MC13077 Ver la hoja de datos (PDF) - Motorola => Freescale

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componentes Descripción

Fabricante

MC13077

ADVANCED PAL/NTSC ENCODER

Motorola => Freescale 

MC13077

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

VCC

Sync Input

1.4 V

Sync Tip Voltage

Gnd

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)

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

TTL Sync

5.1 k 0.1 µ 7

240

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.

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.

6

MOTOROLA ANALOG IC DEVICE DATA

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