AD720-AD720JP-AD721JP Fast Delivery |IC PHOENIX CO.,LIMITED

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AD720-AD720JP-AD721JP
RGB to NTSC/PAL Encoders
FUNCTIONAL BLOCK DIAGRAM
FEATURES
Composite Video Output
Chrominance and Luminance (S-Video) Outputs
No External Filters or Delay Lines Required
Drives 75Ω Reverse-Terminated Loads
Compact 28-Pin PLCC
Logic Selectable NTSC or PAL Encoding Modes
Automatically Selects Proper Chrominance Filter
Cutoff Frequency for Encoding Standard
Logic Selectable Encode or Power-Down Mode (AD720
Only)
Logic Selectable Encode or Bypass Mode (AD721 Only)
Low Power: 200mW typical
APPLICATIONS
RGB to NTSC or PAL Encoding
Drive RGB Signals into 75 Ω Load (AD721 Only)
PRODUCT DESCRIPTION
The AD720 and AD721 RGB to NTSC/PAL Encoders convert
red, green and blue color component signals into their corre-
sponding luminance (baseband amplitude) and chrominance
(subcarrier amplitude and phase) signals in accordance with
either NTSC or PAL standards. These two outputs are also
combined to provide a composite video output. All three out-
puts are available separately at voltages of twice the standard
signal levels as required for driving 75Ω reverse terminated
cables. The AD721 also features a bypass mode, in which the
RGB inputs may bypass the encoder section of the IC via three
gain-of-two amplifiers suitable for driving 75Ω reverse termi-
nated cables.
The AD720 and AD721 provide a complete, fully calibrated
function, requiring only termination resistors, bypass capacitors,
a clock input at four times the subcarrier frequency, and a com-
posite sync pulse. There are two control inputs: one input
selects the TV standard (NTSC/PAL) and the other (ENCD)
powers down most sections of the chip when the encoding func-
tion is not in use (AD720) or activates the triple bypass buffer to
drive the RGB signals when RGB encoding is not required
(AD721). All logical inputs are CMOS compatible. The chip
operates from ±5V supplies.
(continued on page 5)
RGB to NTSC/PAL Encoders
REV.
LOGIC INPUTS (C-SYNC, 4FSC, ENCD, NTSC)
BYPASS AMPLIFIERS (AD721 Only)
VIDEO OUTPUTS
POWER SUPPLIES (APOS, DPOS, VNEG)
AD720/AD721–SPECIFICATIONS
NOTES
1Input scaling resistors provide best scaling accuracy when source resistance is 37.5Ω (75Ω reverse-terminated input).
2Required for driving a 75 Ω double reverse terminated load.
3All outputs are measured at a reverse-terminated load; voltages at IC pins are twice those specified here.
4This is a predistortion (per FCC specifications) that compensates for the chroma/luma delay in the low-pass filter that separates the luminance and chrominance
signals in a television receiver.
5CRMA, LUMA, and CMPS outputs are all connected to 75Ω reverse-terminated loads; full-white signal for entire field.
Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. All min
(TA = +25°C and supplies = ±5V unless otherwise noted)
PIN DESCRIPTIONS
*() pertain only to AD720.
**The luminance, chrominance, and composite outputs are at twice normal
levels for driving 75Ω reverse-terminated lines.
ORDERING GUIDE
PIN CONNECTIONS
28-Lead Plastic Leaded Chip Carrier (PLCC) Package
P-28A
AD720/AD721
RGB TO NTSC/PAL
ENCODER
DGND
SYNC
DPOS
ASNC
DPOS
4FSC
DGND
ENCD
RDIN
AGND
GRIN
AGND
BLIN
STND
AGND
ROUT (NC) APOS (NC)
GOUT (NC)APOS
BOUT (NC)
VNEG
AGNDCRMA
APOSCMPSLUMAVNEGAPOS
NOTE:
CONNECTIONS IN ( ) PERTAIN ONLY TO AD720
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage ±VS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±6V
Internal Power Dissipation . . . . . . . . . . . . . . . . . . . . . .600mW
Operating Temperature Range . . . . . . . . . . . . . . 0°C to +70°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature, Soldering 60sec . . . . . . . . . . . . . .+300°C
NOTE
*Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only, and functional
operation of the device at these or any other conditions above those indicated in the
operational section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended rating conditions for extended periods
may affect device reliability.
Thermal characteristics: 28-pin plastic package: θJA = 100°C.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD720/AD721 features proprietary ESD protection circuitry, permanent damage
75W
4FSC
COMPOSITE VIDEO
Figure 1.AD720/AD721 Evaluation Setup
0.00 0.050.05 0.04 0.07 0.01
1ST2ND3RD4TH5TH6TH
DG DP(NTSC) (SYNC = EXT)
FIELD = 1 LINE = 21
DIFFERENTIAL GAIN (%) MIN = –0.10; MAX = 0.00; p-p/MAX = 0.10
DIFFERENTIAL PHASE (°) MIN = 0.00; MAX = 0.07; p-p = 0.07
Figure 2.Composite Output Differential Phase and Gain,
NTSC (Nulled to Chroma Output)
MICROSECONDS/PRECISION MODE OFF
Figure 3.Modulated Pulse and Bar, NTSC
MICROSECONDS
0.0
Figure 4.100% Color Bars, NTSC
MICROSECONDS
0.0
Figure 5.Multipulse, NTSC
85ns
39.2 IRE
AVERAGE 32 TO 32
Figure 6.Horizontal Timing, NTSC
292.1mV
H TIMING (PAL)
LINE = 17
AD720/AD721–Typical Characteristics
(continued from page 1)
All required low-pass filters are on chip. After the input signals
pass through a precision RGB to YUV encoding matrix, two on-
chip low-pass filters limit the bandwidth of the U and V color
difference signals to 1.2MHz prior to quadrature modulation of
the color subcarrier; a third low-pass filter at 3.6MHz (NTSC)
or 4.4MHz (PAL) follows the modulators to limit the harmonic
content of the output.
Delays in the U and V chroma filters are matched by an on-chip
sampled data delay line in the Y signal path; to prevent aliasing,
prefilter at 5MHz is included ahead of the delay line and a post
filter at 5MHz is added after the delay line to suppress harmon-
ics in the output. These low-pass filters are optimized for mini-
mum pulse overshoot. The overall delay is about 170ns, which
precompensates for delays in the filters used to decode the
NTSC or PAL signal in a television receiver. (This precompen-
sation delay is already present in TV broadcasts.)
The AD720 and AD721 are available in a 28-pin plastic leaded
chip carrier for the 0°C to +70°C commercial temperature range.
THEORY OF OPERATION
Referring to the AD720/AD721 block diagram (Figure 8), the
RGB inputs (each 0mV to 714mV in NTSC or 0mV to
700mV in PAL) are first encoded into luminance and color
difference signals. The luminance signal is called the “Y”
signal and the color-difference signals are called U and V. The
RGB inputs are encoded into the YUV format using the
transformation
Y = 0.299R + 0.587G + 0.114B
U = 0.493 (B-Y)
V = 0.877 (R-Y)
For NTSC operation, the chroma amplitude is increased by the
factor 1.06 prior to summation with the luminance output. The
burst signal is inserted into the Y channel in the encoding matrix.
The three outputs of the encoding matrix, now transformed into Y,
U, and V components, take two paths. The Y (luminance) signal is
passed through a delay line consisting of a prefilter, a sampled-data
delay line, and a post filter. The pre- and post-filters prevent
aliasing of harmonics back into the baseband video. The overall de-
lay is a nominal –170ns relative to the chrominance signal, in
keeping with broadcast requirements to compensate for delays in-
troduced by the filters in the decoding process.
The U and V components pass through 4-pole modified Bessel
low-pass filters with a 1.2MHz –3dB frequency to prevent
aliasing in the balanced modulators, where they modulate a
3.579 545 000MHz (NTSC) or 4.433 618 750MHz (PAL)
signal via a pair of balanced modulators driven in quadrature by
the color subcarrier.
The AD720/AD721 4FSC input drives a digital divide-by-4 cir-
cuit (two flip-flops) to create the quadrature signal. The refer-
ence phase 0° is used for the U signal. In the NTSC mode, the
V signal is modulated at 90°, but in the PAL mode, the V
modulation input alternates between 90° and 270° at half the
line rate as required by the PAL standard. The outputs of the
balanced modulators are summed and low-pass filtered to re-
move harmonics.
AD720/AD721
The filtered output is summed with the luminance signal to cre-
ate a composite video signal. The separate luminance, chromi-
nance, and composite video signals are amplified by gain-of-two
amplifiers for driving 75Ω reverse-terminated lines. The sepa-
rate luminance and chrominance outputs together are known as
“S-Video.”
The digital section of the AD720/AD721 is clocked by the
4FSC input. It measures the width of pulses in the composite
sync input to separate vertical, horizontal, and serration pulses
and to insert the subcarrier burst only after a valid horizontal
sync pulse.
Asserting the ENCD pin to a logical low routes the AD721’s
RGB inputs through three gain-of-two bypass buffers for drivingΩ reverse-terminated lines, bypassing the encoder section of
the AD721. The triple bypass amplifier is utilized to overcome
the loading effects of a “TV-out” connection on the RGB moni-
tor output. When a video encoder is connected to outputs of a
current-out video RAMDAC or VGA controller, the R, G, and
B signals to the monitor are loaded-down. This requires the use
of a gain block to properly drive the monitor.
CHROMINANCE OUTPUT
COMPOSITE OUTPUT
LUMINANCE OUTPUT
75W
75W
0.1mF
–5V FROM ANALOG SUPPLY
COMPOSITE SYNC INPUT
CMOS LOGIC LEVEL
NEGATIVE SYNC TIPS
+5V FROM
DIGITAL SUPPLY
+5V FROM
DIGITAL SUPPLY
4 X SUBCARRIER INPUT
CMOS LOGIC LEVELS
NTCS = 14.318 180MHz
PAL = 17.734 480MHz
ENCODE INPUT
ENCODE = CMOS HIGH
POWER DOWN = CMOS LOW
VIDEO STANDARD
SELECTION INPUT
NTSC = CMOS HIGH
PAL = CMOS LOW
+5V FROM
ANALOG SUPPLY
+5V FROM
ANALOG SUPPLY
–5V FROM
ANALOG SUPPLY
Figure 9.AD720 Application
–5V FROM
ANALOG SUPPLY
BLUE OUTPUT
GREEN OUTPUT
RED OUTPUT
75W
COMPOSITE OUTPUT
LUMINANCE OUTPUT
75W
75W
0.1mF
–5V FROM ANALOG SUPPLY
COMPOSITE SYNC INPUT
CMOS LOGIC LEVEL
NEGATIVE SYNC TIPS
+5V FROM
DIGITAL SUPPLY
+5V FROM
DIGITAL SUPPLY
4 X SUBCARRIER INPUT
CMOS LOGIC LEVELS
NTCS = 14.318 180MHz
PAL = 17.734 480MHz
ENCODE INPUT
ENCODE = CMOS HIGH
BYPASS = CMOS LOW
VIDEO STANDARD
SELECTION INPUT
NTSC = CMOS HIGH
PAL = CMOS LOW
+5V FROM
ANALOG SUPPLY

Partno	Mfg	Dc	Qty	Available	Descript
AD720	N/A	N/a	2	avai	RGB to NTSC/PAL Encoders
AD720JP	AD	N/a	10	avai	RGB to NTSC/PAL Encoders
AD721JP	AD	N/a	4	avai	RGB to NTSC/PAL Encoders