JPS6248960B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to testing the electrical characteristics of a semiconductor integrated circuit (chroma IC) for color television. Television signals are extremely complex signals whose parameters must be decoded at precise times to reproduce and maintain high quality video. It is also well known that the processing methods used for transmitting color TV signals can be broadly classified into three methods: NTSC, PAL, and SECAM. The present invention focuses on the color characteristics (brightness, hue, and saturation) of PAL color signal processing IC (chroma IC).
The present invention provides a method for measuring electrical characteristics proportional to . The PAL system has the same signal as the NTSC system, but the polarity (sign) of one of the color difference signals, RY, is inverted for each line (horizontal synchronization), and the decoding of the PAL color signal is It is done sequentially. Therefore, the exact order must be known for correct decoding. FIG. 1 schematically shows the decoder circuit section of the IC under test (chroma IC) and the chroma signals (burst signal and color difference signal) for testing. To outline the functions of each circuit block, there is a brightness (Y) signal separated from an electric signal (composite video signal) proportional to color characteristics, two types of color difference signals B-Y, R-Y, and color synchronization ( BURST) signal and horizontal synchronization (H) signal are applied as input signals to each circuit. The matrix circuit 4 has a conversion function that uses the outputs of the color difference signal demodulation circuits 1, 2, and 3 and the (Y) signal as input signals to extract electrical signals corresponding to the three primary colors (blue, green, and red). ing.
Further, the demodulation circuit 3 is a circuit that handles the signal obtained by demodulating the color difference signals of the demodulation circuits 1 and 2 as an input signal, and obtains a demodulated output corresponding to the color difference signal G-Y. A carrier signal necessary for demodulation is supplied to the demodulation circuits 1 and 2 directly from the voltage controlled oscillation circuit 5 or via the PAL switch 7. On the other hand, the color synchronization (BURST) signal is the oscillation phase and color of the voltage-controlled oscillation circuit 5 obtained through the automatic phase control (APC) circuit 6 that controls the oscillation phase of the voltage-controlled oscillation circuit 5 and the PAL switch 7. It is applied as an input signal to a verification circuit (ID) 9 that performs verification with the phase of the synchronization signal. On the other hand, the horizontal synchronization (H) signal is applied as an input signal to the flip-flop circuit 8 line by line. Therefore, the output of the flip-flop circuit 8 is normally inverted every two lines to switch the PAL switch 7. The signal sent from the matching circuit 9 to the flip-flop circuit 8 is a switch switching signal generated when the oscillation phase through the PAL switch 7 and the color synchronization (BURST) signal are different in phase. The present invention provides a method for accurately measuring the operation of the above circuit functions, and for this purpose, the necessary test chroma signal and horizontal synchronization (H) pulse are applied to the input of each circuit block and measured. All you have to do is
As shown in Figure 2, the chroma signal and horizontal synchronization pulse used in the PAL system change the phase of the color synchronization signals (bursts) 10 and 10' for each horizontal synchronization (H) signal. 135° or -
135°), the color synchronization signal is extracted from the chroma signal using a gate pulse synchronized with the (H) pulse 11 and sent to the automatic phase control circuit 6 and the matching circuit 9.
is treated as an input signal. Furthermore, the phases of the color signals I and Q corresponding to the color difference signals B-Y and R-Y in the chroma signal are changed to 0° (I) and 90° (Q) every horizontal synchronization, and the demodulation circuit 1 and 2 at the same time. Note that a (Y) signal corresponding to brightness is applied to the matrix circuit 4, but is not directly related to the present invention and will therefore be omitted. Figure 3 A and B are the second
Color synchronization signals 10 and 10' of the test chroma signal in the figure
It is a vector diagram showing the phases of color signals I and Q for the line sequential nH case (the nth horizontal synchronization period) and the case of the line sequential (n+1) case (the n+1)th horizontal synchronization period). It is described as follows. It can be easily understood from FIG. 3 that this is a test chroma signal different from the PAL chroma signal normally used as a broadcasting signal. In other words, there are two characteristics of the PAL system. The polarity of one of the color difference signals B-Y and RY and the phase of the color synchronization signal are also inverted line-by-line, which is well known. The present invention provides a method for accurately measuring the electrical characteristics of a PAL decoder circuit by preparing a chroma signal for testing the decoder circuit, which is different from the chroma signal used in PAL television. There is. As is clear from the vector diagram in FIG. 3, the test chroma signal according to the present invention changes the phase (-180°) of the NTSC color synchronization signal line-sequentially to 135° and -135°.
I am changing it to ゜. Also, from another perspective,
Line sequential in NTSC system with two horizontal synchronization {nH and (n+
1) It can be said that it is repeated every H}. This means that the test chroma signal generator is PAL.
Even if it is not a NTSC system, if it is a device that can change the phase of only the color synchronization signal, it is a PAL system chroma IC.
This shows that it is possible to obtain chroma signals for testing. The relationship between the test chroma signal and the output signals E _B , E _R and E _G of the decoder circuit will be explained with reference to FIGS. 2 to 6. FIG. 4 shows the signal waveforms of the output signals EB, ER, and EG of the decoder circuit when the chroma signal shown in FIG. 2 is applied to the decoder circuit. Further, it is assumed that the demodulation angles of the color difference signal demodulation circuits 1, 2, and 3 are 0° (EB), 90° (ER), and ±135° (±EG). In Fig. 4, the output waveform of EB corresponds to the I signal in Fig. 2 and is a positive output +B (I), and the output waveform of ER corresponds to the Q signal in Fig. 2, and
Positive polarity +R (Q) corresponding to the phase of the BURST signal
and negative polarity -R(Q), and the output waveform of EG also has negative polarity -G(I) corresponding to the I signal in Figure 2, and Q
The solid lines indicate the state in which -G(Q) of negative polarity is obtained as the output of the demodulation circuit during the phase of the BURST signal and +G(Q) of positive polarity during the phase of the BURST signal, respectively. On the other hand, the output indicated by the broken line represents an abnormal state caused by the malfunction shown in FIG. 17. First, explaining only the case of line sequential nH, time-division decoder outputs E _B , E _R and E _G corresponding to chroma signal inputs I and Q to the decoder circuit.
Since the waveform is obtained at the demodulation angle shown in the vector diagrams in Figure 5A and B, each output is E _B = B (I), E _R = R
(Q), E _G =-G(I)-G(Q). E
Since the demodulation angles of _B and E _R have a 90° difference from each other, an output is obtained for only one of the signals for the chroma signal inputs I and Q (the demodulation angle and (This is a case where the phase difference with the chroma signal is not considered). In other words, the demodulation axis

The output E _B obtained from [Formula] is the output +B (I) corresponding to the chroma signal I whose phase matches the demodulation axis (90 degrees with the demodulation axis).
゜An output corresponding to the chroma signal Q having a different phase cannot be obtained). Also, the demodulation axis

The output E _R obtained from [Formula] is the output + R (Q) corresponding to the chroma signal Q whose phase matches the demodulation axis (the output corresponding to the chroma signal I whose phase differs by 90 degrees from the demodulation axis is not obtained). Also, the demodulation axis

Since the output E _G obtained by [formula] has a phase difference between the demodulation axis and the chroma signals I and Q, the outputs corresponding to I - G (I) and Q
The output corresponding to -G(Q) is obtained. The waveforms shown by the broken lines E _R and E _G are generated when the decoder circuit malfunctions, and the cause is malfunction of any one of the PAL switch 7, flip-flop circuit 8, and verification circuit 9 in Fig. 1. It can be assumed that this is the case. Next, explaining the line sequential order by limiting it to (n+1)H, the demodulation axis of the decoder circuit changes as the phase of the color synchronization (BURST) signal changes. In other words,

[Formula] has reversed polarity and is −

[Formula] Tona the law of nature,

【ceremony

[Formula] becomes. or

[Formula] remains unchanged. Therefore, the demodulation axis

The output E _B obtained by [Equation] becomes the output +B(I) corresponding to the chroma signal I, which is similar to the line sequential nH. Demodulation axis -

[Formula] The output E _R obtained at the axis becomes the output -R(Q) corresponding to the chroma signal Q, which is the opposite polarity of R(Q) obtained when the line sequential nH is used. Also, the demodulation axis

The output E _G obtained from [Formula] is the output - G (I) corresponding to the chroma signal I and the output + G (Q) corresponding to the chroma signal Q (the polarity of the demodulation axis corresponding to Q is reversed). Therefore, the polarity of the output waveform is opposite to the axis for line sequential nH and (n+1)H). Note that the waveform shown by the broken line is the output during abnormal operation that appears due to the same cause as the line-sequential nH. As can be understood from the above description, according to the present invention, it is possible to conduct an electrical characteristic test of a PAL decoder circuit without using a PAL chroma signal generator. FIG. 6 shows demodulated output signals E(I) and E obtained corresponding to the test chroma signals I and Q in FIG.
The figure shows how the output level and polarity of each of (Q) changes in response to the phase change (0° to 360°) of the color difference signal. This is shown in Figure 4 for each demodulation output.
In contrast to the case where the demodulation angles of EB, ER, and EG are considered fixed, Fig. 6 shows that the demodulation output level of the chroma signals I and Q changes with respect to the demodulation axis θ (0° to 360°). It shows how it changes in response to I, and I
It also shows the phase relationship between the signal and the Q signal. This means that the phase of the I signal and Q signal is set to 0 in advance.
and 90°, and each demodulated signal EB,
Output E for chroma input I signal of ER and EG
(I) and output E(Q) for chroma input Q signal
and the composite output EC and demodulation axis θ from each output level.
It shows that you are required to. In other words, to measure the demodulation axis θ, fix the phase of the test chroma signal in advance and measure the demodulation output signal levels E(I) and E(Q), respectively, and the combined output EC
and the demodulation axis θ can be measured. The demodulation axis θ is a parameter found by θ=tan ^-1 E(Q)/E(I) ......(1), and E(I) and E
(Q) is a value obtained by actually measuring the demodulated outputs E _B , E _R and E _G . This means that the outputs E (I) and E corresponding to the I and Q input signals of the test chroma signal
By determining (Q), it means that the demodulation axis can also be determined using equation (1) above. Furthermore, the combined output E _c on the demodulation axis is obtained by E _c =√() ² +() ² . . . (2). Therefore, the demodulation axis θ of the demodulation circuit and the composite output E
_c is obtained by actually measuring E(I) and E(Q). In the demodulated outputs E _B , E _R and E _G of Fig. 4, E _B
The output +B(I) is a signal corresponding to E(I) in FIG. Also, the output of E _R +R (Q) (or -
R(Q)) is a signal corresponding to E(Q) in FIG. Also, -G(I) in the output of E _G is E in Figure 6.
(I) and -G(Q) (or G(Q)) are signals corresponding to E(Q) in FIG. 6, respectively. Therefore, when determining the demodulation axis θ _B at E _B , θ _B =0° is obtained by substituting E(I)=+B(I) E(Q)=0 into equation (1). Furthermore, when determining the demodulation axis θ _R at E _R , by substituting E(I)=0 and E(Q)=+R(Q) into equation (1), θ _R =90°. Also, when determining the demodulation axis θ _G at E _G , E(I)=-G(I), E(Q)=-G(Q).
Substituting into equation (1), we get θ _G =-G(Q)/-G(I) (θ _G -θ _B is approximately 235° in the normal PAL system). Next, when determining the demodulated output, the combined output E _cB at E _B is E _cB = +B (I) from equation (2), and the combined output E _cR at E _R is E _cR = +R (Q) from equation (2), The combined output E _cG in E _G is obtained from equation (2) as follows: E _cG =√{−()} ² +{−()} ² . As described above in the embodiments of the present invention, according to the present invention, the electrical characteristics of a PAL decoder circuit can be improved.
It has the feature that it can be tested accurately without using PAL chroma signals, and can be fully applied to methods for testing NTSC decoder circuits.
Additionally, it becomes possible to develop a test device that is compatible with both types. Also, the line sequence in the PAL system {nH or (n+
1) _By reading the polarity of the demodulated output with respect to Output whose polarity inverts sequentially {+R (Q) or -R
(Q)}, but during abnormal operation, an output with the polarity shown by the broken line in FIG. 3 will be obtained).

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the PAL color signal decoder circuit of a semiconductor integrated circuit (chroma IC) used in a PAL color TV receiver, and Figure 2 is a test chroma IC applied to each circuit block. 1 is a schematic diagram of a signal. 1, 2, 3...color difference signals B-Y, RY and G
- Y demodulation circuit, 4... Matrix circuit that converts each of the color difference outputs into three outputs E _B , E _R , and E _G as input, 5... Voltage that generates a carrier signal synchronized with the phase of the color synchronization signal. Controlled oscillation circuit, 6...
automatic phase control (APC) circuit for controlling the phase of the oscillation signal of the oscillation circuit 5, 7...PAL switch for inverting the phase of the carrier signal superimposed on the demodulation circuit 2, 8...flip-flop (F-F) circuit,
9... Verification circuit. 3A and 3B are vector diagrams for each line sequential {nH and (n+1)H} corresponding to the test chroma signal of FIG. 1. Figure 4 shows the matrix circuit 4 in Figure 1.
A diagram showing the waveforms of the output signals E _B , E _R , E _G obtained from the chroma signals in FIG. 2, and FIG. 5 A,
B is the demodulation axis for each line sequential {nH and (n+1)H} {

【formula】

[Formula] and

[Formula] (or

[Formula])} and the phase of the color synchronization (BURST) signal. Figure 6 shows a vector diagram of the outputs E (I) and E (Q) corresponding to the test chroma signals I and Q in Figure 2, and the changes in each output with respect to θ, at the demodulation axis θ of the color difference signal. It is a diagram.

Claims (1)

[Claims] 1 Only the phase of the color synchronization signal is 135 times per horizontal synchronization.
A test chroma signal was constructed in which the angle was changed alternately between 0° and -135°, and the phases of the two color difference signals were 0° and 90°, and these two color difference signals were time-divided within one horizontal synchronization. 1. A method for testing a color signal demodulation circuit, comprising: generating a test chroma signal, supplying this test chroma signal to a PAL system color television signal demodulation circuit under test, and testing the electrical characteristics of the demodulation circuit.