Video Speed Summing Coax Driver

Experiment with Op-Amps while driving a Coaxial cable as summing/differential amplifiers.  Change the gain or use the unique capability to sum several signals without coupling them together.  As a member of the Herdware product line, the resistors are changeable while maintaining good electrical conductivity and layout, no more trying to work around the restrictions of a solderless breadboard. For those looking for a more permanent electronic building block a touch of solder and the assembly is ready to be included in your next DIY project.

The Herdware system is somewhat unique in in that it is an electronic prototyping system suited to analog circuits.  Utilizing high quality machined terminal sockets the resistors may be changed and experimented with without all of the parasitics and disadvantages of a standard solderless breadboard.  When a final selection is made the resistor can then be permanently soldered eliminating long term effects of heat, vibration and other environmental factors… its the best of both worlds for prototyping and permanent installation.

This circuit features the Analog Devices AD812 Current Feedback OpAmp with a programmable gain stage and a 2X Buffer stage.  By multiplying the signal times 2 the voltage divider formed by the series resister and the termination resistor on both sides of the coax are canceled out resulting in the original gain into the final load.

The PCB layout supports the use of BNC or SMA RF connectors for unit and output as well as pin terminals for use when summing multiple signals together on the input.

This product is sold as a kit of easily solderable through-hole components and includes the power cable and standoffs.

AD812 Datasheet

AD812 FEATURES

• Two Video Amplifiers in One 8-Lead SOIC Package
• Optimized for Driving Cables in Video Systems
• Excellent Video Specifications (RL = 150 V):
• Gain Flatness 0.1 dB to 40 MHz
• 0.02% Differential Gain Error
• 0.028 Differential Phase Error
• 145 MHz Unity Gain Bandwidth (3 dB)
• 1600 V/ms Slew Rate

AD812 APPLICATIONS

• Video Line Driver
• Professional Cameras
• Video Switchers
• Special Effects

AD 812 PRODUCT DESCRIPTION

The AD812 is a low power, single supply, dual video amplifier.
Each of the amplifiers have 50 mA of output current and are
optimized for driving one back-terminated video load (150 Ω)
each. Each amplifier is a current feedback amplifier and features
gain flatness of 0.1 dB to 40 MHz while offering differential
gain and phase error of 0.02% and 0.02°. This makes the
AD812 ideal for professional video electronics such as cameras
and video switchers.

 Differential Summing OpAmp Amplifier

From Wikipedia: A differential summing OpAmp amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs.^[1] It is an analog circuit with two inputs  and  and one output  in which the output is ideally proportional to the difference between the two voltages:

where A is the gain of the amplifier.

More information can be found at https://en.wikipedia.org/wiki/Differential_amplifier

Additional information