Abstract:
A video camera recorder comprises an imaging means receiving an optical image and generating an image representative video signal, and a viewfinder for viewing the optical image. A synchronizing signal generator is coupled to the imaging means and to a recording means which is coupled to the imaging means. A control means for optimizing power conservation has a first mode which enables operation of the synchronizing signal generator and inhibits operation of the imaging and recording means. In a second mode the control means enables the synchronizing signal generator and recording means for reproducing a recorded image representative video signal and inhibits operation of the imaging means. In a third mode the control means enables the imaging means, the synchronizing signal generator and the recording means for recording the image representative video signal from the imaging means.

Description:
This invention is directed to the field of portable electronic recording cameras and in particular to the reduction of power consumption and manufacturing costs. 
     BACKGROUND OF THE INVENTION 
     Video recording cameras, or camcorders, typically utilize a solid state imager. The imager generates an image signal which is processed to form a video signal for television viewing or recording. Typically a camcorder includes a viewing device, or viewfinder, for viewing the scene, which may additionally be utilized for reviewing recorded material. The recording section may utilize a magnetic tape recording medium, magnetic disk, or solid state memory. The complete camera and recorder may be battery powered, often by a rechargeable battery. 
     A typical camcorder is illustrated in FIG. 1, and may be considered to comprise the major functional blocks shown. A zoom lens  100  is provided to gather illumination from a scene, and form a focused image on an imaging device  205 . The zoom lens  100 , usually provides control of three parameters namely, focus  110 , zoom or magnification  120 , and iris or aperture  130 . Control of these optical parameters are usually facilitated by physical movement of constituent parts within the lens. For example, the iris or lens opening may be provided by a multi-blade diaphragm, zoom and focus may be facilitated by the repositioning of internal lenses. Often such mechanical movements are provided by electrically powered motors, frequently servo controlled to provide automatic optimization of the controlled parameter. 
     Imaging device  205 , may for example be a charge coupled device or CCD, depicted FIG. 1 as part of a video signal generator  200 . The video signal generator processes signals received from the CCD to stabilize black and white levels therein, to automatically control white balance, and to pre-correct or gamma correct the generated video signal for cathode ray tube, CRT, viewing. In addition processing is provided to enhance picture sharpness and to provide servo control signals for coupling to the lens for focus and iris control. 
     The processed video signals are encoded by encoder  300 , which produces a standard color signal for television viewing. In addition a video signal is generated for coupling to a viewfinder  50 . Luminance and encoded color subcarrier signals are generated by the encoder and record processed by amplifier  505  which is coupled to heads on head drum  510 . 
     Recorder  500  is depicted as a magnetic tape recorder, utilizing a rotating head assembly or drum  510  comprising, for example, record, replay and erase heads. A capstan  520  with pinch roller  530  is employed to move the recording medium. Recorder  500  is shown loaded and threaded with tape  504  withdrawn from tape cassette  501  by threading mechanism and motor  527 . The cassette comprises a tape supply reel  502  and a take up reel  503 . Head drum  510  is rotated by motor  515  and is synchronized with the video signal, similarly capstan  520  is rotated by motor  525  which is also synchronized with the video signal. 
     The luminance and coloring signals are processed by a record and play back amplifier  505  which generates signals for recording and reproduction by heads mounted on the periphery of head drum  510 . Reproduced signals from amplifier  505  are coupled to encoder  300  for viewfinder viewing and for processing to form a standard TV signal. The camcorder is controlled by a microprocessor  400  which operates in conjunction with a recorder mechanism controller  560 . 
     Audio signals are captured by a microphone  70  and amplified by amplifier  75 . In addition amplifier  75  may generate an audio modulated signal for recording and include a demodulator for audio reproduction and output coupling. 
     Camcorder  10  is powered by a battery  600 , which for example, may be a rechargeable type having a nickel cadmium structure. Typically camcorders may function as a recording camera, or a VCR play back device. Battery power consumption is greatest when recording, and increases further with frequency of zoom lens and iris operation. Often a record pause mode is provided which allows recording to be halted and resumed without a visible replay disturbance. However, this mode frequently provides only minimal power savings, since in order to provide rapid resumption of recording, the head drum motor and capstan pinch roller often remain powered. 
     It is desirable that camcorder power consumption be reduced, for example, to provide increased operating time with a specific battery size or chemistry. Reduced power consumption may also, for example, allow the use of physically smaller batteries yielding a smaller or lighter camcorder. Reduced power dissipation may also permit camcorder operation with non-rechargeable or other battery chemistries, for example alkaline cells. 
     Clearly electronic circuit changes may offer opportunities for power reduction. However, both the viewfinder and the sustained synchronous rotation of the head drum and capstan motors represent the major sources of power dissipation. Hence, a significant reduction in power consumption may be achieved only if a corresponding reduction or compromise in operational facilities, camcorder operability, and user convenience is deemed acceptable. 
     SUMMARY OF THE INVENTION 
     A video camera recorder comprises an imaging means receiving an optical image and generating an image representative video signal. A viewfinder for viewing the optical image and a means for generating synchronizing signals is coupled to the imaging means. A recording means is coupled to the synchronizing signal generating means and to the imaging means. A control means for optimizing power conservation, has a first mode of operation in which the control means enables operation of the synchronizing signal generating means and inhibits operation of the imaging means and the recording means, and has a second mode of operation in which the control means enables operation of the synchronizing signal generating means and the recording means for reproducing a recorded image representative video signal and inhibits operation of the imaging means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a block diagram of a video recording camera. 
     FIG. 2 depicts in block diagram form a video recording camera having various inventive features. 
     FIG. 3 depicts in block diagram form an inventive video recording camera with electronic viewfinder. 
    
    
     DETAILED DESCRIPTION 
     The video recording camera depicted in the block diagram of FIG. 1 shows magnetic tape  504  threaded around the periphery of head drum  510  to facilitate either recording or reproduction. Typically two operating modes are provided, namely CAMERA and VCR. The VCR mode allows reproduction from tape  504  and provides a replayed video signal for viewfinder display and an output signal to permit the external review of a recorded video signal on a video monitor or television receiver. The CAMERA mode may, for example, be considered to comprise three sub-modes, namely imaging a scene, recording the imaged scene and pausing the recording. However, the imaging mode assumes the RECORD paused condition whenever a video tape cassette is loaded. The RECORD pause condition provides the user with the ability to change the recorded scene with the camcorder able to rapidly resume recording without a discontinuity in the recorded signal. Typically when the RECORD pause mode is selected the recording process may be sustained with record amplifiers powered, and the cylinder motor rotating in a synchronized condition. However, the tape is stationary with the capstan pinch roller energized and capstan rotation stopped. Hence, although the RECORD pause mode provides user operational convenience, it may offer little saving in power consumption from that dissipated during recording. 
     In FIG. 1 control microprocessor  400  is illustrated connected to battery  600  in all camcorder modes. When the camcorder is OFF this connection represents the major source of battery drain or discharge and is typically considerably greater than the battery internal self discharge. Typically this microprocessor connection is provided to allow remotely controlled activation or to permit tape cassette ejection without turning the camcorder ON. 
     FIG. 2 is a block diagram of an advantageous video recording camera  1000  embodying various inventive features. Elements common to both FIGURES use the same numbers. In FIG. 2, a manually operated zoom lens  1200  is illustrated having, for example, a lever coupled via gears to vary zoom lens magnification. The provision of manual zoom operation, reduces both power consumption, and lens cost. In the manual zoom lens, focus element  110  may no longer be required since the imager size is small, for example 0.25″, with a correspondingly short back focal length, thus fixed focus operation may be achieved. The use of a fixed focus lens further reduces the lens cost and eliminates the need for a focus servo mechanism. The elimination of the focus servo mechanism eliminates focus servo amplifiers and circuitry associated with automatic focus control, thus further reducing both power consumption and product cost. Although the zoom lens is manually operated with fixed focus, an iris diaphragm  130  and servo control loop may be utilized to provide automatic control of video level. 
     In FIG. 2 an optical viewfinder  5000  is illustrated. Viewfinder  5000  may be optically or mechanically coupled to the zoom lens to provide the user with ostensibly the same view and magnification as that imaged. Alternatively a viewfinder may be utilized without lens coupling where the relative image sizes for various zoom magnifications are indicated by an eye piece graticule or by engraving on a viewing screen S. 
     Camcorder  1000  is advantageously powered by battery  6000  which may, for example, comprise primary cells, or primary cells capable of recharging. The use of primary cells, for example, alkaline chemistry cells, permits camcorder operation in situations where battery charging or charger power is unavailable. Alkaline batteries for example, offer user benefits of convenience and wide availability plus extended operational flexibility. Camcorder  1000  may also be powered by conventional rechargeable cells, for example NiCd or lead acid. In addition the camcorder may be powered from an external power source, for example, an AC powered supply or automobile battery coupled via connector J 1 . The microprocessor may detect the coupling of an external power supply and modify or adapt power reduction rationales commensurate with the potentially abundant source of external power. In FIGS. 2 and 3, a DC to DC converter is depicted coupled between the battery and the camcorder loads, however various of the loads, for example, the motors, may be controllably coupled directly to the unregulated battery supply. 
     The use of primary cell power is predicated on advantageous power reduction methods employed in camcorder  1000 . As has been described, useful power savings may be gained from the use of a manually operated zoom lens with a fixed focal length. The manual zoom lens may compromise user operational features, but eliminates battery power dissipation resulting from frequent, and often unnecessary powered zoom operation. In addition, the zoom drive motor and associated circuitry are eliminated together with the focus motor, and auto focus servo system. The use of an optical viewfinder may provide similar savings in terms of both power dissipation and cost. 
     FIG. 2 illustrates a power switch S 1  which provides selection between VCR only operation or camera and VCR operation. Switch S 1  also shows a RECORD/RECORD pause mode, however the RECORD/RECORD pause mode is usually associated with a separate RECORD push button or switch. Switch S 1  depicts the RECORD pause condition to illustrate selective powering of certain circuit functions during the RECORD pause condition. 
     Usually when a camcorder is turned off, current continues to be drawn from an attached battery, until discharged below the operating voltage of range of the camcorder power supply and ultimately the memory retention potential of the microprocessor system. This battery discharge current usually supplies the microprocessor and is significantly greater than the self discharge currents within the battery. Microprocessor power is sustained to enable, for example, remotely controlled camcorder activation or tape cassette ejection. In inventive camcorder  1000 , external current drain from an attached battery is eliminated when mode control switch S 1  is in the OFF position. Thus the microprocessor is nominally off and no longer powered from an attached battery, this eliminates remote controlled activation by IR receiver  4010 , and requires that the camcorder is ON in either the CAMERA or VCR mode in order for cassette ejection. When the camcorder is turned OFF, a clock function and memory associated with the control microprocessor  4000  may be sustained by a small internal, rechargeable battery, such as a lithium cell. In addition camcorder  1000  may provide a mechanical tape cassette ejector for use when power is unavailable. The ejection mechanism may, for example, be spring powered where an ejector spring is coiled or cocked by previous manual cassette insertion. Following emergency mechanical cassette ejection, the ejection mechanism must be reprimed by manually loading a cassette before normal camcorder operation is possible. The trigger mechanism for emergency cassette ejection may concealed and is mechanically interlocked to prevent ejection with the tape threaded. In addition whenever VCR assumes an OFF condition the tape is unthreaded and returned to the cassette. 
     Analysis of camcorder power consumption reveals that the RECORD mode dissipates most power. Clearly, the RECORD mode requires operation of both imaging and recording parts of the camcorder. The camera converts an image into a video signal, and the recorder transports the tape between the reels and powers a synchronized rotating head drum for recording. 
     In many camcorders the power dissipated when RECORD paused is similar to that of the RECORD mode. However, the RECORD pause mode of advantageous camcorder  1000  may be configured to greatly reduce power dissipation. Since an optical viewfinder is employed, there is no camcorder display destination for image video. Hence there is no requirement or need to image the scene and generate a corresponding video signal until the user selects the RECORD mode. Thus, imager  205  and camera video processing section  200  may be advantageously activated and dissipate battery power, only during the RECORD mode. Similarly encoder  300  may be fully powered during recording, powered down during RECORD pause, and may be partially powered to form an output video signal in a VCR playback mode. 
     The power reduction method described for the RECORD pause mode may yield further power savings if additional operational compromises are acceptable. For example, currently when RECORD paused the capstan motor may be stopped with the pinch roller engaged, however the head drum continues to be powered and synchronized. Stopping the head drum in a RECORD pause mode may yield power savings. However, an attendant operational compromise results in that the resumption of recording may be delayed until the head drum is synchronized. Such an operational compromise may be acceptable if of sufficiently short duration, for example, about 2 seconds. Such a recording delay may be largely inconsequential in most user circumstances, and may be signaled to the user by illuminating or changing the condition of an indicator, for example, flashing indicators  5050  or  5060  during record synchronization. 
     Certain video recording formats employ a technique known as back space editing where at the cessation of recording the direction of tape travel is reversed, and backed up a predetermined distance, played and then stopped. On receipt of a user record trigger the previously recorded tape section is replayed and tracking set prior to over recording the last few tracks of the previous record. A further opportunity for power saving may result from halting drum rotation at the cessation of recording and reversing the tape direction as described but then halting tape motion. Thus the tape is backed up the same distance and power is saved by stopping head drum and not moving the tape forward as described. However, on receipt of the user&#39;s record trigger the drum motor must be started, and synchronization achieved prior to setting tracking. In addition the capstan must move the tape to a predetermined location to start over recording. Typically the tape is backed up about 112 tracks, and moved forward about 76 tracks prior to parking in the RECORD paused condition. When record triggered the tape is replayed for about 30 tracks to set tracking, prior to the start of over recording. Thus a duration of about 106 recorded tracks is available to synchronize the drum motor, move the tape and recover tracking information. By changing the back space edit sequence when RECORD paused, significant savings in drum motor dissipation may result with only a minimal increase in recording start delay. Typically the start of recording is delayed by about 30 fields, this delay would become about 106 fields with the proposed method. To reduce drum motor synchronization time an acceleration power supply Vacc may be switched to power the motor drive amplifiers during a start period. FIGS. 2 and 3 show a three position switch connected to head drum motor  515 , an actual realization of the switch functions may be achieved by an integrated circuit motor drive amplifier. However, the three positions illustrated represent a stop mode S, run mode R and an acceleration mode A. Following receipt of the record trigger the higher voltage power supply Vacc is applied during an initial period, for example one second, or until synchronous rotation is achieved, after which time the normal run mode supply voltage is restored. The transition from the acceleration supply to the run supply may be arranged to ramp down in order to avoid unnecessary additional, or lengthened servo lock up time. The use of a higher voltage acceleration supply Vacc may provide drum synchronization times which may enable the delay of 106 fields to be reduced, for example the tape may be backed up a shorter distance than the current 112 tracks. 
     Further consideration of camcorder  1000  suggests that the use of a manual, focus free zoom lens and optical viewfinder, may allow the camera image generation and processing section to be powered only in the RECORD mode. This power saving rationale may result in a compromise where the camera generates only a recording video signal, for example Y and C. An encoded video output signal may be unavailable from the camera during RECORD or RECORD paused modes. A standard encoded video output signal may be generated only during VCR replay, or from the camera when a tape cassette is not loaded. 
     In FIG. 2 head drum  510  is depicted with heads A, B and E, typically heads A and B are utilized for both recording and reproduction with head E providing erasure. Heads A and B are positioned on the drum nominally 180 degrees apart, and by virtue of the angle of tape  504  wrapped around the drum, provide periods when a single head A or B is in contact with the tape, and other times when both beads contact the tape. However, when recording, during periods of single record head contact the other record head, and associated record amplifier are uselessly generating a recording field directed into fresh air. Record amplifier power dissipation may be reduced by turning off, or gating each head and associated record amplifier during periods of non-tape contact. However, the timing of this record gating must permit the required tape edge overlap periods to be recorded. In FIGS. 2 and 3 an exemplary non-tape contact angle of about 120 degrees is illustrated, hence a gated record amplifier may provide a power saving of about 30%. During a RECORD paused condition both recording amplifiers may be turned off thus providing a further power saving. 
     Clearly not all electronic systems within camcorder  1000  can be powered down and still provide the user with an acceptably short recording start time. For example, in FIG. 2, camcorder  1000  is depicted with the control microprocessor  4000 , sync generator  3000  and servo mechanism  560  powered in all modes, but controlled responsive to microprocessor  4000 . If camcorder  1000  is RECORD paused and a RECORD command is received by microprocessor  4000 , the various quiescent systems may be sequentially powered up. For example, to maintain synchronizing pulse stability sync generator  3000  is continuously powered generating sync pulses, power may be applied to the head drum motor  515  and capstan motor  525  to initiate synchronized rotation. The head drum motor lockup time may largely determine the delay in RECORD initiation following an un-pause command. Following motor starting, power may be reapplied to the camera video processor  200  and finally, immediately prior to motor synchronization, power may be reapplied to the video and audio record amplifier  505 . 
     In the exemplary camcorder illustrated in FIG. 3, useful power savings may be achieved by advantageous control of power dissipating loads. For example, a monochrome electronic viewfinder typically employs a cathode ray tube and dissipates just under 1 watt, a color display uses a liquid crystal display with dissipation of slightly more than 1 watt. Hence in a typical camcorder with a total dissipation of approximately 5 watts, useful power savings may be achieved by turning off the viewfinder. However, such power savings may impose operational constraints for the user. Camcorder usage suggests that there are periods when the viewfinder may be powered down providing it may be simply, quickly and automatically reactivated. For example, in a RECORD paused condition, the next wanted scene or image may not occur for some period of time. Hence an exemplary 30 second timer may be set when entering the RECORD paused condition, and if the RECORD mode is resumed within the 30 second period, the timer is reset. However, if the timer is not reset within the 30 second period the viewfinder is automatically turned off. The viewfinder may be turned on by touching any camcorder control, for example, activation of zoom motor  120  may be sensed via coupling  4003 . Typically both monochrome and color displays are operable from power on in about 1 second. 
     Microprocessor  4000  may advantageously monitor external interfaces to the video recording camera, where such external interfaces may comprise user controls and switches, and video, audio and power connectors. For example, microprocessor  4000  may sense the status of the video output connection via coupling  4002 . The presence of coupling to an external video display device may be detected and in response the electronic viewfinder may be deactivated by the microprocessor. Disconnection of the external display device immediately restores viewfinder operation. 
     Microprocessor  4000  normally monitors the status of user controls and switches in order to effect the desired user command, however in addition, these external interface commands may be utilized for adaptively controlling power dissipation within the video recording camera. For example, selection of a replay mode may automatically deactivate the electronic viewfinder during replay of unrecorded tape segments. For example, when replaying or picture searching, following a loss of recorded signals for a predetermined period, the electronic viewfinder is automatically deactivated. The automatic deactivation may for example, result from detecting the absence of sync pulses or the presence of a large amplitude random noise signal. The viewfinder is automatically reactivated with the return of reproduced video, camera video, or at the touch of any camcorder control. 
     An external power source may be coupled to the camcorder via external interface connector J 1 . The presence of the external coupling may be sensed by exemplary connection  4001 , and in response microprocessor  4000  may adaptively determine the degree of power conservation employed by the camcorder. For example, in a RECORD pause condition the presence of external power source may permit sustained operation of various servo controlled motor systems thereby reducing delay in resuming a recording mode. 
     Automatic optical focusing may be required as the image magnification is changed during zooming. Thus the auto focusing system may advantageously powered to adjust and optimize focus only when the zoom control is activated. However, such an auto focusing control rationale may be defeated, hence auto focusing may also be activated by changes in scene brightness, possibly being indicative of change within the scene, and indicated by an auto iris or AGC signal change. By means of selective de-powering unnecessary focus variation is avoided with a consequential power saving. However situations requiring auto focus control are identified and activate the auto focus control servo. This auto focus power saver may be defeated by the user.