Effect of scale down
With the technology scale down, the supply voltage is reduced and the signals switch faster within interconnects (From voltage to scaled voltage). In 0.18µm technology, the switching is about 100ps (Pico-second or 10-12 second), with a 2V swing. Concerning currents, the amplitude of elementary peaks appearing on supply lines of each elementary gates are sharper, but their amplitude remains constant (0.5mA in 100ps, per gate). Consequently, stronger di/dt are observed, leading to increased emission problems.
Parasitic emission increased with scale down
The evolution of the maximum peak of emission for a family of microprocessors is reported in figure 11. The measurement setup uses again the 1Ω serial resistance to probe an image of the conducted current flowing to the ground. From the measured spectrum (in dBµV), we only keep the harmonic with the maximum peak. The global trend corresponds to an increase of the peak energy, mainly due to higher internal clock speeds, increased number of package leads, larger chip dies and interconnect loops.
Low parasitic emission is a key argument
Low parasitic emission is a key commercial argument. The characterization of the electromagnetic emission is usually presented in frequency domain, log/log, with the frequency in X axis, and the emission level in dBµV in Y axis. 0dBµV is 1µV, 40dBµV is 100µV, 80dBµV is equal to 10mV.
For automotive applications, three frequency bands are worth of interest: the FM band near 100MHz, the short distance radio links near 400MHz and the mobile phone 900,1800 and 1900MHz.
The IC in red (Supplier A) exhibits a very high level of harmonics in the three "sensitive" bands. Electronic systems using this component could not comply EMC regulations. The same IC from an other supplier B, pin-to-pin compatible, features a significantly lower level of emission, which will probably be compliant with the customer's specifications.
More complex systems
Embeded electronics for automotive and aeronautic need more and more powerfull and complex processors (32 bits, 500 Mhz micro-controllers) which become the main parasitic sources of radio frequency interference and could affect the FM radio band around 100MHz, the local radio links around 430MHz, and the first GSM band around 900MHz.
The evolution of the maximum peak of emission for a family of microprocessors is reported in figure 11. The measurement setup uses again the 1Ω serial resistance to probe an image of the conducted current flowing to the ground. From the measured spectrum (in dBµV), we only keep the harmonic with the maximum peak. The global trend corresponds to an increase of the peak energy, mainly due to higher internal clock speeds, increased number of package leads, larger chip dies and interconnect loops.
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