Applications of Controlled Impedance
Controlled Impedance should be considered for PCBs used in fast digital applications such as:
- Telecommunications
- Computing 100MHz and above
- High-Quality Analog Video
- Signal Processing
- RF Communication
Impedance Control In PCB Design
Electrical Impedance: A measure of opposition to time-varying electric current in an electronic circuit.
The Problem: “A,” “B,” and “C” signals all reach the component at the same time.
The Solution: Apply Impedance to Circuit “C” to slow the signal enough for the component to first calculate (“A”+B”).
Similar to a cable, the signal encounters a change of impedance arising from a change in material or geometry. Part of the message will be reflected and partly transmitted. These reflections are likely to cause aberrations on the signal, which may degrade circuit performance (e.g., low gain, noise, and random errors). In practice, board designers will specify impedance values and tolerances for board traces and rely on the PCB Manufacturer to conform to the specification.
When rise times continue to reduce, inevitability, the number of traces requiring impedance control will continue to increase. Where impedance control is needed, it is essential to control it accurately, calculating it with the most representative cross-section we can create.
