1. Clock Generation
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2. Required Materials

3. Clock Generation Astable Mulivibrator Inverter-Based Oscillator
555 Timer Circuit

4. Inverter-Based Oscillator

5. Delay Per Stage of the Inverter
(273 pS)
(395 ps)
Period: =122 pS, Delay per stage (TD): =20 pS. Period is 2NTD

6. Oscillation Frequency Calculation
fosc=2.14 GHz
Tosc=467 pS=2NTD
TD=20 pS
N=Tosc/(2TD)=467 pS/(2 20)=11.68
N must be odd.
Choose N as 11.

7. 11 Stage Oscillator

8. 11 Stage Oscillator
Period: nS nS=0.449 nS, Freq=2.227 GHz

9. Astable Multivibrator Circuit

10. 555 configured as a monostable circuit
+ is the pos. of the battery=9V
Resistive divider R R R
+3 V
comparator
FF=flip-flip, depicted as a DPDT switch.
+6 V
- is the neg. term. of the battery=0V
(Assumption: pin #3 is connected to 0V)

11. Comparator We will assume that the FF is in the “up” position when
the 555 timer IC is powered up.
comparator
Each comparator compares two inputs and delivers an output depending on whether the inputs are similar or different.
“UP” and “DOWN” remind you what each comparator does when it is activated.

12. 555 configured as a monostable circuit
0 V
Step 1: Ground pin 2,
The output voltage of comparator A goes up
Pin 7 will be disconnected from the ground.
Step 2:
C4 will get charged through R4.
The voltage at pin 6 will go up.
0 V
You don’t need to memorize this. Just look
at switch drawn in the FF.

13. 555 configured as a monostable circuit
Step 3:
The voltage at pin 6 will take some time
to rise up to 9.
Step 4:
Note that the voltage at pin 5 is fixed to
2/3 of 9 V. When the voltage at pin 6
exceeds the voltage at pin 5, the
output (pin 3) will be grounded and pin 7
will again be connected to ground.
(You don’t need to memorize this. Just
look at the switch in the flipflop.)
0 V
+6V

14. Summary

15. Control the pulse duration

16. Sample Waveform

17. 555 configured as an astable circuit
Explanation on the next slide.

18. Operations of astable timer
Let’s assume that C1 is initially grounded.
Step 1: A low voltage at pin 2 causes the
Comparator to send a “down” signal to FF.
Step 2: The output voltage at (pin 3) goes up
and the pin 7 is disconnected from R2.
(Again, look at the switch in the FF)
Step 3: C1 gets charged up through R1+R2.
Step 4: The voltage across C1 goes up.
Step 5: The voltage at pin 6 exceeds the voltage
at pin 5.
Step 6: The comparator sends a “high” signal
to the flip flop.
Step 7: The voltage of Pin 7 goes to ground and
The voltage goes to ground.
Step 8: C1 discharges through R2.
Step 9: Go back to step 1.

19. Frequency of an Astable Oscillator

20. Summary of astable timer

21. Control the frequency of the astable timer

22. What if you need a clock?

23. Square Wave Oscillator Using 555 Timer IC

24. A Closer Look at the Square Wave Generator

25. Sawtooth Oscillator

26. Low Duty Cycle

27. Pinout Diagram