LC Tunable Oscillator ELG 4135 Electronics III Project

LC Tunable Oscillator ELG 4135 Electronics III Project Team Members: Hubert Mamba Fu Jingyi Wang Jian

Introduction n Tuned oscillators are largely used in data transmissions and radio communications. In RF circuits, mainly LC oscillators are used and their frequency is, most of the time, controlled using a variable-capacitance (varicap) diode. This method is a little bit complicated and costly. We present a single grounded resistance tunable sinusoidal oscillator that n n requires only three transistors, some passive components and no variable-capacitance and the oscillating frequency is controlled through a grounded resistor. Another grounded resistor independently controls the condition of oscillation.

Ø Ø Main Objective: The main objective of this project is to investigate the performance of the new method (Single grounded resistance tunable Sinusoidal Oscillator). The usual method (VCO) requires the use of variablecapacitance diode to control the oscillating frequency value. This VCO is expensive and complicated to fabricate. Differential VCO (Collpitt) Oscillator. (from Lucio Carlo Rodoni “http: //n. ethz. ch/student/rodonil/da/beri cht/node 28. html”

Main Objective (cont’d) The alternative (new) method requires no variable-capacitance, it is not expensive and is easy to implement. Its circuit diagram is shown in the figure bellow.

purposes. Bellow is a circuit analysis of a simple LC oscillator. We can see that the oscillating frequency depends on the value of L and C. Background Knowledge Review LC circuit oscillating frequency calculation:

Circuit analysis result Theoretical calculation: The above formulas are copied from our report.

Theoretical Results The continuous curves are theoretical plot from Matlab The doted curves are got From the Multisim simulation. The simulation on Multisim 8 shows that for k=-1, the oscillating frequency is increasing as R 3 increases, and for k=1, the oscillating frequency decreases as R 3 decreases, it proves that this single resistor control LC circuit is working. The theoretical result is very close to the simulation ones.

Simulation in Multisim The simulation shows that the circuit can oscillate and the oscillating frequency agrees with theoretical result. This oscillating simulation plot is at R 3=0. 56 K ohm, and oscillating frequency is 300 k Hz at K=1.

Simulation in Multisim (cont’d)

Performance of the circuit From the simulation result we can see that theoretical calculation is very close to the simulation result, especially when R 3 is bigger than 40 K ohm, the oscillating frequency tends to merge into one value of different k values. It shows that the design of the circuit on this paper is excellent.

Data recorded from the simulation, for each value of R 3 and K, we found a corresponding frequency f. K=1 K=-1 R 3(kohm) f (k. Hz) R 3(kohm) f ( k. Hz) 5. 1 852 5. 1 288 10 435 10 323 20 373 20 343 30 366 30 356 39 365 39 362 51 359

Conclusion n n The circuit was tested for positive and negative values of k. A good quality sinusoidal signal was obtained for the negative value of k, but the shape of the signal is worse when k is positive, especially for the low values of R 3. The simulation results are in agreement with theory, particularly for negative values of k.

Things to be improved q q q It is not easy to get higher frequency values (Giga hurts) as we would in practice. The transformer ferromagnetic losses, the lag phase brought by Q 1, Q 2 and Q 3, the output impedance of Q 3 and the stray capacity in parallel with R 1//R 2 limit this high frequency value. Designing more powerful amplitude limitation device, based on nonlinear voltage-controlled voltage source Further research to increase the quality factor (by decreasing the value of resistors R 1 and R 2) should allow the improvement of the signal shape for the positive values of k. Higher frequency values should also be obtained.

References 1. J. Bayard ‘ Single grounded resistance tunable sinusoidal oscillator’, IEEE Proc. -Circuits Devices Syst. , Vol 151, No. 2, April 2004. 2. Chen, JJ. , Chen, C. C. , Tsao, H. W. , and Liu, S. I. : ’Current mode oscillators usingle current follower’, Electron Lett. , 1991, 27, (22), pp. 2056 -2059 3. Tao, Y. , and Fidler, J. K. : ’ Electronically tunable dual OTA second order sinusoidal oscillators/filters with non-interacting controls: a systematic synthesis approach’, IEEE Trans. Circuits Syst. I, Fundam, Theory App. L, 2000, 47, (2), pp. 117 -129 4. Cam, U. , Kuntman, H. , and Acar, C. : ’On the realization of OTA-C oscillators’, Int. J. Electron, 1998, 84, (3), pp. 313 -326

Special Words Special thanks to the Prof. Dr. Habbash And The teaching assistants