FRC(Flat Ribbon Cable)

Introduction of Flat Ribbon cable:

FRC is also known as multi wire planar cable because they are the type of cables formed by joining insulated wires in a flat plane forming the Ribbon shape.

In other words, Ribbon cable have many conducting wires running parallel to each other on the same flat plane.

These wires are commonly used for internal peripherals in computers, such as hard drives, CD drives, wired robots, etc.

The ribbon cable was invented in 1956 by Cicoil Corporation, California. This ribbon cable then allowed major companies to replace bulky, stiff round cables with sleek, flexible ribbon cables.

This cable consists of 4,6,8,9,10,14,16,18,20,24, etc. upto 80 conducting wires stuck together in parallel.

FRC is an ideal way to connect two device digitally.

The resultant impedance for any two adjacent wires within the cable is 120 Ohms.

FRC also fold and bend readily, conforming to the mounting area, and they fasten easily with clamps, adhesive, or double-faced tape.

Since the conductors are visible and in a fixed position within the dielectric coding, inspection and circuit tracing are simplified.

Classification of Flat Ribbon cable:

Mono color

Multicolor

The multi colour frc reduces the faulty connections at the end terminals, example making connections in wired robot. Whereas mono coloured frc is used as bus connection, example: connection between hard disk and motherboard.

Round to Flat Cable

Round to flat cable is cabling made with a flat cable core which is twisted or folded into a round shape before it is taped. It is available in double-shielded braided versions and in shielded or unshielded constructions. It is called round to flat cable because the majority of the cable appears in a round formation, but the ends show the flat cable core, enabling use with IDC connectors.

Round to Flat Cable without shielding:

Round to Flat Ribbon Cable without Shielding

Round to Flat Cable with shielding:

Round to Flat Ribbon Cable with Shielding

Configuration of Flat Ribbon cable:

Each dielectric configuration has different high frequency characteristics.

All configuration arrangement have precisely controlled separation supporting easy insertion of mass termination connectors. Also uniform separation makes excellent transmission.

Frequency response of Flat Ribbon cable

From the figure it can be concluded that the effective bandwidth decreases with the increase in square of distance, ie. for ribbon less than 10ft has very good performance.

At 100 ft, the 3.3dB attenuation point occurs at 5 MHz, yielding a rise time of 100ns.

The cables dielectric impacts performance in two ways ie. it controls signal propagation velocity and attenuation.

1. Propagation velocity

It is in ft/ns which is inversely proportional to the square root of electric permittivity.

Cables with a dielectric surrounding the wires exhibit lower speed while cables on a thin, flat plastic sheet are high speed (air carries their field).

2. Attenuation

It depends on the ratio of series resistance to cable impedance.

At high frequencies, skin effect causes series resistance to rise with the square root of frequency causing attenuation.

Also the dielectric causes attenuation by changing the cables characteristic impedance. Cables completely surrounded in a dielectric material exhibit higher effective permittivity, and more attenuation.

3. Rise Time

Rise Time of Flat Ribbon Cable

It is proportional to the square of the length.

The rise time of FRC is given as:

where, K= constant dependent on cable, ft(square)/GHz,
L= length in ft.

Reducing the length by 1/2, reduces rise time by 1/4. This is true because the frequency response for any cable is determined by the cable's inductance, capacitance and resistance/length.

4. Crosstalk

It is an Electromagnetic interference received by one or more wires. Crosstalk can cause errors, noise, or prevent cables from transmitting data

In wireless communication, crosstalk is a signal transmission issue that causes a disruption in another circuit or channel. For example, crosstalk could cause you can hear someone else's conversation.

Crosstalk in ribbon cables varies with the placement of grounds among the signal conductors. Here, both inductive and capacitive crosstalk are present and are nearly equal causing a large reverse coupling coefficient but almost no forward coupling.

Advantages of Flat Ribbon cable

1. Mass Termination

Terminating flat cable is done with the complete group of conductors as a unit, which is more efficient than working with individual conductors at one time.

2. Reliability

The simplicity of flat cable with its parallel conductor geometry eliminates many of the common sources of wiring error and malfunction. Registration of the conductors is one-to-one with the terminating connector or board making proper contact assignment automatically.

3. Space and Weight reduction

The use of flat cable often eliminates much of the conventional wire's weight and bulk. Such things as redundant insulating materials, fillers and tapes are not required. The flat cable construction is so mechanically strong that it does not necessitate to have large conductors for strength. The copper cross-section can thus be reduced to what is required to carry the current load or to satisfy voltage drop requirements.

4. Flexibility

Flat cable is extremely flexible when bent in the plane of its thin cross-section(vertical plane). This flexibility has been utilized in applications where continuous or high flexing is necessary, e.g. drawers, doors, rotating arms, etc. But it does not allow for sideways flexing, so it may only be used in straight-run applications.

5. Greater Strength

Strength is enhanced by the fact that all conductors and insulation equally share tensile loads.

6. Consistent Electrical characteristics

Since the conductor spacing is fixed and the geometry of the cable is constant, the electrical characteristics, such as impedance, capacitance, inductance, time delay, crosstalk and attenuation, are consistent.

7. Greater Current carrying capacity

Flat cables have greater surface-to-volume ratio than their round cable counterparts, consequently having higher efficiency in dissipating heat. This allows a higher current level for a given temperature rise and cross-section of conductor.

8. Skewing effects

When the individual colours do not line up correctly due to timing differences in the CATx cable they are termed as being skewed. Due to the conductors having the exact physical and electrical length, along with a continuous and consistent dielectric, time delays between signals within a given flat cable are minimized.

9. High Density Interconnection

The cabling density achievable using flat cable is superior to that using conventional cable because of the high wire-to-cable cross-sectional density. Layers of flat cable are more effectively packed for higher conductor density than round cable.

10. Ease of Handling

Flat cable folds and bends readily, conforms to the mounting area, fastens easily with clamps, adhesive, or double-faced tape, and eliminates the installation and lacing difficulties associated with round wire cabling. Visible conductors in a fixed position within the dielectric simplify coding, inspection and circuit tracing.