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A configuration using current feedback amplifiers AD844 and multiplier AD534 has been presented, which is capable of realizing Voltage Controlled Floating Inductance (proportional and in-verse proportional). The application of band pass filter in Figure 4(a), notch filter in Figure 5(a) and Hartley oscillator in Figure 6(a) and simulation result in Figures 4(b)-(d), Figures 5(b)-(d), Figures 6(b)-(d) shows the workability of proposed configuration.

Simulation of inductor has been popular area of analog circuit research. Due to the well known difficulties of realizing on chip inductors of moderate to high values and high quality factors, simulated inductors have been the alternative choice for realizing inductor-based integrated circuit. Simulated inductors are also useful in discrete designs in which case they can replace bulky Passive inductors and after the advantages of reduced size, reduced cost and complete elimination of undesirable mutual coupling when several inductors are being used in a circuit.

Electronically controlled inductor such as voltage controlled floating inductance finds application in automatic gain controller, filter and oscillator circuit. A number of configuration using a variety of active elements such as op-amps, operational-mirrored amplifier, current controlled conveyors, OTA and Combination have so far been presented in the literature for realizing such elements in Floating Form [

Recently, the current feedback op-amps (CFOAs) such as AD844 have attracted considerable attention in literature as alternative building blocks for analog circuit design due to the following advantages

i) Widen bandwidth that is relatively independent closed loop gain.

ii) Very high slew rate (2000 V/us).

iii) Ease of realizing various functions with least number of external passive components.

The main objective of paper is therefore to present a new configuration which is capable of realizing voltage controlled Floating inductance both in proportional and inversely proportional form and its application.

The paper is organized as follow:

Terminal Equations of CFA:

・

・

・

・

As shown in

MPY534 as MULTIPLIER

Description

The MPY534 is a highly accurate, general purpose four-quadrant analog multiplier. Its accurately laser trimmed transfer characteristics make it easy to use in a wide variety of applications with a minimum of external parts and trimming circuitry. Its differential X, Y and Z inputs allow configuration as multiplier, squarer, divider, square-rooter and other functions while maintaining high accuracy.

Implementation of voltage controlled floating inductance which is directly proportional to control voltage (V_{c}).

The proposed configuration shown in the

From CFOA (3) applying KCL

From CFOA (4) Applying KCL across capacitor:

Applying KCL again at input port of CFOA (4)

Thus

From CFOA (2)

Applying KCL

From CFOA(1)

Now subtracting the equation no. (5) from equation No. (4)

Now from standard floating inductor:

Putting the value of (V_{1} − V_{2}) and (I_{1} − I_{2}) from Equation (3) and (6)

After simplification we get,

Thus inductance (L) is directly proportional to control voltage (V_{c})

Implementation of voltage controlled floating impedance with inversely proportional to control voltage.

The proposed configuration shown in the

Output of the multiplier

From CFOA (1)

Applying KCL across capacitor

Now from CFOA (2)

Now subtracting the equation No. (1) from equation No. (2)

From CFOA (3) Applying KCL across capacitor we get_{ }

Again applying KCL at input node

rearranging the equation we get,

Now from standard floating inductor:

Putting the value of (V_{1} − V_{2}) and (I_{1} − I_{2}) from Equation (3) and (4)

Putting the value of I_{3}

After simplifying we get,

Thus inductance (L) is inversely proportional to control voltage (V_{c})

Thus inductance is inversely proportional to control voltage (V_{c}).

In

Please see Figures 4(b)-(d).

In the above simulation result, we show the frequency response of band pass filter made from voltage controlled floating inductance, a resistance and a capacitor. The band pass filter was designed for frequency f_{0} = 5 kHz, 7.1 kHz and 10 kHz with different value of inductance as given in _{c} varying from 1 to 4.

Thus from the above result it can be seen that by varying the control voltage (V_{c}) center frequency (F_{c}) of the band pass filter can be changed . Thus we can control the center frequency by varying V_{c}.

In

Please see Figures 5(b)-(d).

In the above simulation result, we show the frequency response of notch filter made from voltage controlled floating inductance, a resistance and a capacitor. The notch filter was designed for frequency f_{0} = 5 kHz, 7.1 kHz and 10 kHz with different value of inductance as given in _{c} varying from 1 to 4.

Thus from the above result it can be seen that by varying the control voltage (V_{c}) center frequency (F_{c}) of the notch pass filter can be changed .Thus we can control the center frequency by varying V_{c}.

In

Please see Figures 6(b)-(d).

In the above simulation results, we show the frequency response of Hartley oscillator made from voltage controlled

V_{REF}/V_{C} | Inductance (L) | Capacitance (C) | Center frequency (f_{c}) |
---|---|---|---|

1 | 0.1 mH | 10 uF | 5 kHz |

0.5 | 0.05 mH | 10 uF | 7.1 kHz |

0.25 | 0.025 mH | 10 uF | 10 kHz |

V_{REF}/V_{C} | Inductance (L) | Capacitance (C) | Center frequency (f_{c}) |
---|---|---|---|

1 | 0.1 mH | 10 uF | 5 kHz |

0.5 | 0.05 mH | 10 uF | 7.1 kHz |

0.25 | 0.025 mH | 10 uF | 10 kHz |

V_{REF}/V_{C} | Inductance (L) | Capacitance (C) | Center frequency (f_{c}) |
---|---|---|---|

1 | 0.1 mH | 100 uF | 1.125 kHz |

0.5 | 0.05 mH | 100 uF | 1.59 kHz |

0.25 | 0.025 mH | 100 uF | 2.25 kHz |

Proposed realization | |||
---|---|---|---|

Reference [ | Case 1 | Case 2 | |

CFOAs | 4 | 4 | 3 |

FET | 1 | 0 | 0 |

Multipliers | 0 | 1 | 1 |

Capacitor | 0 | 1 | 1 |

Resistor | 6 | 3 | 3 |

floating inductance, an op-amp and a capacitor. The Hartley oscillator was designed for frequency f_{0} = 1.125 kHz, 1.59 kHz and 2.25 kHz with different value of inductance as given in _{c} varying from 1 to 4.

From the above result, it can be seen that by varying the control voltage (V_{c}) center frequency of oscillation of Hartley oscillator can be changed .Thus we can control the frequency of oscillation by varying V_{c}.

The proposed circuit in

have used less number of CFOAs and less number of passive components. The use of multiplier nullifies the effect of non linearity of FET. The application of BPF, notch filter a Hartley oscillator have been discussed.

Praween K.Sinha,Dr NeelamSharma,RohitMishra, (2015) A Configuration for Realizing Voltage Controlled Floating Inductance and Its Application. Circuits and Systems,06,189-199. doi: 10.4236/cs.2015.69020