TDA8844 datasheet(48/68 Pages) PHILIPS

48 / 68 page

December 16, 1997

Philips Semiconductors

Tentative Device Speciﬁcation

I2C-bus controlled PAL/NTSC/SECAM TV

processors

TDA884X/5X-N2 series

47. Because of the 2-point black current stabilisation circuit both the black level and the amplitude of the RGB output

signals depend on the drive characteristic of the picture tube. The system checks whether the returning measuring

currents meet the requirement and adapts the output level and gain of the circuit when necessary. Therefore the

typical value of the black level and amplitude at the output are just given as an indication for the design of the RGB

output stage.

The 2-point black level system adapts the drive voltage for each cathode in such a way that the 2 measuring currents

have the right value. This has the consequence that a change in the gain of the output stage will be compensated

by a gain change of the RGB control circuit. Because different picture tubes may require different drive voltage

amplitudes the ratio between the output signal amplitude and the inserted measuring pulses can be adapted via the

I2C-bus. This is indicated in the parameter “Adjustment range of the ratio between the amplitudes of the RGB drive

voltage and the measuring pulses”.

Because of the dependence of the output signal amplitude on the application the soft clipping limiting has been

related to the input signal amplitude.

48. For the alignment of the picture tube the vertical scan can be stopped by means of the VSD bit. In that condition a

certain black level is inserted at the RGB outputs. The value of this level can be adjusted by means of the brightness

control DAC.

49. When the reproduction of 4:3 pictures on a 16:9 picture tube is realised by means of a reduction of the horizontal

scan amplitude the edges of the picture may slightly be disturbed. This effect can be prevented by adding an

additional blanking to the RGB signals. The blanking pulse is derived form the horizontal oscillator and is directly

related to the incoming video signal (independent of the flyback pulse). The additional blanking overlaps the normal

blanking signal with about 1

µs on both sides. This blanking is activated with the HBL bit (only in the

TDA8843/44/47/54/57).

50. Signal-to-noise ratio (S/N) is specified as peak-to-peak signal with respect to RMS noise (bandwidth 5 MHz).

51. This is a current input.

52. The beam current limiting and the vertical guard function have been combined on this pin. The beam current limiting

function is active during the vertical scan period.

53. Via the “blue stretch” (BLS bit) or “extended blue stretch” (EBS bit) function the colour temperature of the bright

scenes (amplitudes which exceed a value of 80% of the nominal amplitude) can be increased. This effect is obtained

by decreasing the small signal gain of the red and green channel signals which exceed the 80% level. The effect is

illustrated in Fig.22.

TDA8844 Datasheet(PDF) 48 Page - NXP Semiconductors