JPS5810984A - Analog television signal generating circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a circuit for producing a digital color television signal, in particular an analog television signal for driving a color picture display tube, comprising at least one digital-to-analog converter. The present invention relates to an analog television signal generation circuit having amplitude adjustment for changing, for example, color saturation and/or contrast.

In such a circuit, after the analog signal is regenerated,
Amplitude adjustment can be achieved by using at least ] controllable amplifiers. However, this means increased manufacturing costs, design effort or redundancy, and when using several analog amplifiers there are often inconsistencies due to variations in characteristics. The precise uniform control needed to eliminate accurate image display cannot be achieved.

SUMMARY OF THE INVENTION An object of the present invention is to make it easier and more accurate to adjust the amplitude of an analog signal.

The present invention relates to a circuit for generating an analog television signal from a digital color television signal, the analog television signal generation circuit having at least one digital-to-analog converter and adjusting the amplitude. It is characterized in that the signal is fed to a digital-to-analog converter, the analog output signal of said converter being also dependent on a reference value, and said reference value being adjustable.

The output signal must be dependent on the reference value according to a predetermined, preferably linear function. When using a digital-to-analyzer converter known per se, which adds different currents and different voltages to each other depending on the value of the digital signal, the a
The differences may undesirably accumulate. In this case, when processing increasing signals such as ramp waves such as sawtooth waves, the difference between a value consisting of the sum of small values and the next value represented by a larger value. There is a risk that there will be a difference in your performance.

The reason for this is that the positive error fluctuation of the smaller value may be larger than the scissors difference fluctuation of the next larger value. In this case, a return to the sawtooth wave (flyback) occurs and a uniform change is no longer achieved.

Preferably, therefore, the set of values of the analog signal is taken from the taps of the resistive voltage divider of III connected to the reference voltage point, and a switch is provided associated with each tap, the switch being adapted to provide a predetermined digital signal value. A digital-to-analog converter is used, which is activated at the time of occurrence, and through which the associated analog value tap of the voltage divider is connected to the output terminal.

With such a converter, each analog value is clearly defined and does not consist of a variety of values, so that successive values can be divided only by the resistance values between the associated taps and their errors IIi! It will cost you $11. In this circuit, even if a situation were to occur where the associated resistor was accidentally bypassed when switching from one tap to the next, the vall
No problem arises, as only a voltage average value that essentially matches the intermediate value connecting the analog values of Preferably, the voltage is supplied to an associated switch connected to a voltage divider. When switching from one digital value to the next, significantly shifted peak-like values often occur during the switch, which can misrepresent the desired result. However, with the p-to-pulse stage described above, the associated digital signal is not transmitted until the switching is complete and the signal is at the desired value.

According to a further embodiment of the invention, the value taken from the voltage divider is supplied to the output signal storage, preferably via a pulse stage. In this case, the relevant analog value is stored for the entire click pulse period, and then the next undisturbed analog value is applied to the output terminal.

The control of the digital-to-analog converter, which allows analog signals to be taken from the taps of the resistive voltage divider, converts the n-bit digital signal and its inverse n-bit digital signal into sn g
control the NOR gates (one HOR gate for each digital value) to produce an output value, which actuates the switch;
This is effectively done by allowing the switch to connect the associated tap of the resistive voltage divider to the output terminal.

The invention will be explained with reference to the drawings.

In FIG. 1, which shows an example of the circuit of the present invention, the color difference signal ! is supplied as digital signals U and V, respectively. )(B
-Y ) and (RY) and the similarly digitized luminance signal y are taken as the starting point for the explanation. These signals are fed to digital-to-analog converters 1.1 and 8, respectively. The output signals of these converters are at terminals 11.11;!
1. ! s and 81,1! Depending on the supply voltage or reference voltage respectively applied to the converters, these converters therefore operate to a certain extent as multipliers. The output terminal is converter 1,! and terminal 11,1 of 8! Ig+11. ! l and 811
In the control unit 8 connected to 111, the required voltage is generated which is controlled by the saturation adjustment signal 8 on the one hand and the contrast adjustment signal K on the other hand. This control is used to adjust the saturation at terminals 11.12 and 21.
By varying the voltage at terminal 81.8 by the required amount,
This can be done by keeping the voltage at g constant so that the luminance signal does not change. On the other hand, in order to adjust the contrast, the multiplier input terminals 11°12.11.
12. Vary all of the signals supplied to 81 and 82 by the required amount.

The color difference signals originating from converters 1 and 2 are passed through an inverter stage 61 (which simultaneously multiplies by a factor of 0.19) and an inverter stage 62 (in a manner known per se).
This inverter stage simultaneously performs multiplication with a multiplication factor of 0.287) and then supplies the signal to an adder stage 68, thereby obtaining a color difference signal (G-Y).

The luminance signal obtained from the output terminal of the converter δ is sent to the summing stage 6.
4, and the value used to increment the brightness setting value by 1 is added at this addition stage. The luminance signal corrected by this is combined with the color difference signal in adder stages 66, 66 and 6, and the analog signals B, G and R are sent to the output terminals as blue signals and f# signals for driving the national image display device. ◎ Figure 3 shows a circuit that mostly corresponds to Figure 1, but also obtains a green color difference signal (G-Y) using a digital-to-analog converter for multiplication. show. For this purpose, the input signal U
is supplied to the digital-to-analog converter 4, and a digital color signal V is supplied to the digital-to-analog converter. Addition stage of the inverted outputs of these converters 4 and ? 1, and other processing is performed in the same manner as described with reference to FIG.

Transducers 4 and b have control input terminals 41.4g and il
, 6g, and these input terminals are connected to a control section 3, which is provided in place of the control section 8 in FIG.

In integrated circuits, the conversion refractories and b can simply be used as shown in FIG. 3 in place of the multiplying inverter stages 61 and 63 of FIG. In particular, the additional controls performed to reproduce the green color difference signal from the other three color difference signals are input terminals 41°, 42 and ! il, 61t-, and in some cases it is also possible to adjust the hue by controlling other voltages at terminals 11, 1! 1.11 and 8s by signal F.

FIG. 8 shows an 8-bit digital signal which is preferably used, for example, as converter l of FIG. 1 in a circuit according to the invention.
An analog converter is shown. The digital color difference signal has eight parallel bit lines BO, B1°B8. Ba, B4. B! 1
1. B6 and B? and 8 bit lines BO, B1
．． B$I, B8. B4゜B5. Supplied via B6 and B. These lines are 256 NOR games)
□ * Gl * G@”””” css* and G1
5B, for each digital value only one of these gates is connected to produce the output value "]". The output terminals of these gates are connected to the switching voltages via field effect transistor paths Ho to H□, which act as clock-controlled switches. The output electrodes of these field effect transistors y0 to 'ssi are all connected to the output electrode 81. The supply voltage of the gate and transistor can be SV, and the field effect transistor 141
It is better to make it with M-KOB or p-gos technology,
Preferably, the resistor "1-wsii" is constructed of polycrystalline silicon.

The number of analog values is generated in a voltage divider consisting of a series circuit of resistors w0 to Wfigl. Each section of this voltage divider is connected to the input electrode of a switching transistor M, ~Mls. Then, only one of these switching transistors conducts and a corresponding analog value appears at the output terminal.

Reference signal terminals 11 and 13 are 10, S and 10a, +
A voltage point that can be selected between SV and SV is applied, thereby setting each different amplitude stage of the analog output signal to the same level.

One of terminals ]1 and ]8 can be grounded so that only amplitude values in one sign direction (positive or noble) are generated. However, it is possible to produce voltages with mutually opposite signs at terminals 11 and 1m so that the resulting anadjust value remains in the 1@ range. 3 converters in one of this kind
When provided for two coordinate directions, multiplication in four quadrants becomes possible.

In order to ensure that any disturbances occurring during switching from one digital value to another do not appear in the output signal, switching paths F10 = HIIB are provided and these switching paths are switched by a clock signal from terminal 82 during switching operation. Operate at unobstructed intervals.

In known digital-to-analog converters with resistive networks, a number of switches corresponding to the number of parallel bit lines are provided, preferably several of these switches being activated simultaneously. Each resulting analog value is therefore the sum of one or more separate values.

Since each separate value has a different error, for example, when displaying a uniformly increasing ramp voltage, the separate steps may not have exactly the same step height as each other. On the other hand, in the converter shown in Fig. 8,
Since each anadjust value is taken from a predetermined voltage divider tap, error variations can only result in minimal deviations from the expected value, for example with respect to the ramp voltage display.

Different values can be chosen for the resistors w14WIIIg so that a non-linear relationship occurs between the digital input signal and the output signal at terminal 8]. Thereby, gamma correction of a television signal corresponding to a power exponent of 0.5 can be easily and double-widthed.

[Brief explanation of drawings]

Figures 1 and 3 are splitter diagrams showing two examples of the present invention, and Figure 8 is a circuit diagram showing an example of a digital-to-analog converter used in the circuit according to the present invention. 1 to 5...Digital-analog converter 8.7s...Control unit 61.62...Inverter stage 68 to 67.7
1... Addition stage.

Claims (1)

[Scope of Claims] L A circuit for generating an analog television signal from a digital color television signal, comprising at least le
In an amplitude-adjusted analog television signal generation circuit having digital-to-analog converters A, digital signals (u, v, y) are converted to digital-to-analog converters (1,
3 and 8), and the analog output signal of the converter is set to the reference value (11, 12i21°22 and 81.82).
1. An analog television signal generation circuit characterized in that the signal is dependent on the reference value and the reference value is adjusted. 1. An analog television signal generation circuit according to claim 1, characterized in that the output signal depends on a reference value according to a predetermined function, which is preferably linear. . & Particularly preferable digital signals for use in the analog television signal generation circuit according to claim 1t.
In an analog converter, the set of values of the analog signal is transferred from the taps (M. to M.6.) of one resistive voltage divider (Wl to Ws, , ) connected to the reference voltage point (11°12). Take out the switch (M, ~M) in relation to each tap.
sss >, the switch is activated when a predetermined digital signal value occurs, and the associated analog voltage value tap of the voltage divider is connected to the output terminal C81) via the switch. Digital to analog converter. 4. In the digital-to-analog converter according to claim 1, a switching reference signal (G0 to G, □) that depends on a predetermined digital value is converted to
,,,)) and then the analog value voltage divider (W1~”II!l
) related switches connected to (M0~M□,)
A digital-to-analog converter, characterized in that the converter is configured to supply (v) A digital-to-analog converter according to claim 4, characterized in that the value taken out from the tap is supplied to an output signal storage device, preferably through a clock pulse stage. . a In the digital-to-analog converter according to any one of claims S-S, an n-bit digital signal and its inverted n-bit digital signal (BO~B? and BO~ny'1' are converted into 3n pieces) supply to the NOR gate,
These NOR gates are divided into one NOR gate for each digital value.
controlling the R gate to produce an output value, which actuates one switch ()Ito-M□,);
This switch creates a resistor voltage divider (W1~"m5ts'
A digital-to-analytical converter, characterized in that the associated taps of the converter are connected to an output terminal (81).