SU758568A1 - Device for measuring differential phase of colour television signals - Google Patents

Description

the reference frequency, the input bandpass filter 3 and the limiting amplifier 4, block 5 for determining the transition through but a reference signal, converter b for the color subcarrier, block 7 for determining the phase quadrant, sampling at 8 signal levels.

The device works as follows.

A test line selected from the video signal, containing a control signal with a dwelling subcarrier superimposed on it, is fed to the input of a bandpass filter 3, the output of which receives a color subcarrier that is fed to the limiting amplifier 4, which ensures that the measurement of the differential signal is independent of input device. From the output of the amplifier-limiter 4, the signal is fed to the converter b of the color subcarrier, at the output of which a function is obtained in intervals

-f;., | hk | x

etc. and on the whole time interval)

where A is a constant coefficient. The waveform at the output of the converter b color subcarrier is shown in FIG. 2 a, b, c, d dotted lines. Converter output

A 6 color subcarrier is connected to the input of the phase quadrant determination unit 7. It is also given a signal from the output of the amplifier limiter 4

and sampling pulses from the sampler of 8 signal levels. Block

The quadrant definition phase performs two main functions. The first function is the elimination of a phase shift greater than 180 ° between the measurement signal and the reference signal located at the blanking level. If the phase shift is greater than 180 °, then the phase quadrant determination unit 7 inverts the signal received from the converter b of the color subcarrier. The second function of the phase quadrant determination unit 7 is to determine whether the phase shift is in the first or

in the second quadrants. From the output of the phase quadrant determination unit 7, a linearly varying triangular signal is fed to the sampler of 8 signal levels. To him, from the unit 5 for determining the transition, the impuses formed at the moments of the transition through the zero of the reference signal produced by the generator 2 of the reference part go through the zero of the reference signal. The discretization of the 8 signal levels is a device consisting of a pulse amplitude modulator, a pulse spreader and a low-pass filter. The amplitude of the samples taken on a linearly varying triangular signal at the time of transition through the zero reference signal is directly proportional to the phase shift between the measurement and reference signals. FIG. 2a, b, c, d (points a, b, c) show sampling impulses sampling the measured signal. From the output of the sampler 8 signal levels, a signal having a stepped form is supplied to the unit 1 for measuring the signal levels. This block contains a black signal fixation circuit, a signal level meter and an indicator device. The latching circuit eliminates the pedestal due to an accidental phase shift between the reference signal and the measurement signal, which is at the level of the blowhole. The result of measuring the differential phase can be indicated, for example, on a scoreboard or recorded on a digital printing machine included in signal level measuring unit 1. The quadrant number in which the measured differential phase is located comes from phase quadrant determination unit 7. From FIG. 2c, d it can be seen that the modulation of the sampling pulses (points A, B, c) in the third and fourth quadrants is negative with respect to the constant component of the measuring signal and the first two quadrants (Fig. 2a, c). This makes it possible to determine in which two quastirants the initial phase shift is. The converter b color subcarrier can be performed, for example, using an integrator made on an operational amplifier. The same block can be performed using band-pass filters, highlighting the odd harmonics of the subcarrier, phase shifters and summation matrix. In this case, the expression

l {v, p, ...) When the differential phase is small (20-30 °), then the transducer b of the color subcarrier may consist of a single bandpass filter element to separate the first harmonic of the measuring signal. This is because the function has a linear relationship between the function and the argument. The main errors of the device for measuring the differential phase are the error of the color subcarrier converter and the sampling error of 8 signal levels. The first of the errors depends on the accuracy of phasing of the harmonics of the phase shifter and on the accuracy of matrixing. The specified error can be reduced to 2-3%. The second error is determined by the shape and duration of the sampling pulse. The error due to the finite pulse duration in this measurement is unchanged at all levels, since the frequency of the signal is constant. This error for a triangular pulse is defined by the expression:

O / Chg

(.48

cJn - relative error

Where

at the point of reference, J LU is the sub-satellite frequency; t is the sampling pulse duration.

The discretization error due to the nonlinearity of its amplitude response can be assumed to be 2-3%. Thus, the total error of the device for measuring the differential phase of color television signals is about 5%.

Claims (1)

1. German patent 2013595, cl. 21 N 77/02, 1970 (prototype). FIG. // // fl IgG GTO - For