By Inigo Gutierrez, Juan Meléndez, Erik Hernández
Varactors are passive semiconductor units utilized in digital circuits, as a voltage-controlled method of storing strength that allows you to advance the volume of electrical cost produced. long ago, using reasonably cheap fabrication procedures comparable to complementary steel oxide semiconductor (CMOS) and silicon germanium (SiGe) have been stored for built-in circuits operating in frequency levels less than the GHz. Now, the elevated operating frequency of radio frequency built-in circuits (RF ICs) for communique units, and the craze of system-on-chip know-how, has driven the necessities of varactors to the restrict. because the frequency of RF purposes keeps to upward push, it truly is crucial that passive units similar to varactors are of optimal caliber, making this a serious layout factor.
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Additional info for Design and Characterization of Integrated Varactors for RF Applications
E1(t) electric ﬁeld in the gate: this generates: ohmic losses in the gate metal. E2(t) electric ﬁeld between the gate contact and the accumulation zone: this is generated as the result of the voltage difference between the two. It produces: capacitance in the gate oxide. E3(t) electric ﬁeld in the N well: this appears as the result of the distribution of voltages in the N well. It causes: parasitic capacitance in the N well; ohmic losses in the N well due to its resistivity. 5 Electrical and magnetic phenomena in an NMOS varactor in accumulation mode.
Consequently, quality is kept almost constant. 12 Variation of the capacitance when varying the number of islands on a PN-junction varactor. 2 Variation of the tuning range and quality with the number of islands. 2 Inﬂuence of the Size of the Islands If, instead of increasing the number of islands, their length is increased but their width maintained, the depletion zone also increases. This has the same effect as increasing the number of islands. 8 mm) and the same number of islands (25). 13 shows the variation in capacitance with the bias voltage of these varactors.
21, with three different-sized varactors: Var 4, Var 5 and Var 7. 5 GHz). In other words, the resonant frequency increases as the size of the varactor decreases. If a designer wants to increase the resonant frequency value for the given capacitance, only the inductance value can be changed. In other words, these values should be minimized in order to increase the working frequency range. As the inductance depends mainly on the external metal connections, to reduce the inductance of these connections, either the length of the connections should be reduced or more connections in parallel should be made.