 # Clock Generation 1/16/12.

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Clock Generation 1/16/12

Required Materials

Clock Generation Astable Mulivibrator Inverter-Based Oscillator
555 Timer Circuit

Inverter-Based Oscillator

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

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.

11 Stage Oscillator

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

Astable Multivibrator Circuit

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)

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.

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.

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

Summary

Control the pulse duration

Sample Waveform

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

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.

Frequency of an Astable Oscillator

Summary of astable timer

Control the frequency of the astable timer

What if you need a clock?

Square Wave Oscillator Using 555 Timer IC

A Closer Look at the Square Wave Generator

Sawtooth Oscillator

Low Duty Cycle

Pinout Diagram