TDA8295_09 Datasheet, PDF (10/83 Pages) NXP Semiconductors – Digital global standard low IF demodulator for analog TV and FM radio

NXP Semiconductors
TDA8295
Digital global standard low IF demodulator for analog TV and FM radio
Table 5.
Type
AI
AO
GND
I
I/O
O
OD
PS
T
Pin type description
Description
analog input
analog output
ground
digital input
digital input and output
digital output
open-drain output
power supply
3-state
8. Functional description
8.1 IF ADC
The low IF spectrum (1 MHz to 10 MHz) from the Silicon Tuner TDA8725A or TDA1827x
is fed symmetrically to the 12-bit IF ADC of the TDA8295, where it is sampled with
54 MHz or 27 MHz. All the anti-aliasing filtering is already done in the Silicon Tuner.
8.2 Filters
The internal filters permit to reduce the sampling rate to 13.5 MHz, and to form a complex
signal to ease the effort of further signal processing. Before this, the DC offset (coming
from the ADC) is removed.
In addition, standard dependent notch filters for the adjacent sound carriers protect the
picture carrier PLL from malfunctioning and avoid disturbances (i.e. moire) becoming
visible in the video output.
8.3 PLL demodulator
The second-order PLL is the core block of the whole IC. It is very robust against adverse
field conditions, like excessive overmodulation, no residual carrier presence or unwanted
phase or frequency modulation of the picture carrier. The PLL output is the synchronously
demodulated channel.
The AFC data is available via the I²C-bus.
8.4 Nyquist filter, video low-pass filter, video and group delay equalizer,
video leveling
The afore-mentioned down-mixed complex signal at the mixer CORDIC output, already
consisting of the demodulated content of the picture carrier together with the sound
carriers (the so-called intercarriers), is running through a Nyquist filter to get a flat video
response and is made real.
Afterwards, a video low-pass filter suppresses the sound carriers and other disturbers.
Next comes the equalizer circuit to remove the transmitter group delay predistortion.
TDA8295_C2_2
Product data sheet
Rev. 02 — 27 November 2009
© NXP B.V. 2009. All rights reserved.
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