1. 7/20/2016 Subject Name: LINEAR IC’s AND APPLICATIONS Subject Code:10EC46 Prepared By: Aparna.P Department: Electronics and Communication Date:30-3-2015

2. UNIT 6 NON LINEAR CIRCUIT APPLICATIONS

3. Introduction Crossing detectors Inverting Schmitt trigger Monostable multivibrator Astable multivibrator Active Filters: LPF HPF

4. Introduction Op – Amps are used in circuits where the output switched between positive and negative values. In zero crossing detector, one input is at ground and input is applied to the other input. The Schmitt trigger is having upper and lower input voltage levels that trigger the output to change from one level to another level. Astable and monostable multivibrators are desig by adding components to crossing detectors or schmitt trigger circuits.

5. Inverting zero Crossing Detector The inverting zero crossing detector is shown in fig. The input is applied to the inverting i/p terminal and the non inverting i/p is connected to ground. When the input is positive the output is –V sat. When the input is negative the output is +V sat.

6. Non Inverting zero Crossing Detector The non inverting zero crossing detector is shown in fig. The input is applied to the non inverting i/p and the inverting i/p is connected to the ground. If the input is positive the output is +V sat. If the input is negative the output is –V sat.

7. Crossing Detectors Voltage level crossing detector: If we are applying some reference voltage instead of zero then that is called voltage level detector. If the input voltage is greater than the reference voltage the output is –V sat. If the input voltage is less than the reference voltage the output is –V sat. Here we are having only one reference voltage.

8. Capacitor coupled crossing detector The capacitor coupled crossing detector has the non inverting terminal is connected to ground via the resistor R 1 to provide a DC bias current path to the op-amp. Inverting terminal is biased to a voltage V B which is grater than zero. When no input is applied the output is -Vsat. If the input voltage is greater than V B the output will shift from –V sat to +V sat If the input voltage is less than the V B the output shift from +V sat to -V sat The resistor is selected as The input to the capacitor may not be symmetrical but the output of capacitor will be symmetrical.

9. Capacitor coupled crossing detector The capacitor value can be chosen very much less compare to the R 1

10. Inverting Schmitt Trigger Here we can provide two triggering points. When the output is at +Vsat the voltage across R2 is positive. And it is compared with the voltage at inverting i/p terminal. If the inverting i/p voltage is greater than the non inverting i/p voltage the output is changed from +Vsat to –Vsat.

11. Inverting Schmitt Trigger The Schmitt trigger characteristics shown in fig. Design R 2 = trigger voltage/I 2 R 1 = (Vo- trigger voltage)/I 2 We can also adjust these trigger points by using diodes in the circuit.

12. Multivibrators A multivibrator is an electronic circuit used to implement a variety of simple two-state systems such as Oscillators, timers and flip- flops. Astable, in which the circuit is not stable in either state it continually switches from one state to the other. It functions as a Relaxation Oscillator. Monostable, in which one of the states is stable and the other state is unstable. A trigger pulse causes the circuit to enter the unstable state. After entering the unstable state, the circuit will return to the stable state after a set time. Such a circuit is useful for creating a timing period of fixed duration in response to some external event. This circuit is also known as a one shot. Bistable, in which the circuit is stable in either state. It can be flipped from one state to the other by an external trigger pulse. This circuit is also known as a Flip-Flop It can be used to store one bit of information.

13. Astable Multivibrator Assume the output is at positive the capacitor starts charging. This voltage is compared with the Non inverting terminal voltage, if it is grater the output is shifted from positive to negative. The capacitor starts charging in another direction, it is compared with the non inverting terminal voltage, if it is less then the output is shifted to the positive value. It will produce a square wave so it is also called as free running oscillator.

14. Astable Multivibrator Input and output characteristics of astable multivibrator.

15. Monostable Multivibrator The input square wave is applied to the high pass filter (RC network ) act as differentiator and the output is applied to the diode which allows only the negative pulses. When the output is in + V sat the diode D 1 is in forward biased and the capacitor charges up to the diode cut in voltage. The same output is applied to the potential divider. When the inverting terminal voltage is greater than the non inverting terminal voltage the output will shift from positive to negative voltage.

16. Monostable Multivibrator Then the diode will be reverse biased and the capacitor charges in the negative direction. Once this voltage is less than the non inverting terminal voltage the output change to positive with out any triggering pulse. The falling part of the output pulse from MMV is often used to trigger another pulse generator circuit thus producing a pulse delayed by a time T with respect to the input pulse. MMV is used for regenerating old and worn out pulses. Various pulses used in computers and telecommunication systems become somewhat distorted during use. An MMV can be used to generate new, clean and sharp pulses from these distorted and used ones.

17. Active Filters: Low pass Filter Which allows low frequencies and attenuate high frequencies is called low pass filter. Passive low pass filter consists of only passive elements. here loading effect will present. To avoid this we are using active element. For lower frequencies the capacitor reactance is very high we will get the output. For higher frequencies the capacitor reactance is very low the output will be small. At cutoff frequency the gain will be 3dB down to the maximum value. The slope of the curve is 20dB/dec or 6dB/octave.

18. Active Filters: Low pass Filter The characteristics of the first order and second order low pass filters are shown in fig. The rate at which the slope of the characteristics will change above the cutoff frequency is called roll off factor. R can be calculated as The capacitor can be calculated as

19. Second order Low pass Filter Second order LPF is shown in fig. R 4 and C 2 will produce 20dB/dec and C 1 with R 3 and R 4 will produce another 20dB/dec. Total of 40dB/dec is the total roll off rate. X C1 = √2 R 2 at fc And C 2 = 2C 1

20. First order High pass Filter The first order high pass filter is shown in fig. It will allow high frequencies and attenuate low frequencies.

21. Second order High pass Filter The second order high pass filter is shown In fig. C 2 and R 3 gives 20dB/dec roll off rate and R 4 with C 1 and C 2 gives another 20dB/dec roll off rate so total it gives the roll off rate of 40dB/dec The frequency response of the first order and second order filters shown in fig.