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GB4550 & GB4550A Monolithic Video Buffer/Clamp
DATA SHEET
FEATURES * adjustable clamp level from -5.5 V to +5.5 V at 10 V supplies. * ultra low differential gain (0.02% typ.) and differential phase (0.03 typ.) * wideband unity gain: GB4550 0.2 dB at 25 MHz GB4550A 0.1 dB at 25 MHz * both drive 150pF loads at full power, flat to 10 MHz. * GB4550A -- tight delay spread of 0.15at colorburst. * convenient 8 pin SIP packaging. * both can be configured as a gain stage with reduced bandwidth. DESCRIPTION The GB4550 and GB4550A are high performance monolithic video buffer/clamps made on Gennum's LSI process. They feature a wideband differential amplifier that can be configured as a gain stage. The output signal voltage is limited to +2V above the clamp level in order to prevent damage to crosspoints connected to the output. The clamping level can be set for normal sync tip clamping by connecting pin 4 to -0.286 volts. For other applications, the clamping voltage level can be varied from -5.5 to +5.5 volts. The GB4550A features a tight delay spread of only 0.15 degrees while the GB4550 maintains a 1.5 degree delay spread. Both devices operate from 9 to 12 V power supplies and will directly interface with Gennum's video crosspoint switches. The 8 pin SIP package is ideally suited for space restricted board layouts. GB4550 and GB4550A APPLICATIONS * Input buffering and clamping to crosspoint switches 1 2 3 4 5 6 7 8 * Inter - system video signal clamping
PIN CONNECTIONS
Pin No. 1 2 3 4 5 6 7 8
GB4550 +IN VCC COMP VCL CX VEE -IN OUT
GB4550A +IN VCC NC VCL CX V EE -IN OUT
Function non-inverting input positive power supply frequency compensation or NC clamp voltage input external capacitor negative power supply inverting input output
CX
(+2 V OUTPUT CLAMP) 100k
(NC on GB4550A)
30k
+
10pF
VCL
COMP
+IN -IN VCC 7mA Nominal VEE OUT
+ 30k
ORDERING INFORMATION
Part Number GB4550 - CSA GB4550ACSA Package Type 8 pin SIP 8 pin SIP Temperature Range 0 to 70oC 0 to 70o C
All resistors in ohms, all capacitors in microfarads unless otherwise stated
SIMPLIFIED CIRCUIT DIAGRAM
Revision Date: February 1994
Document No. 520 - 34 - 4
GENNUM CORPORATION P.O. Box 489, Stn A, Burlington, Ontario, Canada L7R 3Y3 tel. (905) 632-2996 fax: (905) 632-5946
Japan Branch: A-302, Miyamae Village, 2-10-42 Miyamae, Suginami-ku, Tokyo 168, Japan tel. (03) 3334-7700 fax: (03) 3247-8839
ABSOLUTE MAXIMUM RATINGS
PARAMETER Supply Voltage VS Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering, 10 Sec) Differential Video Input Voltage Clamp Input Voltage VALUE 13.5 V 0C TA 70 C -65C TS 150 C 260 C 5 V
CAUTION
ELECTROSTATIC SENSITIVE DEVICES
DO NOT OPEN PACKAGES OR HANDLE EXCEPT AT A STATIC-FREE WORKSTATION
VEE + 2.5 V VCL Vcc - 2.5 V
ELECTRICAL CHARACTERISTICS
PARAMETER Supply Voltage POWER SUPPLIES + Supply Current - Supply Current SIGNAL PATH Maximum Input Voltage Above VCL Insertion Loss Full Power Bandwidth GB4550 SIGNAL PATH Small Signal Bandwidth Frequency Response Signal Path Delay Delay Tolerance Full Power Bandwidth Small Signal Bandwidth GB4550A SIGNAL PATH Frequency Response Signal Path Delay Delay Tolerance Differential Gain SIGNAL PATH Differential Phase Input Resistance Input Capacitance Output Resistance Clamp Voltage Range CLAMP Clamp Accuracy
V S = 10 V, TA = 0 - 70C, R L = 10k, CL = 150 pF, CCOMP = 0 pF unless otherwise shown.
SYMBOL VS I+ IVIN MAX I.L. FPBW SSBW
CONDITIONS Operating Range
MIN 9 1.8
TYP 10 9 9 2.0 18 25 0.05 -8 1.5 20 30 0.1 -7.5 0.15 0.02 0.03 100 2.0 8.6 53 7
MAX 12 13.8 13.8 2.25 0.03 0.05 0.05 +5.5 28
UNITS V mA mA V dB MHz MHz dB deg deg MHz MHz dB deg deg % deg k pF V mV
= 100kHz -3.0dB, V IN = 1V p-p 0.2dB, V IN = 100mV p-p at 10MHz, VIN = 1V p-p
15 20 17 25 80 -
oD
FPBW SSBW
at 3.58MHz at 3.58MHz -3.0dB, V IN = 1V p-p 0,1dB, V IN=100mV p-p, C L=100pF at 10MHz, VIN = 1V p-p
oD
dg dp RIN CIN R OUT V CL
at 3.58 MHz at 3.58MHz at 3.58MHz at 3.58MHz
AV = +1, = 0 to 10MHz AV = +1, = 100MHz
-5.5
VIN = 1V p-p
-
520 - 34 - 4
2
DETAILED DESCRIPTION The GB4550(A) is intended for video applications requiring coarse DC restoration coupled with flat frequency response. As shown in Figure 1, the signal path features a wide band operational amplifier designed to be unity gain stable. While this amplifer is not intended to drive 75 transmission lines, it is ideal for applications where high capactive loads, up to several hundred picofarads, must be driven, such as input buffering and DC restoration of video signals. Optimal frequency response for the GB4550(A) occurs with load capacitances in the range of 80 pF to 100 pF as shown in Figure 4. For smaller loads, an external capacitor can be added to extend the bandwidth and improve the flatness of the device response. The clamping function is achieved through the use of a simple comparator. The inverting input of the comparator is connected to the GB4550(A) output, while the non-inverting input is connected to the clamp voltage reference. For output signal voltages more positive than the clamp reference the comparator output is essentially open-circuit, while signal voltages more negative than the clamp reference result in the charging of CX. The action of the comparator is to provide a positive current which is fed back to the op-amp non-inverting input under conditions where the op-amp 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 level. This is the desired clamp action. The input to the op-amp must be AC coupled using an appropriate size of capacitor, which then acts as a DC "reservoir" for the corrective level shift. Under equilibrium conditions the average current supplied by the comparator output is just sufficient to balance the current discharging the input capacitor. This discharge current is simply the input bias current of the op-amp, typically less than 20 A . However, an external resistor can be added to increase the pull down current. Under dynamic conditions, where the system is adjusting for a change in the signal level, the charging current may be in the milliamp range. Because the corrective current is small under equilibrium conditions, the error voltage at the comparator input is small also, so clamping accuracy to within 7 mV is achievable. The clamp circuit makes use of a "peak hold" capacitor, CX, at the output of the comparator . This gives rise to a more constant voltage at the comparator output which is translated to a more constant corrective current by an internal 100 k resistor connected between the comparator output and the signal input. To avoid excessive phase shift and consequent instability of the clamp feedback loop, the peak hold capacitor needs to be considerably smaller (e.g. 1000 times) than the input coupling capacitor. If a faster clamp is desirable (e.g. for 60 Hz hum elimination) the peak hold capacitor can be removed and a smaller input coupling capacitor employed. In this application some distortion of the signal "tip" is unavoidable.
CX
(+2 V OUTPUT CLAMP) 100k
(NC on GB4550A)
30k
+
10pF
VCL
COMP
+IN -IN VCC 7mA Nominal VEE
All resistors in ohms, all capacitors in microfarads unless otherwise stated.
+ 30k
OUT
Fig. 1 Simplfied Circuit Diagram
3
520 - 34 - 4
+10V 0.1
-10V 0.1
+5V 0.1
4 SIGNAL IN FROM NETWORK ANALYSER *22 1
NON-POLAR
2
6 1 0.1 D.U.T. 8 7 3 10k **RCOMP -5V 4 CLC110 5 8 OUTPUT TO NETWORK ANALYSER
5 75
10n
All resistors in ohms, all capacitors in microfarads unless otherwise stated.
**CCOMP
CLOAD
0.1
NOTES: This circuit can be used for Frequency Response, Delay and Differential Gain and Phase measurements. * This input capacitor must be shorted out when performing Differential Gain and Phase tests. ** RCOMP and CCOMP are only used on GB4550.
Fig. 2 Test Circuit
+10V 0.1
-10V 0.1
GX4314 XPOINT
VIDEO OUT 1
42 0.1 to 22 1
NON-POLAR
6
GX4314 XPOINT 8 7 GX4314 XPOINT
VIDEO OUT 2
VIDEO IN
GB4550 GB4550A
5
3
*RCOMP
VIDEO OUT 3
All resistors in ohms, all capacitors in microfarads unless otherwise stated.
**10n
*CCOMP
CLOAD GX4314 XPOINT VIDEO OUT 4
NOTES: In most applications RCOMP and CCOMP will not be needed since the bandwidth depends on the bus capacitance. In general, the maximum occurs when CLOAD is between 82 pF and 100 pF. They are used to control the roll-off for higher load conditions.
* Not used on GB4550A. **
The value of this capacitor should be proportional to the input capacitor used. The value shown is for a 22 F input capacitor.
Fig. 3 Typical Application Circuit
520 - 34 - 4
4

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