SU984036A2 - Analogue-digital converter for stationary line images - Google Patents

Description

Fig, 1 shows a block diagram of the proposed device; 2, oscillograms explaining how the device works. The analog-digital converter contains detector 1, threshold element 2, generation unit 3, local / pulse generator 4, duration-quantization unit 5-8 performed on matching elements, and also inverter 9 and trigger 10. The analog-digital converter operates as follows in a way. The analog signal (Fig. 2o), pre-modulated by the signal carrier frequency f, is fed to the input of detector 1. The modulated signal (Fig. 25) is detected by detector 1 and fed to the input of threshold element 2 (Fig. 2). In Figs.2o1, b, the minimum signal (dips) corresponds to the black dashed image, and to the white dashes, the maximum signal. The quantization pulse shaping unit 3 forms, from a non-existent frequency signal, quantization pulses of minimum duration with a tracking frequency equal to H shifted by ji relative to the carrier frequency, their vertex coinciding with the maximum amplitude of the carrier frequency signal (Fig. 28). The quantizing pulse shaping unit is a serially connected differentiating chain, a detector and a delay line (not shown) and forms a signal (Fig. 2a). The amplitude-generated signal (Fig.) From the output of the threshold element 2 is fed to the first element

b. match directly, and the second element 5 through the inverter 9. Gating pulses from the quantizing pulse shaping unit 3 are shown to the second inputs of the elements 5 and coincidence (Fig. 2e).

The pulses of the quantizing pulse shaping unit 3, coinciding with the pulses of the threshold element 2, pass to the output of the coincidence element b. In Fig. 2, this corresponds to a signal from white dashes. For reliability, coincidence pulses (Fig. 2d) of block 13 are formed coincident in the middle with detected pulses. carrier frequency, i.e. A shift is provided for d pulses (Fig. 23) of block 3 by comparison with the leading edge of the pulses (Fig. 2d) at the output of the threshold element 2. The first impulse at the output of element b sets the trigger 10 to one state (Fig. 2e).

In the inverter 9, the signal (FIG. 2d) from the threshold element 2 is inverted and enters the input of the element 5 in a soviffera form.

For analog-to-digital conversion of an analog signal by a known converter, the formation accuracy is estimated by the formation error, defined as

d | -c, gcd 2 — where B is normalized brightness shade

images; h is the limiting threshold. V is the aperture distortion factor, which is usually equal to 0.81.

In fact, the image has a range of variances к ks. For this range there is an optics when

threshold value

O error L is minimal.

min

Max

1+

1-B 1-B,

min

Max.

-1 fall. At the output of element 5, quantization pulses will pass (Fig. 2d), which coincide with the inverted pulses of the threshold element 2. In Fig. 2, this corresponds to black dashes. The first pulse at the output of element 5 is a match, i.e. the first subsequent pulse after the last pulse, at the output of the coincidence element 6, set the trigger 10 to the zero state (Figure 2c (). The digital signal (Figure 2e) from the output of the specified trigger goes to a completely analog block consisting of elements 7-10 where the duration of quantization by gating pulses (Fig. 2) of the working clock (channel) frequency ffjT of the local pulse generator b. synchronized with strobes at the reception is carried out. From the condition of ensuring the minimum of the distortions of the duration of the digital signal (quantization errors) of the gating pulse frequency (chosen equal, mfpTf where m is an integer multiple, is much larger than one (t / 100, real m 100-1000). The operating frequency fpr may vary depending on the speed of operation the communication channel. The block from elements 7 to 10 at the working clock frequency fp works similarly to the block consisting of elements 5, 6, 9, 10. At the output of the device, we receive a signal (Fig. 25) for transmission over discrete communication channels . The use of new elements in the proposed device allows directly amplitude-modulated video signal to be converted into

in a nax min

 yin

about

1-6

1-B

NIN

Max

Since the strokes that make up any dashed black and white image are not associated with any patterns with fpT; some of the impulses formed from strokes have a shorter duration and are out of phase with operating cycles (between the operating clock pulses of the generator 6) It will be lost, i.e. will not pass to the output of the device.

Thus, the reduction in the accuracy of the formation leads to a decrease in the reliability of the formation of discrete signals (the loss of part of the narrow strokes) ..

therefore Trt I 1+ 4 (bo J g / 7) T

where N; t is the resolution

images, lin / mm; Ph speed horizontal razvetki

images, mm / s. Accordingly, it is chosen equal to

x

.)

. The maximum formation error for the proposed device after the digital conversion to f ,,. is defined as

A „dks l1o, e) + l (),

where (Tq) TVV TVx ° mirovanna error;

time with

KB

Choosing f mouth, it is possible to ensure the reduction of the second component. With

.. d (TKe) loot -4iio.e) r

If L; 1c.,. B) 0.07, then a (Txv) is 0.05, and the total error is 07 + 0.005 0.75. Practically, the choice can be reduced). To a very small. Value that can be omitted.

Thus, the effectiveness of the invention is to ensure high reliability of the digital conversion of the amplitude-modulated signal by maintaining high accuracy of the formation.

15

Claims (1)

1. USSR author's certificate No. 197681, cl. H 03 K 13/20, 1966 (prototype). / illtiu; jj B t flflflfl JAPLLLLLLLLD flftWWl 9 iiHiiHintiimtunntinunMitm j. j. and I i 11 I 11 It I 111 M I 11 M i 11, v 1 t1