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Signal Generators

Oscillators

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HW:

Due Friday Nov. 9 13.4,13.14,13.23,13.27

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SIGNAL GENERATORS

/OSCILLATORSA positive-feedback

loop is formed by an

amplifier and afrequency-selective

network

In an actual oscillator circuit, no input signalwill be present

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Oscillator-frequency stability

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Limiter Ckt Comparator

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Wien-bridge oscillator

without amplitudestabilization.

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Wien bridge w/ Amp. Stabil.

limiter used for amplitude control.

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Alternate Wien bridge stabil.

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Phase Shift Oscillator

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Phase Shift. Osc. W/ Stabil.

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Quad Osc. Circuit

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Active Tuned Osc.

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OPAMP based Tuned Amp. Osc.

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Colpitts and Hartley Oscillators

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Equiv. Ckt

To simplify the analysis, negtlect Cm and rp

Consider Cp to be part ofC2, and include ro inR.

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Collpits Oscillator

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Piezzoelectric Crystal

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Pierce Oscillator

CMOS inverter as an amplifier.

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Bistable Operation

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Bistable

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Hysteresis

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Noisy Signal

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Limiter circuits = more precise output levels forbistable circuit.

R according to current required for the proper

operation of the zener diodes.

a) L+ = VZ1

+ VD andL=

(VZ2+ VD),

(b)L+ = VZ+ VD1+ VD2

andL=

(VZ+ VD3+ VD4

).Limiter

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Abistable multivibrator with inverting transfer

characteristics in a feedback loop with an RC circuit

results in a square-wave generator.

Astable w/ feedback

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The circuit obtained when

the bistable multivibrator is

implemented with the circuit

c) Waveforms at

various nodes of the

circuit in (b).

(This circuit is

called an

astable

multivibrator.)

Astable

Ckt f t i /

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A general scheme for generating triangular and

square waveforms.

Ckt for triang/square wave

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(a) An op-amp monostable circuit. (b) Signal

waveforms in the circuit of (a).

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internal circuit of the 555 integrated-circuit timer.

555 IC

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a) The 555 timer connected to implement a

monostable multivibrator. (b) Waveforms of the

circuit in (a).

555 for monostable

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(a) The 555 timer connected to

implement an astable multivibrator.

(b) Waveforms of the circuit in (a).

555 for astable

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Using a nonlinear

(sinusoidal) transfercharacteristic to shape

a triangular waveform

into a sinusoid.

Triangle Sinusoid

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(a) A three-segment sine-wave shaper. (b) The input

triangular waveform and the output approximately

sinusoidal waveform.

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A differential pair with anemitter degeneration

resistance used to

implement a triangular-

wave to sine-waveconverter.

S di d

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(a) The superdiode precision half-wave rectifier and(b) its almost ideal transfer characteristic.

when vI> 0 and the diode conducts, the op amp supplies

the

load current, and the source is conveniently buffered,an added advantage.

Superdiode

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(a) An improved version of the precision half-wave rectifier:DiodeD2 is included to keep the feedback loop closed

around the op amp during the off times of the rectifier

diodeD1, thus preventing the op amp from saturating.

(b) Th t f h t i ti f R2 R1