SAA8117HL データシートの表示（PDF） - Philips Electronics

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SAA8117HL

Digital camera USB interface IC

Philips Electronics 

Philips Semiconductors

Digital camera USB interface IC

Product specification

SAA8117HL

8 FUNCTIONAL DESCRIPTION

8.1 Video synchronization

The video synchronization module (see Fig.1) is capable

of locking onto the video signal thereby implementing a

horizontal gate signal HREF (HREF = HIGH when data is

valid) and a VS signal indicating the start of a new video

frame. This module expects, in the PAL mode, 288 active

lines from a total of 292 lines and in the VGA mode,

480 active lines from a total of 486 lines. The module

generates control signals for the CIF formatter.

8.2 CIF formatter

The video data must be progressive (or non-interlaced)

and in 4 : 2 : 2 (UYVY) format. The CIF formatter module

(see Figs 1 and 3) is programmable to perform down

scaling from 512 × 288 (PAL mode) or 640 × 480 (VGA

mode) to 352 × 288 or 176 × 144 without affecting the

aspect ratio.

The horizontal scaling is achieved with a Variable Phase

Delay filter (VPD-4). To avoid aliasing, this module also

contains a prefilter which has three modes:

• Prefilter A (3 taps)

• Prefilter B (7 taps)

• Prefilter B-comb (13 taps).

Prefilter B-comb is similar to prefilter B, but inserts extra

taps with amplification 0.

This prefilter must be chosen by selecting prefilter B and

setting SN_Prefilter_B_Comb. Prefilter B-comb can be

used independently from prefilter A.

The incoming 4 : 2 : 2 data is vertically filtered to 4 : 2 : 0

by throwing away colour samples. In the even lines the

V-samples are discarded, in the odd lines the U-samples.

The vertical scaling in PAL mode is from CIF (352 × 288)

to QCIF (176 × 144) only. This is done via a vertical

prefilter A (3 taps). In VGA mode a VPD-4 vertical filter is

applied to scale from 640 × 480 to CIF and QCIF.

From the QCIF image a sub-QCIF cut (128 × 96) can be

made. Due to the granularity of the cropping origin, a

UV interchange can occur. This interchange can be

corrected with SN_EIRRAH.

In VGA mode the CIF formatter can be bypassed to create

a full resolution snapshot. The snapshot can be in 4 : 2 : 0

and in 4 : 2 : 2 format, selectable with SN_4 : 2 : 2.

8.3 Compression engine

The compression engine module (see Figs 1 and 3) works

on CIF format only. The CIF data is compressed to a fixed

number of bytes per frame. This number can be selected

leading a compression factor of either 3 or 4. As a result

the data stream of CIF 4 : 2 : 0 equals the data stream of

QCIF 4 : 2 : 2 (3 times compression) or QCIF 4 : 2 : 0

(4 times compression). The algorithm is Philips

proprietary. Real-time decoding can be done in software

on any Pentium platform.

handbook, full pagewidth

SN_Prefilter A_On/Off

YUV0 to YUV7

PREFILTER

A

SN_4:2:2

SN_EIRRAH

SN_PAL_VGA

SN_Output_Format_Select

PREFILTER

B

DOWN

SCALER

COMPRESSION

ENGINE

to

transfer

buffer

SN_Prefilter B_On/Off

SN_Prefilter B_Comb

SN_Compress

SN_Compression_Ratio

SN_Clk_Compress_On

FCE132

Fig.3 The CIF formatter and compression engine.

1999 Apr 02

10

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