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MC13077P датащи(PDF) 6 Page - Motorola, Inc |
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MC13077P датащи(HTML) 6 Page - Motorola, Inc |
6 / 14 page MC13077 6 MOTOROLA ANALOG IC DEVICE DATA FUNCTIONAL DESCRIPTION Composite Sync Input Other than the component video inputs to be encoded, only Composite Sync is required for encoding the components into a composite signal compatible with either the NTSC or PAL standard. The Composite Sync input is used internally for determining which standard to encode to, for driving the black level clamps, and to set the timing of the composite sync in the outputs. The Composite Sync/Sync Separator input was designed to accept AC or DC coupled inputs making it possible to drive the sync input from a variety of sources. An interesting note is that composite video can also be used for sync input. The threshold of the sync input is 1.4 Vdc. Figure 2 shows the requirements for sync input. Figure 2. Sync Input Amplitude Requirements Baseline Voltage Sync Tip Voltage VCC 1.4 V Sync Input Gnd Both serrated and block vertical sync can be used for NTSC applications. PAL applications require a serrated vertical sync. The serrations at the horizontal rate trigger the PAL flip–flop to generate the swinging burst. Even though the sync input of the MC13077 is well suited for TTL interface, some functions of the IC are susceptible to the high energy present in such signals and may be disturbed. This disturbance may take the form of a noise spike in the video outputs and/or a disturbance of the 4x oscillator resulting in an incorrect encoding of the chroma information. Therefore, it is recommended that if TTL or other fast–edged inputs are going to be used for the sync input, then either the amplitude and/or the edge speed of the sync input pulse should be reduced. 300 mVpp of sync without a reduction of edge speed has to be shown to produce disturbance free operation. Also, a sync input of 4.0 Vpp and edge rates of 225 ns have been shown to produce similar results. Figure 3 shows a recommended coupling circuit for TTL type composite sync. Figure 3. TTL Sync Input Circuit 5.1 k 240 0.1 µ TTL Sync 7 Luma and Color Difference Clamps Clamping for the MC13077 occurs once every horizontal line during sync. The absence of color creates a color difference component voltage of zero, this null is used to generate a reference voltage for black in the video outputs. The clamp capacitors at Pins 5, 15 and 16 are used to store the reference voltage during the line period. RGB Inputs To encode RGB, the component video inputs (Pins 12, 13, 14) are applied to the Luma (Y) and color difference (R–Y, B–Y) matrix. The color difference signals are then conditioned by Sallen–key low pass filters (f–3dB = 4.0 MHz). The inputs are designed so that 700 mVpp RGB provides 100% color saturation. The first color difference component (R–Y) is created by matrixing the RGB components with the following weights: R–Y = 0.70R – 0.59G – 0.11B (1) The second color difference signal (B–Y) is created in a similar fashion by the equation: B–Y = 0.89B – 0.59G – 0.30R (2) These two components then receive burst flag before being modulated by the color subcarrier to create composite chroma. The luma is also the result of a weighted matrixing of the RGB components. The components and corresponding weights are: Y = 0.30R + 0.59G + 0.11B (3) Composite sync is then added to the result of Equation 3 to create composite luma. The luma information thus created must be eventually recombined with the chroma information. However, since the chroma information created by Equations 1 and 2 is filtered internally before being modulated then bandlimited externally, the resultant encoded chroma experiences a group delay that is the sum of the delay imposed by the internal and external filtering. So, the composite luma is output at Pin 10 so that an external delay can be inserted in the path to match the delay incurred by the composite chroma. The delayed composite luma is then input back into the MC13077 at Pin 6. Color Difference Inputs If the MC13077 is intended to encode color difference signals (YUV or Y, R–Y, B–Y), it becomes necessary to bypass the color difference and luma matrix circuitry. This can be accomplished by inputing directly to the color modulators the color difference signals. 491 mVpp and 349 mVpp should be input to the R–Y and B–Y Clamp pins (Pin 16 and Pin 15) respectively, to achieve 100% color saturation in the composite video output. The luma information can be input in two ways. The luma can be input directly into the RGB inputs (700 mVpp without sync), or through the delay line (1.0 Vpp with sync, sync tip–to–peak white) in which case the RGB inputs should be cap–coupled to ground. In either case, composite sync still needs to be input to the MC13077 at Pin 7 (see Figures 11, 12 and 13). If the R–Y and B–Y inputs also have burst flag, it can also be input along with the color difference signals at these pins. Of course, now since the color difference modulator pre–filtering is circumvented, the delay for the luma information should be matched only to the delay of the bandpass filter. |
Аналогичный номер детали - MC13077P |
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Аналогичное описание - MC13077P |
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