Several nonlinear effects may occur in than the primary resonance, so that the follower gain, and the practice. If the enhanced Q is sufficiently high, can be corresponding compensating current are reduced at frequencies less than 1 at but greater than 1 for some frequency greater above the primary resonance.
The stabilized plots using than because the compensating voltage in the primary is each of the two proposed stabilization methods are shown in proportional to.
In this case, the circuit may oscillate due Fig. Noise Analysis Nonlinear effects occur because of the variation of and at large signal swings. These variations cause to vary To facilitate a theoretical noise analysis of the circuit, an ap- with the voltage across the tank, and can cause oscillation if a propriate noise model for the FETs is required. The noise voltage that appears at the input terminals of the tank across an arbitrary source resistance is of interest.
Using superposition we analyze the contribution to this equiva- lent input referred noise voltage from each noise source in the circuit. The three main noise sources are the thermal noise of in the primary, and the thermal drain current noises of M1 and M2, taking the internal feedback into account. Once again, we neglect and for simplicity. For the case where there is no additional stabilization circuitry, we can neglect the thermal noise contribution from in the secondary because is zero.
The contribution of the thermal noise of may be analyzed using the circuit of Fig. The contributions of the thermal drain noise currents of M1 and M2 may be analyzed by exam- ining Fig.
The noise contributions of , M1, and M2 are shown in Fig. Stabilization method using a resonant tank in the source of M1. Table I, where 17 It should be noted that D tends toward a low value at reso- nance for high Q, so that the noise in the circuit at the resonant frequency is significantly increased as Q is raised. The calculated noise contributions are plotted in Fig.
These results agree with simulated results using a simple lumped element transformer model and Level 1 FET models with. It can be seen that the main contributor to the total input referred noise is the triode FET, M1. The maximum noise is of interest when considering the use of the actively compensated inductance in a circuit application.
The worst case noise voltage across the tank will occur when. Using the equations in Table I, the peak noise due Fig. Stabilized S S 11 A with resonating capacitor in parallel with to M1, M2, and can be written in terms of the compensated secondary coil, S 11 B with parallel resonant LC tank in source of M1.
Q factor, as icant literature on the topic. An accepted expression for FET thermal drain noise current is [10] 18 15 where K is a dimensionless constant given by where is the drain-source conductance at zero and is 19 chosen empirically to match the observed noise behavior of a given fabrication process. Quite often circuit simulators replace The terms inside the square root of 18 represent the peak with , which is strictly valid only for long channel de- noise contributions of M1, M2, and , respectively, as shown vices.
Theoretically, for long channel devices. Recent in Fig. Nicollini [12] has shown that the a stability issue due to the frequency dependence of the posi- following expression agrees closely with measurements on long tive feedback and two possible methods of stabilizing it were channel devices, and is in common use for Level 1 FET models proposed 1 resonating the transformer secondary with a capac- in circuit simulators itor and 2 degenerating the source of M1 with a resonant tank.
Resonating the secondary with a capacitor results in a total input 16 referred noise similar to the case with no stabilization. Simulated input referred noise contributions for R , M1, and M2. The second proposed stabilization technique based on placing a resonant tank in the source of M1 does not change the input re- ferred noise significantly near resonance because the impedance of the stabilizing tank is low, near the resonant frequency of the primary tank. Although the above noise analysis uses simplified models to gain physical insight into the contributions of the various noise sources, a more complete noise modeling approach including all parasitics yields similar results.
Equivalent circuit for calculating input referred noise contribution of a R , b M1, and c M2 with R. However, to maintain the same resonant frequency, the primary capacitance is reduced. Linearity Analysis The net result is that the overall input referred noise does not The main sources of nonlinearity in the circuit are the FETs change appreciably from the case when the secondary capacitor M1 and M2.
In addition to nonlinearities arising due to devia- is not present. Simulated input referred noise contributions for R ;R , M1, and M2 with resonated transformer secondary.
This is due to the relatively high compen- sating current swings required in the secondary winding to attain high Q values. For a realistic case where nH, , and with the circuit operating at 1. The linearity may be improved if the quality of the transformer windings is good along with a good coupling factor.
The Q-enhanced inductor is a 1-port device, making it dif- ficult to apply conventional measures of linearity such as IP3 and P1 dB, which are geared toward a 2-port system. The Q-en- hancement circuit may be considered as a voltage input—cur- rent output device. In simulation, a measure of the linearity of the Q-enhanced inductor can be obtained by applying a voltage drive from a zero impedance source and observing the harmonic content of the input current.
In practice, an ideal voltage source cannot be used to drive the tank and the harmonic content of the Fig. Simulated versus measured S11 for various gate control voltages. An alternative ex- perimental method to measure the linearity performance of the A. A logic enhanced Q, corresponding to different gate voltages applied to process was selected for the implementation because the passive the triode FET, M1. As this was a proof of FET, M1.
The simulated curves in Fig. The discrepancy in implementation. A die micrograph of the circuit is shown in the measured and the simulated results is primarily due to the Fig. The power consumption that was used to fabricate the circuit. To address the challenging needs of small size, wide bandwidth, and low-frequency applicability, a novel phase shifter implementation is introduced that utilizes tunable active differential inductors … Expand. This paper presents a study of Active inductor based VCOs that helps in increasing the tuning range of the VCO , reduces the chip size and phase noise of the circuit.
Design and performance analysis of active inductor based reconfigurable regulated cascode LNA for tunable RF front end. This paper presents reconfigurable low power low noise amplifier for an RF Receiver front end, which is designed and simulated in 0.
The reconfigurable techniques of Regulated … Expand. Design of active inductor at 2. The architecture of the active inductor is based on gyrator-C topology using active components. The intrinsic … Expand.
Correspondence to Hai-Xia Zhang. Reprints and Permissions. Fang, DM. Electrostatically driven tunable radio frequency inductor. Microsyst Technol 16, — Download citation. Received : 07 June Accepted : 24 August Year of fee payment : 4. Year of fee payment : 8. In general, the invention is directed to a tunable inductor that makes use of eddy current effect to tune the inductance of an inductor. The tunable inductor may include a spiral or helical inductor in proximity to one or more sets of eddy current coils.
Each eddy current coil may be coupled to a corresponding switch that controls whether the eddy current coil is grounded or floating. In operation, a first time-varying current through the inductor induces a first magnetic field that, in turn, induces a time-varying voltage in an eddy current coil.
If the eddy current coil is not grounded, an eddy current flows through the eddy current coil. The eddy current, which flows in the opposite direction of the first time-varying current, induces a second magnetic field.
The second magnetic field, which opposes the first magnetic field, reduces the inductance of the tunable inductor. This application claims the benefit of U. The invention relates to inductors including inductors useful in inductor-capacitor LC tanks for radio frequency RF communication.
An inductor is an electrical device that introduces inductance into a circuit or functions by inductance within a circuit. In some applications, it is useful for inductors to be tunable. For example, circuits designed for RF applications may benefit by using tunable inductors.
In particular, tuned circuits that include LC tanks used for loads, filters, impedance matching, or the like may use tunable inductors for tuning center frequencies. The center frequency of an LC tank may be tuned for various reasons. For example, tuning the center frequency of LC tanks may compensate for process variation. In other cases, tuning the center frequency may track a signal frequency that varies. In addition, tuning the center frequency of an LC tank can produce a particular amplitude or phase for a given frequency.
A tunable inductor, having an inductance that may be controlled manually or automatically, typically is tunable only by mechanical means. Variable capacitors, also known as varactors, are sometimes used to tune LC tanks. If a varactor is grounded, banks of switched capacitors may be necessary to properly tune an LC tank. In general, the invention is directed to a tunable inductor that employs eddy current effects to tune the inductance of an inductor.
In particular, a set of eddy current coils may be above, below, or on the same plane as the inductor.
Each eddy current coil may be coupled to a corresponding switch that controls whether the respective eddy current coil is grounded or floating. In operation, a first time-varying current through the inductor may induce a first magnetic field that in turn induces a time-varying voltage in an eddy current coil.
If the eddy current coil is grounded, no eddy current flows through the eddy current coil and the inductance of the tunable inductor remains unchanged. If the eddy current coil is not grounded, however, an eddy current flows through the eddy current coil.
The direction and amplitude of the second magnetic field may be controlled in order to tune the inductance of the inductor. In particular, the direction and amplitude of the second magnetic field may be controlled based on an arrangement of eddy current coils that are not grounded.
By selectively coupling and decoupling one or more eddy current coils to ground, the inductance of the inductor can be selectively tuned. In one embodiment, the invention is directed to a tunable inductor that includes an inductor, a first eddy current coil in proximity to the inductor, and a switch coupled to the first eddy current coil that controls whether the first eddy current coil is grounded or floating.
The inductor has a standard inductance, wherein current through the inductor induces a first magnetic field. The first eddy current coil is capable of carrying an eddy current induced by the magnetic field. The inductance of the inductor can be tuned down from a standard inductance when the first eddy current coil is floating.
Alternatively, the inductance of the inductor can be tune upward from a standard inductance when the first eddy current coil is grounded. In another embodiment, the invention provides a tunable inductor comprising an inductor that induces a magnetic field in response to current flowing through the inductor, an eddy current coil in proximity to the inductor, and a switch to couple the eddy current coil to ground to prevent eddy current from flowing within the eddy current coil in response to the magnetic field, and to decouple the eddy current coil from ground to permit the eddy current to flow within the eddy current coil in response to the magnetic field, wherein the eddy current reduces an effective inductance of the inductor.
In a further embodiment, the invention provides a method for tuning an inductor, wherein the inductor induces a magnetic field in response to current flowing through the inductor. The method comprises coupling an eddy current coil to ground to prevent eddy current from flowing within the eddy current coil in response to the magnetic field, and decoupling the eddy current coil from ground to permit the eddy current to flow within the eddy current coil in response to the magnetic field, wherein the eddy current coil is in proximity to the inductor, and the eddy current reduces an effective inductance of the inductor.
The invention may provide one or more advantages. A variable tank capacitance can cause degradation of linearity or Q. However, a tunable inductor in accordance with the invention can help to avoid these disadvantages. Moreover, the invention provides a technique for tuning an inductor by non-mechanical means. In addition, varactors, which can bring nonlinearity to a system, are not necessary for implementing the invention. Furthermore, banks of switches, which contain resistances that can degrade the Q and performance of the tank, are not detrimental to the circuit.
0コメント