OM8373 datasheet(83/108 Pages) PHILIPS

83 / 108 page

2004 Jan 15

Philips Semiconductors

Tentative Device Speciﬁcation

TV signal processor-Teletext decoder with

embedded

µ-Controller

OM8373; OM8378

26. The capacitor for the Automatic Volume Levelling circuit must be connected to the AVL/SNDIF/REFO multi function

pin. The selection of the function must be made by means of the CMB0 and CMB1 bit in subaddress 22H. More

details about the sub-carrier output are given in the parameters D.10.

The Automatic Volume Levelling (AVL) circuit stabilises automatically the audio output signal to a certain level which

can be set by means of the volume control. This AVL function prevents big audio output fluctuations due to variation

of the modulation depth of the transmitter. The AVL can be switched on and off via the AVL bit in subaddress 29H.

The AVL is active over an input voltage range (measured at the deemphasis output) of 150 to 1500 mVRMS. The AVL

control curve is given in Fig.33. The control range of +6 dB to

−14 dB is valid for input signals with 50% of the

maximum frequency deviation.

27. Signal with negative-going sync. Amplitude includes sync pulse amplitude.

28. This parameter is measured at nominal settings of the various controls.

29. Indicated is a signal for a colour bar with 75% saturation (chroma : burst ratio = 2.2 : 1).

30. The contrast and saturation control is active on the internal signal (YUV) and on the external RGB/YUV input. The

Text/OSD input can be controlled on brightness only. Nominal contrast is specified with the DAC in position 20 HEX.

Nominal saturation as maximum

−10 dB.

31. The YUV/YPBPR input signal amplitudes are based on a colour bar signal with 75/100% saturation.

32. When the decoder is forced to a fixed subcarrier frequency (via the CM-bits) the chroma trap is always switched-on,

also when no colour signal is identified. In the automatic mode the chroma trap is switched-off when no colour signal

is identified.

33. Valid for a signal amplitude on the Y-input of 0.7 V black-to-white (100 IRE) with a rise time (10% to 90%) of 70 ns

and the video switch in the Y/C mode. During production the peaking function is not tested by measuring the

overshoots but by measuring the frequency response of the Y output.

34. The ratio between the positive and negative peaks can be varied by means of the bits RPO1 and RPO0 in

subaddress 2EH (see Table 118). For ratios which are smaller than 1.8 the positive peak is not affected and the

negative peak is reduced.

35. The coring can be activated in the low-light part of the picture. This effectively reduces the noise while having

maximum peaking in the bright parts of the picture. The setting the video content at which the coring is active can be

adapted by means of the COR1/COR0 bits in subaddress 2DH.

36. For video signals with a black level which deviates from the back-porch blanking level the signal is “stretched” to the

blanking level. The amount of correction depends on the IRE value of the signal (see Fig.34). The black level is

detected by means of an internal capacitor. The black level stretcher can be switched on and off via the BKS bit in

subaddress 2DH. The values given in the specification are valid only when the luminance input signal has an

amplitude of 1 Vp-p.

37. The Dynamic Skin Tone Correction circuit is designed such that it corrects (instantaneously and locally) the hue of

those colours which are located in the area in the UV plane that matches to skin tones. The correction is dependent

on the luminance, saturation and distance to the preferred axis. Because the amount of correction is dependent on

the parameters of the incoming YUV signal it is not possible to give exact figures for the correction angle. The

correction angle of 45 (

±22.5) degrees is just given as an indication and is valid for an input signal with a luminance

signal amplitude of 75% and a colour saturation of 50%. A graphical representation of the control behaviour is given

in Figure 35 on page 95.

38. Via the ‘blue stretch’ (BLS 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 Figure 37 on page 96.

39. The slicing level is independent of sync pulse amplitude. The given percentage is the distance between the slicing

level and the black level (back porch). When the amplitude of the sync pulse exceeds the value of 350 mV the sync

separator will slice the sync pulse at a level of 175 mV above top sync. The maximum sync pulse amplitude is 4 Vp-p.

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