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GB4570 Monolithic Video Buffer/Clamp
DATA SHEET
FEATURES * accurate sync tip clamping ( 2 mV typical) * less than 1 mV clamping distortion * variable clamping voltage (VEE + 3 V to VCC -4.5 V) * 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
DESCRIPTION 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. 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. The GB4570 features a tight delay spread of only 0.15 at color burst frequencies and less than 1 millivolts clamping distortion.
PIN CONNECTIONS GB4570
GND V IN V CLAMP CHOLD 1 2 3 4 8 7 6 5 VCC VOUT VEE NC
APPLICATIONS * * * Sync tip clamping of NTSC, PAL, SECAM and RGB Video Signals Input buffering and clamping Inter-system video signal clamping
SIMPLIFIED CIRCUIT DIAGRAM
VCC 8
AVAILABLE PACKAGING 8 pin PDIP 8 pin SOIC
VIN COUPLING CAP 2
7 VOUT
ORDERING INFORMATION
Part Number Package Temperature Range
6 50k +
VEE
GB4570-CDA GB4570-CKA GB4570-CTA
8 pin PDIP 8 pin SOIC
0 to 70C 0 to 70C
3 VCLAMP
8 pin SOIC Tape 0 to 70C
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 Supply Voltage Operating Temperature Range Storage Temperature Range Lead Temperature (soldering, 10 seconds) Differential Video Input Voltage Strobe Input Voltage VALUE/UNITS 13.5 V 0C T A 70C -65C T 150C S 260C 5 V -V S VSTROBE +VS
CAUTION
ELECTROSTATIC SENSITIVE DEVICES
DO NOT OPEN PACKAGES OR HANDLE EXCEPT AT A STATIC-FREE WORKSTATION
ELECTRICAL CHARACTERISTICS
PARAMETER Supply Voltage POWER SUPPLIES + Supply Current - Supply Current Small Signal B.W. (flattened response) Phase Delay Differential Gain Differential Phase Input Voltage SIGNAL PATH Input Resistance Input Capacitance Output Resistance Insertion Loss
V S = 5 V, TA = 0 to 70C, RL = 10k, CL = 10 pF, unless otherwise shown.
SYMBOL VS I+ IB.W.
CONDITIONS
MIN 4.5 -
TYP 5 9 9 -
MAX 13.2 14 14 -
UNITS V mA mA MHz
0.1 dB after insertion loss, VIN=100 mV p-p
80
od g p VIN RIN CIN ROUT I.L. PSRR S/N VCLAMP
at 3.58 MHz and 4.43 MHz at 3.58 MHz and 4.43 MHz at 3.58 MHz and 4.43 MHz
-1.85 VEE+3V 25 -
-2.0 0.01 0.01 2.0 8.6 20 0.03 2 -
-2.15 0.02 0.02 VCC-3V 10 40 0.05 VCC-4.5 7 1
deg % deg V k pF dB dB dB dB V mV mV
= 0 to 1 MHz = 100 MHz = 100 kHz = 1 kHz = 10 MHz VSIG=1 Vp-p VIN = 1 Vp-p, VIN = 0.5V to 2Vp-p Amplitude during sync
50 30 75 VEE +3.0 -
Power Supply Rejection Ratio PP Signal / RMS Noise Clamp Voltage Range Accuracy Clamping Distortion
521 - 18 - 01
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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. 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 . 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. 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. 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 k 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 0.1
VEE 0.1
VIDEO 22 75 VCLAMP
8 VIN 2 3 CHOLD 1.1nF
6 7 1
GB4570 SYNC TIP CLAMP
4
ROUT
CLAMPED VIDEO OUTPUT CLOAD
All resistors are in ohms, all capacitors in microfarads unless otherwise stated
Fig. 1 Typical Application Circuit
3
521 - 18 - 01
+5V 0.1
-5V
0.1 0.1
+5V
NETWORK ANALYSER Sweep: 1-100MHz Level: 0dBM 75
1 10 2
8
6 RS 7 3 CL 0.01 +5V 10k 0.1 4 1
CLC110
GB4570
4
8
5
VIDEO OUTPUT TO NETWORK ANALYSER I/P
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 = o
4.0
CL = 68pF CL = 82pF CL = 100pF GAIN (dB)
0.05
0
GAIN (dB)
CL = 120pF
2.0
-0.05
CL = 180pF
0.0
RS = 32.5 CL = 27pF RS = 39 CL = 18pF RS = 43 CL = 10pF
1 10 100
-0.1
CL = 270pF
-2.0 1 10 100
-0.15
-0.2
FREQUENCY (MHz)
FREQUENCY (MHz)
Fig. 3 GB4570 Frequency Response
Fig. 4 Flattened Frequency Response
1
1
RS = o
0 -1 0 -1
PHASE (deg)
PHASE (deg)
-2 -3
C L = 270pF CL = 180pF C L = 120pF
RS = 32
-2 -3 -4 -5 -6
CL = 27pF
RS = 40 CL = 18pF RS = 43 CL = 10pF
-4
CL = 82pF
-5 -6 -7
1
10
1
10
FREQUENCY (MHz)
FREQUENCY (MHz)
Fig. 5 Phase vs Frequency
Fig. 6 Phase vs Frequency
521 - 18 - 01
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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. (c) Copyright September 1994 Gennum Corporation. All rights reserved. Printed in Canada.
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521 - 18 - 01

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