SAA7104E Datasheet, PDF (64/70 Pages) NXP Semiconductors – Digital video encoder

Philips Semiconductors
Digital video encoder
Product specification
SAA7104E; SAA7105E
12.1 Reconstruction filter
Figure 16 shows a possible reconstruction filter for the
digital-to-analog converters. Due to its cut-off frequency of
∼6 MHz, it is not suitable for HDTV applications.
12.2 Analog output voltages
The analog output voltages are dependent on the total
load (typical value 37.5 Ω), the digital gain parameters and
the I²C-bus settings of the DAC reference currents (analog
settings).
The digital output signals in front of the DACs under
nominal (nominal here stands for the settings given in
Tables 41 to 48 for example a standard PAL or NTSC
signal) conditions occupy different conversion ranges, as
indicated in Table 117 for a ¹⁰⁰⁄₁₀₀ colour bar signal.
By setting the reference currents of the DACs as shown in
Table 117, standard compliant amplitudes can be
achieved for all signal combinations; it is assumed that in
subaddress 16H, parameter DACF = 0000b, that means
the fine adjustment for all DACs in common is set to 0%.
If S-video output is desired, the adjustment for the C
(chrominance subcarrier) output should be identical to the
one for VBS (luminance plus sync) output.
Table 117 Digital output signals conversion range
SET/OUT CVBS, SYNC TIP-TO-WHITE VBS, SYNC TIP-TO-WHITE
RGB, BLACK-TO-WHITE
Digital settings
see Tables 41 to 48
see Tables 41 to 48
see Table 36
Digital output
1 014
881
876
Analog settings
e.g. B DAC = 1FH
e.g. G DAC = 1BH
e.g. R DAC = G DAC = B DAC = 0BH
Analog output
1.23 V (p-p)
1.00 V (p-p)
0.70 V (p-p)
12.3 Suggestions for a board layout
Use separate ground planes for analog and digital ground.
Connect these planes only at one point directly under the
device, by using a 0 Ω resistor directly at the supply stage.
Use separate supply lines for analog and digital supply.
Place the supply decoupling capacitors close to the supply
pins.
Use L_bead (ferrite coil) in each digital supply line close to
the decoupling capacitors to minimize radiation energy
(EMC).
Place the analog coupling (clamp) capacitors close to the
analog input pins. Place the analog termination resistors
close to the coupling capacitors.
Be careful of hidden layout capacitors around the crystal
application.
Use serial resistors in clock, sync and data lines, to avoid
clock or data reflection effects and to soften data energy.
2004 Mar 04
64