TDA4884 Datasheet, PDF (11/28 Pages) NXP Semiconductors – Advanced monitor video controller for OSD

Philips Semiconductors
Three gain control video pre-amplifier for OSD
Product specification
TDA4884
Notes to the characteristics
1. Definition of levels:
a) Artificial black level: internal signal level behind input emitter follower during input clamping and signal clipping.
This level is inserted instead of the input signal during blanking.
b) Reference black level: DC voltage during output clamping at voltage outputs, not influenced by contrast or gain
setting, adjustable by cut-off stabilization.
c) Cut-off level: corresponding DC voltage at CRT cathode in closed feedback loop.
d) Black level: actual signal black level at either voltage outputs or cathode. At voltage outputs the black level is
equal to reference black level because there is no brightness control via TDA4884. At cathode the black level is
equal to cut-off level. Brightness can be adjusted via grid 1.
e) Ultra-black level, switch-off level: lowest adjustable reference black level, lowest signal level at voltage outputs.
f) The minimum guaranteed control range for reference black level is 0.1 to 1 V.
The ultra-black level is dependant on the external resistor R_O at pins 13, 16 and 19 (voltage outputs) to ground.
g) V_{bl (SO)} ≈ _{3----.--5-----k--R-Ω}---^O---₊-----R-----_O- × 4.65 V
h) Signal processing see Fig.4.
2. Linear control range is 1 to 6 V for V_i(CC), independent of supply voltage. Open pin 6 leads to absolute maximum
contrast setting. It is recommended not to exceed V_i(CC) = V_P − 1 V to avoid saturation of internal circuitry. For
V_i(CC) < V_i(CC)(min) ≈ 0.7 V a small negative signal (≈ −40 dB) will appear. For frequency dependency of contrast
control see note 14. Typical contrast characteristic see Fig.5.
3. Definition for nominal output signals: input V_i(b-w) = 0.7 V, gain pins 3, 1 and 11 open-circuit, contrast control
V_i(CC) = V_i(CC)(nom).
4.
∆ G_track
=
20 × maximum of



log



A--A---₁^-1-₀^-
×
-A-A---²-₂-⁰-



;
log



A--A---₁^-1-₀^-
×
A--A---_{3-3-0- }
;
log



A--A---₂^-2-₀^-
×
-A-A---³-₃-⁰-






dB
A_x: signal output amplitude in channel x at any contrast setting between 1 and 6 V.
A_x0: signal output amplitude in channel x at nominal contrast and same gain setting.
5. Typical step in contrast voltage and response at signal outputs for nominal input signal V_i(b-w) = 0.7 V. Typical OSD
fast blanking input/output see Fig.7.
6. Linear control range is 1 to 6 V for V_i(GC), independent of supply voltage. Typical gain characteristic see Fig.6.
7. The internal reference voltage can be measured at pins 18, 15 and 12 during output clamping (V_i(HBL) = 2 V) in closed
feedback loop. Typical variation of V_ref(int) with temperature and power supply voltage see Fig.8.
8. Slow variations of video supply voltage V_CRT (see Fig.1) will be suppressed at CRT cathode by cut-off stabilization.
Change of V_CRT by 5 V leads to specified change of cut-off voltage.
9. The test mode allows testing without input and output clamping pulses. The signal inputs (pins 2, 5 and 8) have to
be biased via resistors to the previously measured clamp voltages of approximately 3 V (artificial black level + V_BE).
Signal blanking is not possible during test mode.
10. The signal-to-noise ratio is calculated by the formula (frequency range 1 to 70 MHz):
N-S-- ^{= 20 × log p----e---a----k------t-o-------pR---e--M-a----kS----v--v-a--a--l-lu-u--e--e---o--o--f-f--t-t-h-h--e-e----n-n---o-o--m-i-s---ie-n----ao---l-u--s-t--pi-g--u--n-t--a--v-l--o-o--l--tu-a--t--gp---eu---t---v---o----l-t--a---g---e-- dB}
11. Large output swing e.g. I_o(b-w) = 50 mA leeds to signal depending power dissipation in output transistors.
Thermal V_BE variation is compensated.
12. Composite signals will not disturb normal operations because an internal clipping circuit cuts all signal parts below
black level. Typical sync clipping see Fig.10.
1997 Nov 26
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