features of the transceiver can be seen in combination with the rest of the transceiver circuits as described below. 
         [0042]    Theory of transmitter circuit operation: Referring now to  FIG. 2 , the components of the transmitter section of the transceiver circuitry are seen on the top half of the schematic diagram. 
         [0043]    The transmitter of this example, is shown to accept an audio input from a microphone MIC 1 , but could easily be slightly modified by a person reasonably skilled in the art to accept a baseband input from another circuit that produces audio signals (including data modulated into an audio form, such as with a modem). 
         [0044]    The transmitter circuit has five main sections. These include the audio section (comprised of MIC 1  and preamp U 1 , along with their supporting components), oscillator Q 1  and its associated components, X3 multiplier Q 2  and its associated components, X3 multiplier Q 3  and its associated components, and the transmit antenna section that includes the tuning components surrounding the batteries BT 1  and BT 2  (the batteries, in this example, are part of the antenna circuit). 
         [0045]    TX Audio Section: The output of microphone MIC 1  is coupled to the input (pin  3 ) of preamp U 1  via DC blocking capacitor C 73  and resistor R 14 . Filter capacitors C 1  and C 61  prevent stray RF signals from being impressed upon the input of preamp U 1 . Filter capacitors C 2  and C 74  prevent any signals generated by preamp U 1  from being coupled to the power source present at connection point VBAT_TX_AA. The voltage divider network comprised of resistors R 5  and R 6  set the operational bias for preamp U 1 . Resistor R 11  sets the gain characteristics of preamp U 1 . Capacitor C 15  prevents high-frequency oscillations from being generated by preamp U 1 . Audio signals amplified by preamp U 1  are coupled to the base of oscillator Q 1  via DC blocking capacitor C 10 , resistor R 55  and R 12 . Capacitor C 80  provides an RF path to ground, preventing RF signals at the base of oscillator Q 1  from leaking into the preamplifier circuitry. 
         [0046]    TX VCXO: The transmitter uses a voltage-controlled crystal oscillator Q 1 , which also acts as the transmitter modulator when an audio signal is impressed upon its base. Pin  3  of crystal Y 1  is directly connected to the base of oscillator Q 1 , causing oscillator Q 1  to oscillate at a very stable frequency that is frequency-modulated by audio when it is also present at the base of oscillator Q 1 . The voltage divider network formed by resistors R 9  and R 17  provide the proper DC biasing voltage to the base of oscillator Q 1 . Resistor R 18  provides a path for DC current to flow through the emitter of oscillator Q 1 . Inductor L 3  provides a path for DC current to flow through the collector of oscillator Q 1 . Inductor L 3  additionally forms part of the oscillator Q 1  tuning circuit that also includes capacitors C 14 , C 18 , C 19 , C 81  and C 82 . The filter network formed by resistor R 1  and capacitor C 3  prevent the RF energy generated by oscillator Q 1  from leaking into the power source. Capacitor C 25  provides an RF path to ground for oscillator Q 1 . The output of oscillator Q 1  is coupled to the input of X3 multiplier Q 2  via DC isolation capacitor C 17 . 
         [0047]    First X3 Multiplier: The first X3 multiplier Q 2  triples the frequency of the RF signal received at its input (base). The voltage divider network formed by resistors R 8  and R 15  provide the proper DC biasing voltage to the base of X3 multiplier Q 2 . Resistor R 19  provides a path for DC current to flow through the emitter of X3 multiplier Q 2 . Inductor L 2  provides a path for DC current to flow through the collector of X3 multiplier Q 2 . Inductor L 2  additionally forms part of the X3 multiplier Q 2  output tuning circuit that also includes capacitors C 11  and C 12 . The filter network formed by resistor R 2  and capacitor C 4  prevent the RF energy generated by X3 multiplier Q 2  from leaking into the power source. Capacitor C 83  provides an RF path to ground for X3 multiplier Q 2 . The RF output from the first X3 multiplier Q 2  is coupled to the input of the second X3 multiplier Q 3  via DC blocking capacitor C 16 . 
         [0048]    Second X3 Multiplier: The second X3 multiplier Q 3  triples the frequency of the RF signal received at its input (base). The voltage divider network formed by resistors R 7  and R 16  provide the proper DC biasing voltage to the base of X3 multiplier Q 3 . Resistor R 20  provides a path for DC current to flow through the emitter of X3 multiplier Q 3 . Inductor L 1  provides a path for DC current to flow through the collector of X3 multiplier Q 3 . Inductor L 1  additionally forms part of the X3 multiplier Q 3  output tuning circuit that also includes capacitors C 8  and C 9 . The filter network formed by resistor R 3  and capacitor C 5  prevent the RF energy generated by X3 multiplier Q 3  from leaking into the power source. Capacitor C 83  provides an RF path to ground for X3 multiplier Q 3 . The RF output from the second X3 multiplier Q 3  is coupled to the transmit antenna circuit via DC blocking capacitor C 57 . 
         [0049]    Transmit Antenna: The transmit antenna circuit, in this example, is comprised of the resistor network containing resistors R 0 , R 38  and R 39 , coupling capacitor C 27 , inductors L 4 , L 5 , L 6 , L 7 , and capacitors C 31 , C 59  and C 65 . With this circuit arrangement, the batteries BT 1  and BT 2  also become part of the tuned transmit antenna circuit. 
         [0050]    Theory of Receiver Circuit Operation: Referring again to  FIG. 2 , the components of the receiver section of the transceiver circuitry are seen on the bottom half of the schematic diagram. 
         [0051]    The receiver is shown, in this example, to produce an audio output that drives an earphone EAR 1 , but could easily be slightly modified by a person reasonably skilled in the art to produce a baseband output that can drive another circuit that accepts audio signals (including data modulated into an audio form, such as with a modem). 
         [0052]    The receiver circuit has four main sections. These include receive antenna ANT 1  and its associated components, which feed low-noise RF amplifier (LNA) Q 4  and its associated components, which in turn feed receiver chip U 7  and its associated components, which demodulate the baseband signal to produce audio that is fed to the audio amplification section that includes baseband amplifiers U 3  and U 4  along with their associated components. 
         [0053]    Receive Antenna: In operation, antenna ANT 1  passes RF signals impressed onto its elements through inductors L 12  and L 13 , capacitor C 53  and inductor L 14  onto the base of LNA Q 4 . 
         [0054]    Low-noise Amplifier (Lna): LNA Q 4  has the following supporting components: 
         [0055]    Capacitors C 48 , C 70 , C 79  and C 85  are used to filter to ground any RF signals that would otherwise be modulated onto the DC power source. R 34  and R 36  form a voltage divider network that uses current available from connection point VBAT_LNA to set the bias on the base of LNA Q 4 . Inductor L 14  and capacitor C 54  compose the input tuning elements of LNA Q 4 . Inductor L 15 , capacitor C 58  and capacitor C 84 , in combination, compose the output tuning elements of LNA Q 4 . Resistor R 32  and R 37  provide the appropriate DC biasing voltages to LNA Q 4  when it is in a quiescent state. 
         [0056]    When operational, LNA Q 4  amplifies the received RF signal, and couples the amplified signal to the RF input (pin  8 ) of receiver chip U 7  via DC isolation capacitor C 55  and inductor L 11 . Note that inductor L 11 , capacitor C 46  and capacitor C 47 , in combination, form an RF band filter to eliminate out-of-band signals that have been amplified by LNA Q 4 . 
         [0057]    Receiver Chip: Receiver chip U 7  is a very-low-current ‘receiver-on-a-chip’ component that contains the well-known circuits commonly used in RF receivers. Receiver chip U 7  has the following external supporting components: 
         [0058]    Capacitor C 32  is connected directly between circuit ground and pin  1  of receiver chip U 7 , providing tuning of chip-internal de-emphasis for the received audio. Resistor R 48 , capacitors C 39  and C 40  and inductor L 8  are connected across pins  2  and  3  of receiver chip U 7 , determining the operating frequency of the internal local oscillator of receiver chip U 7 . Crystal Y 2  and inductor L 17  are connected across pins  4  and  5  of receiver chip U 7 , providing tuning to the chip-internal RF oscillator of receiver chip U 7 . Capacitors C 43 , C 52  and C 44  and inductor L 10  are connected across pins  8  and  9  of receiver chip U 7 , providing tuning elements to the chip-internal receiver&#39;s front-end stages. Capacitors C 46  and C 47  and inductor L 11  form an input filter network, connecting the output of LNA Q 4  to the RF signal input pin  8  of receiver chip U 7 . Resistor R 49  is connected between ground and pin  10  of receiver chip U 7 , providing a pull-down condition to the chip-internal comparator of receiver chip U 7 . Capacitor C 51  is connected between ground and pin  11  of receiver chip U 7 , providing a filter for receiver chip U 7 . Resistor R 33  is connected between ground and pin  13  of receiver chip U 7 , setting the output audio volume of receiver chip U 7 . Capacitors C 30 , C 42  and C 77 , along with ferrite bead M 1 , provide filtration of RF energy from the DC source for receiver chip U 7 . The audio signal output of receiver chip U 7  is coupled from pin  12  across capacitor C 56 , and through DC blocking capacitor C 45  and resistor R 30  to the input pin  3  of baseband amplifier U 3 . 
         [0059]    Audio Amplifier Section: The audio amplifier section of the receiver is comprised of baseband amplifiers U 3  and U 4  along with their associated components. 
         [0060]    Baseband amplifiers U 3  and U 4  are arranged as a differential pair, having the following associated components: 
         [0061]    Audio received at the input (pin  3 ) of baseband amplifier U 3  is amplified and coupled from its own output pin  4 , directly to the bottom input pin of earphone EAR 1 , as well as through resistor R 25 , across RF filter capacitor C 76 , to the input (pin  1 ) of the second baseband amplifier U 4 . Filter capacitor C 78  prevents stray RF signals from being impressed upon the input of baseband amplifier U 3 . Filter capacitor C 29  prevents any signals generated by baseband amplifiers U 3  or U 4  from being coupled to the power source present at connection point VBAT_TX_AA. The voltage divider network comprised of resistors R 24  and R 26  set the operational bias for baseband amplifier U 3 . Resistor R 27  sets the gain characteristics of baseband amplifier U 3 . Capacitor C 34  prevents high-frequency oscillations from being generated by baseband amplifier U 3 . Audio received at the input (pin  1 ) of baseband amplifier U 4  is amplified and coupled from its own output pin  4 , directly to the top input pin of earphone EAR 1 . Filter capacitor C 76  prevents stray RF signals from being impressed upon the input of baseband amplifier U 4 . The value of resistor R 28  sets the operational bias for baseband amplifier U 4 . Resistor R 29  sets the gain characteristics of baseband amplifier U 4 . Capacitor C 37  prevents high-frequency oscillations from being generated by baseband amplifier U 4 . 
         [0062]    Theory of Power Management Circuit Operation: Referring once again to  FIG. 2 , the batteries BT 1  and BT 2 , and their associated components, are seen on the left-hand side of the schematic diagram at about the vertical midpoint of the diagram. Switch Q 6  is seen in  FIG. 2  directly above receiver chip U 7 . 
         [0063]    Still referring to  FIG. 2 , the following electrical connection points are labeled: VBAT 1 , VBAT 2 , VBAT_TX_AA, VBAT_SW, TX_VCC, CURRENT_SENSE, VBAT_LNA, CXR_DET, and VBAT 1 _OFF. Each of these electrical connection points has at least one mating, identically-labeled, electrical connection point in the schematic section shown in  FIG. 1 . 
         [0064]    Now referring back to  FIG. 1 , microcontroller U 9  is seen on the bottom-center of the schematic diagram. Dual P-channel digital field-effect transistor (FET) Q 5  is seen at the top center of the schematic diagram. Operational amplifier U 11  is seen on the top, right-hand side of the schematic diagram. These components are used to control the availability of current to various portions of the transceiver from each of the available sources. 
         [0065]    Referring once again to  FIG. 2 , it can be seen that battery BT 1  and battery BT 2  provide a center-tapped power source for the transceiver&#39;s transmit and receive circuits. The negative side of battery BT 1  is the DC power ground for the transceiver circuits. The positive side of battery BT 1  (connected directly to the negative side of battery BT 2 ) provides, via inductor L 16 , a positive 1.4 volts current source (VBAT 1 ) to the emitter of switch Q 6 . The positive side of battery BT 2  provides, via inductors L 7 , L 4  and L 5 , a positive 2.8 volts current source (via connection point VBAT 2 ) to pin  1  of FET Q 5 , pin  4  of FET Q 5  and pin  1  of microcontroller U 9  (all seen in  FIG. 1 ). 
         [0066]    Operational amplifier U 11  (seen in  FIG. 1 ), using feedback from R 53  (seen in  FIG. 2 ) via the CURRENT_SENSE signal and resistor R 54  (seen in  FIG. 1 ), provides a constant supply current via connection point TX_VCC to the transmitter circuit. Filter capacitor C 72  prevents stray RF signals from being impressed onto the input pin  1  of operational amplifier U 11 . Filter capacitor C 67  drains to circuit ground any RF energy present at DC power input pin  5  of operational amplifier U 11 . 
         [0067]    Control of the each of the various current sources used by the transceiver is handled by microcontroller U 9  through the connections and components described below. Later in this disclosure, the simple logic programmed into microcontroller U 9  is described in detail under the heading of “Microcontroller Logic.” 
         [0068]    When pin  5  of microcontroller U 9  is set to a logical low output condition, pin  5  of FET Q 5  is driven simultaneously to a logical low input condition. 
         [0069]    During the times that pin  5  of FET Q 5  is pulled to a logical low input condition, an internal short circuit is created between pins  3  and  4  of FET Q 5 . This allows current to flow from current source VBAT 2  to all connection points in common with connection point VBAT_LNA. This is the source of current used to power the low-noise amplifier (LNA) Q 4  of the receiver circuit shown in  FIG. 2 ). The current that flows through the LNA Q 4  circuit is drained into connection point VBAT 1 _SW, thus providing an additional current source to any components that use VBAT 1 _SW as a source of power input. 
         [0070]    Alternately, when pin  5  of microcontroller U 9  is raised to a logical high output condition, pin  5  of FET Q 5  is driven simultaneously to a logical high input condition. 
         [0071]    During the times that pin  5  of FET Q 5  is pulled to a logical high input condition, an internal open circuit is created between pins  3  and  4  of FET Q 5 . This prevents current from flowing from current source VBAT 2  to any connection points in common with connection point VBAT_LNA. This is the source of current used to power the low-noise amplifier (LNA) Q 4  of the receiver circuit shown in  FIG. 2 ). 
         [0072]    Referring back to  FIG. 2 , receiver chip U 7 , whose VSS (ground) is on pin  14 , and whose input power is on pins  15  through  17 , has two sources of input power. 
         [0073]    Current for receiver chip U 7  is available via resistor R 53 , the VBAT 1 _SW connection point and ferrite bead M 1  during the times that any or all of oscillator Q 1 , X3 multiplier Q 2  and X3 multiplier Q 3  are conducting current between their collector and emitter. 
         [0074]    Current for receiver chip U 7  is also available from connection point VBAT 1 , via switch Q 6 , when switch Q 6  is turned on (allowing current to flow between its emitter and collector) by presence of a logical low signal on its base. The collector of switch Q 6  provides VBAT 1 -sourced current to connection point VBAT 1 _SW (and therefore to receiver chip U 7  via ferrite bead M 1 ). 
         [0075]    Microcontroller Logic: Now referring to  FIG. 1 , microcontroller U 9  is programmable by placing a ‘programming voltage’ on its own pin  4  (via connection point TP 1 ), while providing binary program data serially into its own pin  7  via connection point TP 2 . Microcontroller U 9  is programmed with simple well-known internal logic functions that perform the following operations: 
         [0076]    First, microcontroller U 9  is in sleep mode (internal oscillator running, internal system clock stopped) most of the time. The internal logic of microcontroller U 9  assumes an initial condition of the logical CXR_DET signal input (on its own pin  6 ) to be at a logical low. The CXR_DET signal is generated by receiver chip U 7  (on its own pin  10 , as seen in  FIG. 2 ) when sufficient RF signal is being received to allow clear communications. 
         [0077]    Second, every 17 milliseconds, microcontroller U 9  “wakes up” upon receipt of an interrupt signal generated by an internal watchdog timer. Microcontroller U 9  counts 30 of these interrupt signals before it initiates a detection cycle, thus minimizing the amount of time that the internal comparator of microcontroller U 9  and the RF receiver circuit are turned on (drawing current from the batteries). This results in the processing of a single detection cycle every 510 ms. 
         [0078]    Third, upon receipt of the first interrupt of a detection cycle, microcontroller U 9  turns on its internal comparator, and then drives its own pin  5  to a logical low level, which causes power to be connected to receiver chip U 7  and LNA Q 4  (both seen in  FIG. 2 ). Then microcontroller U 9  sleeps until it receives the next interrupt from its internal watchdog timer. 
         [0079]    Fourth, upon receipt of the second interrupt of a detection cycle, microcontroller U 9  goes back to sleep to give the receiver chip U 7  another 17 ms to power-up and establish reception of sufficient RF carrier signal, if any is present. 
         [0080]    Fifth, upon receipt of the third interrupt of a detection cycle, microcontroller U 9  checks its internal comparator to determine the logical signal level present on its own pin  6 . The input on pin  6  is a logical CXR_DET signal received from receiver chip U 7  (seen in  FIG. 2 ). If sufficient RF carrier signal is not detected by receiver chip U 7 , receiver chip U 7  outputs a logical high as the CXR_DET signal. When sufficient RF carrier signal is detected by receiver chip U 7 , receiver chip U 7  outputs a logical low as the CXR_DET signal. 
         [0081]    Sixth, if a logical low is detected on pin  6  of microcontroller U 9  (sufficient RF carrier signal is detected), microcontroller U 9  drives its own pin  3  to a logical low level, thus connecting power to the transceiver&#39;s transmitter circuitry by pulling pin  2  of FET Q 5  low, which causes FET Q 5  to create an internal short circuit between its own pins  4  and  6 . This allows current available at connection point VBAT 2  to be delivered to all points connected to connection points VBAT_TX_AA (audio circuits) and TX_VCC (transmitter circuits). Then microcontroller U 9  goes back to sleep with both the transmitter and receiver circuitry powered on. Microcontroller U 9  wakes up and checks its own pin  6  condition upon reception of each subsequent interrupt signal from its internal watchdog timer. If the condition is still a logical low (sufficient received RF carrier is still present), microcontroller U 9  goes back to sleep until the next received interrupt signal. 
         [0082]    Seventh, if, in the third interrupt of the detection cycle (or one of those subsequent interrupts when the condition of its own pin  6  is checked), microcontroller U 9  finds its own pin  6  condition at a logical high (there is not sufficient received RF carrier signal), microcontroller U 9  drives both of its own pins  5  and  3  to a logical high level, thus disconnecting power from the receiver and transmitter circuits. Microcontroller U 9  then internally turns off power to its internal comparator, goes to sleep, and returns to step 2 above (restarts the whole cycle). 
         [0083]    Microcontroller Power Savings Strategies: Microcontroller U 9  uses an internal R/C oscillator that operates at 4 MHz, and has a 1-microsecond instruction time. Microcontroller U 9  executes about 10 instructions in a 50 ms wait cycle, and about 15-17 instructions in any of its other active modes. This means that microcontroller U 9  is only awake for a maximum of 17 microseconds out of every 17 ms, or a 1:1000 cycle. This makes the power conservation of an already low-power microcontroller several orders of magnitude better. 
         [0084]    Regarding the 500 ms carrier-detect cycle strategy: If no received RF carrier signal is detected by receiver chip U 7  (seen in  FIG. 2 ), microcontroller U 9  turns on its internal comparator, along with receiver chip U 7  and LNA Q 4  for only 34 ms out of 500 ms, a duty cycle of 1:15. In this manner, the actions of microcontroller U 9  decrease the net current consumption of the receiver to 1/15 of that which would be drawn if those same receiver circuits were turned on continuously. 
         [0085]    Thus, the inventive features and advantages are incorporated into the preferred embodiment of the transceiver represented by the schematic drawings of  FIG. 1  and  FIG. 2 . 
         [0086]    Alternative Preferred Embodiments of the Invention: To those reasonably skilled in the art, it can be seen that the alternative embodiment of the inventive transceiver (represented by the schematic drawing shown in  FIG. 3  and  FIG. 4 ) incorporates the novel features and advantages claimed in the present invention. It can also be seen that, while some specific component values of the alternate embodiment vary from those shown in the preferred embodiment (seen in  FIG. 1  and  FIG. 2 ), these value changes do not impact the inventive features incorporated into the transceiver design. 
         [0087]    Now referring to  FIG. 3 , the power control section of an alternate embodiment of the inventive transceiver is schematically represented. In this embodiment, microcontroller U 2  operates to control the various current sources available to the transmitter and receiver circuits of the transceiver in the same manner as does the preferred embodiment. Adjunct microcontroller U 3  works in concert with microcontroller U 2 . FET Q 1  is controlled by microcontroller U 2  to turn on and off the current sources that are used by the transmitter and receiver circuits of the transceiver. This is accomplished in the same manner that is described above in the detailed description of the preferred embodiment of the invention. In the preferred embodiment (seen in  FIG. 1 ), microcontroller U 9  is the functional equivalent of microcontroller U 2  of the alternate embodiment, and FET Q 5  is the functional equivalent of FET Q 1  of the alternate embodiment. 
         [0088]    Now referring again to  FIG. 3 , operational amplifier U 1  is used to provide a constant current source to the transmitter circuits of the transceiver in the same way the U 11  of the preferred embodiment (seen in  FIG. 1 ) performs this function. 
         [0089]    In the alternate embodiment of the power control section shown in  FIG. 3 , switch Q 2  is the functional equivalent to switch Q 6  of the preferred embodiment (seen in  FIG. 2 ). Switch Q 2 , under the direct control of microcontroller U 2 , is used to control the current available to receiver chip U 7  from connection point VBAT 1 . 
         [0090]    Now referring to  FIG. 4 , a schematic view of an alternate embodiment of the transmitter, receiver and battery circuits of the inventive transceiver is seen. In the alternate embodiment, receiver chip U 7  operates exactly as detailed in the description of the preferred embodiment (the preferred embodiment&#39;s receiver chip is seen in  FIG. 2  as U 7 ). 
         [0091]    Still referring to  FIG. 4 , the alternate embodiment of the inventive transceiver has essentially the same transmitter circuit blocks and receiver circuit blocks as does the transceiver of the preferred embodiment of the invention. 
         [0092]    These circuit blocks include, in the transmitter section, an external microphone, or other audio source, connected to an audio preamplifier U 4 , (via connection points Z 1  and Z 2 ). Preamplifier U 4  impresses baseband onto the base of voltage controlled crystal oscillator (VXCO) Q 5 , thus modulating the audio onto the RF signal generated by VXCO Q 5 . First X3 multiplier Q 3  and second X3 multiplier Q 4  raise the modulated RF carrier signal to the operating frequency of the transmitter. In the alternate embodiment of the inventive transceiver, the transmit antenna circuit does not utilize the batteries (as does the preferred embodiment). The batteries, in the alternate embodiment, are connected through connection points Z 3 , Z 4  and Z 5  to mechanical switch SW 1 . Mechanical switch SW 1  is used to turn disconnect the externally connected batteries from connection points VBAT 1  and VBAT 2 . 
         [0093]    These circuit blocks also include, in the receiver section, a receive antenna (using the microphone cable as part of the antenna) connected to the input of a low noise amplifier Q 6 , which feeds received RF signals to receiver chip U 7 . Receiver chip U 7  down-converts and demodulates the received RF signal and passes the baseband signal to baseband amplifiers U 5  and U 6 , which operate as a differential pair to drive a speaker or headphone (via connection points Z 8  and Z 9 ). 
         [0094]    Still referring to  FIG. 4 , it is notable that receiver chip U 7 , of the alternate embodiment of the inventive transceiver, has the same current sources available as are described in the detail of the preferred embodiment. Thus receiver chip U 7  of the alternate embodiment reuses current from the transmitter circuits, as well as from LNA Q 6  and the bias resistors R 1  and R 6  (seen in  FIG. 3 ). Additionally, the logic used by microcontroller U 9  (of the preferred embodiment of the inventive transceiver seen in  FIG. 1 ) to control the current sources available to the rest of the transceiver (and to conserve on its own power usage), is the same logic used to by microcontroller U 2  of the alternate embodiment (seen in  FIG. 3 ). 
         [0095]    It can therefore be understood that the alternate embodiment of the invention (shown in  FIG. 3  and  FIG. 4 ), while having different component values and arrangements than those of the preferred embodiment (seen in  FIG. 1  and  FIG. 2 ), the resulting conservation of power is essentially accomplished in the same manner, with essentially the same results. 
         [0096]    The above disclosure is sufficient to enable one of ordinary skill in the art to practice the invention, and provides the best mode of practicing the invention presently contemplated by the inventor. While there is provided herein a full and complete disclosure of the preferred embodiments of this invention, it is not desired to limit the invention to the exact construction, dimensional relationships, and operation shown and described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true spirit and scope of the invention. Such changes might involve alternative materials, components, structural arrangements, sizes, shapes, forms, functions, operational features or the like. 
         [0097]    Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is defined by the appended claims.