MAX7450 [MAXIM]
Video-Signal Conditioners with AGC and Back-Porch Clamp; 视频信号调理器，带有AGC和后肩钳位
| 型号： | MAX7450 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Video-Signal Conditioners with AGC and Back-Porch Clamp |
| 文件： | 总9页 (文件大小：254K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3267; Rev 2; 11/04
Video-Signal Conditioners with AGC and
Back-Porch Clamp
General Description
Features
♦ Back-Porch Clamp to GND (MAX7450/MAX7451)
♦ Adjustable Back-Porch Clamp (MAX7452)
The MAX7450/MAX7451/MAX7452 complete front-end
video-signal conditioners are designed to improve the
quality of standard-definition video signals. The devices
restore the DC level of the video input, correct for
amplitude errors up to ±±dꢀ, detect fault conditions,
and filter out-of-band noise. The MAX7450/MAX7451/
MAX7452 optimize the signal quality for further video
processing through a crosspoint switch or video
decoder (ADC). Each device integrates an input video
clamp, automatic gain control (AGC), loss-of-sync
(LOS) detector, and an out-of-band noise/lowpass filter.
These devices also incorporate a user-selectable
buffer gain (0 or +±dꢀ) and an AGC-disable function.
♦ Automatic Gain Control (±±dB ꢀanꢁe) Normaliꢂes
Siꢁnals to Standard Video Level
♦ Input Fault Detection with LOS Output
♦ Inherent 50Hꢂ/±0Hꢂ Input ꢀejection of ±0dB
♦ Sinꢁle-Supply Operation: MAX7452 (+5V)
♦ Out-of-Band Noise Filter
♦ Output Buffer Drives Standard 150 Video Load
with 0dB or +±dB Gain
The MAX7450 and MAX7451 operate from dual power
supplies of ±5ꢁ or ±ꢂ.ꢂꢁ respectively, and they restore
the video blanking level to GND. The MAX7452 operates
from a single +5ꢁ supply and features a user-adjustable
clamp level.
♦ Dual-Supply Operation
MAX7450 (±5V)
MAX7451 (±ꢃ3ꢃV)
♦ Tiny 8-Pin SO Packaꢁe
The devices are available in an 8-pin SO package with
an exposed pad and are specified for operation over
the extended (-40 C to +85 C) temperature range.
Ordering Information
PIN-
SUPPLY
†
PAꢀT
TEMP ꢀANGE
PACKAGE VOLTAGE (V)
Applications
MAX7450ESA
MAX7451ESA
MAX7452ESA
-40 C to +85 C 8 SO-EP*
-40 C to +85 C 8 SO-EP*
-40 C to +85 C 8 SO-EP*
5
ꢂ.ꢂ
+5
Signal Conditioner for Standard-Definition
ꢁideo Inputs
Security ꢁideo Systems
ꢁideo-Switching Systems
*EP = Exposed pad.
†Package code = S8E-12.
Functional Diagram
V
CC
GAIN SET (0dB OR +6dB)
75
OUT
IN
NOISE
FILTER
VIDEO
INPUT
6dB
0 OR +6dB
75
SYNC SEPARATOR
AND AMPLITUDE
DETECTOR
LOS
AGCD
MAX7450
MAX7451
GND
V
SS
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Video-Signal Conditioners with AGC and
Back-Porch Clamp
ABSOLUTE MAXIMUM ꢀATINGS
ꢁ
to GND
All Other Pins
MAX7450/MAX7451...................(-0.ꢂꢁ + ꢁ ) to (ꢁ
MAX7452................................................-0.ꢂꢁ to (ꢁ
CC
MAX7450/MAX7452...........................................................+±ꢁ
MAX7451 ...........................................................................+4ꢁ
+ 0.ꢂꢁ)
+ 0.ꢂꢁ)
SS
CC
CC
ꢁ
to GND
Maximum Current into Any Pin ............……………………±50mA
SS
MAX7450.............................................................................-±ꢁ
Continuous Power Dissipation (T = +70°C)
A
MAX7451.............................................................................-4ꢁ
OUT
MAX7450/MAX7451 ..........................................-2.5ꢁ to +ꢂ.5ꢁ
8-Pin SO (derate 18.9mW/°C above +70°C)..............1509mW
Operating Temperature ꢄange ...........................-40°C to +85°C
Storage Temperature ꢄange.............................-±5°C to +150°C
Junction Temperature......................................................+150°C
Lead temperature (soldering, 10s) ..................................+ꢂ00°C
MAX7452................................................-0.ꢂꢁ to (ꢁ
GSET, AGCD, LOS.....................................-0.ꢂꢁ to (ꢁ
+ 0.ꢂꢁ)
+ 0.ꢂꢁ)
CC
CC
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTꢀICAL CHAꢀACTEꢀISTICS
(ꢁ
= ±5ꢁ ±5ꢃ (MAX7450), ꢁ
= ±ꢂ.ꢂꢁ ±5ꢃ (MAX7451), ꢁ
= +5ꢁ ±5ꢃ (MAX7452), ꢄ =150 to GND, C = 0 to
SUPPLY
SUPPLY
SUPPLY
L
L
20pF, GSET = 1, AGCD = 1, T = T
to T
, unless otherwise noted. Typical values are at T = +25 C.)
MAX A
A
MIN
PAꢀAMETEꢀ
SYMBOL
CONDITIONS
MIN
TYP
MAX
±50
±50
2.4
UNITS
MAX7450/MAX7451, relative to GND
Clamp Accuracy
mꢁ
MAX7452, relative ꢁ
= 1.5ꢁ
ꢀPLꢁL
GSET = 0
GSET = 1
1.5
1.2
ꢀack-Porch Level Input ꢄange
Clamp ꢄesponse Time
ꢁ
MAX7452
ꢁ
ꢀPLꢁL
2.0
ꢀlanking level at the output to 1ꢃ of final
value
t
70
Lines
CLAMP
GSET = 0, relative
±10
±10
to ꢁ
= 1ꢁ
P-P
OUT
AGCD = 0,
= 0.5ꢁ
AGC Accuracy
ꢃ
ꢁ
to 2ꢁ
P-P
IN
P-P
GSET = 1, relative
to ꢁ = 2ꢁ
OUT
P-P
AGC Input ꢄange
Gain Flatness
AGCD = 0, relative to ꢁ = 1ꢁ
IN
-±.0
-0.ꢂ
+±.0
+0.ꢂ
dꢀ
dꢀ
P-P
G
f = 5MHz relative to 100kHz
F
Noise-Filter Cutoff
Fc
10
1
MHz
GSET = 0
GSET = 1
0.95
1.85
1.05
2.05
15
Low-Frequency Gain
f = 100kHz
ꢁ/ꢁ
2
Group-Delay Deviation
Differential Gain
t
G
ꢂ.58/4.4ꢂMHz relative to 100kHz
Five-step modulated staircase (ꢁ = 1ꢁ
ns
ꢃ
dG
d
)
)
0.2
0.2
0.±
IN
P-P
P-P
Differential Phase
Five-step modulated staircase (ꢁ = 1ꢁ
0.±
Degrees
IN
2
_______________________________________________________________________________________
Video-Signal Conditioners with AGC and
Back-Porch Clamp
ELECTꢀICAL CHAꢀACTEꢀISTICS (continued)
(ꢁ
= ±5ꢁ ±5ꢃ (MAX7450), ꢁ
= ±ꢂ.ꢂꢁ ±5ꢃ (MAX7451), ꢁ
= +5ꢁ ±5ꢃ (MAX7452), ꢄ =150 to GND, C = 0 to
SUPPLY
SUPPLY
SUPPLY
L
L
20pF, GSET = 1, AGCD = 1, T = T
to T
, unless otherwise noted. Typical values are at T = +25 C.)
MAX A
A
MIN
PAꢀAMETEꢀ
SYMBOL
CONDITIONS
GSET = 0,
= 1ꢁ
MIN
TYP
MAX
UNITS
±8
Output signal
peak-to-peak to ꢄMS
noise (100Hz to 5MHz)
ꢁ
OUT
P-P
Signal-to-Noise ꢄatio
SNꢄ
dꢀ
GSET = 1,
= 2ꢁ
±5
ꢁ
OUT
P-P
Line Time Distortion
Field Time Distortion
Input Leakage Current
Output Dynamic ꢄange
H
18µs, 100 IꢄE bar
0.2
0.5
5
ꢃ
ꢃ
DIST
ꢁ
1ꢂ0 lines, 18µs, 100IꢄE bar
DIST
I
1
2
µA
IN
ꢁ
ꢁ
= 1ꢁ , dG / dP < ꢂꢃ / degrees
P-P
2.4
ꢁ
P-P
IN
AGCD = 1
ꢂ0
+ 100mꢁ
,
CC
P-P
Power-Supply ꢄejection ꢄatio
Supply Current
PSꢄꢄ
dꢀ
AGCD = 0 with
maximum gain
f = ꢂ.5MHz
20
MAX7450
MAX7451
MAX7452
ꢂ5
ꢂ0
20
mA
0.7 x
Logic-High Input
Logic-Low Input
Logic-High Output
ꢁ
ꢁ
ꢁ
ꢁ
IH
ꢁ
CC
0.ꢂ x
ꢁ
IL
ꢁ
CC
ꢁ
-
CC
ꢁ
I = 500µA
SOUꢄCE
OH
0.5
Logic-Low Output
ꢁ
I
I
= 500µA
SINK
0.4
10
10
ꢁ
OL
Input Current Logic-High
Input Current Logic-Low
Logic input sink
µA
µA
IH
I
Logic input source
IL
_______________________________________________________________________________________
ꢃ
Video-Signal Conditioners with AGC and
Back-Porch Clamp
Typical Operating Characteristics
ꢁ
= ±5ꢁ ±5ꢃ (MAX7450), ꢁ
= ±ꢂ.ꢂꢁ ±5ꢃ (MAX7451), ꢁ
= +5ꢁ ±5ꢃ (MAX7452), ꢄ = 150 to GND, C = 0 to
SUPPLY L L
SUPPLY
SUPPLY
20pF, GSET = 1, AGCD = 1. T = +25 C, unless otherwise noted.
A
GROUP DELAY vs. FREQUENCY
2T RESPONSE
DIFFERENTIAL GAIN
MAX7450 toc02
60
50
40
30
20
10
0.4
0.2
0
-0.2
-0.4
1st
2nd
3rd
4th
5th
6th
IN
DIFFERENTIAL PHASE
200mV/div
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
OUT
200mV/div
0.1
1
10
1st
2nd
3rd
4th
5th
6th
t = 200ns/div
FREQUENCY (MHz)
PASSBAND AMPLITUDE vs. FREQUENCY
AMPLITUDE vs. FREQUENCY
8
6
10
0
GAIN = 2V / V
GAIN = 1V / V
4
GAIN = 2V / V
-10
-20
-30
-40
-50
-60
-70
2
0
-2
-4
-6
-8
-10
GAIN = 1V / V
0.1
1
10
0.1
1
10
100
FREQUENCY (MHz)
FREQUENCY (MHz)
BACK-PORCH VOLTAGE
vs. TEMPERATURE
SUPPLY CURRENT vs. TEMPERATURE
35
33
31
29
27
25
0
-1
-2
-3
-4
-5
-6
MAX7450
MAX7450
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE ( C)
TEMPERATURE ( C)
4
_______________________________________________________________________________________
Video-Signal Conditioners with AGC and
Back-Porch Clamp
Typical Operating Characteristics (continued)
ꢁ
= ±5ꢁ ±5ꢃ (MAX7450), ꢁ
= ±ꢂ.ꢂꢁ ±5ꢃ (MAX7451), ꢁ
= +5ꢁ ±5ꢃ (MAX7452), ꢄ = 150 to GND, C = 0 to
SUPPLY L L
SUPPLY
SUPPLY
20pF, GSET = 1, AGCD = 1. T = +25 C, unless otherwise noted.
A
OUTPUT BACK-PORCH LEVEL (MAX7450)
AGC RESPONSE ENVELOPE (V = 2V
)
IN
P-P
AGC RESPONSE ENVELOPE (V = 0.5V
)
IN
P-P
MAX7450 toc08
MAX7450 toc10
MAX7450 toc09
AGCD = 0
= 2V
AGCD = 0
= 2V
V
OUT
P-P
V
OUT
P-P
IN
AC-COUPLED
200mV/div
500mV/div
500mV/div
OUT
200mV/div
BACK-PORCH = 0V
1 s
400ms/div
400ms/div
Pin Description
PIN
NAME
FUNCTION
MAX7450/
MAX7451
MAX7452
Positive Power Supply. Connect +5ꢁ to ꢁ
for the MAX7451. ꢀypass to GND with 1µF and 0.1µF capacitors as close to the pin as possible.
for the MAX7450/MAX7452. Connect +ꢂ.ꢂꢁ to ꢁ
CC
CC
1
1
ꢁ
CC
2
ꢂ
2
ꢂ
IN
GND Ground
Negative Power Supply. Connect -5ꢁ to ꢁ for the MAX7450. Connect -ꢂ.ꢂꢁ to ꢁ for the
ꢁideo Input. AC-couple video signal through a 0.1µF capacitor.
SS
SS
4
—
4
ꢁ
SS
MAX7451. ꢀypass to GND with 1µF and 0.1µF capacitors as close to the pin as possible.
ꢀack-Porch Level Input. When gain = 2ꢁ/ꢁ (GSET = 1), output back-porch level is equal to
—
ꢀPLꢁL
ꢀPLꢁL input. When gain = 1ꢁ/ꢁ (GSET = 0), output back-porch level is equal to ꢁ
/1.5.
ꢀPLꢁL
Automatic Gain-Control Disable Input. Disable AGC by driving AGCD to ꢁ . Enable AGC by
CC
driving AGCD to GND.
5
±
7
5
±
7
AGCD
OUT
ꢁideo Output
Gain-Setting Input. Drive GSET high to set buffer gain to +±dꢀ. Drive GSET low to set buffer
gain to 0dꢀ.
GSET
Loss-of-Sync Logic Output. LOS is high when video sync is lost for more than 15 horizontal
lines. LOS goes low when video sync is present.
8
8
LOS
EP
—
—
Exposed Pad. Connect to ꢁ (MAX7450/MAX7451). Connect to GND (MAX7452).
SS
_______________________________________________________________________________________
5
Video-Signal Conditioners with AGC and
Back-Porch Clamp
V
CC
GAIN SET (0dB OR +6dB)
75
OUT
IN
NOISE
FILTER
VIDEO
INPUT
6dB
0 OR +6dB
75
MAX7452
SYNC SEPARATOR
AND AMPLITUDE
DETECTOR
LOS
AGCD
BPLVL
GND
Figure1. MAX7452 Functional Diagram
Back-Porch Clamp
Detailed Description
The MAX7450/MAX7451/MAX7452 feature a back-
porch clamp to set the output blanking level. The
devices sense the voltage during back porch and feed
back into a control system. The control system provides
the appropriate DC-level shift to clamp the output to
ground (MAX7450/MAX7451) or to a voltage set by
As shown in Figure 1, the devices include a 2nd-order
lowpass filter intended to reject out-of-band noise. The
MAX7450/MAX7451 clamp the back-porch voltage to
ground, and the MAX7452 clamps to a user-supplied
reference voltage. These devices also include an auto-
matic gain control (AGC), which automatically adjusts
the gain to ensure the sync amplitude is normalized to
a standard video level; an AGC disable function; and
an output driver that drives a standard video load
ꢁ
(MAX7452). This restores the DC level for fur-
ꢀPLꢁL
ther video processing such as on-screen display (OSD)
insertion and analog-to-digital conversion. The back-
porch clamp to ground also eliminates the need for
large output-coupling capacitors that can introduce
unwanted line-time distortion (tilt) and cost. This can
also reduce board space. The feedback network and
the on-chip capacitors introduce a finite settling time
after power-up or after any dramatic shift in input volt-
age (see the Electrical Characteristics section).
(150 ) with a full 2ꢁ
P
video signal (GSET = 1) or 1ꢁ
P-
P-P
video signal (GSET = 0).
The clamp and the AGC work concurrently. Interaction
between the two different control loops is eliminated by
the large difference in time constants. The time con-
stant of the clamp settles within 100 lines, while the
AGC loop is digitally stepped so that it settles between
1000–±4,000 lines.
Back-Porch Level Input (MAX7452)
The MAX7452 features an adjustable back-porch level
The AGC control works independently of the gain set-
ting of the output buffer. The overall gain is the multipli-
cation of the AGC gain and the output buffer gain. The
maximum overall gain is +12dꢀ and the minimum gain
is -±dꢀ.
at the output as shown in Figure 1. ꢁ
sets the
ꢀPLꢁL
back-porch clamp level. The back-porch clamp-output
level is defined by the following equations.
GSET = 1 (Gain = 2ꢁ / ꢁ), ꢁ
= ꢁ
ꢀACKPOꢄCHLEꢁEL
ꢀPLꢁL
GSET = 0 (Gain = 1ꢁ / ꢁ), ꢁ
=
ꢀACKPOꢄCHLEꢁEL
/ 1.5
ꢁ
ꢀPLꢁL
±
_______________________________________________________________________________________
Video-Signal Conditioners with AGC and
Back-Porch Clamp
Noise Filter
Table 13 Gain-Control Settinꢁs
The MAX7450/MAX7451/MAX7452 feature a simple 2nd-
order lowpass filter to reject out-of-band noise that may
be introduced by the long cable connection between the
cameras and the switching matrix.
AGCD
GSET
OUTPUT
0
0
1
1
0
1
0
1
1ꢁ
2ꢁ
fixed
fixed
P-P
P-P
ꢁ
= ꢁ
IN
OUT
LOS Detector
The LOS detector of the MAX7450/MAX7451/MAX7452
outputs a logic high when the sync is not present (loss
of video signal) for at least 15 horizontal lines on the
input. This can be used to indicate a fault condition of
the camera or cable.
ꢁ
= 2ꢁ
IN
OUT
Automatic Gain Control (AGC)
The MAX7450/MAX7451/MAX7452 have an integrated
automatic gain-control circuit to ensure the sync ampli-
tude is normalized to the standard level, thus normalizing
the overall amplitude to a standard level. The accuracy
of the normalized amplitude assumes the ratio of active
video to sync amplitude is correct in the input video sig-
nal. The gain is adjusted automatically by detecting and
comparing the amplitude of the sync pulse to a fixed
internal reference. If the sync amplitude is less than this
value, the overall gain is increased until the sync ampli-
tude equals this reference. However, if the sync ampli-
tude is high, the overall gain is reduced accordingly.
Disable the AGC loop by driving AGCD high.
Applications Information
Connecting the MAX7450/MAX7451 to a
Crosspoint Switch
The MAX7450/MAX7451/MAX7452 are designed to
directly interface to a video crosspoint switching device
such as those used in security systems (see Figure 2).
The MAX7450/MAX7451 clamp the video output to
GND, making the devices an ideal interface to the
MAX4ꢂ58 crosspoint switches and the MAX4455 OSD.
The MAX7450/MAX7451 and the MAX4455 have their
outputs referenced to ground, ensuring the amplitudes
and the brightness of the OSD relative to the video
signal are accurate.
When designing the overall system, it is important to note
that the AGC can correct for termination problems. First,
disable the AGC and verify that the terminations are cor-
rect, and then enable the AGC for proper operation.
Interfacing the MAX7452 to an ADC
The MAX7452 can be directly connected to an ADC or
video decoder as shown in Figure ꢂ. The video output
of the MAX7452 is DC-coupled to a single-ended video
input on the ADC. The voltage on the ꢀPLꢁL pin sets
the black level of the video signal at the output of the
MAX7452. Use a stable voltage reference for the
ꢀPLꢁL voltage, ideally the same reference that is used
Output Buffer
The output buffer of the MAX7450/MAX7451/MAX7452
is designed to drive either standard video loads or
high-impedance loads, independent of the buffer gain.
Logic levels on GSET and AGCD set the gain of the
MAX7450/MAX7451/MAX7452. Table 1 shows the dif-
ferent gain-setting configurations.
CAM 1
MAX7450
MAX7451
MONITOR 1
MAX4358
32 x 16
CROSSPOINT
CAM 32
MAX7450
MAX7451
MONITOR 16
MAX4455
OSD
MAX4455
OSD
Figure 2. MAX7450/MAX7451 in a 32 x 16 Crosspoint Application
_______________________________________________________________________________________
7
Video-Signal Conditioners with AGC and
Back-Porch Clamp
V
CC
GAIN SET (0dB OR +6dB)
OUT
IN
NOISE
FILTER
VIDEO
INPUT
6dB
0 OR +6dB
ADC
DSP
REF
MAX7452
SYNC SEPARATOR
AND AMPLITUDE
DETECTOR
VIDEO DECODER
LOS
AGCD
BPLVL
V
SS
Figure 3. MAX7452 Interfaced to a Video Decoder
for the analog-to-digital conversion. This voltage must
be scaled by a ratio of two resistors to set the black
level of the video signal to the appropriate level (to
match the input range of the converter).
Chip Information
Pin Configuration
TꢄANSISTOꢄ COUNT: ±ꢂ1±
PꢄOCESS: ꢀiCMOS
If the ADC or video decoder has a built-in clamp circuit,
the output of the MAX7452 must be AC-coupled into
the ADC with the capacitor value recommended for the
converter. In this situation, set the ꢀPLꢁL on the
MAX7452 to the midpoint of the specified range for
optimum performance. In addition, the stability of this
voltage is not critical, provided that it stays within the
specified range.
TOP VIEW
V
1
2
3
4
8
7
6
5
LOS
CC
IN
Power-Supply Bypassing and Layout
ꢀypass all supply pins to GND with 0.1µF and 1µF
capacitors. These capacitors filter higher frequencies in
the MHz range. Place all external components as close to
GSET
OUT
MAX7450
MAX7451
MAX7452
GND
the devices as possible. Connect EP to ꢁ
for the
V
SS
(MAX7450/MAX7451)
BPLVL (MAX7452)
SS
AGCD
MAX7450/MAX7451. Connect EP to GND for the
MAX7452. Placing the IC onto a copper area the size of
the pad is recommended for proper power dissipation.
ꢄefer to the MAX7450 Evaluation Kit for a proven PC-
board layout example.
SO-EP*
*CONNECT EP TO V FOR THE MAX7450/MAX7451
SS
8
_______________________________________________________________________________________
Video-Signal Conditioners with AGC and
Back-Porch Clamp
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www3maxim-ic3com/packaꢁes.)
PACKAGE OUTLINE
8L SOIC, .150" EXPOSED PAD
1
21-0111
B
1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9
© 2004 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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