What Causes Jitter?
The ubiquitous noise associated with all semiconductor circuits is one source of jitter. Wireless applications expose communications circuits to a wider range of interference. Radio signals are susceptible to atmospheric effects, lightning, RFI, and reflections from nearby structures. Cell phones and mobile wireless systems are vulnerable to signal multipaths, making the system especially vulnerable to jitter’s information-corrupting effects. Power supply transients and faulty connections also take their toll. Figure 2 shows how a logic gate’s noise creates variable triggering. In this example, the circuit’s vulnerability to thermal and other noise is exaggerated for simplicity of explanation. The logic gate is designed to make a transition whenever the rising edge of the triggering waveform reaches approximately 2.5 V. That is Vdd/2 for 5-V systems. Circuit designers are actually less concerned with absolute triggering voltage than consistency of triggering at some voltage near this 2
