Index


Oscillator circuits

    General information

    An oscillator is an electronic device used for the purpose of generating a signal. Oscillators are found for example in computers, wireless receivers and transmitters, and audio-frequency equipment, and music synthesizers. Every oscillator has at least one active device.This active device acts as an amplifier.There are many types of oscillator devices, but they all operate according to the same basic principle: an oscillator always employs a sensitive amplifier whose output is fed back to the input in phase. Thus, the signal regenerates and sustains itself. This is known as positive feedback.

    Sinewave oscillators

    Sine wave oscillators are useful in applications likeaudio signal generation, reference signals for differentapplications and in measurement applications.To vary the frequency of a traditional RC filter based sine-wave oscillator, you should generally use a pair of ganged variable resistors, and you should thoroughly match their characteristics over the entire variation range to satisfy the oscillator's balancing conditions. This restriction leads to problems in the tuning range and high cost, thereby limiting the range of applications.

    • 68HC11 synthesizes accurate sine wave - you can use a 68HC11 and a 12-bit serial DAC to generate accurate sine waves without using floating-point arithmetic    Rate this link
    • Audio signal (sinewave) generators - wien bridge oscillators, twin-t network oscillator and RC phase shift oscillator    Rate this link
    • Audio Test Oscillator - Wein Bridge Basic Circuit    Rate this link
    • Current-feedback amp yields simple oscillator - handful of components configures a current-feedback op amp as a large-amplitude sine-wave oscillator with independent adjustment of amplitude and frequency    Rate this link
    • Digital signals produce pure sine waves - Analog oscillators produce excellent sine waves but are temperamental and hard to design. They also require extensive redesign every time you change the oscillation frequency. Digital oscillators are easier to design than analog oscillators, and digital signals already exist in digital systems. Thus, it is often cost-effective to derive sine waves from digital signals.    Rate this link
    • Gate Deep Oscillator - This is just a variable oscillator based on a bf245 or k 161 fet. By changing the coil it can generate frequency between 0.5 and 300 MHZ. this circuit is useful to test radio circuit such as filter, receiver, transmitter and so on . It can be use for coil tuning thanks to the 100microamo meter built in.    Rate this link
    • Gates provide low-cost sine-wave generator - simple device to generate 300 to 4000 Hz test signals    Rate this link
    • GIC resonator has inherent amplitude control - This circuit is based on a classic GIC (generalized impedance converter). The sine-wave-oscillator circuit has inherent amplitude stabilization and normally operates from dual power supplies. However, if you connect a few additional resistors, you can operate the circuit with one supply.    Rate this link
    • Grounded resistor tunes oscillator - To vary the frequency of any sine-wave oscillator, you usually have to use a pair of ganged variable resistors, and you should thoroughly match their characteristics over the entire variation range to satisfy the oscillator's balancing conditions. This restriction leads to problems in the tuning range and high cost, thereby limiting the range of applications. This sine-wave oscillator is free of the cited disadvantage. You can tune it over a wide frequency range using only one variable resistor. The variable resistor connects to ground, an advantageous fact in many applications. PSpice simulations prove the possibility of tuning the oscillation frequency over three decades (20 Hz to 20 kHz) by varying R1 from 1.2 M. to 1.2 k.    Rate this link
    • Grounded resistor tunes oscillator - To vary the frequency of any sine-wave oscillator, you should use a pair of ganged variable resistors, and you should thoroughly match their characteristics over the entire variation range to satisfy the oscillator's balancing conditions. This restriction leads to problems in the tuning range and high cost, thereby limiting the range of applications. This sine-wave oscillator design is free of the cited disadvantage.    Rate this link
    • Microcontroller emulates numerically controlled oscillator - Microcontrollers commonly add intelligence or digital functions to products, but they can also provide a variety of analog signals. An 18-pin PIC 16C54 microcontroller, combined with an inexpensive, 8-bit DAC and a simple lowpass filter, can generate sine waves from dc to approximately 50 kHz with a tuning resolution of 24 bits.    Rate this link
    • Op-amp oscillators simplify RF designs - a novel circuit that uses a low-cost, high-speed op amp as a crystal-controlled RF sine-wave oscillator    Rate this link
    • Programmable oscillator uses digital potentiometers - This Design Idea describes an oscillator in which setting the resistance of two digital potentiometers independently programs the oscillation amplitude and frequency. This design idea uses diode-stabilized Wien-bridge oscillator that generates accurate sine waves from 10 to 200 kHz.    Rate this link
    • Simple circuit generates clean sine waves - technique for generating a high-quality sine wave from a square-wave source    Rate this link
    • Sine reference is synchronous with ac line - Many applications require a sinusoidal reference voltage synchronized to the ac line voltage. You cannot derive such a reference voltage directly from the ac line because the waveform of the ac line is distorted because of nonlinear loads connected to the line and because the amplitude of the line signal varies.    Rate this link
    • Voltage controls sine-wave frequency - generates a 50-Hz to 1-kHz sinusoidal waveform that exhibits lower than 60-dB THD    Rate this link

    Noise generators

    Noise generators are generally used in various measurements. The mostcommon way to generate noise signals are to use a randon-bit-sequence generator or to amplify the thermal noise of some electronic component(usually diode or transistor). The most commonly needed noise sourcesin audio measurements are "white noise" and "pink noise". White noiseis pure random noise, and the pink noise is specifically filtered whitenoise. In some digital telecommunication testing applications streams of random or semi-random bitstreans are needed. Those random orsemi-random bitstreams are generated using a random-bit-sequence generator.

    Voltage controller oscillators

    A voltage controlled oscillator or as more commonly known, a VCO, is an oscillator where the control voltage controls the oscillatoroutput frequency. VCO can be built using many circuit techniques.For RF applications the principal variable or tuning element is a varactor diode. This kind of RF voltage controlled oscillator is tuned across its band by a "clean" dc voltage applied to the varactor diode to vary the net capacitance applied to the tuned circuit.

    Timer circuits

    Timer circuits are circuit which are trigged by input pulses.When they are triggered, they will wait for a predeterminedtime to change the output state. The most commonly used timer circuitsare monostable multivibrators and time delay circuits.A time delay circuit works so that when the input comes active,the output gets activated after a predetermined time.A monostable multivibrator works so that a trigger pulse actives it,the output turns active. After a predetermined time the monostablecircuit deactivates itself and the output.Many astable timer circuits are based on 555 timer IC.Designing astable circuits using the industry-standard 555 timer is a straightforward process when duty cycles are 50% or greater. This IC can also be used for many other applications.

    Microcontrollers used as oscillators

    • Tone Generation - A general purpose resonator routine is implemented using a PIC17C42. This routine is used to generate multiple tones. A tone signal is normally generated using extensive table lookup schemes.When a multiple tone signal is desired, each tone must have its own lookup table, thus requiring a large amount of storage space, especially when various frequencies are to be generated. This application note implements tone generation using recursive techniques. The algorithm for a resonator is developed and implemented using PIC17C42.    Rate this link


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