unit 3.pptx
- 1. SINUSOIDAL OSCILLATOR An oscillator is an electronic circuit that produces a periodic signal. Sinusoidal Oscillator produces sine wave as output. It converts the input energy from a DC source into an AC output energy of a periodic signal. This periodic signal will be having a specific frequency and amplitude.
- 2. SINUSOIDAL OSCILLATOR □ The loop gain Avβ of oscillator must be greater than or equal to unity. □ The total phase shift of a sinusoidal oscillator must be either 00 or 3600
- 3. RC Phase Shift Oscillator
- 6. The negative sign indicates a phase shift of 180° Thus circuit will work as an oscillator which will produce a sinusoidal waveform if the gain is 29 and total phase shift around a loop is 360°. audio frequency range i.e. about 20 Hz up to 100 kHz. At this Frequency
- 7. RC PHASE SHIFT OSCILLATOR The op-amp is operating in inverting mode. It provides a phase shift of 1800. Each RC section provides a phase shift of 600. The circuit provides a total phase shift of 3600 at some frequency. The output frequency of a RC phase shift oscillator is f=1/(2ΠRC√6) The gain Av of an inverting amplifier should be greater than or equal to -29, □ i.e., −Rf/R1≥−29
- 9. Op-amp is operating in Non-inverting mode. it provides a phase shift of 00 So, the feedback network present in the above circuit should not provide any phase shift. Have to balance the bridge in such a way that there should not be any phase shift. So, the above circuit provides a total phase shift of 00 at some frequency. The output frequency of Wien bridge oscillator is f=1/2ΠRC The gain Av of the non-inverting amplifier should be greater than or equal to 3 □ i.e.,1+Rf/R1≥3 WIEN BRIDGE OSCILLATOR
- 10. To satisfy Barkhausen criterion that Aβ ≥ 1 it is necessary that the gain of the noninverting op-amp amplifier must be minimum 3. R1, R2 and C1, C2 are not equal R1, R2 and C1, C2 are equal
- 11. Peak Detector Compute the peak value of the input. Circuit follows the voltage peak and stores the highest value on capacitor. When Vi>Vc , diode D forward biased and he circuits acts asvoltage follower. When Vi<Vc , Diode D reverse biasedand the capacitor holds the charge .
- 12. Peak Detector Capacitor voltage can be reset by connecting low leakage MOSFET switch across the capacitor.
- 13. Positive Clipper Clipping level is determined by Vref Portion of output voltage Vo > Vref is clipped off.
- 14. Positive Clipper
- 15. Negative Clipper Clipping level is determined by Vref Portion of output voltage Vo < Vref isclipped off.
- 16. Negative Clipper
- 17. Clamper DC inserter or dc restorer Output is clamped to adesired dc level If dc level is positive – positive clamper If dc level is negative – negative clamper Clamper circuit with variable positive dc voltage applied at the + terminal is shown
- 18. Clamper
- 19. Clamper For positive Vref ,the V’ispositive , hence Diode D forward biased, circuit acts asvoltage follower Vo = +Vref Vi = Vm.Sin(wt) During negative half cycle of Vi, diode D conducts Capacitor gets charged through diode D to negative peak voltage of Vm
- 20. Clamper For positive half cycle of Vi, D is reverse biased. Capacitor retains at voltage of Vm. SinceVi is in series with C, the output voltage is equal to Vi+Vm. Total output voltage = Vi+Vm+Vref
- 21. Clamper
- 22. Sample and Hold Circuit Samples an input signal and holds on to its last sampled value until next sample. The n-channel E-MOSFET acts aswitch controlled by Vc. Vi to be sampled is applied to the drain of MOSFET and Vc is applied to its gate. When Vc is positive, MOSFET turns ON and capacitor charges to instantaneous value of Vi
- 23. Sampleand Hold Circuit ⚫ When Vc is Zero, E-MOSFET turns OFF ⚫ Capacitor faces high input impedance of A2. ⚫ Capacitor holds the voltage across it.
- 24. Sampleand Hold Circuit Sample period Ts – Voltage across the capacitor is equal to input Voltage. Hold period TH – capacitor voltage ished constant. Frequency of the Vc should be higher than input. Atleast It should be twice that of the frequency of input signal