Texas Instruments THS7364 Evaluation Module THS7364EVM THS7364EVM 데이터 시트
제품 코드
THS7364EVM
CVBS
R
SOC/DAC/Encoder
S-Video Y’
R
R
PU
R
PU
R
PU
S-Video C’
R
Y'/G'
R
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
SD1 OUT
SD2 OUT
SD3 OUT
Disable SD
GND
Disable FHD
FHD1 OUT
FHD2 OUT
FHD3 OUT
Bypass FHD
SD1 IN
SD2 IN
SD3 IN
NC
V
S+
NC
FHD1 IN
FHD2 IN
FHD3 IN
Bypass SD
THS7364
Bypass
SD LPF
Bypass
LPF
FHD
P' /B'
B
R
P' /R'
R
R
+2.7 V to
+5 V
Disable FHD
Disable SD
75 W
75 W
330 F
m
(2)
+
75 W
Y' Out
75 W
330 F
m
(2)
+
75 W
P’ Out
B
75 W
330 F
m
(2)
+
75 W
Y' Out
75 W
330 F
m
(2)
+
75 W
P' Out
B
75 W
330 F
m
(2)
+
75 W
P' Out
R
75 W
330 F
m
(2)
+
To GPIO or
GND/V
GND/V
S+
To GPIO or
GND/V
S+
+V
+V
+V
+V
+V
+V
0.1 F
m
(1)
0.1 F
m
(1)
0.1 F
m
(1)
0.1 F
m
(1)
0.1 F
m
(1)
0.1 F
m
(1)
+2.7 V to +5 V
www.ti.com
SBOS530 – AUGUST 2010
(1) AC-coupled input is shown in this example. DC-coupling is also allowed as long as the DAC output voltage is within the allowable linear
input and output voltage range of the THS7364. To apply dc-coupling, remove the 0.1-
input and output voltage range of the THS7364. To apply dc-coupling, remove the 0.1-
m
F input capacitors and the R
PU
pull-up resistors along
with connecting the DAC termination resistors (R) to ground.
(2) This example shows an ac-coupled output. DC-coupling is also allowed by simply removing these capacitors.
Figure 82. Typical AC Input System Driving AC-Coupled Video Lines
The use of other type of filters, such as elliptic or
LOW-PASS FILTER
chebyshev,
are
not
recommended
for
video
applications because of the very large group delay
Each
channel
of
the
THS7364
incorporates
a
variations near the corner frequency resulting in
sixth-order,
low-pass
filter.
These
video
significant overshoot and ringing. While these filters
reconstruction filters minimize DAC images from
may help meet the video standard specifications with
being passed onto the video receiver. Depending on
respect to amplitude attenuation, the group delay is
the receiver design, failure to eliminate these DAC
well beyond the standard specifications. Considering
images can cause picture quality problems because
this delay with the fact that video can go from a white
of aliasing of the ADC in the receiver. Another benefit
pixel to a black pixel over and over again, it is easy to
of the filter is to smooth out aberrations in the signal
see that ringing can occur. Ringing typically causes a
that some DACs can have if the internal filtering is
display to have ghosting or fuzziness appear on the
not very good. This benefit helps with picture quality
edges of a sharp transition. On the other hand, a
and ensures that the signal meets video bandwidth
Bessel filter has ideal group delay response, but the
requirements.
rate of attenuation is typically too low for acceptable
Each
filter
has
an
associated
Butterworth
image rejection. Thus, the Butterworth filter is an
characteristic.
The
benefit
of
the
Butterworth
acceptable compromise for both attenuation and
response is that the frequency response is flat with a
group delay.
relatively steep initial attenuation at the corner
The THS7364 SD filters have a nominal corner
frequency. The problem with this characteristic is that
(–3 dB) frequency at 9.5 MHz and a –1-dB passband
the group delay rises near the corner frequency.
typically at 8.2 MHz. This 9.5-MHz filter is ideal for
Group delay is defined as the change in phase
SD NTSC, PAL, and SECAM composite video
(radians/second) divided by a change in frequency.
(CVBS) signals. It is also useful for S-Video signals
An increase in group delay corresponds to a time
(Y’C’), 480i/576i Y’/P’
B
/P’
R
, Y’U’V’, broadcast G’B’R’
domain pulse response that has overshoot and some
signals, and computer R'G'B' video signals. The
possible ringing associated with the overshoot.
9.5-MHz, –3-dB corner frequency was designed to
Copyright © 2010, Texas Instruments Incorporated
35
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