8-1

Semiconductor

January 1999

CA3256

25MHz, BiMOS Analog

Video Switch and Amplifier

CAUTION: These devices are sensitive to electrostatic discharge. Users should follow proper IC Handling Procedures.

Harris Corporation 1999

File Number

1769.5

Features

· 5 Multiplex Video Channels

- 1 Independent Channel

- 4 Channels with Enable

· 4 LED Channel Indicator Outputs

· Wideband Video Amplifier . . . . . . . . 25MHz Unity Gain

· Adjustable Video Amplifier Gain

· High Signal-Drive Capability

Applications

· Video Multiplex Switch

· 75

Video Amplifier/Line Driver

· Video Signal-Level Control

· Monitor Switching Control

· TV/CATV Audio/Video Switch

· Video Signal Adder/Fader Control

Description

The CA3256 BiMOS analog video switch has five channels
of CMOS multiplex switching for general-purpose video-
signal control. One of four CMOS channels may be selected
in parallel with channel 5. The CMOS switches are inputs to
the video amplifier but may be used in bilateral switching
between channels 1 to 4 and channel 5. The analog
switches of channels 1 to 4 are digitally controlled with logic
level conversion and binary decoding to select 1 of 4
channels. The enable function controls channels 1 to 4 but
does not affect channel 5. LED output drivers are selected
with the channel 1-to-4 switch selection to indicate the ON-
channel. Channel 5 may be used as a monitor output for
data or signal information on channels 1 to 4. The
transmission gate switches shown in the block diagram of
the CA3256 are configured in a "T" design to minimize
feedthrough. When the switch is off, the shunt or center of
the "T" is grounded.

The amplifier has high input impedance to minimize the R

transmission gate insertion loss. The amplifier output imped-
ance is typically 5

in a complementary symmetry output.

The amplifier can directly drive a nominal 75

coaxial cable

to provide line-to-line video switching. The gain of the ampli-
fier is programmable by different feedback resistor values
between pins 8 and 9. Compensation may also be used
between these pins for an optimally flat frequency response.
An internal regulated 5V bias reference with temperature
compensation permits stable direct-coupled output drive and
minimizes DC offset during signal switching.

Pinouts

Part Number Information

PART NUMBER

TEMP.

RANGE (

PACKAGE

PKG.

NO.

CA3256E

-40 to 85

18 Ld PDIP

E18.3

CA3256M

-40 to 85

20 Ld SOIC

M20.3

CA3256

(PDIP)

TOP VIEW

CA3256

(SOIC)

TOP VIEW

CONTROL B

CONTROL A

IN 1

IN/OUT 5

LED 1

LED 2

IN 2

LED 3

IN 3

LED 4

IN 4

GND

ENABLE

FEEDBACK

CONTROL C

AMP OUT

V-

V+

IN3

LED4

IN4

GND

V-

ENABLE

FEEDBACK

CONTROL C

AMP OUT

LED3

CONTROL B

CONTROL A

IN1

IN2

V+

IN/OUT5

LED1

LED2

[ /Title
(CA32
56)
/Sub-
ject
(25MH
z,
BiMO
S Ana-
log
Video
Switch
and
Ampli-
fier)
/Autho
r ()
/Key-
words
(Har-
ris
Semi-
con-
ductor,
4x1,
video
cross-
point
switch,
multi-
plexer
multi-
plexor,
cable
driver,
5x1,
moni
tor out-
put,
adjust-
able
gain,

OBSOLETE PR

ODUCT

NO RECOMMENDED REPLA

CEMENT

Call Central Applications 1-800-442-7747

or email: centapp@harris.com

8-2

Block Diagram

Switch Control Logic

CHANNEL

NUMBER

ENABLE

5 + (1-4) (Note)

Channel 1-4

Channel 5 Only

None

NOTE: For Maximum Video Bandwidth, Use Single Channel Selections

V-

ENABLE

V+

5 4 3 2 1

IN/OUT

AMPLIFIER

OUTPUT

CHANNEL 1

CHANNEL 2

CHANNEL 3

CHANNEL 4

FEED BACK

LOGIC

LEVEL

CONV.

BINARY

1 OF 4

WITH

ENABLE

V-

V+

OUT

OPEN

OUT

CLOSED

OUT

CONTROL

LED DRIVER

OUTPUTS

10K

BIAS

REG

(DIP PIN OUT)

CA3256

8-3

Absolute Maximum Ratings

Thermal Information

DC Supply Voltage Range (V+ to V-) . . . . . . . . . . . . . . . . . . . . . 18V
Control Input Voltage Range, All Inputs . . . . . . . . . . . . . . . . V+ to V-
Signal Input Voltage Range, Channel 1-5 . . . . . . . . . . . . . . . .3V

P-P

Amplifier Output Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30mA
DC LED Sink Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30mA

Operating Conditions

Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . -40

C to 85

Thermal Resistance (Typical, Note 1)

(

C/W)

PDIP Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maximum Junction Temperature (Die). . . . . . . . . . . . . . . . . . . . 175

Maximum Junction Temperature (Plastic Package) . . . . . . . . 150

Maximum Storage Temperature Range . . . . . . . . . -65

C to 150

Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . . 300

(SOIC - Lead Tips Only)

CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation
of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.

NOTE:

is measured with the component mounted on an evaluation PC board in free air.

Electrical Specifications

= 25

C, V+ = 12V; V- = GND

PARAMETER

SYMBOL

TYPICAL VALUES

UNITS

Power Supply Voltage V+ to V-

10 to 17

Power Supply Current

SWITCH

AMPLIFIER

Open Loop Gain

Programmable Gain, FB Adjustment Range

-0.8 A

Full Power Bandwidth

MHz

Unity Gain Bandwidth, 1k

, 7pF Compensation

MHz

Insertion Loss

-0.8

Signal Feedthrough, 5MHz

-66

Input Impedance

Output Impedance

OUT

Maximum Input Voltage

I(MAX)

2.5

P-P

Maximum Output Voltage, Clipped

O(MAX)

P-P

Reference Bias Output Voltage (V

- V-)

Differential Gain

Differential Phase

Degree

Off Isolation, Channel to Channel, Z

= 75

-66

LLC Switch Turn On/Off Time Delay

0.5

Maximum LED Sink Current

Typical Output Source Current

Channel Control Switch A, B, C and E

Threshold

(Notes 2, 3)

Approximately (V+ - V-)/2

CAUTION: Connect the V- power supply voltage before or during the V+ turn-on.

NOTES:

2. Threshold value is referenced to GND.

3. V

is restricted by the equation, V

< V+ -1.

CA3256

8-4

Electrical Specifications

= 25

C, V+ = 12V, V

LED

= 12V, V- = GND, Pin 4 = GND, Feedback Switch Closed, V

HIGH

= 9V, V

LOW

= 3V

(See Figure 1), Unless Otherwise Specified

PARAMETERS

INPUTS

CHANNEL SWITCH CONTROL

MIN

TYP MAX UNITS

CH 1

CH 2

CH 3

CH 4

CH 5

ENABLE NOTE 6

TEST

PIN#

PIN 15 PIN 17

PIN 1

PIN 3

PIN 13 PIN 16 PIN 18

PIN 7

PIN 6

Supply Current,
V

LED

= 0V

Dual Supply Current
V+ = +7V, V- = -5V

14/5

Amplifier Output
Voltage, Open Loop
V

LED

= 0V

8.5

Amplifier Output
Voltage, Closed Loop,
V

LED

= 0V

4.8

5.1

5.4

OUT (MAX)

(Source)

Open Loop

Note 4

-70

-25

OUT (MAX)

(Sink)

Open Loop

Note 5

Input Leakage
Channel 1-5

1, 3, 15,

-15

Channel Control
Input A, B, C,
Enable Leakage

Measure at 3V, 9V each;

Enable and Channel

Switching Control Inputs

6, 7, 16,

-20

LED Off Voltage, V

OFF

Select Channel 0-5

2, 10,

11, 12

11.97 11.99

LED On Voltage, V

Select Channel 0-5

2, 10,

11, 12

0.1

0.3

Switch Resistance,
R

100

A Input Each Switch,

Channel 1-4 + 5

Select Channel

1-4

0.8

1.1

1.4

Match

Calculation: (Max R

- Min R

)/Min R

3.6

Amplifier Output
Offset, V

, Feedback

Switch Closed
V+ = +7V, V- = -5V

-100

100

Closed Loop Gain

-0.5

-0.1

0.5

NOTES:

4. V

OUT

= +7V.

5. V

OUT

= +3V.

6. DIP Pinout.

CA3256

8-5

Test Circuits

Application Information

CMOS analog switches are available in a wide variety of
forms, and have been known and used for some time. There
are a number of advantages to using the CMOS transmis-
sion gate as a switch:

· Ideal Suitability to Series Cascade Arrangements
· Simple Multiple Parallel Input Switching Arrangements
· No Bipolar Junctions and, Hence, No Offset
· Very Low Power Consumption
· Wide Signal-Swing Capability
· Fast Multiplexing and Video Switching
· Wide Bandwidth
· Low R

Channel Resistance

· Bidirectional Signal Handling

An Integrated Video-Switch Amplifier

Commonly, integrated video-switch amplifiers have been fabri-
cated in the bipolar technology using differential amplifiers in a
current-switching mode. In this form, two differential pairs are
needed for two input-signal sources. The handling of multiple
sources is very much more complex. The advantages of the
CMOS video-switch amplifier have already been noted. While
the bipolar video switch has high output drive and switching

speed as advantages, the price is high in voltage offset and cur-
rent drain. The integrated device solution that is offered here is
in the use of the BiMOS technology, where both the CMOS and
bipolar processes complement each other to provide CMOS
switching with bipolar amplifiers. The BiMOS process allows
several CMOS switches to be coupled to a bipolar drive-ampli-
fier in the same process to exploit the best of two technologies.

Other advantages are gained when the BiMOS process is
used for an IC video-switch amplifier design. The BiMOS
process calls for a P-substrate and, therefore, isolated N-epi-
taxial wells can be built for both N and P channel parts. The
boats provide for better isolation of the N and P channels.
The N and P wells in a transmission-gate cell can be
switched between source and rail; therefore, they have a
smaller body effect on both N and P devices, which results in
better gain linearity. Where desired, oxide capacitors are
available for bipolar amplifier compensation.

CA3256 Video-Switch Amplifier

The Block Diagram shows the functional diagram of the
CA3256, which consists of five MOS channels, each com-
prising a three-element T-switch. The output of the five
switches is made common and fed into the input of a bipolar

CONTROL INPUTS (CHANNEL SELECT)

+12 V

10K

OUTPUT

AMP

FEEDBACK

SWITCH

AMP

OUT

1.1K

GND

IN 1

IN 2

IN 3

IN 4

IN/OUT 5

ENABLE

BIAS

REG

+12 V

LLC ENABLE

AND CHAN 1-4

SELECT

TG-1

TG-2

TG-4

TG-3

TG-5

V+

V-

BIAS

LED

FIGURE 1. CA3256 TEST CIRCUIT (DIP PINOUT)

(V- +5V)

CA3256

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