PNX3000 View Datasheet(PDF) - Philips Electronics

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Description

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PNX3000

Analog front end for digital video processors

Philips Electronics 

Philips Semiconductors

Analog front end for digital video

processors

Preliminary specification

PNX3000

7 FUNCTIONAL DESCRIPTION

7.1 Vision IF

The IF amplifier contains 3 AC-coupled control stages

which have a total gain control range of more than 66 dB.

The video signal is demodulated by means of an

alignment-free PLL carrier regenerator with an internal

VCO. This VCO is calibrated by means of a digital control

circuit which uses the external crystal frequency as a

reference. The frequency setting for the various standards

(33.4 MHz, 33.9 MHz, 38 MHz, 38.9 MHz, 45.75 MHz and

58.75 MHz) is realised via the I2C-bus. To improve

performance for phase modulated carrier signals the

control speed of the PLL can be increased by setting bit

FFI.

The AFC output is generated by the digital control circuit of

the IF PLL demodulator and can be read via the I2C-bus.

For fast search tuning systems the window of the AFC can

be increased with a factor of three with bus bit AFW.

The AGC-detector operates on top sync or top white level.

The demodulation polarity is switched via the I2C-bus. The

AGC detector capacitor is integrated. The time-constant

can be chosen via I2C-bus bits AGC1 and AGC0. The

AGC has also an external mode which is activated by bit

AGCM. In this mode the IF gain is determined by an

external voltage on pin DTVIFAGC.

The IC has an integrated sound trap filter. The filter is

constructed as a cascade of three separate traps, to

realize sufficient suppression of the first and second sound

carriers. The trap frequencies are selected via the I2C-bus.

The IC has an integrated group delay correction filter. The

filter can be switched between the PAL BG curve and a flat

group delay response characteristic. This has the

advantage that in multi-standard receivers the video SAW

filter does not need to be switchable.

7.2 DTV IF

Apart from processing analog TV signals, the IF circuit can

also be used to preprocess digital TV signals before they

are sent to a DTV channel decoder. For this application the

two modes of operation are DTV 1st IF and DTV 2nd IF.

For both operating modes the IF PLL must be set to

synthesizer mode.

In DTV 1st IF mode only the AGC function of the IF circuit

is used, so the DTV channel decoder must be able to

handle the 1st IF frequency. Because the AGC detector

operates on the down-mixed 2nd IF signal, it is still

important to program a valid frequency for the IF VCO. It is

recommended to set the frequency of the VCO to a value

that is approximately 4 MHz higher than the incoming

1st IF centre frequency.

In DTV 2nd IF mode the 2nd IF signal is obtained by

down-mixing the incoming DTV IF signal with the IF VCO

signal. The low-pass filtered DTV 2nd IF signal is available

as a differential signal at the DTV output. This signal may

have a maximum bandwidth of 10 MHz. The VCO

frequency is programmed via the I2C-bus in steps of

250 kHz.

In DTV mode the AGC time constant is determined by a

capacitor on pin DTVIFAGC. There are two AGC modes:

internal and external. In the internal AGC mode the gain is

controlled by an internal AGC detector. The external AGC

mode is activated by bit AGCM. In this mode the

appropriate AGC pin is used as input, so that the IF gain

can be controlled by the DTV channel decoder.

The IF PLL has two pins for connection of the PLL loop

filters, one for analog TV and one for DTV. This allows

each loop filter to be optimized for its application.

7.3 Sound IF

The PNX3000 has a separate sound IF input to enable

quasi-split sound applications. The sound IF amplifier is

similar to the vision IF amplifier and has a gain control

range of about 55 dB. The AGC detector measures the

average level of the AM or FM SIF carrier and ensures a

constant signal amplitude for the AM demodulator and

Quasi-Split Sound (QSS) mixer.

The single reference QSS mixer is realised by a multiplier.

In this multiplier the SIF signal is converted to the

intercarrier frequency by mixing it with the regenerated

picture carrier from the video IF VCO. With this system a

high performance stereo sound processing can be

achieved.

For applications without a SIF SAW filter the IC can also

be used in intercarrier mode. In this mode the composite

video signal from the VIF amplifier is fed to the QSS mixer

and converted to the intercarrier frequency.

AM sound demodulation is realised in the analog domain

by the QSS mixer. The modulated SIF signal is multiplied

in phase with the limited SIF signal. The demodulator

output signal is low-pass filtered for suppression of the

carrier harmonics. The demodulated AM signal can be

digitized by one of the audio ADCs.

The QSS mixer can also be used for down-mixing an

FM radio IF signal to an intercarrier frequency, so that it

can be demodulated by the digital decoder. The IF PLL

must be set to synthesizer mode in this case. The

preferred solution is to supply the FM radio signal via a

2004 Oct 04

11

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