JPS5941325B2 - D-A converter for digital television - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for converting a digitized television signal into an analog television signal for use in a television system that digitizes and transmits or processes the television signal.

2. Description of the Related Art Recently, as a method for high-quality transmission or signal processing of television signals, a method of digitizing television signals for transmission and processing has been attracting attention. An example of such a system is shown in FIG. 1 and will be described. Here, 1 is a signal source circuit, 2 is a signal processing or transmission circuit,
3 is a display circuit. In the signal source circuit 1, the input terminal 4
The analog television signal applied to the TV is first clamped by the clamp circuit 5 to determine the DC level, and then sampled at the required period by the sampling circuit 6 to be output to the PA.
The signal is sampled into M samples, and further encoded into a PCM digital signal with the required number of bits by the DA conversion circuit 7. Then, in addition to the signal processing or transmission circuit 2, the signal is transmitted via a telephone line or an antenna path, or subjected to signal processing such as recording/reproduction or signal processing, and is then transmitted to the display section circuit 3. In the display section circuit 3, this is first received or amplified by the reception or amplification circuit 8. When used in a television transmission system, this part corresponds to a general tuner, VIF circuit, video detection circuit, etc., and when used in a signal processing system, it corresponds to a buffer amplifier circuit, etc. Thereafter, the digitized television signal is reconverted into an analog television signal by a DA converter circuit 9, amplified by an amplifier circuit 10, and then supplied to a cathode ray tube 11 to display a television image. By using digital television signals for signal processing or transmission in this way, digital equipment such as computers can be used for signal processing, allowing high-speed processing and improving accuracy during transmission. can be further improved. The present invention relates to a D-A converter used for reconverting a digital television signal into an analog television signal in such a system, and is capable of simultaneously converting the television signal from digital to analog and adjusting contrast at the same time. The purpose is to provide a simple device that can

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG.

In the figure, 12a to 12n are input terminals for each bit of a digitized television signal, and 13 is an output terminal for an analog television signal obtained by converting the input terminals. In this device, first, a series circuit of first transistors 14a to 14n, second transistors 15a to 15n, and resistors 16a to 16n is provided for each bit of a digitized television signal, and such a series circuit is connected to the number of bits. (in this case, n bits) are connected in parallel, and a common resistor 19 is connected between the common connection point 17 of the series circuit and the power supply 18. Then, each bit of the digitized television signal is input from the input terminals 12a to 12n to the first terminal of each series circuit.
is applied to the base C of each of the transistors 14a to 14n.

Furthermore, as a feature of this device, a variable voltage for contrast adjustment is commonly applied from a variable resistor 20 to the bases of the second transistors 15a to 15n of each series circuit. The analog television signal is taken out from the common connection point 17 and sent to the output terminal 13 via a transistor 21 for buffer amplification.
Output to. With this configuration, when a digitized television signal is applied from the input terminals 12a to 12n, the first bit of the series circuit corresponding to the bit that is at a high level is
, the second transistor is rendered conductive, and the television signal converted into analog by dividing the power supply voltage by the combined value of the resistors connected to the series circuit in which these transistors are rendered conductive and the common resistor 19 is output to the terminal. 13 can occur.

Moreover, in this device, the second transistors 15a to 15
Since the base voltage of n is adjusted by the variable resistor 20, the current flowing through these series circuits can be adjusted arbitrarily, and the amplitude of the output analog digital signal can be adjusted and displayed as desired. It is possible to easily adjust the contrast of a television image, and it has an effective effect without requiring a separate contrast adjustment means as in a normal television receiver. Since such a circuit can be easily constructed using integrated circuit elements, it also has the advantage that it can be made compact and at low cost. As described above, according to the present invention, the first,
A plurality of series circuits of a second transistor and a resistor are provided in parallel corresponding to the number of bits of the digitized television signal, and a common resistor is further connected to this, and a series circuit of a second transistor and a resistor is connected to the first transistor. Each bit is added to extract an analog signal from a common connection point, and a variable voltage for contrast adjustment is applied to the base of the second transistor so that the amplitude of the output television signal can be adjusted. Therefore, the present invention has a great practical effect in that it is possible to adjust the contrast with an extremely simple structure, and to obtain a low-cost D-A converter for digital television that is suitable for the integrated circuit element 1c.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of a digital television system, and FIG. 2 is a circuit diagram of a D-A converter for digital television according to an embodiment of the present invention. 12a-12n...Manual terminal, 13...
- Output terminal, 14a-14n...First transistor, 15a-15n...Second transistor, 16a-16n...Resistor, 17...
・Common connection point, 18...Power supply, 19...
・Common resistance, 20...variable resistor.

Claims (1)

[Claims] 1 A plurality of series circuits each consisting of a first transistor, a second transistor, and a resistor are arranged in parallel according to the number of bits of the digital television signal, and a common resistor is provided between the common connection point of the series circuit and the power supply. are connected to each other, a signal of each bit of the digitized television signal is applied to the base of the first transistor of the plurality of series circuits, and a signal of each bit of the digitized television signal is applied to the base of the second transistor of the plurality of series circuits for contrast adjustment. A D-A converter for digital television, which applies a variable voltage in common and outputs an analog television signal from the common connection point.