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18 February 2016

The Fundamentals of Coherent Signals

These two coherent lightwaves have a constant phase offset
Figure 1: These two coherent light waves have
a constant phase offset
Optical communications have come a long way from the simple direct detection of amplitude-modulated transmissions. Today's long-haul optical networks make use of coherent detection, and for good reason. Using coherent detection, receivers can track the phase of the incoming signal and thereby extract any information conveyed using phase and/or frequency modulation. Thus, coherent detection facilitates much higher capacity without using more bandwidth.

01 February 2016

USB Type-C Cable Detection

The four possible states of connection for a USB Type-C cable
Figure 1: The four possible states of
connection for a USB Type-C cable
Having examined some of the basics regarding the USB Type-C connector and the Power Delivery 2.0 specification that complements the Type-C spec itself, we'll turn our attention to the topic of cable detection. The Type-C connector is reversible, which is to say there are four ways a cable can be connected between upstream- and downstream-facing ports (Figure 1). Not only that, but there are different types of Type-C cables. So how do the devices discern what's between them?