MC1377P View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

Manufacturer

MC1377P

COLOR TELEVISION RGB to PAL/NTSC ENCODER

Motorola => Freescale 

MC1377

Figure 11. Nulling Residual Color in Black

VB

12 470k

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11

470k

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VB

Figure 12. Delay of Chroma Information

Figure 14(a) shows the output of the MC1377 with low

resolution RGB inputs. If no bandwidth reduction is employed

then a monitor or receiver with frequency response shown in

Figure 14(b), which is fairly typical of non–comb filtered

monitors and receivers, will detect an incorrect luma

sideband at X′. This will result in cross–talk in the form of

chroma information in the luma channel. To avoid this

situation, a simpler bandpass circuit as shown in Figure

15(a), can be used.

Figure 13. MC1377 Output with

Low Resolution RGB Inputs

XX

X

X

Luminance

Chroma

1.0 2.0 3.0 3.58 4.0 5.0

(a) Encoder Output with Low Resolution Inputs

and No Bandpass Transformer

The Chroma Coupling Circuits

With the exception of S–VHS equipped monitors and

receivers, it is generally true that most monitors and receivers

have color IF 6.0 dB bandwidths limited to approximately

±0.5 MHz. It is therefore recommended that the encoder

circuit should also limit the chroma bandwidth to

approximately ±0.5 MHz through insertion of a bandpass

circuit between Pin 13 and Pin 10. However, if S–VHS

operation is desired, a coupling circuit which outputs the

composite chroma directly for connection to a S–VHS

terminal is given in the S–VHS application (see Figure 19).

For proper color level in the video output, a ±0.5 MHz

bandwidth and a midband insertion loss of 3.0 dB is desired.

The bandpass circuit shown in Figure 7, using the TOKO

fixed tuned transformer, couples Pin 10 to Pin 13 and gives

this result. However, this circuit introduces about 350 ns of

delay to the chroma information (see Figure 13). This must be

accounted for in the luminance path.

A 350 ns delay results in a visible displacement of the color

and black and white information on the final display. The

solution is to place a delay line in the luminance path from

Pins 6 to 8, to realign the two components. A normal TV

receiver delay line can be used. These delay lines are usually

of 1.0 kΩ to 1.5 kΩ characteristic impedance, and the

resistors at Pins 6 and 8 should be selected accordingly. A

very compact, lumped constant delay line is available from

TDK (see Figure 25 for specifications). Some types of delay

lines have very low impedances (approx. 100 Ω) and should

not be used, due to drive and power dissipation

requirements.

In the event of very low resolution RGB, the transformer

and the delay line may be omitted from the circuit. Very low

resolution for the MC1377 can be considered RGB

information of less than 1.5 MHz. However, in this situation, a

bandwidth reduction scheme is still recommended due to the

response of most receivers.

X X′

1.0 2.0 3.0 3.58 4.0 5.0

(b) Standard Receiver Response

A final option is shown in Figure 15(b). This circuit provides

very little bandwidth reduction, but enough to remove the

chroma to luma feedthrough, with essentially no delay. There

is, however, about a 9 dB insertion loss from this network.

It will be left to the designer to decide which, if any,

compromises are acceptable. Color bars viewed on a good

monitor can be used to judge acceptability of step

luminance/chrominance alignment and step edge transients,

but signals containing the finest detail to be encountered in

the system must also be examined before settling on a

compromise.

The Output Stage

The output amplifier normally produces about 2.0 Vpp and

is intended to be loaded with 150 Ω as shown in Figure 16.

This provides about 1.0 Vpp into 75 Ω, an industry standard

level (RS–343). In some cases, the input to the monitor may

be through a large coupling capacitor. If so, it is necessary to

connect a 150 Ω resistor from Pin 9 to ground to provide a low

impedance path to discharge the capacitor. The nominal

average voltage at Pin 9 is over 4.0 V. The 150 Ω dc load

causes the current supply to rise another 30 mA (to

approximately 60 mA total into Pin 14). Under this (normal)

condition the total device dissipation is about 600 mW. The

calculated worst case die temperature rise is 60°C, but the

typical device in a test socket is only slightly warm to the

touch at room temperature. The solid copper 20–pin lead

frame in a printed circuit board will be even more

effectively cooled.

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MOTOROLA ANALOG IC DEVICE DATA

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