SAA4981/V1 Просмотр технического описания (PDF) - Philips Electronics

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SAA4981/V1

Monolithic integrated 16 : 9 compressor

Philips Electronics 

Philips Semiconductors

Monolithic integrated 16 : 9 compressor

Preliminary specification

SAA4981

Controller

The controller generates the clocks and the horizontal start

signals for the SC line memories and, also, the control

signals for the output multiplexers. The timing for the start

reading signal for three different screen positions (left,

centre and right) and the control signals for the

multiplexers (C1 and C2) is fixed. For the uncompressed

signals a bypass via the SC line memories and a bypass

not via the SC line memories is available. When the

signals do not pass the line memories, the frequency

response is not affected by the si-function. The

compression and bypass mode via the line memories is

delayed by one line with respect to the bypass mode not

via the line memory.

The 16 : 9 compressor is controlled via the control signals

CTRL1, CTRL2 and CTRL3 (see Table 1). The test input

must be LOW level.

Signals for the side panels

The luminance and chrominance of the side panels is

determined by the external signals YSIDE, BYSIDE and

RYSIDE. This external generated side panel signal can be

referenced to the internal black level reference signal via

the output CLAOUT (pin 5).

Horizontal timing (see Fig.3)

The horizontal timing refers to the positive edge of the

input HREF signal.

The following timing parameters are valid for a horizontal

frequency of 15.625 kHz.

Input clamping typically starts at tA = 1.55 µs and ends at

tB = 3.78 µs.

Table 1 Functions of the control signals

CTRL1 CTRL2 CTRL3

FUNCTION

LOW LOW LOW bypass (through the line

memories)

LOW HIGH LOW compression, left position

HIGH LOW LOW compression, centre position

HIGH HIGH LOW compression, right position

LOW LOW HIGH bypass (not through the line

memories)

Internal post filters

The output signals of the SC line memories have to be

filtered with three 6.7 MHz low-pass filters to eliminate the

high frequencies caused by the time discrete signal

processing. The cut-off frequency of 6.7 MHz is necessary

because, as a result of the 3⁄4 compression factor, the

frequencies are shifted to a higher frequency band with the

inverse compression factor (e.g. 5 MHz → compression →

6.67 MHz). Due to the common bandwidth requirements

for all three outputs of the SC line memories the same

transfer function for the filters can be used.

Remark: These filters do not provide an si-correction. This

means that an input signal with a frequency of 5 MHz will

be damped by 2.1 dB at the output if the signal passes an

SC line memory.

1995 Oct 05

6

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