TDA4887PS datasheet(45/68 Pages) PHILIPS

45 / 68 page

2001 Oct 19

Philips Semiconductors

Product speciﬁcation

160 MHz bus-controlled monitor video

preampliﬁer

TDA4887PS

Calculation of compensation (see Fig.22):

1. Gain adjustment is in 255 steps from 20 to 100%

which equates to 4.6 V per step at maximum contrast.

One step =

which is equal to

187 mV at the cathode with video gain = 13 for the

white area.

2. For 18.8% drive (used for black level adjustment) the

output changes only 2.7 mV (35 mV at the cathode)

per gain step.

3. The black level adjustment range (at feedback inputs)

is 1.9 V in 255 steps, which is 7.45 mV per step

(

∆ black level of 97 mV at the cathode with feedback

gain = 1

⁄13). It follows that the optimum compensation

is one step black level for

or approximately

three steps of gain.

0.8

4.6 V

255

----------------------------

14.4 mV

------

2.8

handbook, full pagewidth

MHB953

FIXED

MAXIMUM

GAIN

4.6 / 0.7 V

PREAMPLIFIER

CONTRAST

−40 dB

(0.5 / 100%)

255 steps

BRIGHTNESS

−10/30%

of 4.6 V

255 steps

× GAIN

20 /100%

255 steps

VIDEO GAIN

≈13

CRT

signal

amplitude

60 V (max.)

≈25 V cut-off

level variation

4.6 V

(max.)

0.7 V

(nom.)

5.75

to 3.95 V

× BLACK REFERENCES

range 1.9 V

255 steps

FEEDBACK GAIN

≈1/13

Fig.22 Signal amplification and feedback references.

12.4.1.4

Example of automatic factory alignment

This procedure shows a realization of the alignment

description, it depends on disposable equipment.

Gamma = 2.25, maximum luminance = 102.8 cd/m2,

video gain = 13, feedback gain = 1

⁄13, white D; see Fig.23.

1. Initialization

a) Set grid 2 voltage to minimum

b) Set R, G, B gains to the centre values (80H,

subaddresses 04H, 05H, 06H)

c) Set R, G, B black references to centre values (80H,

subaddresses 07H, 08H, 09H)

d) Set contrast to maximum (FFH, subaddress 02H).

2. Vg2 and black levels

a) Set brightness to 18.8% drive (B8H,

subaddress 01H, control bit BRI=0)

b) Apply black video

c) Increase Vg2 manually until one colour appears

d) Activate the alignment computer

e) The computer will continuously adjust the R, G, B

black levels to meet the following three conditions:

x = 0.131

y = 0.329

the centre of the min/max setting remains at 80H

(this will leave some margin for the compensation

steps that follow)

f) Fine tuning of Vg2 (or Vg1) until Y = 2.4 cd/m2 with

the computer still active.

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