1. ELECTRONIC
COMMUNICATIONS
SYSTEMS
PART 2-1
Fall 2001
ENZO PATERNO

2. SIGNAL
GENERATION
Fall 2001
ENZO PATERNO

3. SIGNAL GENERATION OSCILLATORS PHASE-LOCKED LOOPS
FREQUENCY SYNTHESIZERS
Fall 2001
ENZO PATERNO

4. OSCILLATORS THUS ……. OSCILLATORS FEEDBACK OSCILLATORS
MANY ELECTRONIC COMMUNICATIONS SYSTEMS
(MODULATORS) REQUIRE CONTINUOUS PERIODIC WAVEFORMS (SINUSOIDAL AND NONSINUSOIDAL)
THUS …….
OSCILLATORS
FEEDBACK OSCILLATORS
FUNCTION GENERATORS
VCO
Fall 2001
ENZO PATERNO

5. THUS ……. FREQUENCY SYNTHESIS PHASE-LOCKED LOOPS LSI PRESCALERS
MANY ELECTRONIC COMMUNICATIONS SYSTEMS
REQUIRE A NUMBER ( > 1 ) OF THESE PERIODIC WAVEFORMS AT DIFFERENT FREQUENCIES RELATED TO EACH OTHER (SCALAR MULTIPLES )
THUS …….
FREQUENCY SYNTHESIS
PHASE-LOCKED LOOPS
LSI PRESCALERS
Fall 2001
ENZO PATERNO

6. THUS ……. PHASE-LOCKED LOOPS FREQUENCY SYNCHRONIZATION
MANY ELECTRONIC COMMUNICATIONS SYSTEMS
REQUIRE A NUMBER OF PERIODIC WAVEFORMS OF VARIOUS FREQUENCIES THAT MUST BE SYNCHRONIZED TO EACH OTHER.
THUS …….
FREQUENCY SYNCHRONIZATION
PHASE-LOCKED LOOPS
Fall 2001
ENZO PATERNO

7. OSCILLATORS
Fall 2001
ENZO PATERNO

8. OSCILLATORS OSCILLATE: TO VIBRATE, TO FLUCTUATE
BETWEEN ONE STATE TO ANOTHER
OSCILLATOR: IS A DEVICE THAT PRODUCES
OSCILLATIONS (i.e. GENERATES A REPETITIVE
WAVEFORM)
FREE-RUNNING OSCILLATOR: IS A SELF_SUSTAINING
OSCILLATOR (OUTPUT WAVEFORM IS CONTINUOUS &
REPETITIVE). NO EXTERNAL INPUT REQUIRED
TRIGGERED/ONE-SHOT OSCILLATOR: REQUIRES AN
EXTERNAL INPUT SIGNAL (TRIGGER). BURSTY OUTPUT
Fall 2001
ENZO PATERNO

9. FEEDBACK OSCILLATORS A FEEDBACK OSCILLATOR IS AN AMPLIFIER WITH A
FEEDBACK LOOP
A FREE-RUNNING OSCILLATOR IS AN EXAMPLE
OF A FEEDBACK OSCILLATOR WITH POSITIVE
FEEDBACK (REGENERATIVE FEEDBACK)
Fall 2001
ENZO PATERNO

10. FEEDBACK OSCILLATORS UNTUNED OSCILLATOR WIEN-BRIDGE OSCILLATOR
HARTLEY OSCILLATOR
COLPITTS OSCILLATOR
CLAPP OSCILLATOR
CRYSTAL OSCILLATOR
FUNCTION GENERATOR
VCO
Fall 2001
ENZO PATERNO

11. APPLICATION CRITERIA DESIRED FREQUENCY OF OPERATION
REQUIRED FREQUENCY STABILITY
VARIABLE OR FIXED FREQUENCY
DISTORTION REQUIREMENTS
DESIRED OUTPUT POWER
PHYSICAL SIZE
DIGITAL OR ANALOG APPLICATIONS
RELIABILITY & DURABILITY
DESIRED ACCURACY
Fall 2001
ENZO PATERNO

12. FEEDBACK CIRCUIT MODEL
AMPLIFIER +
R(S)
E(S)
C(S)
G(S)
INPUT
OUTPUT
FEEDBACK
B(S)
H(S)
WHEN THE ANALYSIS OF FEEDBACK SYSTEMS IS DONE IN THE FREQUENCY DOMAIN, (RATHER THAN THE
TIME DOMAIN), WE CALL THIS ANALYSIS APPROACH
THE TRANSFER FUNCTION APPROACH. IT INVOLVES
LAPLACE TRANSFORMS WHERE:
TRANSFER FUNCTION
Fall 2001
ENZO PATERNO

13. FEEDBACK CIRCUIT MODEL
AMPLIFIER +
R(S)
E(S)
C(S)
G(S)
INPUT
OUTPUT
FEEDBACK
B(S)
H(S)
G(S): FORWARD TRANSFER FUNCTION
H(S): FEEDBACK TRANSFER RATIO
R(S): INPUT SIGNAL
C(S): OUTPUT SIGNAL
CLOSED_LOOP
TRANSFER FUNCTION
Fall 2001
ENZO PATERNO

14. FEEDBACK ANALYSIS WITH: WITH: USING: BECOMES: AND: ENZO PATERNO
Fall 2001
ENZO PATERNO

15. FEEDBACK ANALYSIS
CLOSED-LOOP TRANSFER FUNCTION
Fall 2001
ENZO PATERNO

16. OP-AMP FEEDBACK CIRCUIT
Aol
AMPLIFIER +
Vin
Vout
FEEDBACK B
Aol: OPEN LOOP GAIN, Vout: OUTPUT
(NO FEEDBACK)
B: FEEDBACK RATIO, Vin: INPUT
CLOSED
LOOP
GAIN
Fall 2001
ENZO PATERNO

17. OP-AMP FEEDBACK CIRCUIT
Vin
Vout
BAol > 0, Acl , NEGATIVE FEEDBACK
(DEGENERATIVE ACTION)
BAol < 0, | BAol | < 1, Acl , POSITIVE FEEDBACK
(REGENERATIVE ACTION)
BAol = 1, , OSCILLATION
WHEN THE CIRCUIT OSCILLATES, Vin CAN THEN BE
REMOVED.
Fall 2001
ENZO PATERNO

18. FEEDBACK OSCILLATORS REQUIREMENTS
AMPLIFICATION ONE OR MORE ACTIVE DEVICES
CAPABLE OF VOLTAGE AMPLIFICATION (GAIN)
POSITIVE FEEDBACK MUST HAVE THE CORRECT
PHASE AND AMPLITUDE SO TO MAINTAIN A
CONTINUOUS SUSTAINED OSCILLATION
(PREVENT CEASING OF OSCILLATION OR
AMPLIFIER SATURATION)
FREQUENCY CONTROL NEED TO BE ABLE CONTROL
FREQUENCY OF OPERATION
POWER SOURCE POWER SUPPLY TO POWER CIRCUIT
Fall 2001
ENZO PATERNO

19. FREE RUNNING OSCILLATOR
FEEDBACK NETWORK
B(f)
FEEDBACK LOOP
A(f)
AMPLIFIER
Vin’(t)
Vout(t)
POWER
SOURCE
CONTINUOUS OSCILLATIONS
A(f): AMPLIFICATION
B(f): FEEDBACK
FUNCTION OF FREQUENCY.
A(f), B(f) ALTER THE MAGNITUDE AND PHASE OF THE SIGNAL
NO INPUT SIGNAL - ONLY OUTPUT FEEDBACK
Fall 2001
ENZO PATERNO

20. FEEDBACK ANALYSIS ORIGINALLY, WITH INITIAL SIGNAL Vin’(t)
(AT POWER UP)
PRODUCES A NEW Vin’’(t) ( ECHOED INPUT SIGNAL)
AFTER n TRIPS AROUND THE LOOP, THE NEW ECHO:
Fall 2001
ENZO PATERNO

21. FEEDBACK ANALYSIS NET LOOP GAIN THE ECHO FADES AWAY IF
NEGATIVE FEEDBACK IF
THE ECHO GROWS WITH TIME
POSITIVE FEEDBACK IF
THE ECHO REMAINS CONSTANT
OSCILLATION
Fall 2001
ENZO PATERNO

22. BARKHAUSEN CRITERION FOR A FEEDBACK CIRCUIT TO SUSTAIN OSCILLATIONS,
THE NET VOLTAGE GAIN AROUND THE FEEDBACK LOOP
(LOOP GAIN) MUST BE UNITY
THE NET PHASE SHIFT AROUND THE LOOP IS A
POSITIVE INTEGER MULTIPLE OF 360 degrees
(i.e. Vout(t) & Vin(t) ARE IN PHASE = ZERO DEGREES)
Fall 2001
ENZO PATERNO

23. INITIAL CONDITIONS THE FEEDBACK PROCESS HAS TO BE STARTED BY
AN INITIAL SMALL FLUCTUATION OF THE
CORRECT FREQUENCY
FORTUNATELY, ANY SMALL BRIEF FLUCTUATION
WHICH CONTAINS SOME POWER AT FREQUENCY, f,
WILL START A SEQUENCE OF STEADY OR GROWING
OSCILLATIONS
SWITCHING THE OSCILLATOR AMPLIFIER ON IS
ENOUGH TO INITIATE THE FEEDBACK PROCESS.
AS WELL, THE INTERNAL UNCORRELATED NOISE
IS ENOUGH TO INITIATE THE PROCESS (NO EXTERNAL
SIGNAL REQUIRED TO INITIATE THE OSCILLATION)
Fall 2001
ENZO PATERNO

24. WIEN-BRIDGE OSCILLATOR
Aol R C R1
Fall 2001
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25. WIEN-BRIDGE OSCILLATOR
Vout R R2 C
Vin
Aol
Vout R C R1
NON-INVERTING AMPLIFIER
Fall 2001
ENZO PATERNO

26. NON-INVERTING AMPLIFIER
VOLTAGE DIVIDER
(FEEDBACK RATIO)
SINCE 1
Fall 2001
ENZO PATERNO

27. WIEN-BRIDGE OSCILLATOR
Vout = Acl Vin R Zs R2 C
Vin
Acl A R C Zp R1
Fall 2001
ENZO PATERNO

28. WIEN-BRIDGE OSCILLATOR
Fall 2001
ENZO PATERNO

29. WIEN-BRIDGE OSCILLATOR
MULTIPLY NUMERATOR & DENOMINATOR BY:
Fall 2001
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30. WIEN-BRIDGE OSCILLATOR
Fall 2001
ENZO PATERNO

31. WIEN-BRIDGE OSCILLATOR
MULTIPLY NUMERATOR & DENOMINATOR BY:
Fall 2001
ENZO PATERNO

32. WIEN-BRIDGE OSCILLATOR
WE KNOW THAT: B
BARKHAUSEN CRITERION REQUIRES:
ZERO PHASE SHIFT
UNITY GAIN
Fall 2001
ENZO PATERNO

33. WIEN-BRIDGE OSCILLATOR
ZERO PHASE SHIFT CRITERIA:
FOR A ZERO PHASE,
Im PART IS ZERO
THUS;
PHASE = 0, WHEN:
Fall 2001
ENZO PATERNO

34. WIEN-BRIDGE OSCILLATOR
PHASE = 0, WHEN:
Fall 2001
ENZO PATERNO

35. WIEN-BRIDGE OSCILLATOR
Fall 2001
ENZO PATERNO

36. WIEN-BRIDGE OSCILLATOR
UNITY GAIN CRITERIA (WHILE PHASE = 0): B
THUS;
AND;
Fall 2001
ENZO PATERNO

37. WIEN-BRIDGE OSCILLATOR
Aol
Acl = 3 R C R1
WE WANT Acl = 3, THUS R2/R1 = 2
Fall 2001
ENZO PATERNO

38. WIEN-BRIDGE OSCILLATOR
TO GUARANTEE THAT THE AMPLIFER WILL NEVER
GET INTO SATURATION (DUE TO OVER REGENERATION)
AND TO GUARANTEE THAT THE AMPLIFIER WILL NOT
CEASE TO OSCILLATE (DUE TO OVER DEGENERATION =
STARVATION), WE DESIRE FOR R1 TO BE VARIABLE.
AUTOMATIC GAIN CONTROL
Fall 2001
ENZO PATERNO

39. WIEN-BRIDGE OSCILLATOR
Aol
Acl = 3 R C R1 R1
Rectifier
FET IS USED IN ITS VOLTAGE
CONTROLLED RESISTANCE
REGION
Fall 2001
ENZO PATERNO

40. EXAMPLE FOR THE WIEN OSCILLATOR: FIND AT fo, R = Xc, THUS Zs IS:
Fall 2001
ENZO PATERNO

41. EXAMPLE FOR THE WIEN OSCILLATOR: AT fo, R = Xc, THUS Zp IS:
Fall 2001
ENZO PATERNO

42. EXAMPLE FOR THE WIEN OSCILLATOR: AT fo, R = Xc, THUS B IS: +
Fall 2001
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43. EXAMPLE FIND THE PHASE ANGLE FOR A FREQUENCY ONE OCTAVE ABOVE fo:
Fall 2001
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44. EXAMPLE FIND THE PHASE ANGLE FOR A FREQUENCY ONE OCTAVE ABOVE fo:
Fall 2001
ENZO PATERNO

45. EXAMPLE FIND THE PHASE ANGLE FOR A FREQUENCY ONE OCTAVE ABOVE fo:
Fall 2001
ENZO PATERNO

46. TUNED OSCILLATORS TUNED OSCILLATORS ARE OSCILLATOR CIRCUITS
THAT UTILIZE LC TANK CIRCUITS
THE FREQUENCY OF OPERATION OF AN LC TANK
CIRCUIT IS THE RESONANT FREQUENCY OF THE
PARALLEL LC NETWORK
Fall 2001
ENZO PATERNO

47. HARTLEY OSCILLATOR L C THE FREQUENCY OF OSCILLATION IS: ENZO PATERNO
Fall 2001
ENZO PATERNO

48. COLPITTS OSCILLATOR THE FREQUENCY OF OSCILLATION IS: ENZO PATERNOCa L Cb
THE FREQUENCY OF OSCILLATION IS:
Fall 2001
ENZO PATERNO

49. FREQUENCY STABILITY FREQUENCY STABILITY IS THE ABILITY OF AN
OSCILLATOR TO REMAIN AT A FIXED FREQUENCY
SHORT TERM STABILITY IS A FUNCTION OF
FLUCTUATIONS OF DC OPERATING VOLTAGES IN THE
OSCILLATOR CIRCUIT MAKEUP
LONG TERM STABILITY IS A FUNCTION OF COMPONENT
AGING (“LIFE_SPAN”)
STABILITY IS POOR FOR THE RC PHASE SHIFT
OSCILLATOR (WIEN) AND THE LC TANK CIRCUIT
OSCILLATORS (HARTLEY, COLPITTS)
Fall 2001
ENZO PATERNO

50. FREQUENCY STABILITY FREQUENCY STABILITY IS GIVEN AS A PERCENTAGE
OF CHANGE IN FREQUENCY (TOLERANCE)
EXAMPLE:
COMMERCIAL FM BROADCAST STATIONS: CARRIER
FREQUENCIES MUST BE WITHIN
(88 MHz MHz)
COMMERCIAL AM BROADCAST STATIONS: CARRIER
FREQUENCIES MUST BE WITHIN
(535 kHz kHz)
Fall 2001
ENZO PATERNO

51. FREQUENCY STABILITY FREQUENCY STABILITY IS ALSO GIVEN IN TERMS
OF PARTS PER MILLION, PPM.
THE MOST COMMON STABILITY VALUES ARE 25, 50, 100
PPM. THE 100 PPM STABILITY FACTOR IS THE MOST
POPULAR AS IT IS SUFFICIENT TO RUN
MICROPROCESSORS.
TELECOMMUNICATION SYSTEMS REQUIRE A TIGHTER
STABILITY (i.e. 50 PPM, 25 PPM, 15 PPM)
THE LOWER THE PPM, THE MORE EXPENSIVE IS THE
CLOCK OSCILLATOR. PRECISION OSCILLATOR (5 PPM)
Fall 2001
ENZO PATERNO