particularly harmful in noise environments since they reduce the noise immunity of the device. Basic rectification theory states that the rectified current in a pn junction is where n is the rectification efficiency and is the prf power absorbed into the junction. The theory also tells us that in the microwave frequency range where no is a constant dependent on junction construction and bias conditions, while f is the frequency of the rf energy. In other words, junction efficiency is inversely proportional to frequency squared. The theory is useful since it allows one to extrapolate measurements that are made at frequencies other than the 2.45 GHz SPS frequency. Assume, for example, that a measurement is made at frequency f1, where the device absorbs a power rPf1 and produces a rectification current IR1 _. Further assume that this is the level of . current where interference effects are first noted (interference threshold). Thus, one can write that If the threshold measurement were made at a different frequency, f2, one should expect that the same interference threshold would be reached when While these formulas are approximate, they do show that interference threshold can be expected to vary as the square of frequency. Measurements were made at 0.91 and 3.0 GHz on three types of integrated circuits, a 7500 bipolar NAND gate, a 4011 CMOS NAND gate, and a 5474 flip flop (Roe, 1975). A summary of these measurements is given in Table 5, where the interference thresholds are defined as that point where deviation in the device normal or quiescent
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