1 Find the characteristic impedance typical value of modernd

1. Find the characteristic impedance (typical value) of modern-day printed circuit board. If you are to drive a CMOS device on such a circuit board, devise a termination method .

2.  Find a practical example of series termination (no general case please!). Explain why and how it works.

3. Briefly explain the function (or purpose) of series termination, do the same for parallel termination.

4. You are using Thevenin termination for a line with Zo =100 Ohm. Assume TTL circuit and 5V Vcc. One of your goals is to reduce power dissipation. What value do you choose for the two resistors used in Thevenin termination?

Solution

The characteristic impedance or surge impedance (usually written Z₀) of a uniform transmission line is the ratio of the amplitudes of voltage and current of a single wave propagating along the line; that is, a wave travelling in one direction in the absence of reflections in the other direction. Characteristic impedance is determined by the geometry and materials of the transmission line and, for a uniform line, is not dependent on its length. The SI unit of characteristic impedance is theohm.

The characteristic impedance of a lossless transmission line is purely real, with no reactive component. Energy supplied by a source at one end of such a line is transmitted through the line without being dissipated in the line itself. A transmission line of finite length (lossless or lossy) that is terminated at one end with an impedance equal to the characteristic impedance appears to the source like an infinitely long transmission line and produces no reflections.