GENNUM GB4570-CTA

GB4570 Monolithic
Video Buffer/Clamp
DATA SHEET
FEATURES
DESCRIPTION
• accurate sync tip clamping (± 2 mV typical)
The GB4570 is a high performance video buffer/clamp used
primarily for sync tip clamping of video signals. Key features
include operation from ± 4.5 to ± 13.2 V supply voltages, ± 0.1
dB flatness to 80 MHz and availability of industry standard DIP
and SOIC packages.
• less than 1 mV clamping distortion
• variable clamping voltage (VEE + 3 V to VCC -4.5 V)
In a typical video application, the GB4570 clamps the sync tip
to a known voltage. The clamping level can be set for normal
sync tip clamping by connecting pin 3 to - 0.286 volts. For
applications requiring non-standard sync tip clamping, the
clamping voltage applied to pin 3 may be varied.
• ultra low differential gain and differential phase
• less than ± 0.15° phase delay variation at 3.58 MHz
• ± 0.1 dB flatness to 80 MHz
• ± 4.5 to ±13.2 V supply voltage range
The GB4570 features a tight delay spread of only ± 0.15° at
color burst frequencies and less than ± 1 millivolts clamping
distortion.
APPLICATIONS
PIN CONNECTIONS
GB4570
•
Sync tip clamping of NTSC, PAL, SECAM and RGB
Video Signals
GND
1
8
VCC
•
Input buffering and clamping
V IN
2
7
VOUT
•
Inter-system video signal clamping
V CLAMP
3
6
VEE
CHOLD
4
5
NC
SIMPLIFIED CIRCUIT DIAGRAM
VCC
8
AVAILABLE PACKAGING
8 pin PDIP
VIN
8 pin SOIC
2
COUPLING
CAP
7 VOUT
ORDERING INFORMATION
Part Number
Package
Temperature Range
GB4570-CDA
8 pin PDIP
0° to 70°C
GB4570-CKA
8 pin SOIC
0° to 70°C
GB4570-CTA
8 pin SOIC Tape 0° to 70°C
6
VEE
+
50k
3 VCLAMP
4
CHOLD
Document No. 521 - 18 - 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
ABSOLUTE MAXIMUM RATINGS
PARAMETER
VALUE/UNITS
±13.5 V
Supply Voltage
0°C ≤ T A ≤ 70°C
Operating Temperature Range
Lead Temperature (soldering, 10 seconds)
260°C
±5 V
Differential Video Input Voltage
Strobe Input Voltage
ELECTRICAL CHARACTERISTICS
-V S ≤ VSTROBE ≤ +VS
V S = ± 5 V, TA = 0° to 70°C, RL = 10kΩ, CL = 10 pF, unless otherwise shown.
PARAMETER
SYMBOL
521 - 18 - 01
CONDITIONS
MIN
TYP
MAX
UNITS
± 4.5
±5
± 13.2
V
Supply Voltage
± VS
+ Supply Current
I+
-
9
14
mA
- Supply Current
I-
-
9
14
mA
Small Signal B.W.
B.W.
80
-
-
MHz
(flattened response)
SIGNAL
PATH
DO NOT OPEN PACKAGES OR HANDLE
EXCEPT AT A STATIC-FREE WORKSTATION
-65°C ≤ T ≤150°C
S
Storage Temperature Range
POWER
SUPPLIES
CAUTION
ELECTROSTATIC
SENSITIVE DEVICES
± 0.1 dB after insertion loss,
VIN=100 mV p-p
Phase Delay
ød
at 3.58 MHz and 4.43 MHz
-1.85
-2.0
-2.15
deg
Differential Gain
∂g
at 3.58 MHz and 4.43 MHz
-
0.01
0.02
%
Differential Phase
∂p
at 3.58 MHz and 4.43 MHz
-
0.01
0.02
deg
Input Voltage
VIN
VEE+3V
-
VCC-3V
V
Input Resistance
RIN
25
-
-
kΩ
Input Capacitance
CIN
-
2.0
-
pF
Output Resistance
ROUT
ƒ= 0 to 1 MHz
ƒ= 100 MHz
-
8.6
20
10
40
Ω
Ω
Insertion Loss
I.L.
ƒ= 100 kHz
-
0.03
0.05
dB
Power Supply Rejection Ratio
PSRR
ƒ= 1 kHz
ƒ= 10 MHz
50
30
-
-
dB
dB
PP Signal / RMS Noise
S/N
VSIG=1 Vp-p
75
-
-
dB
Clamp Voltage Range
VCLAMP
VIN = 1 Vp-p,
VEE +3.0
-
VCC-4.5
V
Accuracy
VIN = 0.5V to 2Vp-p
-
±2
±7
mV
Clamping Distortion
Amplitude during sync
-
-
±1
mV
2
DETAILED DESCRIPTION
The GB4570 is intended for video applications requiring DC
restoration. The GB4570 signal path consists of a wideband
Darlington emitter follower for maximum bandwidth
performance. With this configuration, the GB4570’s small
signal frequency response remains within ± 0.1 dB of 0 dB out
to 80 MHz.
With this automatic adjustment system, the need for an external
sync separator circuit to enable the clamping action is
eliminated.
The input to the GB4570 must be AC coupled using an
appropriately sized capacitor. This capacitor acts as a DC
reservoir for corrective level shifts. Under equilibrium
conditions, the average current supplied by the comparator
output is just sufficient to balance the current discharging the
input coupling capacitor. Under dynamic conditions, where
the system is correcting for a change in the signal level, the
charging current may be in the milliamp range. Since the
corrective current is small under equilibrium conditions, the
error voltage at the comparator input is also small making
clamping to within ± 2 mV achievable.
Optimal frequency response for the GB4570 occurs with load
capacitance in the range of 15 pF. For smaller loads, an
external capacitor can be added to maximize the bandwidth
of the device. As shown in Figure 1, a small resistor, ROUT ,
should be included in series with the GB4570 output to obtain
optimal response flatness. For a nominal load of 15 pF, ROUT
should be chosen to be approximately 40 Ω.
The DC restoration function is achieved through the use of a
simple comparator. The non-inverting input of the comparator
is connected to the clamp reference voltage, while the inverting
input is connected to the GB4570 output. For output signals
more positive than the clamp reference voltage, the comparator
output is essentially open-circuit, while signal voltages more
negative than the clamp reference voltage result in the charging
of CHOLD, an external non-polar capacitor connected to pin 4.
The action of the comparator is to provide a positive current
which is fed back to the input under conditions where the
device output is more negative than the clamp reference
voltage. This negative feedback raises the DC level of the
input signal to the point where all signal fluctuations occur at
voltages above the clamp reference voltage.
The circuit makes use of a ‘peak hold’ capacitor, CHOLD, at the
output of the comparator. This gives rise to a more constant
voltage at the comparator output. This constant voltage is
translated to a more constant corrective current by an internal
50 kΩ resistor between the comparator output and the signal
input.
To avoid excessive phase shifts and consequent instability of
the clamp feedback loop, the peak hold capacitor should be
considerably smaller (eg. 1000 times smaller) than the input
coupling capacitor. If faster clamping is desirable, the peak
hold capacitor can be removed and a smaller input coupling
capacitor employed. In this application, some distortion of the
signal tip will occur.
VCC
VEE
0.1
0.1
8
VIDEO
VIN
VCLAMP
ROUT
2
GB4570
SYNC TIP
CLAMP
7
3
4
1
22
75
6
CLAMPED
VIDEO
OUTPUT
CLOAD
CHOLD
1.1nF
All resistors are in ohms, all capacitors in microfarads unless otherwise stated
Fig. 1 Typical Application Circuit
3
521 - 18 - 01
-5V
+5V
+5V
0.1
0.1
0.1
1
NETWORK
ANALYSER
8
6
RS
10
2
GB4570
7
4
1
CLC110
8
VIDEO OUTPUT
TO NETWORK
ANALYSER I/P
5
Sweep: 1-100MHz
Level: 0dBM
4
3
75
CL
10k
0.01
0.1
+5V
All resistors are in ohms, all capacitors in microfarads unless otherwise stated
Fig. 2 Frequency Response Test Circuit
TYPICAL PERFORMANCE CURVES
6.0
0.1
RS = ø
CL = 68pF
0.05
CL = 82pF
4.0
0
GAIN (dB)
GAIN (dB)
CL = 100pF
CL = 120pF
2.0
CL = 180pF
RS = 32.5Ω
CL = 27pF
-0.05
-0.1
RS = 39Ω
CL = 18pF
0.0
-0.15
CL = 270pF
-2.0
RS = 43Ω
CL = 10pF
-0.2
1
10
100
1
10
100
FREQUENCY (MHz)
FREQUENCY (MHz)
Fig. 3 GB4570 Frequency Response
Fig. 4 Flattened Frequency Response
1
1
RS = ø
0
0
-1
C L = 270pF
-2
PHASE (deg)
PHASE (deg)
-1
CL = 180pF
-3
C L = 120pF
-4
CL = 82pF
RS = 43Ω
CL = 10pF
-5
-6
1
10
FREQUENCY (MHz)
-6
1
10
FREQUENCY (MHz)
Fig. 6 Phase vs Frequency
Fig. 5 Phase vs Frequency
521 - 18 - 01
RS = 40Ω
CL = 18pF
-3
-4
-5
-7
RS = 32Ω
CL = 27pF
-2
4
DOCUMENT
IDENTIFICATION
PRODUCT PROPOSAL
This data has been compiled for market investigation purposes
only, and does not constitute an offer for sale.
ADVANCE INFORMATION NOTE
This product is in development phase and specifications are
subject to change without notice. Gennum reserves the right to
remove the product at any time. Listing the product does not
constitute an offer for sale.
PRELIMINARY DATA SHEET
The product is in a preproduction phase and specifications are
subject to change without notice.
DATA SHEET
The product is in production. Gennum reserves the right to make
changes at any time to improve reliability, function or design, in
order to provide the best product possible.
Gennum Corporation assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement.
© Copyright September 1994 Gennum Corporation. All rights reserved. Printed in Canada.
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521 - 18 - 01