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GB4571-CDA の電気的特性と機能

GB4571-CDAのメーカーはETCです、この部品の機能は「Video Buffer with Precision Strobed DC Restore」です。


製品の詳細 ( Datasheet PDF )

部品番号 GB4571-CDA
部品説明 Video Buffer with Precision Strobed DC Restore
メーカ ETC
ロゴ ETC ロゴ 




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GB4571-CDA Datasheet, GB4571-CDA PDF,ピン配置, 機能
GB4571 Video Buffer with
Precision Strobed DC Restore
DATA SHEET
FEATURES
DESCRIPTION
accurate clamping to within ± 1 mV
less than 1 mV clamping distortion
variable clamping range (VEE + 3.0 V to VCC - 4.5 V)
ultra low differential gain and differential phase
fast recovery from sudden changes in DC offsets
less than ± 0.15° phase delay variation at 3.58 MHz
± 0.1 dB flatness to 80 MHz
± 4.5 V to ±13.2 V supply voltage range
PIN CONNECTIONS
GB4571
C HOLD
VIN
VCLAMP
STROBE
1
2
3
4
8
7
6
5
VCC
VOUT
VEE
GND
AVAILABLE PACKAGING
The GB4571 is a high performance video buffer with DC
restore used primarily for accurate back porch clamping. Key
features include operation from ± 4.5 V to ± 13.2 V supply
voltages, fast recovery from sudden changes in DC offset,
± 0.1 dB flatness to 80 MHz and availability of industry standard
DIP and SOIC packages.
In the typical back porch clamping application, a negative
going back porch pulse from an external sync separator (such
as the GS4881 or GS4882) is applied to the GB4571's STROBE
input. While STROBE is low, the GB4571 determines the
correct DC level shift that should be applied to the input signal
by integrating over the entire back porch period. This reduces
sensitivity to noise and improves the accuracy of the DC
restoration compared to systems using sample and hold
techniques. Typical clamping accuracy of ± 1 mV is achieved
by the GB4571.
APPLICATIONS
• Clamping of NTSC, PAL, SECAM & RGB Video Signals
• Multimedia Graphics Overlay
• Production Switchers
• Linear Keyers
SIMPLIFIED CIRCUIT DIAGRAM
VCC
8
8 pin PDIP
8 pin SOIC
ORDERING INFORMATION
VIN 2
COUPLING
CAP
Part Number
GB4571-CDA
GB4571-CKA
GB4571-CTA
Package
Temperature Range
8 pin PDIP
0° to 70°C
8 pin SOIC
0° to 70°C
8 pin SOIC Tape 0° to 70°C
NON-LNEAR
V TO I
CONVERTER
HIGH Z
BUFFER
-
+
5
GND
1
CHOLD
7 VOUT
6 VEE
3 VCLAMP
4 STROBE
Document No. 521 - 17 - 01
GENNUM CORPORATION P.O. Box 489, Stn A, Burlington, Ontario, Canada L7R 3Y3 tel. (905) 632-2996 fax: (905) 632-2055
Japan Branch: A-302, Miyamae Village, 2-10-42, Miyamae, Suginami-ku, Tokyo 168, Japan tel. (03) 3247-8838 fax. (03) 3247-8839

1 Page





GB4571-CDA pdf, ピン配列
DETAILED DESCRIPTION
The GB4571 is intended for video applications requiring
precision DC restoration. The GB4571's signal path consists
of a simple Darlington emitter follower for maximum bandwidth
performance. With this configuration, the GB4571’s small
signal frequency response remains with ± 0.1 dB of 0 dB out
to 80 MHz.
Optimal frequency response for the GB4571 occurs with load
capacitance in the range of 18 pF. For smaller loads, an
external capacitor can be added to maintain the bandwidth of
the device. As shown in Figure 1, a small resistor, ROUT, should
be included in series with the GB4571 output to obtain optimal
response flatness. For a nominal load of 18 pF, R should
OUT
be chosen to be approximately 30 .
The resulting voltage is buffered and fed back to the GB4571
input through a non-linear V to I converter. This feedback
current transfers charge to the GB4571's input coupling
capacitor which act as a DC reservoir for corrective level
shifts.
The non - linear V to I converter feeds back larger corrective
currents to the GB4571's input for larger differences between
VCLAMP and VIN than it does for proportionally smaller
differences between VCLAMP and VIN voltages. The non-linear
V to I converter thus provides for substantially faster recovery
from large changes in input signal DC offset while maintaining
the overall stability of the device during near-steady-state
operation.
The DC restoration function is achieved through the use of a
strobed operational transconductance amplifier (OTA). The
OTA receives its input from a differential low pass filter. This
filter has a corner frequency of 600 kHz which attenuates the
color burst and any high frequency noise that may be present
in the signal. One input to the low pass filter senses the output
of the GB4571, while the other input is connected to the clamp
voltage reference. When enabled by taking STROBE low, the
OTA sources or sinks current depending on whether the
output of the GB4571 is below or above VCLAMP respectively.
The output current from the OTA is integrated by the hold
capacitor connected to pin 1, CHOLD. CHOLD develops a
corrective voltage during the period when the clamp is enabled
and holds the corrective voltage while the clamp is disabled.
A 400 resistor in series with the input provides some phase
advance to improve the stability of the DC restoration feedback
loop. The ratio of the capacitors CIN:CHOLD should be
maintained at approximately 20,000:1 to ensure closed loop
stability. Additional reductions in recovery time from changes
in DC offset may be obtained by reducing the values of CIN
and CHOLD.
In the application shown in Figure 1, the STROBE signal is
provided by the back porch pulse of the GS4881 sync
separator. The GS4881 generates back porch pulses which
remain at horizontal rate throughout the vertical interval.
Constant rate STROBE pulses eliminate the possibility of
introducing a DC offset due to a change in duty cycle.
VCC
0.1
VEE
0.1
VIDEO
75k
COLOR
BURST
FILTER
22
VCLAMP
0.1
2
GS4881 8
SYNC
SEPARATOR
45
6
680k
0.1
86
GB4571
2 STROBED 7
DC RESTORE
31
45
CHOLD
1.0nF
VCC
0.1
BACK
PORCH
PULSE
ROUT
CLAMPED
VIDEO
CLOAD OUTPUT
All resistors in ohms, all capacitors in microfarads unless otherwise stated.
Fig. 1 GB4571 Typical Application Circuit
3
521 - 17 - 00


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部品番号部品説明メーカ
GB4571-CDA

Video Buffer with Precision Strobed DC Restore

ETC
ETC


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