JPH05268622A - Cy correcting circuit - Google Patents

Abstract

PURPOSE:To fix a ratio of the color signal to the luminance signal at the time of correcting the luminance signal by converting the color signal to a signal current proportional to the magnitude of the input luminance signal and that of the corrected luminance signal. CONSTITUTION:A current IS1 flows to the collector of a transistor TR Q1 by a first differential amplifier consisting of TRs Q1 and Q2 and a resistance R1, and a current IS<2> flows to the collector of a TR Q3 by a second differential amplifier consisting of TRs Q3 and Q4 and a resistance R2. These currents IS1 and IS2 are subjected to logarithmic conversion and exponential conversion by TrQ5, Q6 and Q7, Q8, and as the result, they flow as collector currents of TRs Q7 and Q8 in a current ratio of IS3:IS4=IS2:IS1. Consequently, the magnitude of a carrier chrominance signal Cout of the output is proportional to the luminance signal, and an amplitude output where the color signal is accurately proportional to the corrected luminance signal is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to color signal correction of a video image signal, and more particularly to color signal correction when a luminance signal is corrected and output.

[0002]

2. Description of the Related Art As a color signal correction circuit when a luminance signal is corrected, a method of comparing an input luminance signal (that is, a luminance signal before correction) with a corrected luminance signal and correcting the magnitude of the color signal is usually used. is there.

The CY correction circuit shown in FIG. 3 shows this conventional color signal correction circuit, and this characteristic is shown in FIG.
(A) and FIG. 4 (B) are shown. In FIG. 3, E1 is a constant voltage, VCC is a power supply voltage, I1 is a constant current, Q1, Q3, Q.
5 to Q9 are NPN transistors, R1 to R4 are resistors, Y is an input luminance signal voltage, Y'is a corrected luminance signal, CIN is an input carrier color signal, and COUT is an output carrier color signal.

In the conventional CY correction circuit configured as described above, the voltage difference between the input luminance signal and the corrected luminance signal is converted into a current by the resistors R1 and R2. This current is logarithmically converted by transistors Q5 and Q6, and Q7 and
Exponential conversion is performed by a differential amplifier composed of a transistor of Q8, and the color signal current generated by CIN, Q9, and R4 is controlled and passed through a resistor R3, and output as an output carrier color signal. The values of each part at this time are calculated as follows. The collector currents of Q1 and Q3 are ICQ1 = I1 / 2 + (Y−Y ′) / (R1 + R2) ... (1) ICQ3 = I1 / 2− (Y−Y ′) / (R1 + R2) ... (2) In Q5 and Q6, ICQ5 = IS × EXP (q · VBE5 / kT) ≈ICQ1 ... (3) ICQ6 = IS × EXP (q · VBE6 / kT) ≈ICQ3 ... (4) Collectors of Q7 and Q8 The current is ICQ7 = IS × EXP (q · VBE7 / kT) (5) ICQ8 = IS × EXP (q · VBE8 / kT) (6) where VBE7−VBE8 = VBE6−VBE5 ・ ・ ・(7) Where, IS is the saturation current of the transistor.
From (5) ÷ (6) ICQ7 / ICQ8 = EXP (q. {VBE7-VBE8} / kT) = EXP (q. {VBE6-VBE5} / kT) = ICQ6 / ICQ5 ... (8) That is, the current ratio Are equal. This will be described with reference to the drawings. As shown in FIG. 4A, when the luminance signal is input Y1 and the corrected luminance signal is Y1 ′, the color signal is input C1 and the output signal is C1 ′. Thus, when the luminance signal becomes large, the color signal also becomes large, and CY correction can be performed.

[0005]

However, in the above-mentioned configuration, the magnitude of the color signal does not completely match the luminance signal. That is, it will be described using an equation.

Consider the case where there is no correction as a reference. At this time, VBE of the transistors Q5, Q6 and Q7, Q8 becomes equal, and COUT0 = CIN * R3 / R4.

Next, a case where correction is applied will be considered. COUT '= CIN x (R3 / R4) x {ICQ7 / (ICQ7 +
ICQ8)} (9) Here, the calculation in {} is performed.

{} = (ICQ7 / ICQ8) / [(ICQ7 / ICQ87) +1] = (ICQ6 / ICQ5) / [(ICQ6 / ICQ5) +1] ≈ (ICQ3 / ICQ1) / [(ICQ3 / ICQ1) +1] = [I1 / 2 + (Y−Y ′) / (R1 + R2)] / [I1 / 2− (Y−Y ′) / (R1 + R2)] (10) Therefore, COUT′∝Y ′ cannot be obtained. (Where Y '
Is the magnitude from the pedestal voltage. In view of the above point, the present invention provides an accurate CY correction circuit in which a color signal is controlled to have a ratio of an input luminance signal to a corrected luminance signal in accordance with an input luminance signal and a corrected luminance signal. The purpose is to

[0009]

In order to solve the above problems, the CY correction circuit of the present invention has a first resistor having an emitter resistance on the transistor on the input luminance signal side and having no emitter resistor on the pedestal voltage side. The magnitude of the input luminance signal and the magnitude of the corrected luminance signal are controlled by the differential amplifier and the second differential amplifier that has the emitter resistance in the corrected luminance signal side transistor and has no emitter resistance in the pedestal voltage side. A current that is proportional to the input current is supplied, and logarithmic conversion and exponential conversion are performed to convert the color signal into a signal current that is proportional to the magnitude of the input luminance signal and the magnitude of the corrected luminance signal.

[0010]

According to the present invention, the color signal is accurately converted into the corrected luminance signal by converting the color signal into a signal current proportional to the magnitude of the input luminance signal and the magnitude of the corrected luminance signal. A proportional amplitude output can be obtained.

[0011]

1 and 2 show a CY correction circuit according to a first embodiment of the present invention. FIG. 1 is a circuit diagram of the CY correction circuit, and FIG. 2 shows the luminance signal as shown in FIG. The characteristic of the demodulated color signal when corrected in this way is shown in FIG. Hereinafter, description will be given with reference to FIGS. 1 and 2.

In FIG. 2, E1 is a constant voltage, E2 is a pedestal voltage, VCC is a power supply voltage, I1 and I2 are constant currents,
Q1 to Q9 are NPN transistors, R1 to R4
Is a resistor, Y is an input luminance signal voltage, Y'is a corrected luminance signal, CIN is an input carrier color signal, and COUT is an output carrier color signal.

In the CY correction circuit of the present invention constructed as described above, the current IS1 flows through the crestor of the transistor Q1 by the first differential amplifiers Q1, Q2 and R1.
A current IS2 flows through the collector of the transistor Q3 by the second differential amplifiers Q3, Q4 and R2. The currents IS1 and IS2 flowing here are logarithmically and exponentially converted by the transistors Q5 and Q6 and the transistors Q7 and Q8, and as a result, collector currents of the transistors Q7 and Q8 flow at a current ratio of IS3: IS4 = IS2: IS1. .. The values of each part at this time are calculated as follows. The collector current of Q1 is IS1 = (Y-E2) / R1 ... (11) The collector current of Q3 is IS2 = (Y'-E2) / R1 ... (12) In Q5 and Q6, VBE5 = kT / q · ln (IS1 / IS) ・ ・ ・ (13) VBE6 = kT / q ・ ln (IS2 / IS) ・ ・ ・ (14) The collector current of Q7 and Q8 is Is3 = IS × EXP (q ・ VBE7 / kT ) (15) IS4 = IS × EXP (q · VBE8 / kT) (16) where VBE7−VBE8 = VBE6−VBE5 (17) From (5) ÷ (6) Is3 / IS4 = EXP (q. {VBE7-VBE8} / kT) = EXP (q. {VBE6-VBE5} / kT) = IS2 / IS1 ... (18) = (Y'-E2) / (Y-E2) ... (19) The formula when Y = Y 'is: IS3 / IS4 = (Y-E2) / (Y-E2) (20) Therefore, the input luminance signal and correction Degree signal is equal Y = Y '
COUT '/ COUT = (Y'-E2) / (Y-E2) from equations (19) and (20), where COUT is the magnitude of the carrier color signal output at time and COUT' is the output at normal time. (21) As described above, according to this embodiment, the magnitude of the output carrier color signal is proportional to the luminance signal (the magnitude of the luminance signal from the pedestal voltage) as shown in the equation (11). Become. That is, carrier wave colors having exactly the same CY ratio can be output.

[0014]

As described above, according to the present invention, the transistor on the input luminance signal side has the emitter resistance, and the pedestal voltage side does not have the emitter resistance. The transistor has an emitter resistance,
On the pedestal voltage side, a current that is proportional to the magnitude of the input luminance signal and the magnitude of the corrected luminance signal is made to flow by a second differential amplifier that has no emitter resistance, and a logarithmic conversion circuit and exponential conversion circuit are configured, By converting the signal into a signal current that is proportional to the input luminance signal and the magnitude of the corrected luminance signal, it is possible to obtain chrominance that is proportional to the magnitude of the luminance signal. The practical effect is extremely large in realizing the optimum control of the color signal output when the control for obtaining the luminance output waveform is performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a CY correction circuit according to an embodiment of the present invention.

2A is a luminance signal correction characteristic diagram of the CY correction circuit of FIG. 1B is a carrier color signal characteristic diagram

FIG. 3 is a circuit diagram showing a conventional CY correction circuit.

FIG. 4A is a luminance signal correction characteristic diagram of a CY correction circuit. FIG. 4B is a carrier color signal characteristic diagram.

[Explanation of symbols]

 Y input luminance signal Y'corrected luminance signal E2 pedestal voltage COUT carrier color signal output

Claims (5)

[Claims] 1. A difference between a pedestal voltage and an input luminance signal voltage is converted into a first signal current, a difference between a pedestal voltage and a corrected luminance signal voltage is converted into a second signal current, and an input carrier color signal is converted into the first signal. A third current proportional to the current and the second current, respectively
A CY correction circuit that divides into a signal current and a fourth signal current and outputs the fourth signal current. 2. The CY correction circuit according to claim 1, wherein the input carrier color signal is a color-controlled carrier color signal. 3. A first differential amplifier comprising a first transistor having a base to which an input luminance signal is input and a emitter having a first resistance and a base to which a pedestal voltage is input, and a corrected luminance signal to the base. A second differential amplifier composed of a third transistor having a second resistance input to the emitter thereof and a fourth transistor having a pedestal voltage input to the base thereof, and a fifth transistor having an emitter connected to the collector of the first transistor, A sixth transistor having an emitter connected to the collector of the third transistor, a first DC voltage connected to the bases of the fifth transistor and the base of the sixth transistor, and a base input of the emitter of the fifth transistor. 7th transistor and 8th transistor to which the emitters of said 6th transistor are base input A third differential amplifier composed of a transistor, the emitters of the seventh and eighth transistors each have a carrier color signal current, and the collector of the seventh transistor has a third resistor; A CY correction circuit which is controlled by a third differential amplifier and flows into the third resistor to output a carrier color signal. 4. The CY correction circuit according to claim 3, wherein the input carrier color signal is a color-controlled carrier color signal. 5. The CY correction circuit according to claim 3 or 4, wherein the resistance value of the first resistor and the resistance value of the second resistor are equal.