VSP9427B Ver la hoja de datos (PDF) - Micronas

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VSP9427B

PRIMUS Powerful Scan-Rate Converter including Multistandard Color Decoder

Micronas 

VSP 94x2A

DATA SHEET

511

upper headroom

511

upper headroom

442

446

white

256

black

144

64

16

0

0

Fig. 2–2: CVBS, Y and C Amplitude Characteristics.

lower headroom

When using the sync height based AGC mode, the A/D

gain increases or decreases depending on the incom-

ing signal. When using overflow detection only, the

gain is set to maximum and is reduced whenever an

’overflow’ occurs.

The signal is low pass filtered so that chrominance and

noise are not used for detection. The threshold can be

adjusted by PWTHD. A setting of ’11’ equals 511 and

means an overflow of the ADC. Other settings react for

a lower level. The gain only becomes higher when a

change of the channel is detected or is manually reset

by AGCRES. AGCFRZE holds the current AGC value.

A manual setting of the ADCs gain control is possible

using the parameters AGCADJ1 and AGCADJ2.

The conversion range (CR) is bigger than the signal

range (SRY, SRC) leaving a headroom for overshoots

(see Fig. 2–2).

.

Gain Control Characteristic

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1

0.9

0.8

0.7

0.6

0.5

0

8

16

24

32

40

48

56

64

AGCADJ1, AGCADJ2 (I²C)

Fig. 2–3: CVBS ADC Characteristic

2.1.3. Clamping

The timing of the clamping (pulse) control signals for

the analog inputs are derived from its corresponding

CVBS input signal. The clamping algorithm works with

a split measurement pulse and a clamping pulse. The

measurement pulse is used to detect the clamping

error. The clamping pulse is used to enable current

sources for reducing the detected clamping errors. The

start and length of the measurement signals are inde-

pendently adjustable for both channels (CLMPST1,

CLMPD1, CLMPST2, CLMPD2).

The same applies for the clamping signals

(CLMPST1S, CLMPD1S, CLMPST2S, CLMPD2S).

Clamping and measurement signals for RGB channel

are not separate. Clamping for these ADC are con-

trolled by CLMPST2S and CLMPD2S only. Clamping

can be suppressed for some lines by CLMPLOW and

CLMPHIGH to ignore copyprotection information. No

external sync signals are required.

CLMPST1

CLMPST1S

CLMPD1S

CLMPD1

Measurement ADC1

Clamping ADC1

CLMPST2

CLMPST1S

CLMPD2S

CLMPD2

Measurement ADC2

Measurement and Clamping RGBF

Clamping ADC2

Fig. 2–4: Clamping Signals

8

Aug. 16, 2004; 6251-552-1DS

Micronas

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