e991052.pdf

TEST & MEASUREMENT

multiburst

video test signal from two ICs

In many instances,

suspect television

receivers and moni-

tors can be tested

with a simple test pat-

tern generator as

described in this arti-

cle. The circuit pro-

posed in this, which

consists of only a

handful of compo-

nents, generates a

series of test bars, the

so-called multiburst.

INTRODUCTION

Although modern television receivers

and monitors are highly immune to

noise and interference, there will

always be a need for a test pattern gen-

erator. The compact circuit presented

enables many of the basic functions of

a television receiver or monitor to be

checked. Owing to its simplicity, it pro-

vides only a black-and-white pattern,

of course.

ing different frequencies at a level of

420 mV p-p (average value 650 mV).

The multiburst enables the frequency

response, and certain other properties

of the system on test to be measured. In

a properly adjusted receiver or moni-

tor, all components, with the possible

exception of the 5.8 MHz burst, may be

present. The reference bar and the 2 T

pulse are repeated in line 330, so the

pulse repetition rate (ppr)of these

important test signals is 50 Hz.

The multiburst also enables the

video amplifiers, sync(hronization) se-

parator and output amplifiers to be

tested.

Disregarding the power supply, the

Design by W. den Hollander

DESIGN

CONSIDERATIONS

The simple test pattern of grey bars,

called a multiburst, generated by the

circuit consists of a wave train contain-

Elektor Electronics

1/99

generator

generator is based on two ICs: an in-

system programmable logic assembly)

and a VCO (voltage-controlled oscilla-

tor). The circuit diagram is shown in

Figure 1 .

100n

R14

820

CIRCUIT DESCRIPTION

The in-system programmable IC (IC 1 )

contains 36 macrocells and a total of

800 gates. In the present application, it

is used to generate the sync(hroniza-

tion) signal, CS, the blanking signal,

CB, and the control voltage for the

VCO.

The sync signal, which meets inter-

national standards, is available at pin 7

of IC 1 , and from there applied to out-

put amplifier T 1 via resistor R 14 .

The blanking signal, manifested by

a logic low level at pin 14 of IC 1 , is used

to disable the oscillator in IC 2 during

the sync pulse.

As shown by the timing diagram in

Figure 2 , a pulse appears at each of

outputs D 0 –D 7 during the line period

(64 µs). These pulses are converted into

a staircase consisting of direct voltage

steps. The staircase signal is used to

control the VCO in IC 2 via pin 9, result-

ing in a frequency-modulated output

signal – the multiburst – at pin 4 of IC 2 .

The central frequency of the VCO is

determined by the values of R 12 and

C 3 and the setting of P 1 . With values as

specified and P 1 adjusted for a central

frequency of 1 MHz, the output fre-

quency rises in eight steps to a value of

10.5 MHz.

The d.c. operating point of output

amplifier T 1 is determined by the val-

ues of R 15 and R 16 . The video and sync

signals are superimposed on this via

R 13 , R 14 and C 4 . The amplifier is

designed to have an output impedance

of 75

R11

IC1

R10

100n

270

IC2

560

Ω R8

R15

1k5

2k2

PLL

3k0

8p2

3k9

CIN

R13

2k2

VCOIN

VCOUT

4k7

SIN

BC547B

ZEN

XC9536-15-

PC44

R12

DEMO

R18

INH

R16

R17

74HCT4046

500 Ω

10p

CLKI

CLK

IC3

10M

> 8V

7805

1N4001

R19

C12

C11

C10

10MHz

25V

330n

63V

22p

980095 - 11

The circuit is pow-

ered by a simple sup-

ply whose output is

stabilized at 5 V by regulator IC 3 .

Diode D 2 prevents damage through

inadvertent incorrect polarity of the

input voltage. Diode D 1 is a supply-on

indicator. The input voltage may be

derived from a simple mains adaptor

with an output of 9–12 V.

Figure 1. Circuit dia-

gram of the multiburst

generator.

ure 4 (available ready-

made – see Readers

Services towards the

end of this issue) .

IC 1 should be placed in a suitable

socket: mind the polarity. Do not over-

look the wire bridge alongside R 10 .

at an output voltage of 1 V p-p .

The important signals in the circuit

are summarized in Figure 3 . In this dia-

gram, the sync signal, on to which the

output signal of the VCO is superim-

posed, is on the top line. The blanking

signal is on the second line and the

staircase control voltage for the VCO

on the third.

The output signal of the generator

is on the bottom line. This shows

clearly that at the onset of each hori-

zontal line, that is, every 64 µs, the

oscillator is disabled.

Note that the irregularities on the

screen images are caused by the sam-

pling process of the oscilloscope used.

TESTING

When the generator has been built and

inspected thoroughly, switch on the

mains supply to the adaptor. Connect

an oscilloscope to the output and

adjust P 1 so that the lowest frequency

CONSTRUCTION

The generator is conveniently built on

the printed-circuit board shown in Fig-

630

640

650

660

670

680

690

700

710

720

730

Figure 2. The in-system

programmable IC gen-

erates a number of dig-

ital signals that are the

basis of the output test

signal.

630

640

650

660

670

680

690

700

710

720

730

980095 - 12

Elektor Electronics

1/99

220

is 1 MHz.

The generator is intended for test-

ing television receivers or monitors

that have a field frequency of 50 Hz

and 625 lines per picture. If different

frequencies are desired, the value of

resistors R 3 –R 10

should be altered as

required.

Note that, in contrast to proprietary

multiburst generators, the present one

does not provide a sinusoidal output.

[980095]

980095 - 14

Figure 3. Oscillogram of

the signals at four loca-

tions in the generator.

Parts list

Resistors :

R 1 = 10 M Ω

R 2 , R 6 , R 13 , R 15 = 2.2 k Ω

R 3 = 4.7 k

Ω

R 10 = 270 Ω

R 11 = 1.2 k Ω

R 14 = 820

Ω

R 16 = 1.8 k

R 17 = 100 Ω

R 18 = 75 Ω

R 19 = 2.7 k

P 1 = 500

preset

Capacitors :

C 1 , C 2 = 22 pF

C 3 = 0.001 µF

C 4 = 8.2 pF

C 5 = 10 pF

C 6 –C 9 = 0.1 µF, ceramic

C 10 = 10 µF, 63 V, radial

C 11 = 0.33 µF

C 12 = 220 µF, 25 V, radial

Figure 4. Printed-circuit

board for the multiburst

generator.

Semiconductors :

D 1 = LED, high efficiency, red

D 2 = 1N4001

T 1 = BC547B

IC3

C10

R19

R11

R10

Integrated circuits :

IC 1 = XC9536-15-PC44 (Xilinx); avail-

able ready programmed under

Order no. 986520-1*

IC 2 = 74HCT4046

IC 3 = 7805

Miscellaneous :

X 1 = crystal, 10 MHz

PCB Order no. 980095-C*

Diskette with Jedec source file: Order

no. 986029-1*

R13

R14

R15

IC2

*(see Readers Services towards the

end of this issue)

R12

OUT1

980095-1

Elektor Electronics

1/99

R 4 = 3.9 k

Ω

R 5 = 3.00/3.01 k Ω

R 7 , R 12 = 1.5 k Ω

R 8 = 1 k

Ω

R 9 = 560

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