Patent GB-1417425-A (GB)
Title: Waveform generator
IPC: H04N17/04
Filed: 1972-09-07
Abstract: 1417425 Television signal generator GRANADA TV RENTAL Ltd [7 Sept 1972] 41671/72 Heading H4F  A colour-bar generator comprises: an oscillator 1, Fig. 1a, for generating oscillations at a frequency equal to the colour subcarrier frequency; a first chain of frequency dividers 7, 8 connected to said oscillator to produce oscillations at line frequency; a second chain of frequency dividers 10, 11 connected to the output of said first chain of dividers to produce an oscillation at the field frequency; a third chain of frequency dividers 12 connected to an intermediate point in said first chain and arranged to provide an oscillation at a multiple of line frequency, said multiple being related to the number of vertical bars the generator is to produce; a priority of logic circuits, Fig. 1b, connected to said chain of dividers and arranged to receive said line frequency oscillation, said field frequency oscillation and oscillations from appropriate points in said chains to provide line synchronizing, line blanking, field synchronizing, field blanking, colour burst gating signals and PAL line switching signals; a fourth chain of frequency dividers 36, 37, 38 comprising three binary stages connected to the output of said third chain of frequency dividers; and means for applying blanking signals to said fourth chain to inhibit counting thereby during blanking periods, said three binary stages thereby providing respectively signals corresponding to the red, green and blue signals required to form the successive colour bars. A matrix circuit is arranged to derive from said red, green and blue signals a luminance signal, a red colour difference signal and a blue colour difference signal (outputs 39, 40, 41). The carrier pulses A, Fig. 3a, are fed to the input of a four stage binary counter 7 to produce signals B, C and D at the outputs of the first, second and fourth stages, respectively. Signals B and C combine to produce a signal at half the carrier frequency which is fed to a four stage counter 12, This has its stages so interconnected that it produces a signal C at a frequency <SP>1</SP>/ 28 th of the carrier frequency. Ten cycles of signal C occur during one line period, whereby said signal C defines the positions of the ten vertical colour bars. Output signal E of counter 7 at <SP>1</SP>/ 16 th of the carrier frequency is fed to the input of a second four stage binary counter 8 The outputs of the first and second stages of counter 8 are combined with outputs from counter 7 in NAND gate 14 to produce a line resetting signal K which signal resets counters 7 and 8 and is transmitted over line B. The output signal I of counter 8 at line frequency sets a JK flip-flop 9 which is reset by the line reset signal K to produce a line blanking pulse L. The line sync. pulse M is produced by a flip-flop 27, Fig. 1b, which is set by a signal on line F as delayed by a circuit 47 and produced by a NAND gate from the outputs G and H of second counter 8 and reset by signal I from the output of counter 8. The colour burst defining signal N is produced by a flip-flop 26 set by a signal being the inverse of signal J from flip-flop 9 and cleared by the inverse of signal Q from the output of counter 12. Counters 10 and 11 receive the output of flip-flop 9V at half-line frequency and by successive divisions down by factors 12, 13 produce a signal E<SP>1</SP> at field rate which signal E<SP>1</SP> is used as a field blanking pulse. The inverse of the field blanking pulse is used to set a bi-stable 31 which is cleared after an interval of two lines to produce the field sync. pulses. The field sync. pulses and the line sync. pulses M are combined on line Y by diodes 32 and 33. Line blanking pulses L, line reset pulses K and horizontal bar defining pulses Q are fed to a series of JK flip-flops 36, 37, 38 whereby signals S, T and U are thereby respectively produced defining when the blue, red and green signals should be present to produce the required colour bar sequence of white, yellow, cyan, green, magenta, red, blue and black. The blanking pulses L ensure that the JK flip-flops 36, 37, 38 are inoperative during the blanking period. The signals F, T and U are combined by resistive networks to produce signals representing the luminance, the red minus luminance and the blue minus luminance signals. These three signals may be modulated on to a sub-carrier, Fig. 1c.