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

DESCRIPTION

The GB4550 and GB4550A are high performance mono-
lithic 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.

APPLICATIONS

Input buffering and clamping to crosspoint switches

Inter - system video signal clamping

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

0.15

at colorburst.

convenient 8 pin SIP packaging.

both can be configured as a gain stage with reduced
bandwidth.

Document No. 520 - 34 - 4

GB4550 & GB4550A

Monolithic Video Buffer/Clamp

DATA SHEET

1 2 3 4 5 6 7 8

GB4550 and GB4550A

Pin No.

GB4550

GB4550A

Function

+IN

non-inverting input

positive power supply

COMP

frequency compensation or NC

clamp voltage input

external capacitor

negative power supply

-IN

inverting input

OUT

output

+IN

10pF

COMP

OUT

30k

100k

7mA
Nominal

-IN

30k

(+2 V OUTPUT CLAMP)

(NC on

GB4550A)

SIMPLIFIED CIRCUIT DIAGRAM

ORDERING INFORMATION

Part Number Package Type Temperature Range

GB4550 - CSA 8 pin SIP 0 to 70

GB4550ACSA 8 pin SIP 0 to 70

PIN CONNECTIONS

All resistors in ohms, all capacitors in microfarads unless otherwise stated

Revision Date: February 1994

520 - 34 - 4

ABSOLUTE MAXIMUM RATINGS

PARAMETER

VALUE

Supply Voltage V

13.5 V

Operating Temperature Range

Storage Temperature Range

-65

150

Lead Temperature (Soldering, 10 Sec)

260

Differential Video Input Voltage

5 V

Clamp Input Voltage

+ 2.5 V

- 2.5 V

Supply Voltage

Operating Range

+ Supply Current

I+

13.8

- Supply Current

I-

13.8

Maximum Input Voltage
Above V

IN MAX

2.0

2.25

Insertion Loss

I.L.

= 100kHz

0.03

Full Power Bandwidth

FPBW

-3.0dB, V

= 1V p-p

MHz

Small Signal Bandwidth

SSBW

0.2dB, V

= 100mV p-p

MHz

Frequency Response

at 10MHz, V

= 1V p-p

0.05

Signal Path Delay

at 3.58MHz

-8

- deg

Delay Tolerance

at 3.58MHz

1.5

- deg

Full Power Bandwidth

FPBW

-3.0dB, V

= 1V p-p

MHz

Small Signal Bandwidth

SSBW

0,1dB, V

=100mV p-p, C

=100pF

MHz

Frequency Response

at 10MHz, V

= 1V p-p

0.1

Signal Path Delay

at 3.58 MHz

-7.5

- deg

Delay Tolerance

at 3.58MHz

0.15

- deg

Differential Gain

at 3.58MHz

0.02

0.05

Differential Phase

at 3.58MHz

0.03

0.05

deg

Input Resistance

100

Input Capacitance

2.0

Output Resistance

OUT

= +1, = 0 to 10MHz

8.6

= +1, = 100MHz

Clamp Voltage Range

-5.5

+5.5

Clamp Accuracy

= 1V p-p

PARAMETER

SYMBOL

CONDITIONS

MIN TYP MAX UNITS

ELECTRICAL CHARACTERISTICS

VS =

10 V, TA = 0 - 70

C, R

= 10k

, CL = 150 pF, CCOMP = 0 pF unless otherwise shown.

POWER

SUPPLIES

SIGNAL

PATH

GB4550

SIGNAL

PATH

GB4550A

SIGNAL

PATH

SIGNAL

PATH

CLAMP

CAUTION

ELECTROSTATIC

SENSITIVE DEVICES

DO NOT OPEN PACKAGES OR HANDLE

EXCEPT AT A STATIC-FREE WORKSTATION

1.8

520 - 34 - 4

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 C

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, C

, 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.

+IN

10pF

COMP

OUT

30k

100k

7mA
Nominal

-IN

30k

(+2 V OUTPUT CLAMP)

(NC on

GB4550A)

All resistors in ohms, all capacitors in microfarads unless otherwise stated.

Fig. 1 Simplfied Circuit Diagram

520 - 34 - 4

D.U.T.

**C

COMP

**R

COMP

SIGNAL IN
FROM
NETWORK
ANALYSER

10n

OUTPUT TO
NETWORK
ANALYSER

NON-POLAR

0.1

+10V

-10V

LOAD

*22

+5V

-5V

0.1

10k

CLC110

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.

5 3

GB4550

GB4550A

GX4314
XPOINT

VIDEO

10n

VIDEO OUT 1

VIDEO OUT 2

VIDEO OUT 3

VIDEO OUT 4

NON-POLAR

0.1

+10V

-10V

LOAD

0.1 to 22

COMP

NOTES

: In most applications R

COMP

and C

COMP

will not be needed since the bandwidth depends on the bus capacitance.

In general, the maximum occurs when C

LOAD

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.

All resistors in ohms,
all capacitors in microfarads
unless otherwise stated.

Fig. 3 Typical Application Circuit

Fig. 2 Test Circuit

520 - 34 - 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.

0.5

0.4

0.3

0.2

0.1

-0.1

-0.2

-0.3

-0.4

-0.5

FREQUENCY (MHz)

GAIN (dB )

150 pF

120 pF

82 pF

= 180 pF

123456789012345678901234567890121234567890123

-3

-4

-5

-6

-7

-8

-9

-10

Fig. 5 GB4550 Phase Delay Spread

Fig. 4 GB4550 Frequency Response

FREQUENCY (MHz)

= 100 pF

0.5

0.3

0.1

-0.1

-0.3

-0.5

= 100 pF

= 82 pF

= 180 pF

GAIN ( dB )

FREQUENCY (MHz)

-3

-4

-5

-6

-7

-8

-9

-10

2 3 4 5 6

FREQUENCY (MHz)

Fig. 6 GB4550A Frequency Response

Fig. 7 GB4550A Phase Delay Spread

1234

12345

1234

12341234

1234

12345

1234

123

1234

123

1234

123

1234

123

1234

= 100pF

TYPICAL PERFORMANCE CURVES

Unless otherwise shown V

10V

DEGREES

0.05

0.03

0.01

-0.01

-0.03

-0.05

FREQUENCY (MHz)

Fig. 8 Differential Gain and Phase

= 40 IRE

dg (%) / dp (

)

REVISION NOTE: Detailed Description added

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ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: GB4550-CSA