By Inigo Gutierrez, Juan Meléndez, Erik Hernández
Varactors are passive semiconductor units utilized in digital circuits, as a voltage-controlled method of storing power which will improve the volume of electrical cost produced. some time past, using inexpensive fabrication techniques equivalent to complementary steel oxide semiconductor (CMOS) and silicon germanium (SiGe) have been stored for built-in circuits operating in frequency levels under the GHz. Now, the elevated operating frequency of radio frequency built-in circuits (RF ICs) for communique units, and the fad 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's crucial that passive units corresponding to varactors are of optimal caliber, making this a severe layout issue.Initially describing the actual phenomena that happen in passive units inside of commonplace IC fabrication techniques, layout and Characterization of built-in Varactors for RF purposes is going on to:- current details at the layout of vast band electric varactor versions (up to five GHz) which permit the exact prediction of equipment performance;- suggest a particular technique for the size of built-in varactors, overlaying on-wafer size constructions, the calibration procedure, and precise descriptions of the mandatory equipment;- clarify de-embedding recommendations and likewise examine self assurance point and uncertainty associated with the try set-up;- study the layout of a voltage managed oscillator (VCO) circuit as a pragmatic instance of the employment of tools mentioned within the ebook. supplying the reader with the mandatory technical wisdom for facing not easy VCO designs, this publication is a vital consultant for training RF and microwave engineers engaged on the layout of digital units for built-in circuits. it's also an invaluable reference for postgraduate scholars and researchers drawn to digital layout for RF functions.
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Extra info for Design and Characterization of Integrated Varactors for RF Applications
Integrated varactors are passive components with a wide range of applications in the field of radio-frequency communications (RF). Depending on the type of application, the geometry of the varactors differs, giving rise to various classes of integrated varactors. This type of varactor is examined as follows. References Aparicio, R. and Hajimiri, A. (2002) Capacity limits and matching properties of integrated capacitors. IEEE Journal of Solid State Circuits, 37(3), 384–393. Ashby, K. B. et al. (1996) High Q inductors for wireless application in a complementary silicon bipolar process.
10 shows the typical variation for an NMOS varactor with B D S (Andreani and Mattison, 2000). The varactor is usually characterized by a variable capacitance and a resistance that represents the possible losses generated (Svelto, 1999). The total capacitance of the NMOS varactor is given by: CPMOS ¼ C Á W Á l ð3:3Þ where W is the width of the PMOS channel, l is the length of the PMOS channel and C represents the capacitance per unit of area. The maximum possible capacitance value per unit of area of the varactor (Cmax ) is reached in the strong inversion and accumulation zones where the flow of carriers is greater than in the other zones.
The resistance of the varactor might be expected to increase in proportion to the distance between the islands, but this is not so due to the fact that most integrated technologies include an Nþ type low-resistivity buried layer under the N well. Most of the RF currents between the Pþ and Nþ islands flow along this Nþ layer, minimizing the resistive effect of the N well. 17 shows the effect of the buried layer on the RF currents. 4. As the capacitance is kept almost constant for each varactor, the presence of the buried layer avoids a high reduction in the quality.