DE2937714C2 - "Multi-frequency color burst signal generator for testing television video signal circuits" - Google Patents

Description

There is a need for quality control in the field of television broadcasting in order to be safe go that the composite video signal without distortion when traversing the entire video system is maintained. For this purpose, various test signals have been developed Test the quality of a video system. A widely used test signal is the multi-frequency color burst signal, hereinafter also referred to as multiple burst.

The multiple burst consists of a series of bursts of sine wave signals with the same amplitude from 0.5 MHz to 4.2 MHz (in the NTSC television system) and white and black reference levels. The signal also includes composite synchronization so that the entire signal is passed through the normal way various television signals and circuits. The multi-frequency burst signal is im generally used to determine the gain as a function of the frequency response. One of the critical areas of frequency response in color video equipment is the frequencies between the Reference color carrier at 3.58 MHz and the audio subcarrier at 4.5 MHz. The video device must be accurate set to attenuate the video signal that could interfere with the audio signal. Therefore, it is desirable to have an apparatus and method capable of doing this Determine video device frequency response in the range specified above. Previous procedures exist therein, the multi-frequency burst signal with an oscilloscope monitor on a monitor and estimate the cutoff frequency by the last burst (4.2 MHz) of the multiple burst signal is observed. According to the present invention is the last Burst in a multiple burst signal adjustable over a wide frequency range. During the time of the last burst the normal burst current becomes variable made. The changeable burst current gives the last burst a width of 3.6 MHz to 4.6 MHz. A Switching signal blocks the transmission of normal multiple burst signals and makes them changeable Burst current is effective by creating a continuous sine wave of the last burst frequency, which is easy with a conventional frequency counter can be monitored is provided. Hence can critical frequency responses can be determined with previously unattainable accuracy.

It is therefore an object of the present invention to provide an apparatus for generating a multi-frequency color burst signal, which has an adjustable burst frequency, which is used to determine the frequency response of television transmission equipment and circuits can be used in a simple manner.

These objects are achieved according to the invention by the measures specified in claim 1.

Further developments of the invention are given in the subclaims.

Details and advantages of the invention emerge from the following description of a drawing illustrated embodiment.

The drawing shows a multi-frequency color burst signal generator with one according to the invention changeable last burst.

In the drawing is a multi-frequency color burst signal generator constructed in accordance with the present invention. The illustrated multi-frequency color burst signal generator has an adjustable sixth or final burst frequency; however, any one of the burst frequencies may according to specific Test requirements can be made variable. In the arrangement of the drawing is a function generator 10, which generates the multi-frequency color burst signals. The function generator 10 is powered by constant current sources 40-90, with one power source for each generated pulse frequency. Of the Current from the current sources 40-90 is fed to the function generator 10 via switches 45-95, which are switched from a read only memory (ROM) 30 can be controlled. The output of the function generator 10 on the Line 12 is applied to the unit under test 200 (UUT). The frequency behavior of the Unit (UUT) 200 can be determined by using a frequency counter 20, for example to measure the frequency of the signals passing through it.

The frequencies of the six bursts of sine waves, usually generated by an NTSC multi-frequency color burst signal generator are generated are:

First burst
Second burst
Third burst
Fourth burst

0.5 MHz
1.5MHz
2.0MHz
3.0 MHz

Fifth burst
Sixth burst

3.58MHz 4.2MHz

In the exemplary embodiment according to the drawing, the sixth burst can be set in order to enable an exact determination of the cut-off frequency in the range between the frequency of the reference color carrier and the audio intermediate carrier. The frequency is varied by adjusting the voltage applied to current source 90. Read-only memory connects the six current sources to function generator 10 by closing switches 45-95 in the order appropriate to generate the conventional multi-frequency color burst signal. The read-only memory (ROM) 30 is triggered by the line frequency pulses via the input line 120. The current sources 40-90 each output a constant current at the level necessary to enable the function generator 10 to generate sine waves with the correct burst frequencies to cause.

If the variable burst part of the present invention is not made effective, then the multi-frequency color burst signal generator operates as a conventional multi-frequency color burst signal generator. During each television scan line, read-only memory 30 opens and closes each switch 45-95 to apply a current pulse from each current source 40-90 to function generator 10 for a period of time. The six current pulses cause function generator 10 to generate six bursts of sine wave signals, one at each of the six frequencies mentioned above. These bursts are then applied to an output circuit (not shown) where luminance information is added to the test waveform. This test waveform is then fed to the unit under test 200 and monitored on an oscilloscope screen (not shown) after passing through the circuitry under test. The operator then attempts to make accurate determinations of frequency response by estimating frequencies from the oscilloscope display.

Closing the variable burst switch 105 makes the variable burst part of the present invention effective. The part for variable bursts works in two ways, the calibrated and the norma.en Art. When a calibration switch 11 is also closed, so the read-only memory (ROM) 30, the current sources 40-80 is switched off by the switch 45 -95 to be kept open. The power source 90 is continuously made operative by the read only memory (ROM) 30 which holds the switch 95 closed. Therefore, the function generator 10 now generates a continuous sine wave with the predetermined frequency of the sixth burst. Since the

ίο switch for the variable burst is closed, the potentiometer 100 can be used to vary the voltage applied to the current source 90 and consequently its output current. As mentioned above, the change in the current flowing into function generator 10 will change the frequency of its output sine wave. Even if the switch 115 is closed, the read-only memory (ROM) 30 switches off the output circuit (not shown) via the line 32, which, among other things, adds the luminance signal to the multifrequency burst waveform. In the exemplary embodiment shown in the drawing, the frequency of the last burst can be changed from 3.6 MHz to 4.6 MHz via a potentiometer 100 .

The variable sine wave signal can be fed into the frequency counter 20 via the output line 12 from the output of the function generator 10. The signal can easily be monitored by a conventional frequency counter 20 since it is a continuous sine wave, ie it is not faded in. Also, because the frequency of the sine wave signal can be changed, the ability of the unit under test (UUT) 200 to pass a particular video frequency can be easily determined and circuit adjustments can be made.

If the unit under test (UUT) 200 will not accept a continuous sine wave signal, the calibration switch 115 can be opened. If the calibration switch is open, read only memory (ROM) 30 will activate switches 45-85 and generate

of causing bursts at fixed frequencies together with the sixth burst of variable frequency. The sixth burst will occupy the frequency that is measured by the counter in the calibration mode. The sixth burst can still be changed from 3.6 MHz to 4.6 MHz by changing potentiometer 100 .

1 sheet of drawings

Claims (4)

Patent claims: 1. Multi-frequency color burst signal generator for Testing television video signal circuitry characterized by a sine wave generator (10), the frequencies of the output sine waves corresponding to the current levels supplied to it changes, through several constant current sources (40, 50, 60, 70, 80, 90) for the generation of Currents that can be fed to the sine wave geraior (10) for variable frequencies, at least one of the constant current sources (40, 50, 60, 70, 80, 90) has an adjustable output level and by a clock signal circuit (30) responsive to signals at the television line frequency Clock signals for continuously making at least one of these constant current sources effective (40, 50, 6C, 70, 80, 90) to generate the sine wave generator (10) for outputting a continuous Initiate output signal. 2. Multi-frequency color burst signal generator according to claim!, Characterized by on the clock signals Responsive switches (45, 55, 65, 75, 85, 95) for the controlled connection of the constant current sources to the input of the sine wave generator (10). 3. Multi-frequency color burst signal generator according to claim 1, characterized in that the Circuit (30) for clock signals includes a read-only memory which is responsive to the signals at the television line frequency appeals to. 4. Use of the multi-frequency color burst signal generator specified in claim 1 for determining the frequency response of a television signal video device, the generated Burst signal of variable frequency is monitored with a frequency counter (20).