SU748902A2 - Monitoring device of image signal a-d converter - Google Patents

Description

(54) DEVICE FOR CONTROL OF ANALOG-DIGITAL CONVERTER OF IMAGE SIGNALS

The invention relates to television systems and can be used to control the quality of the operation of analog-to-digital converters of a television video signal used in 5 communication systems with pulse-code modulation.

According to the main author. St. No. 434619, a device for controlling an analog-digital image signal converter, comprising a test signal generator, consisting of a sawtooth voltage generator, a half-frame sync pulse generator and a horizontal sync pulse generator, 15 And elements, a shift register, two delay elements, a differentiating element, a frequency divider, prohibition element, OR element and video control unit tl .20

However, the known control device has low measurement accuracy and low speed.

The aim of the invention is to improve. 25 measurement accuracy and speed increase.

For this, an analog-to-digital image signal converter control device containing a generator

the torus of the test signals, consisting of a sawtooth voltage generator, a semi-frame sync pulse generator and a horizontal sync pulse generator, AND elements, shift register, two delay elements, a differentiating element, a frequency divider, an interdiction element, an OR element and a video monitoring unit, a reference mark generator was entered, and the output of the OR element is connected to the input of the video monitoring unit through the input inverse summation unit, while the input of the reference mark generator is connected to the output of the horizontal sync generator oimpulsov and etgshonnyh tag generator output is connected to a second input of the inverse summing.

The inverse summation unit contains the first and second OR elements and the first and second inverters, the AND element, and the outputs of the first and second inverters through the first OR element are connected to the first input of the AND element, the second input of which is connected to the output of the second OR element, and the first input of the second OR element and. the input of the first inverter is the first input of the inverse summation unit, the second input of which is the second input of the second OR element and the input of the second inverter.

The drawing shows a structural electrical circuit of the proposed device.

The proposed device contains a tested analog-to-digital converter 1, a generator of 2 test signals, consisting of a generator 3 saw voltage, a generator of 4 half-frame sync pulses, an oscillator and a generator 5 horizontal sync pulses, And 6, 7, 8, shift register elements, the element 10 delays, a differentiating element 11, a frequency divider 12, a delay element 13, a differentiating element 14, a prohibition element 15, an OR element 16, a video monitor unit 17, a reference mark generator 18 and an inverse summation unit 19 consisting of ne first- and second-inverters 20, 21, first and second OR elements 22, 23 and AND gates 24

The proposed device operates as follows.

When a signal from the generator 3 output of the sawtooth voltage is fed to the input of the tested A / D converter, the code pulses from the outputs of its bits go to the corresponding elements Ib, 7, 8, which in turn, for a given number of rows of any frame, use the shift register 9 the outputs of the bits of the ADC 1 to the video monitor unit 17 (the drawing shows a block diagram of a device intended for monitoring a 3-bit ADC).

The number of rows is determined using a dividers 12 frequency that controls the shift register 9 by decreasing the frequency of the horizontal sync pulses riocpyped from the generator output of five horizontal sync pulses.

In order to more closely compare the real and nominal quantization characteristics, as well as to accurately and quickly measure the error parameters of the tested A / D converter, a sequence of vertically positioned marks is formed on the screen of the video monitor unit 17, the position of which corresponds to the switching times of the quantizing characteristic. Vertical marks are formed by the generator 18 reference marks, which start from the generator 5 horizontal sync pulses. The width of the marks is determined by the pulse duration at the output of the generator 18 of the reference marks and is chosen equal to the width of one image element in the line of the television raster.

In the output codes of the tested ADC 1, received on the video control unit 17, the logical O corresponds to the black level; logical 1 corresponds to the white level of the information video signal. The impulse mark at the output of the generator 18 reference marks corresponds to the white level. Therefore, at the moment of arrival of the information signal corresponding to the white level, it is almost impossible to distinguish a label against the background of information. In order to distinguish the label from the background of information, corresponding to the real quantization characteristic, with the help of inverters 20 and 21, the elements OR 22 and 23, and the element 24, an inverse pulse-tag is generated that is fed to the information input of the video monitoring unit 17.

The tracking pulse period TM is determined by the bit number of the checked A / D converter 1, whose operation is currently monitored and is selected from the following relationship:

- t. l tTg / -g%

P

where is t

- the period of sawtooth voltage;

i is the number of the controlled bit of the ADC.

In the absence of a tag at the output of the generator 18 reference marks, the logical 1 appears at the output of the first inverter 20, which through the first element ID 22 arrives at the input of the AND 24 element. Thus, the signal at the input of the video monitor 17 is determined by the information at the output of the element OR 16.

If there is a label pulse at the output of the second element OR 23, logical 1 appears. Information from the output of the OR element 16 is inverted by the first inverter 20 and through the first element OR 22 enters the input of the AND 2 element. Thus, the label signal will have a value inverse to the information signal. signal.

The proposed device in comparison with the known has the following advantages:

improved measurement accuracy due to the presence of calibration bands on the image of the real quantization characteristic;

the laboriousness of the measurement process and the time spent on determining the real quantization characteristic and error – integral and differential linearity parameters are reduced, as a result of which labor productivity increases sharply;

reduced requirements to the operator's qualification while simultaneously improving the accuracy of measurements.

Claims (1)

1. Control device of the analog-digital converter of the signals of an image according to the author. St. № 434619, about t l and