Gennum Corporation GB4571-CTA, GB4571-CKA, GB4571-CDA Datasheet

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GB4571 Video Buffer with

Precision Strobed DC Restore

DATA SHEET

FEATURES

• accurate clamping to within

± 1 mV

• less than 1 mV clamping distortion

• variable clamping range (V

+ 3.0 V to VCC - 4.5 V)

EE

• ultra low differential gain and differential phase

• fast recovery from sudden changes in DC offsets

• less than

•

± 0.1 dB flatness to 80 MHz

•

± 4.5 V to ±13.2 V supply voltage range

± 0.15° phase delay variation at 3.58 MHz

PIN CONNECTIONS

GB4571

8

C

HOLD

V

IN

V

CLAMP

STROBE

1

2

3

4

V

CC

7

V

OUT

6

V

EE

5

GND

DESCRIPTION

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

AVAILABLE PACKAGING

8 pin PDIP

8 pin SOIC

V

IN

COUPLING
CAP

2

VCC
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8

7

ORDERING INFORMATION

6

Part Number Package Temperature Range

GB4571-CDA 8 pin PDIP 0° to 70°C

NON-LNEAR
V TO I
CONVERTER

HIGH Z
BUFFER

-
+
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3

GB4571-CKA 8 pin SOIC 0° to 70°C
GB4571-CTA 8 pin SOIC Tape 0° to 70°C

4

5

GND

GENNUM CORPORATION P.O. Box 489, Stn A, Burlington, Ontario, Canada L7R 3Y3 tel. [phone] fax: [phone]

Japan Branch: A-302, Miyamae Village, 2-10-42, Miyamae, Suginami-ku, Tokyo 168, Japan tel. [phone] fax. [phone]

1

C

HOLD

Document No. 521 - 17 - 01

V

OUT

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V

EE

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V

CLAMP

STROBE

ABSOLUTE MAXIMUM RATINGS

PARAMETER VALUE/UNITS

Supply Voltage ±13.5 V
Operating Temperature Range 0°C ≤ T
Storage Temperature Range -65°C ≤ T

≤ 70°C

A

≤150°C

S

Lead Temperature (soldering, 10 seconds) 260°C
Differential Video Input Voltage ±5 V
Strobe Input Voltage -V

ELECTRICAL CHARACTERISTICS V

≤ V

S

= ±5 V, TA = 0° to 70°C, RL = 10kΩ, CL = 10 pF, unless otherwise shown.

S

STROBE

≤ +V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

±

V

S

POWER

SUPPLIES

Supply Voltage
+ Supply Current I+ - 10 15 mA

- Supply Current I- -1015 mA
Small Signal B.W. B.W. ±0.1 dB after insertion loss, 80 - - MHz

(flattened response) VIN=100 mV p-p

Phase Delay ø

D

at 3.58 MHz and 4.43 MHz -2.85 -3.0 -3.15 deg

Differential Gain ∂g at 3.58 MHz and 4.43 MHz - 0.01 0.03 %
Differential Phase ∂p at 3.58 MHz and 4.43 MHz - 0.01 0.05 deg
Input Voltage V
Input Resistance R
Input Capacitance C
Output Resistance R

IN

IN

IN

OUT

ƒ= 0 to 1 MHz - 8.6 10 Ω
ƒ= 100 MHz - 20 40 Ω

Insertion Loss I.L. ƒ= 100 kHz - 0.03 0.05 dB

SIGNAL

PATH

Power Supply Rejection Ratio PSRR ƒ= 1 kHz 50 - - dB

ƒ= 10 MHz 20 - - dB
PP Signal / RMS Noise S/N V
Strobe Pulse Width t

PWL

SIG

Active low 2.0 2.5 - µs
Accuracy VIN = 0.5V to 2Vp-p, - ±1 ±2mV

STROBE pulses at H rate
Recovery Time Scan rate 15.7kHz & 2µs strobe pulses

0.5V offset - 1 3 ms

0.1V offset - 190 600 µs

Clamping Distortion Distortion amplitude - - ±1mV

Distortion duration (amp. within 0.1 mV) - - 3 µs

V

CLAMP

STROBE

NOTE: 1. V

Clamp Voltage Range VCLAMP VIN= 1 Vp-p VEE+3 - VCC-4.5 V
Input Logic High V
Input Logic Low V
Strobe Input Current IIL, I

= +1 Vp-p output taken from OUTPUT

A or B

2 . V

= +1 Vp-p output taken from V

C

IH

IL

IH

V

or

A

B

CAUTION

ELECTROSTATIC

SENSITIVE DEVICES

DO NOT OPEN PACKAGES OR HANDLE

EXCEPT AT A STATIC-FREE WORKSTATION

S

±4.5 ±5.0 ±13.2 V

VEE+3 - VCC-3 V
25 - - kΩ

- 2.0 - pF

=1 Vp-p 75 - - dB

1.8 - - V

- - 0.8 V

--20µA

521 - 17 - 00

2