Synchronous noise

A second strategy is, of course, to avoid the generation of synchronous noise in the system. Typical sources of coherent noise are cavity dumpers, pulse pickers, and picosecond diode lasers. For the shielding of these devices the same rules should be applied as for detector shielding. 

Are there any circuits that are particularly noise-sensitive These include analog-to-digital and digital-to-analog converters, video monitors, etc. This may dictate that the supply has additional filtering or may need to be synchronized to the sensitive circuit. 

Power Supply Cookbook, Second Edition has been updated with the latest advances in the field of efficient power conversion. Efficiencies of between 80 to 95 percent are now possible using these new techniques. The major losses within the switching power supply and the modern techniques to reduce them are discussed at length. These include synchronous rectification, lossless snubbers, and active clamps. The information on methods of control, noise control, and optimum printed circuit board layout has also been updated. 

As we have seen in Section 9.5.3, in the case of resistance thermometry, the signal produced by a low-temperature thermometer is very low (microvolt range). Low-pass filters are not sufficient to narrow the detection bandwidth in order to get a suitable signal to noise ratio (S/N). Bandpass filters are needed. The most commonly used method is the synchronous demodulation, usually simply called lock-in technique, as shown in the block diagram of Fig. 10.7. 

Figure 4. Llinas and Ribary (1993) identified in humans a synchronized gamma rhythm centred on 40 c/s during waking and sleep. In the two subjects (JV and ER), it was much more present during waking (A) and REM sleep (C) than during slow wave sleep (B, 6 sleep). D shows the noise of the system. Thirty-seven superimposed traces. Reprinted from Proceedings of National Academy of Science, with permission.

Wayman and Wilson, 1988] Wayman, J. and Wilson, D. (1988). Some improvements on the synchronized-overlap-add method of time scale modification for use in realtime speech compression and noise filtering. IEEE Trans. Acoust., Speech, Signal Processing, 36(1) 139-140. 

---