Video Camera Synchronizer

1. Field of the Invention

The present invention relates to video recording, and more particularly refers to an apparatus which may be utilized to synchronize two or more color video cameras or other video devices for simultaneous operation.

2. Prior Art

Because of their many advantages, video cameras are used almost exclusively for photographing programs which are to be utilized for television broadcasting, as well as for video recording.

In a television studio, many color video signals are brought together at one point where they are selected, mixed, and/or altered. This point may be called the "switcher". The resultant signal leaves the switcher and goes to a transmitter for "airing" or to a video tape recorder for storage. In order for the switcher to do an adequate and acceptable job, it is required that all video signals at the switcher input be synchronized.

The human eye decodes light as parallel data decoding hue, saturation, and luminance. In contrast, a television system scans the scene and encodes this data as serial information. In order for a television system to convert parallel information to serial, a top (vertical sync) and a left (horizontal sync) must be determined. Additionally, chrominance information (hue and saturation) must be encoded and referenced to color sync. These three sync units are required so that the television receiver can decode the encoded information so that it can faithfully reproduce the scene as the camera views it.

One conventional method of synchronizing signals from several cameras is to have a master sync generator, usually close to the switcher. The master sync generator ator signals are distributed to all of the equipment which originates the video feeding the switcher, i.e., television cameras, title generators, film chains, etc. These cameras, etc., which are synchronized to each other are referred to as being "driven". By being driven, the video equipment is forced to stay in step with other driven video equipment in the system. As it takes only a small amount of time for a signal to go through a cable, and since this time is proportional to the length of the cable, all cables from synchronized, composite video must be electrically the same length from their source to the switcher. Normal practice dictates that the longest video line is run directly into the switcher, the other video lines are then electrically lengthened in order to match. This normally is a tedious operation. In contrast, in the present invention, it is accomplished by automatic timing.

A relatively inexpensive camera relies on digital techniques to generate vertical, horizontal, and color sync within the source. One of these cameras combined with a video tape recorder can provide a consumer with a means of making video home movies. As these cameras have no simple means of being externally synchronized, more than one video source cannot normally be used.

Presently, many different versions of N.T.S.C. (National Television Systems Committee) internal sync generators are in common use. However, most are of the digital type and derive the various synchronizing components from a 14.318180 MHz crystal-controlled oscillator, and use a countdown formula to arrive at the necessary color sync and drive components. Some equipment, such as inexpensive color cameras, use only a single, specially-designed, integrated circuit for a sync, with the only input being the 14.3 MHz crystal input.

The apparatus used for synchronizing video cameras in other forms of the prior art also have a number of disadvantages. The electronic equipment must be custom tailored to fit each make and model camera. This requires an inordinant amount of time to be spent in final engineering of the system. The custom tailored equipment is much too expensive and complicated. It depends on a non-standard, two-conductor, shielded drive cable between the camera and the synchronizer. The camera modification requires the incorporation of a switching-type jack to allow the camera to revert to normal, free running operation when disconnected from the synchronizing unit. The use of such a jack in itself causes reliability problems. The camera modification generally contains a negative voltage power supply which at times causes interference problems. Additionally, the cameras must be matched to the synchronizer with which they are to be used. There is no uniformity between cameras. A further disadvantage is the lock-up (synchronization) time is generally too long, often five minutes or more. This results from the fact that the apparatus simply speeds up or slows down the driven camera voltage-controlled oscillator. Further, the vertical odd/even fields detector circuits are unstable and require frequent realignment. After the unit locks-up (synchronizes the cameras), it sometimes unlocks and starts hunting again when the cameras are moved about (changing scenes and light levels). Further, after even a slight adjustment, one often must wait a long time for the unit to re-lock, to determine whether or not it is working properly. A further disadvantage of the prior art is that the voltage-controlled oscillator which drives voltage to the driven camera is often very noisy and must be carefully adjusted. Another disadvantage is that because of the large number of component parts which must be utilized, the circuit board is too large, crowded and complicated, making assembly and final testing extremely difficult. Final alignment requires much expertise and can only be accomplished by an engineer with very sophisticated equipment. Additionally, the power supply operates at maximum capacity, leaving no reserve for expansion to add additional driven camera outputs. Finally, the inherent color phase correction circuits are sometimes unstable and repeatability of system set-up can be a problem. Additionally, the manual phase control operation may be erratic.

As the term video camera is used herein, it is intended that the term also include other video devices.

In the drawings:

FIG. 1 is a block diagram of the synchronizing apparatus of the invention;

FIG. 2 is a circuit diagram of a portion of the apparatus shown in FIG. 1, showing the circuitry associated with the master camera;

FIG. 3 is a circuit diagram of a remainder of the apparatus shown in FIG. 1, associated with the slave camera; and,

FIG. 4 is a circuit diagram of a portion of the apparatus shown in FIG. 1, showing circuitry for combining the signals generated by the master and slave apparatus and generating signals to synchronize the slave camera to the master camera.

Referring to FIG. 1, a block diagram of the invention is shown comprising video cameras 10 and 11, camera 10 being the master camera and camera 11 being the slave camera, each camera having similar electrical components connected thereto. Associated with the master camera is an input clamp and buffer 12, a sync separator 13 and a burst gate timer 14. Also in the circuitry is a ramp generator comprising a chroma filter 16, a data latch 17 and a ramp output 18. The ramp output 18 is in turn connected to a sample and hold fine horizontal color phase sync 19.

Camera 11 output is connected to an input clamp and buffer 22, the output of which is connected to a sync separator 23 and a burst gate timer 24.

The input clamp and buffer 22, the sync separator 23 and the burst gate timer 24 are connected to a pulse generator 25 comprising a chroma filter 26, a data latch 27 and a sample pulse generator 28. The output of the sync separator 13 and the output of the sync separator 23 are connected to the input of a sync pulse coincidence error detector 31, the output of which is connected to an oscillator pulse generator 32. The output of the ramp output 18 and the sample pulse generator 28 are connected to the input of a sample and hold fine horizontal and color phase generator 19. The oscillator pulse generator 32 and the sample and hold color phase generator 19 are connected to the inputs of VCO control generator 33. The output of the VCO control generator 33 is connected to the input of a VCO slave drive unit 34, and the output of the VCO slave drive unit 34 is connected to the appropriate input of the slave camera 11 and controls its speed of operation.

Referring to FIG. 2, the circuitry associated with the master camera is shown. The circuit includes an input clamp and buffer 12 which comprises an input coil 40 receiving a signal from the master camera. The circuit additionally comprises resistors 41, 42, 43 and 44, capacitors 45 and 46, and NPN transistors 47 and 48.

The sync separator 13 comprises resistors 50, 51 and 52, a capacitor 53, a PNP transistor 54, diodes 55 and 56, and a NAND gate 57.

The burst gate timer 14 comprises an integrated circuit 59 which is one-half of a dual, monostable, multivibrator, capacitors 60 and 61, resistor 62, variable resistor 63 and resistor 64. The circuit also includes NAND gates 65, 66 and 67.

The ramp generator 15 includes a chroma filter 16 which comprises capacitor 68 and resistor 69. The generator also includes a data latch 17 which includes an integrated circuit 70 which is a high-speed, dual line receiver, which converts the incoming color bursts to TTL pulses, one-half used for the master camera channel and the other half used for the slave camera channel. The circuit additionally includes capacitors 71 and 72, a resistor 73, a flip-flop integrated circuit 74, a capacitor 75 and a NAND gate.

The ramp output 18 includes a capacitor 78, diodes 79 and 80, PNP transistors 81, and 83, NPN transistor 82, and resistors 84-91. Resistor 88 is a variable resistor.

Referring to FIG. 3, the circuitry associated with the slave camera is shown. Generally, the circuitry is similar to that associated with the master camera except in certain specified circuitry differences. Similar to the circuitry of FIG. 2, the circuitry associated with the slave camera comprises an input clamp and buffer 22, which comprises an input coil 96 connected with the slave camera 11, resistors 97, 98, 99 and 100, capacitors 101 and 102, and PNP transistors 103 and 104.

The sync separator 23 comprises resistors 107, 108 and 109, a capacitor 110, PNP transistor 111, diodes 112 and 113, and a NAND gate 114.

The burst gate timer 24 comprises an integrated circuit 117, capacitors 118 and 119, resistor 120, a variable resistor 121 and a fixed resistor 122. The circuit additionally includes NAND gates 123, 124 and 125.

The chroma filter 26 includes a capacitor 128 and a resistor 129.

The data latch 27 comprises an integrated circuit TTL burst former 131, capacitors 132 and 133, a resistor 134, and integrated circuit (74221) 135 which is an extra integrated circuit to adjust the slave camera sync phase. The data latch 27 circuit also includes a capacitor 136, resistors 137, 138, 139 and a variable resistor 140. Additional components are a FET transistor 141, a flip-flop integrated circuit 142, a capacitor 143, and a NAND gate 144.

The sample pulse generator 28 comprises a capacitor 146, resistors 147 and 148, a diode 149, and a PNP transistor 150.

Referring to FIG. 4, the sync pulse error detector 31 comprises NAND gates 154, 155 and 156, flip-flop integrated circuits 157 and 158.

The oscillator pulse generator 32 comprises NAND gates 161 and 162, a capacitor 163, resistor 164 and 167, a PNP transistor 165, and an NPN transistor 167.

The sample and hold color phase synchronizer 19 comprises a resistor 171, a field effect transistor 172, a capacitor 173, an OP AMP 174, a resistor 175, capacitors 176 and 177, resistors 178, 179, 180, 181, 182 and 183, a variable resistor 184, and an NPN transistor 186.

The VCO control generator 33 comprises diodes 187 and and 188, resistor 190, an NPN transistor 191, and a PNP transistor 192.

The VCO slave drive unit 34 comprises capacitors 196, 197, 198 and 199, resistors 200, 201, 202, 203, and 210, a diode 204, a 100 microhenry choke coil 205, and a resistor 206. Additionally, a 9 volt DC regulator 207 and a conventional voltage control oscillator assembly 208 are utilized.

In the drawings, letters A, B, C and D are utilized to indicate the inter-connections among the circuits of FIGS. 2, 3 and 4. For example, the lead A of FIG. 2 is connected to lead A of the color phase sample and hold unit; lead B from FIG. 2 is connected to lead B of FIG. 4 at the sync pulse error detector 31. Lead C of FIG. 3 is also connected to lead C of the sync pulse error detector 31, and lead D of FIG. 3 is connected to lead D of FIG. 4 to the color phase sample and hold unit 19.

Preparing for operation, the synchronizer unit is connected to the master and slave video cameras. The composite sync from the master and slave sync separators is fed to the sync pulse coincidence detector circuit. This circuit develops positive error pulses if the master and slave video signals are not synchronized. These error pulses are "anded" with the slave composite sync. The result is a series of sharp, negative-going oscillator shut-off pulses which are present mainly during the slave vertical sync pulse. Because of the inverse voltage to frequency operation of the slave VCO unit, the slave, although hunting during this vertical sync period, keeps itself horizontally locked the balance of time during the framing process. The negative-going oscillator shut-off pulses occur at the master horizontal rate during the slave vertical period and the slave 14.318180 MHz oscillator keeps turning on and off, effectively slowing the slave sync generator down until the master catches up with it. The instant the master is in step with the slave, the output of the sync pulse coincidence detector goes low, turning off the oscillator stop pulses. The ramp signal developed from the color burst is monitored together with the color burst signal from the slave unit and any error voltage adjusts the voltage fed to the VCO and speeds up or slows down the output frequency of the VCO to maintain the master and slave video cameras in synchronization.

Although other components having other values may be substituted for those shown, the components designated in the specifications and drawings have the values shown on the following listings:

Although the discussion above has dealt primarily with synchronizing master and slave video cameras, the present invention may also be used to synchronize video signals from other sources. The prime requisites for so doing are that the devices must operate as follows:

1. Derive synchronizing pulses from a 14.318180 MHz control or its equivalent.

2. The composite video output of the generator must be in accordance with NTSC-RS-170a, or its equivalent.

Among the video signal-generating devices other than video cameras which may be synchronized are the following:

1. Color background generators.

2. Black burst generators.

3. Film and slide chains.

4. Test signal and pattern generators.

5. Video tape recorder time base connectors.

6. Computers.

7. Video signals taken off the air.

It is to be understood that the invention is not to be limited to the exact details of construction, operation, or exact materials or embodiments shown and described, as obvious modifications and equivalents will be apparent to one skilled in the art, and the invention is therefore to be limited only by the full scope of the appended claims.