Oscillators are electronic circuits that produce a constant oscillating signal that can be a sinusoid, a square wave or a triangular wave.

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1 Oscillators Oscillators are electronic circuits that produce a constant oscillating signal that can be a sinusoid, a square wave or a triangular wave. Oscillators are classified as linear or harmonic oscillators if their output is a sinusoidal waveform.. Feedback a. RC Wien bridge Phase shift Twin-T Quadrature Robinson b. LC Armstrong/Meissner Hartley Colpitts Gouriet/Clapp ackář Cross-coupled Meacham bridge Seiler c. Crystal Pierce Butler. Negative resistance Oscillators are classified as nonlinear or relaxation oscillators if their output is a square, a sawtooth or a triangular waveform.. Multivibrators a. Astable b. Monostable c. Bistable. Ring. Pearson-Anson or neon lamp. Delay line 5. Royer Some oscillators are simply classified as generators and their output is a square or a triangular waveform: 6. Square wave generator 7. Square/triangle waves generator 8. Triangle/square waves generator

2 Notes:. Oscillators such as Hartley, Colpitts and Gouriet/Clapp can be configured to be oltage-controlled Oscillators (CO). The frequency of the oscillators depends on input voltage. The ackář oscillator is described as a ariable-frequency Oscillator (FO). Its frequency can be tuned with a variable capacitor. Its output is nearly constant over its frequency range of operation. Crystal oscillators were developed in the 9s and 9s and provided better frequency stability than tuned oscillators because they are affected by temperature to a much lower degree (they are more stable). The Tri-tet oscillator is described as an Electron-Coupled Oscillator (ECO).

3 RC oscillators RC oscillators contain resistors and capacitors. They are typically used for low frequency (audio range or up to khz). Wien bridge oscillator The circuit was first conceived by Prussian physicist Max Wien in 89. Because of limitations during his time, the circuit was not constructed until American engineer William Hewlett revisited it in 99 for his master s degree thesis. Shortly after that, Hewlett-Packard was founded and one of the company s first products was a sine-wave oscillator based on the Wien bridge circuit. The final product proved to be very successful and it became very popular because it was stable and inexpensive. R R OS OUT 7 OS + + U AD7 6 5 dc + dc - R C k n R C k n Wien bridge oscillator The Wien bridge oscillator uses positive feedback which is provided by a bandpass filter made up by two RC circuits, one in parallel (R and C ) and one in series (R and C ). R is a variable resistor and R, at the time of Hewlett, was a light bulb ms.5ms.ms.5ms.ms.5ms.ms.5ms.ms.5ms.5ms (U:OUT) Transient response of the Wien bridge oscillator

4 The ideal set of parameters is the following: R R R C C C R R R, the light bulb, has a selected resistance: R 57 The value for R can be easily calculated: R R The gain is given by the following expression: A The oscillating frequency is: o i R R 57 f 7. khz RC k nf The oscillating frequency from the simulation is 6.896kHz. Note: modern Wien bridge oscillators use other nonlinear elements such as diodes, thermistors, field effect transistors or photocells in place of light bulbs.

5 Quadrature oscillator This circuit uses positive and negative feedback to generate two sinusoidal waves of similar properties, one of them being a sine and the other one being a cosine. C through C must be matched. All resistors should also be matched, except for R which must be slightly less than R and R to cause the circuit to oscillate. D through D avoid clipping at the outputs (breakdown voltage is 8.). D D + - Dbreak Dbreak D D C SINE Dbreak Dbreak dc dc u C R 9 - U - OS 6 OUT OS ua7 R k R - U - OS 6 OUT OS + - u + ua7 COSINE k C u Quadrature oscillator s.98s.98s.986s.988s.99s.99s.99s.996s.998s.s (D:) (D:) The oscillating frequency is: f 59Hz RC where R=R =R and C=C =C =C. The oscillating frequency from the simulation is 6Hz. Transient response of the quadrature oscillator 7

6 LC oscillators LC oscillators contain inductors and capacitors. They are typically used for high frequency (radio range or above khz). Hartley oscillator This circuit was invented by American engineer Ralph inton Lyon Hartley in 95. The oscillating frequency of this circuit depends on L, L and C. The Hartley oscillator is the dual circuit of the Colpitts oscillator which follows next. R R dc k k C C Q nf L nf QN.5uH R k R.k C nf C nf L 5.8uH Hartley oscillator -.98ms.98ms.98ms.986ms.988ms.99ms.99ms.99ms.996ms.998ms 5.ms (R:) (C:) Transient response of the Hartley oscillator 8

7 If the inductors are not coupled, L is given by: L L L If the inductors are coupled, L is given by: L L L k L L where k is the coupling coefficient, a number between and. The oscillating frequency for the circuit is given by: f. 9kHz LC 58.H nf The oscillating frequency from the simulation is khz. 9

8 Colpitts oscillator This circuit was invented by American engineer Edwin Henry Colpitts in 98. The oscillating frequency of this circuit depends on C, C and L. The Colpitts oscillator is the dual circuit of the Hartley oscillator discussed above. R dc R k k C Q nf QN C nf R k R.k C nf C L 7.uH nf Colpitts oscillator ms.98ms.98ms.986ms.988ms.99ms.99ms.99ms.996ms.998ms 5.ms (:+) (R:) Transient response of the Colpitts oscillator

9 The oscillating frequency for the circuit is given by: f. 6kHz CC nf nf L 7.H C C nf nf The oscillating frequency from the simulation is khz.

10 Gouriet/Clapp oscillator This circuit was independently discovered and first published by American electrical engineer James Kilton Clapp in 98. However, the circuit was invented by Geoffrey George Gouriet and it was used as early as 98 at the BBC but this was not made public until after World War II due to the fact the circuit was kept secret. Essentially, the Gourier-Clapp oscillator is a Colpitts oscillator with an additional capacitor in series with the inductor. R 9dc R k k C Q nf QN C nf L R uh k R.k C5 nf C C R5 uf uf Meg Gouriet-Clapp oscillator Note: R 5 is placed to force PSpice A/D to start ms 9.98ms 9.98ms 9.986ms 9.988ms 9.99ms 9.99ms 9.99ms 9.996ms 9.998ms.ms (:+) (L:) Transient response of the Gouriet-Clapp oscillator

11 The oscillating frequency for the circuit is given by: khz F F nf F C C C L f 6 7. The oscillating frequency from the simulation is kHz.

12 ackář oscillator This circuit was published in a paper by Czech engineer Jiří ackář in 99 but he attributed the invention of the oscillator that dates back to 95 to a firm called Radioslava in Czechoslovakia. C pf J L uh JN89 C 6pF C nf L 6.uH 5dc C 7.nF ackář oscillator ms.998ms.998ms.9986ms.9988ms.999ms.999ms.999ms.9996ms.9998ms 5.ms (:+) (C:) Transient response of the ackář oscillator The oscillating frequency from the simulation is MHz.

13 Multivibrators Multivibrators are circuits designed to implement a two-state logic system and they can be of three types: astable, monostable and bistable. Astable multivibrators constantly oscillate between two states. Monostable multivibrators can be placed in a transient state by an external signal and return to the initial stable state after a specific time. Bistable multivibrators stay in either of two stable states and alternate between them depending on an external trigger. Astable multivibrator This circuit constantly oscillates between two states. CC CC 5dc R k R 68k R 8k R k + C - - C + nf 5nF Q Q QN QN Astable multivibrator 5..5 SEL>> 5. (C:).5 s ms ms ms ms 5ms 6ms 7ms 8ms 9ms ms (C:) Transient response of the astable multivibrator 5

14 The astable multivibrator frequency depends on the values of R, C, R and C : f 75. Hz T ln 5 R C R C ln 68k nf 8k 5nF The frequency from the simulation is 7.9Hz. As shown in the simulation, the circuit oscillates between two states. Note: if R =R and C =C the duty cycle will be exactly 5%. 6

15 Monostable multivibrator This circuit can be placed in a transient state by an external signal and return to the initial stable state after a specific time. CC CC 5dc R k R 5k R k + C - R 6nF 68k Q Q QN =.7 = TD = ms TR = ns TF = ns PW = ms PER = ms QN Monostable multivibrator 75m 5m 5m SEL>> -m (C:) 5..5 s ms ms ms ms 5ms 6ms 7ms 8ms 9ms ms (C:) (R:) Transient response of the monostable multivibrator 7

16 As shown in the simulation, Q is initially on and Q is off. External signal brings the base of Q down to which turns off Q and turns on Q. When goes back up to.7 the circuits goes back to its initial state. The time the monostable multivibrator stays in the transient state depends on the values of R and C : R C ln 5k 6nF. ms t ln 79 75m 5m 5m (C:) 5..5 SEL>> -. 9.ms 9.5ms 5.ms 5.5ms 5.ms 5.5ms 5.ms 5.5ms 5.ms (C:) (R:) Transient response of the monostable multivibrator (detail) As shown above, the circuit goes back to the initial state after about ms. 8

17 Bistable multivibrator This circuit stays in either of two stable states and it alternates between them depending on an external trigger. This circuit is also referred to as flip-flop because it can store bit of information. CC CC 5dc R k R k R R k k Q Q QN QN =.7 = TD = ms TR = ns TF = ns PW = ms PER = 5ms Reset =.7 = TD = ms TR = ns TF = ns PW = ms PER = 5ms Set Bistable multivibrator 75m 5m 5m (Q:b) (Q:b) 5..5 SEL>> -. s ms ms ms ms 5ms 6ms 7ms 8ms 9ms ms (R:) (R:) Transient response of the bistable multivibrator 9

18 As shown in the simulation, at ms, Q and Q are initially on so the circuit is in an undetermined state. At ms a ms external trigger called Set brings the base of Q down to which turns off Q and turns on Q. At ms a ms external trigger called Reset brings the base of Q down to which turns off Q and turns on Q. The circuit alternates between two states. It is in one state at ms-ms and 6ms- 8ms. It is the opposite state at ms-6ms and 8ms-ms.

19 Square wave generator This circuit uses positive and negative feedback in order to generate a square wave. R k + - C u - + U - - OS 6 OUT 5 7 OS + + ua7 dc dc R k R k Square wave generator. -. ms ms ms 6ms 8ms 5ms 5ms 5ms 56ms 58ms 6ms (R:) Transient response of the square wave generator The oscillating frequency is: f 6Hz R RC ln R The oscillating frequency from the simulation is Hz.

20 Square/triangle waves generator This circuit generates square and triangular waveforms. U integrates the output of U and flips it. + - dc dc C u - + U - - OS 6 OUT 5 7 OS + + ua7 R SQUARE k R R k - + U - - OS 6 OUT 5 7 OS + + ua7 TRIANGLE k Square/triangle waves generator. -.. (U:OUT) SEL>> -. ms ms ms 6ms 8ms 5ms 5ms 5ms 56ms 58ms 6ms (R:) Transient response of the square/triangle waves generator The oscillating frequency is: R f 5Hz R C R The oscillating frequency from the simulation is 55Hz.

21 Triangle/square waves generator This circuit generates square and triangular waveforms. The frequency of the outputs can be modulated by the input voltage so this circuit is a oltage-controlled Oscillator (CO). R C 5k 5nF TRIANGLE 5dc R 5k R ua OS OUT + 7 OS U + + 5k 6 5 ua OS OUT + 7 OS U + + R6 6 5 SQUARE k + - R 5k R7 5k dc dc Q R5 QN k Triangle/square waves generator s ms ms 6ms 8ms ms ms ms 6ms 8ms ms ms ms 6ms 8ms ms (:+) (C:) (U:OUT) Transient response of the triangle/square waves generator For this circuit the ratio R /R must be fixed to /. Reducing the value of C by half doubles the frequency. Increasing the value of by two also doubles the frequency which confirms this is a CO. The oscillating frequency from the simulation is about 5Hz. The circuit can be implemented with a MOSFET instead of a BJT.

555 timer IC The 555 timer IC was designed by Swiss electronics engineer Hans R. Camenzind in 97 or 97 and introduced on the market by Signetics in 97.

Internally, the IC can be implemented with BJTs or MOSFETs. Depending on the manufacturer and the implementation, the 555 timer IC has transistors, resistors and diodes.

22 555 timer IC The 555 timer IC was designed by Swiss electronics engineer Hans R. Camenzind in 97 or 97 and introduced on the market by Signetics in 97. It is a classical circuit and it can be configured to function just like a multivibrator, an oscillator or a flip-flop with the addition of a few external components such as capacitors and resistors. Internally, the IC can be implemented with BJTs or MOSFETs. Depending on the manufacturer and the implementation, the 555 timer IC has transistors, resistors and diodes. The chip is available in an 8-pin configuration. The 556 version of the timer has pins and it contains 555 chips. 558 and 599 versions come in 6-pin chips and they contain modified 555 chips. The NE555 was the first 555 timer IC chip, it was released by Signetics and it was designed for operation between C and +7 C. The SE555 was designed for the military with a temperature range of -55 C to +5 C. A suffix was used for a plastic package and a T suffix was used for the metal package so that, for example, the SE555T was a military metal packaged 555 timer IC. The 555 timer IC has the following pins: The chip can be configured to work in the following modes: Astable or free-running mode Monostable or one-shot mode Bistable or Schmitt-trigger mode For the following simulations, the TLC555 by Texas Instruments is configured to work in the astable, monostable and bistable modes. Pin 5, the control pin, is always connected to a nf capacitor that goes to ground. 5

23 The internal schematic of the BJT implementation of the LM555 timer IC by Texas Instruments The internal schematic of the CMOS implementation of the TLC555 timer IC by Texas Instruments 6

24 Astable mode The astable or free-running mode produces an astable multivibrator. For this circuit, the only external components needed are resistors and capacitors. R 5dc R.k k Cont dd Reset Disch Out Thresh Trig Gnd U TLC555 C C n 5n The 555 timer IC in astable mode ms 9.55ms 9.6ms 9.65ms 9.7ms 9.75ms 9.8ms 9.85ms 9.9ms 9.95ms.ms (U:OUT) Transient response for the 555 timer IC in astable mode The oscillating frequency is: f 8. 7 khz ln C R R ln5nf.k k The on-time for the pulse is: t on C R R ln5nf.k k.7s ln The off-time for the pulse is: t off C R ln5nf k.s ln The oscillating frequency from the simulation is 7.5kHz, the on-time is 6µs and the off-time is µs. 7

25 Monostable mode The monostable or one-shot mode produces a monostable multivibrator. For this circuit the only external components needed are resistor and capacitors. Pin, the trigger pin, is active low. When the pin is brought low, it will initiate the pulse. R 5dc C.k C 5 8 Cont dd 7 Reset Disch Out 6 Thresh Trig Gnd U TLC555 = 5 = TD = 5ms TR = ns TF = ns PW = us PER = m 5n n The 555 timer IC in monostable mode (:+).5 SEL>>.9ms.9ms.9ms.96ms.98ms 5.ms 5.ms 5.ms 5.6ms 5.8ms 5.ms (U:OUT) (C:) The time of the pulse is: Transient response for the 555 timer IC in monostable mode t p R C ln.k 5nF 5.8s ln The pulse ends when the voltage across C is / of the supply voltage. The time of the pulse from the simulation is 55.µs. 8

26 Bistable mode The bistable or Schmitt-trigger mode produces a bistable multivibrator. For this circuit the only external component needed is capacitor. Pin, the trigger pin, is active low. When the pin is brought low, it will set the output to a high state. Pin, the reset pin, is also active low. When the pin is brought low, it will reset the output to a low state. 5dc = 5 = TD = ms TR = ns TF = ns PW = us PER = m SET = 5 = TD = 7ms TR = ns TF = ns PW = us PER = m RESET C n 5 8 Cont dd Reset 6 Disch Out 7 Thresh Trig Gnd U TLC555 The 555 timer IC in bistable mode 5..5 SEL>> (U:TRIG) 5..5 (:+) 5..5.ms.5ms.ms.5ms 5.ms 5.5ms 6.ms 6.5ms 7.ms 7.5ms 8.ms (U:OUT) Transient response for the 555 timer IC in bistable mode 9

PHYS225 Lecture 18. Electronic Circuits

PHYS225 Lecture 18. Electronic Circuits PHYS225 Lecture 18 Electronic Circuits Oscillators and Timers Oscillators & Timers Produce timing signals to initiate measurement Periodic or single pulse Periodic output at known (controlled) frequency