For a non-inverting Scmitt trigger VHL and VLH formula are as given below:
---------(i)
and
---------(ii)
Where Vsat is the positive rail saturation voltage and V- is the voltage at inverting pin of the op amp. ( Refer the figure below)
Given VHL = 0 V and VLH = 5 V. Adding equations (i) and (ii) we get
substituting VHL and VLH we get
-------------(iii)
subtracting equation (ii) from (i) we get
Assuming Vsat = 8 volts ( considering the drop in the op amp) we get
Thus if R2 = 5 kilo Ohms R1 = 16 kilo Ohms.
Substituting in equation (iii) we get
or
We use resistor divider to get the required V- voltage. If R3 and R4 make up the resistor divider as shown
Then V- is given by
Thus if R4 = 1 kilo ohms R3 = 3.7 kilo ohms ( approximately ).
With these values the non-inverting schmitt trigger circuit looks as follows
Note that the input source is just a test sine wave of amplitude 9 volts. The output of the circuit is given below:
Next we design an op- amp integrator.
By the concept of virtual short, current through resistor R is
In this case we want I < 1 mA. Vin comes from the schmitt trigger with amplitude 8 volts thus
So R should be greater than or equal to 8 kilo ohm. Lets take R = 10 kilo Ohms.
We want a change of voltage of 5 volts at the output of integrator when an input of 8 volts drive it in a time of 10 us. The output of integrator is given by
We want the output to change by 5 volts in 10 us when input is 8 volts. Using these values
Rigging up the circuit along with the schmitt trigger we get the circuit given below.
Note that in the schematic LM741 is used but it is not recommended for such a high frequency application. For demonstration the frequency is lowered by using 1.6 uF capacitor instead of 1.6 nF. The plot below depicts the output. The purpose of using LM741 was its a common op amp and is available everywhere.
I hope it helps. For any doubts or queries that you have, leave a comment below, I'll be happy to help. All the best. :)
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