The ML6426 are a family of triple video filters with
buffered outputs. There are several versions of the
ML6426, each with different passband cut-off frequencies
of 6.7MHz, 12MHz, 24MHz, 30MHz, 36MHz, and
48MHz. Each channel contains a 4th-order Butterworth
lowpass reconstruction video filter. The filter is optimized
for minimum overshoot and flat group delay and
guaranteed differential gain and phase at the outputs of
the integrated cable drivers.
All input signals from DACs are AC coupled into the
ML6426. All channels have DC restore circuitry to clamp
the DC input levels during video H-sync, using an output
feedback clamp. An external H-sync signal is required for
this purpose.
All outputs must be AC coupled into their loads. Each
output can drive 2V
have a gain of 2 (6dB) at 1V
into a 150W load. All channels
P-P
input levels.
P-P
FEATURES
■ 5V ±10% operation
■ RGB/YUV filters for ATSC Digital Television VESA
Standard
■ 2:1 Mux Inputs for multiple RGB/YUV inputs
■ Triple Reconstruction Filter options for 6.7, 12, 24, 30,
36, and 48MHz to handle various line rates
■ Multiple ML6426 outputs can be paralleled to drive
RGB/YUV outputs at different frequencies for various
line rates by means of Disable/Enable pin.
Bank <A> and Bank <B> video inputs.
This pin is internally pulled high.
2RINA/YINAUnfiltered analog R- or Y-channel
input for Bank <A>. Sync must be
provided at SYNC IN pin.
3GNDAnalog ground
4V
CC
Analog 5V supply
5RINB/YINBUnfiltered analog R- or Y-channel
input for Bank <B>. Sync must be
provided at SYNC IN pin.
6GINA/UINA Unfiltered analog G- or U-channel
input for Bank <A>. Sync must be
provided at SYNC IN pin.
7GINB/UINB Unfiltered analog G- or U-channel
input for Bank <B>. Sync must be
provided at SYNC IN pin.
PINNAMEFUNCTION
8BINA/VINA Unfiltered analog B- or V-channel
input for Bank <A>. Sync must be
provided at SYNC IN pin.
9BINB/VINBUnfiltered analog B- or V-channel
input for Bank <B>. Sync must be
provided at SYNC IN pin.
10B
11G
12V
13R
OUT
OUT
CCO
OUT
Analog B or V-channel output
Analog G or U-channel output
5V power supply for output buffers
Analog R or Y-channel output
14GNDOAnalog ground
15DISABLEDisable/Enable pin. Turns the chip off
when logic high. Internally pulled low.
16SYNC INInput for an external H-sync logic
signal for filter channels. CMOS
level input. Active High.
2
November, 1999
Page 3
ABSOLUTE MAXIMUM RATINGS
ML6426
Absolute maximum ratings are those values beyond which
the device could be permanently damaged. Absolute
maximum ratings are stress ratings only and functional
Storage Temperature Range ..................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ..................... 260°C
0.8 x fC Attenuation1.2dB
StopBand Rejection (All Channels ³ 4 fC)fIN ³ 4 fC, Note 3–40dB
SB
NOISEOutput Noise (R, G, B,)Fullband1.0mV
X
TALK
CrosstalkInput of 0.5V
at 1 MHz–55dB
P-P
Between any two Channels
X
T
DT
TALK
A/B MUX CrosstalkInput of 0.5V
Group Delay (R, G, B,)100kHz16ns
PD
Group Delay Deviation from Flatnessto 10MHz0.5ns
PD
at 3.58/4.43MHz–54dB
P-P
(R, G, B,)to 40MHz2n s
Note 1. Limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions.
Note 2. Sustained short circuit protection limited to 10 seconds.
Note 3. 38dB is based on tester noise limits.
RMS
November, 1999
5
Page 6
ML6426
FUNCTIONAL DESCRIPTION
The ML6426 is a triple monolithic continuous time video
filter designed for reconstructing video signals from an
YUV/RGB video D/A source. The ML6426 is intended for
use in AC coupled input and output applications.
The filters approximate a 4th-order Butterworth
characteristic with an optimization toward low overshoot
and flat group delay. All outputs are capable of driving
2V
into AC coupled 150W video loads, with up to 35pF
P-P
of load capacitance. All outputs are capable of driving a
75W load at 1V
P-P
.
All channels are clamped during sync to establish the
appropriate output voltage swing range (DC restore). Thus
the input coupling capacitors do not behave according to
the conventional RC time constant. In most applications,
the ML6426's input coupling capacitors are only 0.1µF.
RINA/YINA
2
0.1µF
0.1µF
0.1µF
RINB/YINB
5
GINA/UINA
6
GINB/UINB
7
BINA/VINA
8
BINB/VINB
9
A/B MUX
1
R
IN
G
IN
B
IN
MUX
TRANSCONDUCTANCE
ERROR AMP
MUX
TRANSCONDUCTANCE
ERROR AMP
MUX
TRANSCONDUCTANCE
ERROR AMP
An external CMOS compatible H
pulse is required
SYNC
which is Active High on the SYNC IN Pin. See Figure 2.
During sync, the feedback clamp sources/sinks current to
restore the DC level. The net result is that the average
input current is zero. Any change in the input coupling
capacitors' value will linearly affect the clamp response
times.
Each channel is essentially tilt-free. Each input is
clamped by a feedback amp which responds to the output
during sync.
The ML6426 is robust and stable under all stated load and
input conditions. Bypassing both V
pins directly to
CC
ground ensures this performance.
5V5V
+
–
+
–
+
–
V
12
CCO
0.5V
0.5V
0.5V
4
V
CC
4th-ORDER
4th-ORDER
4th-ORDER
FILTER A
FILTER B
FILTER C
×2
×2
×2
R
OUT/YOUT
G
OUT/UOUT
B
OUT/VOUT
220µF
13
220µF
11
220µF
10
75Ω
75Ω
75Ω
R
G
B
SYNC IN
6
16
SYNCIN
ACTIVE HIGH
DISABLE
15
Figure 1. Typical Application Schematic
V
= 2.5V
PW
MIN
IH
VIL = 1.0V
= 2µS
50% x V
Figure 2. SYNC IN Pulse Width
November, 1999
GNDO
14
GND
3
SYNC IN
Page 7
TYPICAL APPLICATIONS
ML6426
RECONSTRUCTION FILTER SELECTION FOR HDTV AND
VGA SIGNAL FILTERING
The filtering requirements for HDTV and VGA standards
vary depending on the resolution of the image to be
displayed, and its refresh rate. The actual refresh rate of
the display is not necessarily the same as the transmission
rate of the frames of images. Some formats use a frame
rate of 30Hz, but the display of those formats cannot be
scanned onto the CRT at 30Hz. Excessive large area
70448016:9 and 4:360P, 60I, 30P,24P
6404804:360P, 60I, 30P,24P
P=progressive scan, I=interlaced scan
Table 1: HDTV / Advanced TV Applications: (From Table 10.3 from ATSC document A54)
flicker would result. Such kinds of flicker can be seen on
a PAL display with its brightness set high. To avoid this,
the video will need to be stored in a frame buffer. This
buffer already exists in the MPEG decoder of HDTV
systems, so there is no cost penalty. The buffer is read out
at twice the rate as the frame rate for 30Hz systems, thus
getting us a refresh rate of 60Hz. Similar things are done
for the 24Hz frame rate formats to boost them to a 60Hz
refresh rate.
P=progressive scan, I=interlaced scan, na = not available
Note 1: NTSC display rates, can be fed directly into NTSC encoder (set top box)
Note 2: 60 Hz also includes 59.94Hz
Note 3: custom frequencies ranging ± 3 to 6MHz can be special cut to order
Table 2: Choosing the Correct Reconstruction Filter and Video Amplifier for TV Applications, ML6426 options
MICRO LINEAR
FILTER TO USE
(Note 3)
November, 1999
7
Page 8
ML6426
TYPICAL APPLICATIONS (Continued)
Pixel clock rates for the output D/A converters can be
roughly determined from the Table 1. Don’t forget that the
deflection system of a CRT display needs retrace time for
the vertical and horizontal.
This retrace time can vary from one design of an HDTV
set to another, as it only involves tradeoffs between the
frame buffer in the MPEG decoder and the CRT deflection
system. Allowing for 10% retrace time for the vertical and
20% for the horizontal, the appropriate Reconstruction
Filter is summarized in Table 2.
For VGA or RGB monitors, the following resolutions can
use the corresponding Reconstruction Filter and Video
Amplifier as shown in Table 3.
Figures 4, 5, and 6 show system diagrams when the
ML6426 provides a good solution. Figure 7 provides a
more detailed description for advanced TV applications
using various resolutions for legacy video, SDTV, and
HDTV.
USING THE ML6426 IN MULTIPLE RESOLUTIONS
Several ML6426 devices can be used in parallel to
construct a selectable filter selection block ranging from
frequencies between 6.7 MHz to 50MHz. Each ML6426
can be individually controlled via the disable pin. In a
parallel configuration, as shown in Figure 3 and 7, several
ML6426 devices can be used and selected via general
purpose I/O or other logic to perform the proper
reconstruction filtering for the resolution of choice. This
configuration allows for a minimum of bill of materials
and reduces cost. Micro Linears ML6426 EVAL Kit
demonstrates multi-resolution designs. Furthermore, since
the ML6426 pin-out is identical for all the options, the
filters can be interchanged. This allows for ease of product
migration to integrate newer resolutions to filter and drive
various DAC outputs at different sampling frequencies.
Products described herein may be covered by one or more of the following U.S. patents: 4,897,611; 4,964,026; 5,027,116;
5,281,862; 5,283,483; 5,418,502; 5,508,570; 5,510,727; 5,523,940; 5,546,017; 5,559,470; 5,565,761; 5,592,128; 5,594,376;
5,652,479; 5,661,427; 5,663,874; 5,672,959; 5,689,167; 5,714,897; 5,717,798; 5,742,151; 5,747,977; 5,754,012; 5,757,174;
5,767,653; 5,777,514; 5,793,168; 5,798,635; 5,804,950; 5,808,455; 5,811,999; 5,818,207; 5,818,669; 5,825,165; 5,825,223;
5,838,723; 5.844,378; 5,844,941. Japan: 2,598,946; 2,619,299; 2,704,176; 2,821,714. Other patents are pending.
Micro Linear makes no representations or warranties with respect to the accuracy, utility, or completeness of the contents
of this publication and reserves the right to make changes to specifications and product descriptions at any time without
notice. No license, express or implied, by estoppel or otherwise, to any patents or other intellectual property rights is granted
by this document. The circuits contained in this document are offered as possible applications only. Particular uses or
applications may invalidate some of the specifications and/or product descriptions contained herein. The customer is urged
to perform its own engineering review before deciding on a particular application. Micro Linear assumes no liability
whatsoever, and disclaims any express or implied warranty, relating to sale and/or use of Micro Linear products including
liability or warranties relating to merchantability, fitness for a particular purpose, or infringement of any intellectual property
right. Micro Linear products are not designed for use in medical, life saving, or life sustaining applications.
November, 1999
DS6426-01
17
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