
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. 
 Clamping of NTSC, PAL, SECAM & RGB Video Signals
 Multimedia Graphics Overlay
 Production Switchers
 Linear Keyers
Part Number
Package
        Temperature Range
GB4571-CDA      8 pin PDIP
 0
°
 to 70
°
C
GB4571-CKA      8 pin SOIC
 0
°
 to 70
°
C
GB4571-CTA      8 pin SOIC Tape
 0
°
 to 70
°
C
  DATA SHEET
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
GB4571 Video Buffer with
Precision Strobed DC Restore
FEATURES
DESCRIPTION
AVAILABLE PACKAGING
8 pin PDIP
8 pin SOIC
PIN CONNECTIONS
1
2
3
4
8
7
6
5
V
CC
V
OUT
V
EE
GND
C
HOLD
V
IN
V
CLAMP
STROBE
GB4571
ORDERING INFORMATION
APPLICATIONS
 accurate  clamping to within 
±
 1 mV
 less than 1 mV clamping distortion
 variable clamping range (V
EE
 + 3.0 V to V
CC
 - 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
Document No.  521 - 17 - 01
SIMPLIFIED CIRCUIT DIAGRAM
C
HOLD 
GND
VCC
V
EE
V
IN
COUPLING
V
OUT
STROBE
V
CLAMP
-
+
7   
3   
1 
5 
2   
HIGH Z
NON-LNEAR
     V TO 
I
CONVERTER
4   
6 
8