# Some common Analog terms

1. ## Some common Analog terms

1)Why db ranging mostly from 0 to negative? peak at 0 level and as it decreases it goes negative? why no positive?

2)noise floor in -155dBm/Hz what's dBm? why its over frequency?

3)why resisitity express in ohm-cm? why cm which is length? not not ohm-area?

4)what 's a epi versus non epi wafer?

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2. ## Re: Some common Analog terms

1) dB can be positive or negative. It's often negative for noise levels and positive for gain or signal-to-noise ratio.

2) dBm is the signal power relative to 1 mW. Thus -10dBm is 10dB below 1mW or 0.1mW.
The noise is given per Hz (a 1 Hz bandwidth) so you can calculate the total noise in a given bandwidth because the total noise is proportional to the square-root of the bandwidth.

3) Resistivity is given per distance for a (theoretical) infinite area of the test material. This means the measured resistance is simply proportional to the distance between the test probes (in this case in cm) times the resistivity.

4) A epi wafer has an epitaxial layer, whereas obviously a non-epi wafer doesn't.

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