MC13077

8

MOTOROLA ANALOG IC DEVICE DATA

Figure 5. Relationship Showing the Counts of a 3.58 MHz Clock

versus a 4.43 MHz Clock at the End of a Horizontal Period

fsc

fsc/256

256

512

NTSC: (3.58 MHz) (63.56

µs) = 227.5 counts

PAL: (4.43 MHz) (64

µs) = 283.75 counts

Chroma Band Limiting and Luma Delay

Once the color difference and burst flag envelopes have

been modulated, the two components are internally summed

and applied to an output buffer that will drive the external

bandpass circuitry before entering the chip again at Pin 20.

The sum of the color difference modulators produces an

output that is high in harmonic content. For this reason, and

to reduce the possibility of cross color, a chroma bandpass

transformer is used to band–limit the chroma. Suggested

bandpass filters and specifications for NTSC and PAL are

shown in Figure 6a and 6b. For each of

these filters,

approximately 300 ns of group delay is experienced by the

filtered chroma. There is also an internal delay on the order of

100 ns due to internal filtering that must be considered. Thus

a 400 ns luma delay line is used to equalize the timing of the

luma and the chroma. Suitable 400 ns delay lines are the

T O KO

H321LNP–1436PBAB

and

the

TDK

DL122401D–1533. The delay of the luma channel is inserted

between Pins 10 and 6. Pin 10 is the buffered output of the

luma from the RGB matrix. This output is capable of driving

the external passive delay line with no external gain or

buffering required.

0

TOKO H286BAlS–6276DAD

NTSC Bandpass Filter

0.2

0.4

1.0

2.0

3.0

4.0

5.0

6.0

7.0

40

30

20

10

50

FREQUENCY (MHz)

Figure 6a. Group Delay and Magnitude

Response of the TOKO Bandpass Filter

Intended for NTSC Applications

Attenuation

Group Delay

1.0 k

1.0 k

17

4.7 nF

20

60

0

8.0

9.0

0

0.2

0.4

1.0

2.0

3.0

4.0

5.0

6.0

7.0

40

30

20

10

50

FREQUENCY (MHz)

8.0

Figure 6b. Group Delay and Magnitude

Response of the TOKO Bandpass Filter

Intended for PAL Applications

Attenuation

Group Delay

60

0

9.0

1.0 k

1.0 k

17

TOKO H286BAIS–4963DAD

PAL Bandpass Filter

3

4

4.7 nF

20

1

6

3

4

1

6

Characteristics of TOKO Bandpass Filter

(H286BAIS – 6276DAD)

Frequency (MHz)

Attenuation (dB)

Group Delay (

µs)

2.0

8.0 (min)

0.12

2.8

3.0

± 3.0

0.25

3.58

Ins. Loss 3.5 (max)

0.290

± 0.030

4.3

3.0

± 3.0

0.24

6.2

15 (min)

0.05

Characteristics of TOKO Bandpass Filter

(H286BAIS – 4963DAD)

Frequency (MHz)

Attenuation (dB)

Group Delay (

µs)

2.50

10 (min)

0.075

3.73

3.0

± 3.0

0.24

4.43

Ins Loss 2.0 (max)

0.295

± 0.035

5.13

3.0

± 3.0

0.24

6.50

12 (min)

0.05