Abstract:
In a de-emphasis circuit designing method for minimizing the number of peripheral components of a video signal processing integrated circuit (IC), a circuit device for determining the level of a reproduced video signal of the de-emphasis circuit is included in the video signal processing IC. The number of components is reduced by designing all circuit elements of the circuit device for determining the level of the reproduced video signal of the de-emphasis circuit so that they are incorporated into the video signal processing IC at the time of design of the video signal processing IC, thereby reducing cost and reducing any deviation in the playback (PB) level due to external component deviation. The video signal processing IC comprises the de-emphasis circuit and a video level setting unit, the latter comprising an amplifier connected to an output of the de-emphasis circuit, a plurality of resistance elements, and a plurality of respective switches for ON/OFF switching of the resistance elements, thereby setting the gain of the amplifier and the level of the reproduced video signal.

Description:
CLAIM OF PRIORITY 
   This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my application DE-EMPHASIS CIRCUIT DESIGN METHOD OF VIDEO SIGNAL PROCESSING IC AND IC USING THEREOF filed with the Korean Industrial Property Office on Sep. 5, 2000 and there duly assigned Ser. No. 52372/2000. 
   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to a video signal processing integrated circuit (IC) and an IC designing method and, more particularly, to a method for designing a de-emphasis circuit for a video signal processing IC in order to reduce operating steps and material costs by minimizing the number of components of external application circuits of a de-emphasis output terminal of the video signal processing IC, and to an IC made by the method. 
   2. Related Art 
   A typical video cassette recorder (VCR) playback circuit includes a video head  110 , a rotary transformer, a pre-amplifier, and a video signal processing IC. In the playback (PB) mode, a modulated video signal is detected by the video head, is input to the pre-amplifier via the rotary transformer for amplification with a predetermined gain, and is then input to the video signal processing IC which blocks a low-frequency component color signal among the signals input thereto and allows a frequency-modulated (FM) luminance signal having a high-frequency component to pass through. The high-pass filtered FM luminance signal is demodulated, and the demodulated luminance signal is subject to high-frequency component noise reduction and is then applied to a de-emphasis unit. 
   The de-emphasis unit compensates the demodulated luminance signal so that it has a frequency characteristic of the luminance signal before recording. The PB video level varies according to a gain which is set during manufacture of the video signal processing IC. Since the gain is set by means of a resistor having a certain value, an error in the PB level may be generated in the actual manufacturing process depending on deviation in the value of the resistor. 
   As described above, the video signal processing IC is designed such that a variable resistor or fixed resistor is necessarily added to the de-emphasis output pin port of the video signal processing IC. This increases the number of components, thereby lowering the manufacturing efficiency, increasing the cost of the product, and causing a deviation in the PB level due to resistance variation of the fixed resistor on the exterior of the IC. 
   SUMMARY OF THE INVENTION 
   To solve the above problems, it is an object of the present invention to provide a de-emphasis circuit designing method for a video signal processing integrated circuit (IC) in order to minimize the number of peripheral components of the video signal processing IC by incorporating a circuit device for determining the level of a reproduced video signal of the de-emphasis circuit, and to an IC made by the latter method. 
   Accordingly, to achieve the above object, there is provided a method for designing a video signal processing IC incorporating a luminance signal processing block and a color signal processing block having a de-emphasis circuit. A circuit element for determining the level of a reproduced video signal of the de-emphasis circuit is incorporated into the video signal processing IC, and the circuit element is connected to a ground exclusively used for luminance signal processing. 
   According to another aspect of the present invention, there is provided a video signal processing IC incorporating a circuit for determining the level of a reproduced video signal of a de-emphasis circuit having a reproduced video level setting unit. The reproduced video level setting unit includes an amplification unit for amplifying a demodulated luminance signal output from the de-emphasis circuit, and a gain-controlled switching unit connected to a plurality of resistance elements for determining the gain of the amplification unit, for switching electrical connection of the plurality of resistance elements according to the reproduced video level during manufacture of the video signal processing IC, and for determining the gain of the amplification unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, and wherein: 
       FIG. 1  is a schematic diagram illustrating a reproducing circuit of a video cassette recorder (VCR) having a video signal processing IC; 
       FIG. 2  is a schematic diagram illustrating a reproducing circuit of a video cassette recorder (VCR) having a video signal processing IC according to the present invention; 
       FIG. 3  is a diagram illustrating the relationship between modulation/demodulation of a frequency modulated (FM) signal and a video signal; and 
       FIG. 4  is a detailed circuit diagram illustrating the PB level setting unit shown in  FIG. 2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   This invention will now be described in more detail with reference to the drawings, in which  FIG. 1  is a schematic diagram illustrating a reproducing circuit of a video cassette recorder (VCR) having a video signal processing IC. 
   As shown in  FIG. 1 , a video cassette recorder (VCR) playback circuit includes a video head  110 , a rotary transformer  120 , a pre-amplifier  130 , and a video signal processing integrated circuit (IC)  140  comprising a high-pass filter (HPF)  141 , a limiter  142 , a demodulator  143 , a low-pass filter (LPF)  144 , a de-emphasis unit  145 , a playback (PB) level setting unit  146  and a mixer  147 . 
   In the PB mode, a modulated video signal detected by the video head  110  is input to the pre-amplifier  130  via the rotary transformer  120  for amplification with a predetermined gain by the pre-amplifier  130 , and is then input to the HPF  141  of the video signal processing IC  140 . 
   The HPF  141  blocks a low-frequency component color signal among the signals input thereto, and allows a frequency-modulated (FM) luminance signal having a high-frequency component to pass through. The high-pass filtered FM luminance signal passes through the limiter  142 , which prevents black-and-white inversion occurring during demodulation, and is then demodulated in the demodulator  143 . The demodulated luminance signal is then input to the LPF  144 , which reduces high-frequency component noise, and the output of LPF  144  is then applied to the de-emphasis unit  145 . 
   The de-emphasis unit  145  is designed to have a frequency characteristic inversely symmetrical with respect to that of pre-emphasis in the recording mode. Accordingly, the de-emphasis unit  145  functions to compensate the demodulated luminance signal so that it has a frequency characteristic of the luminance signal before recording. The PB video level varies according to the gain of an amplifier is the de-emphasis unit  145 . The gain of the PB level setting unit  146  is determined during manufacture of the video signal processing IC  140 . That is, during manufacture of the video signal processing IC  140 , the gain of the PB level setting unit  146  is set in accordance with a resistance of resistor R 1  attached to pin P 1 . Thus, an error in the PB level may be generated in the actual manufacturing process depending on variation in the resistance of the resistor R 1 . 
   The luminance signal output from the de-emphasis unit  145  is mixed with a color signal output from a color signal playback processing procedure by the mixer  147 , and is then output to pin P 2 . 
   As described above, the video signal processing IC is designed such that a variable resistor or fixed resistor for determining gain is necessarily added to the de-emphasis output pin port of the video signal processing IC. This increases the number of components, thereby lowering manufacturing efficiency, increasing the cost of the product, and causing a deviation or variation in the PB level due to a resistance variation of the fixed resistor on the exterior of the IC. 
     FIG. 2  is a schematic diagram illustrating a reproducing circuit of a video cassette recorder (VCR) having a video signal processing IC according to the present invention. 
   As shown in  FIG. 2 , a reproducing circuit for a VCR having a video signal processing IC according to the present invention includes a video head  210 , a rotary transformer  220 , a pre-amplifier  230 , and a video signal processing IC  240  having a high-pass filter (HPF)  241 , a limiter  242 , a demodulator  243 , a low-pass filter (LPF)  244 , a de-emphasis unit  245 , a playback (PB) level setting unit  246 , and a mixer  247 . 
   In general, the de-emphasis unit  245  and the PB level setting unit  246  are incorporated into a single de-emphasis circuit, and are thus processed in a single circuit block. 
   The detailed circuitry of the PB level setting unit  246  is shown in  FIG. 4 , as discussed below. 
   First, the basic operation of the VCR will be described. During a reproduction mode, a modulated video signal detected by video head  210  is input to the pre-amplifier  230  via the rotary transformer  220 , and is amplified with a predetermined gain in the pre-amplifier  230  for output to the HPF  241  of the video signal processing IC  240 . 
   The HPF  241  blocks low-frequency color signal components contained in the modulated video signal, and produces an FM luminance signal having a high-frequency component. 
   The FM luminance signal output from the HPF  241  is a mixed signal comprising a low-frequency FM wave having a large amplitude and a high-frequency FM carrier wave having a low amplitude. Signal components are easily volatile at a low-amplitude area of a high-frequency portion of the FM wave, resulting in black-and-white inversion during demodulation. In order to prevent the black-and-white inversion, the high-pass filtered FM luminance signal is limited to a constant reference level by the limiter  242 . 
   The demodulator  243  receives the output of the limiter  242 , and demodulates the same to restore the FM luminance signal having a frequency deviation of 1 MHz into an unmodulated state signal. Then, the demodulated luminance signal is noise-attenuated by the LPF  244  for input to the de-emphasis unit  245 . 
   The de-emphasis unit  245  includes an internal amplifier circuit which has a frequency characteristic inversely symmetrical with respect to pre-emphasis before modulation. The signal from LPF  244  has its gain adjusted by the de-emphasis unit  245  so as to adapt the output level of a reproduced video signal to a prescribed level, and that adjustment is performed by the PB level setting unit  246 . 
   The reproduced video signal is defined so as to have a level of 1 Vpp by demodulating an FM video signal having a frequency deviation of 1 MHz in accordance with the Video Home System (VHS) standard, as shown in  FIG. 3 , which is a diagram illustrating the relationship between modulation/demodulation of a frequency modulated (FM) signal and a video signal. However, the slope of the linear relationship between the reproduced luminance signal level and a frequency deviation during demodulation may decrease or increase, as indicated by dotted arrow a or c, due to a difference or variation in the characteristics of circuit elements caused during the process of manufacturing the video signal processing IC  240 . Accordingly, in the course of manufacturing the video signal processing IC  240 , the PB level setting unit  256  controls so that the reproduced luminance signal level is accurately set to 1 Vpp with respect to the frequency deviation of 1 MHz in a graphical representation of the relationship between the reproduced luminance signal level and the frequency deviation during demodulation. 
   The operation of the PB level setting unit  246  will now be described with reference to  FIG. 4 , which is a detailed circuit diagram illustrating the PB level setting unit shown in  FIG. 2 . 
   The output signal of the de-emphasis unit  245  is applied to a base terminal of the transistor Q 1 . The circuit formed by the transistor Q 1  and resistors R 0 , R 1 , . . . , Rn is an amplification unit. The gain of the amplification unit is determined by the value of the resistors R 1 , R 2 , . . . , Rn which are parallel-connected to a collector terminal of the transistor Q 1 . 
   The resistors R 1 , R 2 , . . . , Rn are grounded through switches SW 1 , SW 2 , . . . , SWn, respectively. Thus, the resistors connected to those of the switches SW 1 , SW 2 , . . . , SWn which are in the OFF state do not affect the gain value, and only the resistors connected to switches in the ON state affect the gain value of the amplification unit. In particular, the ground to which the switches SW 1 , SW 2 , . . . , SWn are connected is a ground used exclusively for luminance signal processing, and is different from the ground used for color signal reproduction processing. This feature (separation of the grounds used for luminance signal processing and color signal processing, respectively) is for the purpose of preventing noise generated in the course of processing a color signal from affecting the luminance signal. 
   The FM luminance signal having a frequency deviation of 1 MHz is input to the demodulator  243  of the video signal processing IC  240  of  FIG. 2  during manufacture of the video signal processing IC  240  using the above-described principle. Then, the gain level of the amplification unit constituting the PB level setting unit  246  is determined such that the reproduced video signal level output from the video signal processing IC  240  becomes 1 Vpp under a termination condition of 75Ω. Then, ON/OFF switching of the switches SW 1 , SW 2 , . . . , SWn of the gain-controlled switching unit  10  of  FIG. 4  is carried out, depending on the determined gain, to determine the resistance value of the collector terminal of the transistor Q 1 . 
   The switches SW 1 , SW 2 , . . . , SWn constituting the gain-controlled switching unit  10  are, preferably, constructed using Zener diodes, and can be designed so as to determine ON/OFF switching using Zener breakdown characteristics of the Zener diodes. In other words, if a voltage greater than a breakdown voltage is applied to a Zener diode so that it is switched on, a Zener breakdown phenomenon, in which the resistance of the Zener diode becomes substantially zero, occurs and the Zener diode is shorted (this is generally called “Zener Zapping”). 
   As described above, according to the present invention, all circuit elements constituting a circuit which determines the level of a reproduced video signal of de-emphasis circuit  245  are incorporated into video signal processing IC  240  at the time of design of the video signal processing IC  240 , thereby removing external circuit elements, including a resistor at the output terminal of the de-emphasis circuit  245  of the video signal processing IC  240 . 
   In the embodiment of the present invention, the amplification unit in the PB level setting unit  246  is designed using a single transistor Q 1  and resistors R 1 , R 2 , R 3 , . . . , Rn. There may be a case in which the amplification unit is designed using a differential amplifier. 
   According to the embodiment of the present invention, the number of components can be reduced by designing all circuit elements constituting a circuit which determines the level of a reproduced video signal of de-emphasis circuit  245  so as to be incorporated into a video signal processing IC  240  at the time of design of the video signal processing IC  240 , thereby reducing cost. Also, deviation in the PB level due to external component deviation can be reduced. Further, the material cost can also be reduced. 
   It should be understood that the present invention is not limited to the particular embodiment disclosed herein as the best mode contemplated for carrying out the present invention, but rather that the present invention is not limited to the specific embodiments described in this specification except as defined in the appended claims.