Colpitts, Hartley, and Pierce oscillators are three common oscillator designs used to generate a stable signal in radio circuits.

• Colpitts oscillator : It uses a capacitor divider to create feedback, with inductors and capacitors in the resonant circuit.
• Hartley oscillator: It uses an inductor (with a tapped coil) for feedback, allowing it to generate a range of frequencies.
• Pierce oscillator: It is a variant of the Colpitts, typically using a crystal to stabilize the frequency for accurate signal generation.

These designs are chosen based on their stability, ease of implementation, and frequency characteristics in RF applications.

How to rule out the distractors:

• Taft: There is no widely recognized oscillator called "Taft."
• Negative feedback: While it's a technique used in amplifiers, it is not an oscillator circuit.
• Fenner and Beane: These are not recognized names for oscillators, they are probably just made up.

Memory tip: the correct answer starts with "C"

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Microphonics or microphony describes the phenomenon wherein certain components in electronic devices transform mechanical vibrations into an undesired electrical signal (noise). The term comes from analogy with a microphone, which is intentionally designed to convert vibrations to electrical signals. In the case of oscillator frequency this mechanical vibration can sometimes cause interference.

More at Wikipedia: https://en.wikipedia.org/wiki/Microphonics

Test tip: the only answer without microphone.

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The Hartley oscillator is an electronic oscillator circuit in which the oscillation frequency is determined by a tuned circuit consisting of capacitors and inductors, that is, an LC oscillator. The circuit was invented in 1915 by American engineer Ralph Hartley. The distinguishing feature of the Hartley oscillator is that the tuned circuit consists of a single capacitor in parallel with two inductors in series (or a single tapped inductor), and the feedback signal needed for oscillation is taken from the center connection of the two inductors.

http://en.wikipedia.org/wiki/Hartley_oscillator

Test Tip: Hartley is pretty close to Harley, which are notorious for leaking oil. Coil is pretty close to oil.

Test Tip: Hartley has "tl" in it. Tapped L

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http://en.wikipedia.org/wiki/Colpitts_oscillator

Think C for Colpitts and Capacitor, and voltages supplied by dividers.

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The Pierce oscillator is a type of electronic oscillator particularly well-suited for use in piezoelectric crystal oscillator circuits. Named for its inventor, George W. Pierce (1872-1956), the Pierce oscillator is a derivative of the Colpitts oscillator.

Components: a single digital inverter, two resistors, two capacitors, and the quartz crystal, which acts as a highly selective filter element.

http://en.wikipedia.org/wiki/Pierce_oscillator

Memory aids:

• Pierce = Piezo
• Don't get pierced with a quartz crystal.
• "Pierced" ears have crystal earrings.

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A Colpitts oscillator is a type of LC oscillator, so called because it consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C. It mimics a Hartley oscillator, in that the inductive voltage divider from a pair of coils, or a tapped coil is fed into the LC circuit.

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Hint: Colpitts and Hartley is the only answer with two types of oscillators. A Zener is a diode voltage regulator, Armstrong and De Forest were inventors and all oscillators employ some sort of negative feedback.

Memory tip: ...oscillator circuits are commonly... and Colpitts in the correct answer

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Microphonic effects (think of a microphone) are electrical changes in component properties caused by mechanical effects such as vibration, sharp impulses, or the like.

In oscillator circuits, capacitors can slightly change their value due to mechanical stress, leading to changes in the resonant frequency of 'tank' circuits (remember \(\frac{1}{2\pi\sqrt{LC}}\)?) that form the heart of the oscillator. In vacuum tube oscillator designs, mechanical vibration of e.g. the grid or filaments can alter their electrical properties and cause the same thing.

Mechanical insulation / isolation of the oscillator circuit will minimize these microphonic effects.

For more, see these:

https://en.wikipedia.org/wiki/Microphonics

https://e2e.ti.com/blogs_/b/precisionhub/archive/2014/12/19/stress-induced-outbursts-microphonics-in-ceramic-capacitors-part-1

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Please refer to this link:

http://www.learningaboutelectronics.com/Articles/What-is-a-NPO-ceramic-capacitor

NP0 stands for negative-positive 0 ppm/°C, meaning that for negative or positive shifts in temperature, the capacitance changes 0 part per million (ppm), meaning that it has a flat response across a wide range of temperatures; the capacitance of the NP0 capacitor stays constant (at the same value) despite variations in temperature.

They are also very suitable for oscillator construction in order to compensate for frequency drift with temperature.

Hint: A Negative plus a Positive = 0, or NP0

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The phrase "digital to analog converter" can only be present in "a direct digital synthesizer." None of the other answers has "Digital" in them.

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Direct Digital Synthesis (DDS) is a method of producing a sine wave by generating the wave in digital form and then converting it to analog using a digital-to-analog converter. Rather than computing the value of the sine function on every clock cycle, a lookup table is often used to store precomputed sine values. By stepping through this table at different strides, sine waves of various frequencies can be generated.

Hint: "Direct Digital" in the question, "Desired" in the correct answer. These are the only words that start with a 'D'.

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Both the direct digital synthesizer (DDS) and the phase-locked loop (PLL) synthesizer have issues with spectral purity. The major spectral impurity components of direct digital synthesizers are spurious signals at discrete frequencies. (E7H11)

A spurious emission (signals) is any radio frequency not deliberately created or transmitted, especially in a device which normally does create other frequencies. A harmonic or other signal outside a transmitter's assigned channel would be considered a spurious emission.

More at: Wikipedia - Spurious emission

Trick: The question asks about "components", which is plural. The correct answer includes the word "signals" which is also plural. All other answer choices are singular.

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Load capacitance is an important specification when using parallel-resonant oscillation mode.

http://www.maximintegrated.com/en/app-notes/index.mvp/id/726

Silly memory aid: provide "Crystal" with a "cap" (capacitance).

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A standard quartz crystal oscillator is usually of the AT cut type, which has a frequency deviation on the order of several parts per million over a commercial or industrial temperature range. This stability is unsuitable for many demanding applications where maximum deviations of hundreds of parts per billion are required over a large temperature range, or low drift vs. time is required (aging effect). The most basic is a temperature-compensated crystal oscillator, which as the name implies attempts to pull the crystal into tight tolerance by measuring a nearby temperature sensor. The second type mentioned is a rubidium reference, which is a type of atomic reference with good long-term stability characteristics derived from a rubidium-based physics package. Third, a GPS signal reference is one that can be used to create a GPS-disciplined oscillator, which is a type of oscillator that is kept synchronized by using signals derived from atomic references on GPS satellites, with corrections that are traceable to NIST. The result is an oscillator with zero effective long-term drift and good local stability provided by a high-quality ovenized oscillator.

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A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input signal. While there are several differing types, it is easy to initially visualize it as an electronic circuit consisting of a variable frequency oscillator and a phase detector.

More information....

Hint 1: The correct answer is the only one with "loop" and "phase" in the answer.

Hint 2: A "phase-locked loop" has to "detect" the phase to lock it up. The answer has "phase detector"

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A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input signal. While there are several differing types, it is easy to initially visualize as an electronic circuit consisting of a variable frequency oscillator and a phase detector.

Phase-locked loops can be used to demodulate a signal (FM demodulation), recover a signal from a noisy communication channel, and generate a stable frequency at multiples of an input frequency (frequency synthesis).

Hint: Functions (from question), frequency (from correct answer)

Phase-locked Loop (Wikipedia page)

Block diagram of a phase-locked loop

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