TDA8844 datasheet(14/68 Pages) PHILIPS

14 / 68 page

December 16, 1997

Philips Semiconductors

Tentative Device Speciﬁcation

I2C-bus controlled PAL/NTSC/SECAM TV

processors

TDA884X/5X-N2 series

Overvoltage conditions (X-ray protection) can be detected

via the EHT tracking pin. When an overvoltage condition is

detected the horizontal output drive signal will be

switched-off via the slow stop procedure but it is also

possible that the drive is not switched-off and that just a

protection indication is given in the I2C-bus output byte.

The choice is made via the input bit PRD. The IC’s have a

second protection input on the

ϕ2 filter capacitor pin. When

this input is activated the drive signal is switched-off

immediately and switched-on again via the slow start

procedure. For this reason this protection input can be

used as “flash protection”.

The drive pulses for the vertical sawtooth generator are

obtained from a vertical countdown circuit. This countdown

circuit has various windows depending on the incoming

signal (50 Hz or 60 Hz and standard or non standard). The

countdown circuit can be forced in various modes by

means of the I2C-bus. During the insertion of RGB signals

the maximum vertical frequency is increased to 72 Hz so

that the circuit can also synchronise on signals with a

higher vertical frequency like VGA. To obtain short

switching times of the countdown circuit during a channel

change the divider can be forced in the search window by

means of the NCIN bit. The vertical deflection can be set

in the de-interlace mode via the I2C bus.

To avoid damage of the picture tube when the vertical

deflection fails the guard output current of the TDA

8350/51 can be supplied to the beam current limiting input.

When a failure is detected the RGB-outputs are blanked

and a bit is set (NDF) in the status byte of the I2C-bus.

When no vertical deflection output stage is connected this

guard circuit will also blank the output signals. This can be

overruled by means of the EVG bit.

Chroma and luminance processing

The circuits contain a chroma bandpass and trap circuit.

The filters are realised by means of gyrator circuits and

they are automatically calibrated by comparing the tuning

frequency with the X-tal frequency of the decoder. The

luminance delay line and the delay for the peaking circuit

are also realised by means of gyrator circuits. The centre

frequency of the chroma bandpass filter is switchable via

the I2C-bus so that the performance can be optimised for

“front-end” signals and external CVBS signals. During

SECAM reception the centre frequency of the chroma trap

is reduced to get a better suppression of the SECAM

carrier frequencies. All IC’s have a black stretcher circuit

which corrects the black level for incoming video signals

which have a deviation between the black level and the

blanking level (back porch). The timeconstant for the black

stretcher is realised internally.

The resolution of the peaking control DAC has been

increased to 6 bits. All IC’s have a defeatable coring

function in the peaking circuit. Some of these IC’s have a

YUV interface (see table on page 2) so that picture

improvement IC’s like the TDA 9170 (Contrast

improvement), TDA 9177 (Sharpness improvement) and

TDA 4556/66 (CTI) can be applied. When the CTI IC’s are

applied it is possible to increase the gain of the luminance

channel by means of the GAI bit in subaddress 03 so that

the resulting RGB output signals are not affected.

Colour decoder

Depending on the IC type the colour decoder can decode

PAL, PAL/NTSC or PAL/NTSC/SECAM signals. The

PAL/NTSC decoder contains an alignment-free X-tal

oscillator, a killer circuit and two colour difference

demodulators. The 90

° phase shift for the reference signal

is made internally.

The IC’s contain an Automatic Colour Limiting (ACL)

circuit which is switchable via the I2C-bus and which

prevents that oversaturation occurs when signals with a

high chroma-to-burst ratio are received. The ACL circuit is

designed such that it only reduces the chroma signal and

not the burst signal. This has the advantage that the colour

sensitivity is not affected by this function.

The SECAM decoder contains an auto-calibrating PLL

demodulator which has two references, viz: the 4.4 MHz

sub-carrier frequency which is obtained from the X-tal

oscillator which is used to tune the PLL to the desired

free-running frequency and the bandgap reference to

obtain the correct absolute value of the output signal. The

VCO of the PLL is calibrated during each vertical blanking

period, when the IC is in search or SECAM mode.

The frequency of the active X-tal is fed to the Fsc output

(pin 33) and can be used to tune an external comb filter

(e.g. the SAA 4961).

The base-band delay line (TDA 4665 function) is

integrated in the PAL/SECAM IC’s and in the NTSC IC

TDA 8846A. In the latter IC it improves the cross colour

performance (chroma comb filter). The demodulated

colour difference signals are internally supplied to the

delay line. The colour difference matrix switches

automatically between PAL/SECAM and NTSC, however,

it is also possible to fix the matrix in the PAL standard.

The “blue stretch” circuit is intended to shift colour near

“white” with sufficient contrast values towards more blue to

obtain a brighter impression of the picture.

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