oscillatori, generatori di segnale, rc, lc, oscillator

Oscillatori

General

Every oscillator has at least one active device. This active device acts as an amplifier.

• 555 timer IC information page - This is a very commonly used IC for making simple timing circuits and oscillators.
• Oscillator Basics - Introduction to LC oscillators.
• Oscillators - This web page is devoted to oscillators. This page has general information on very many oscillator types and link for more information.
• Rules of thumb aid in time-constant analysis - information on calculating time constands on RC circuits

RC and LC clock oscillators

Clock oscillators are circuits which generate square wave or nearly square wave signals suitable for digital electronics circuit as clock signal. The most common simple clock oscillator types are resistor-capacitor (RC) and inductor-capacitor (LC) oscillators.

• CMOS Oscillator - 4 MHz oscillator using 74HC14 and inductor
• CMOS inverter VCO tunes octave to UHF - robust and versatile vco provides a stable output to 300 MHz
• CMOS RC circuits - includes CMOS 555 timer clock oscillator and schmitt-trigger RC oscillator
• Crystal 32.768KHz CMOS Oscillator
• Design and construction of radio frequency oscillators - Some people regard the design of RF Oscillators to be something akin to a "black art".
• Sqaure Wave Oscillator - two gates from a CMOS 4011 NAND chip form a simpel square wave oscillator where the mark space ratio can also be independantly controlled by varying the value of the resistors

Crystal oscillators

Crystal oscillators are oscillators where the primary frequency determining element is a quartz crystal. Because of the inherent characteristics of the quartz crystal the crystal oscillator may be held to extreme accuracy of frequency stability. Crystal oscillators are usually, fixed frequency oscillators where stability and accuracy are the primary considerations. Temperature compensation may be applied to crystal oscillators to improve thermal stability of the crystal oscillator.

General information

• 10 Quick Tips for VCXO Specifications
• High system speeds are making clock design a critical problem - Clock signals distributed within a printed-circuit board andaround a system must be clean, stable, synchronized, and have as near toa 50:50 duty cycle as possible

Desing articles

• Circuit Techniques for Clock Sources - pdf file with many circuit examples
• Crystal Oscillators - General information and one circuit example for 150 MHz crystal oscillator.
• Crystal oscillators: looking good in wireless systems - with the assistance of stabilization and tuning tricks, crystals makes an ideal frequency reference for wireless systems
• Design Of A Low-Power Crystal Oscillator
• Oscillators for microcontrollers - lots of information on crystal oscillator design, 40 pages pdf document, 900 kilobytes in size

Circuits

• 2 MHz Oscillator
• 50 - 150MHz Overtone Oscillator
• Crystal 32.768KHz CMOS Oscillator
• Crystal Oscillator - from 1 MHz to 40 MHz using CMOS or HCMOS inverter
• Oscillator lowers distortion and phase noise - this low-distortion crystal oscillator is essentially a modified Clapp oscillator that uses a four-transistor voltage follower instead of a single transistor and connects the crystal to a virtual ground at node G
• Crystal oscillator overcomes typical drawbacks - drive heavy loads, the duty cycle is adjustable from 25 to 75%; and feedback minimizes the drift
• Very low power gated crystal oscillator - continuously operating 32KHz crystal oscillator to the input of a C-MOS buffer when clock pulses are needed, standby power consumption to a very low 1uA when used with a 3v supply, pdf file

Sinewave oscillators

Sine wave oscillators are useful in applications like audio signal generation, reference signals for different applications and in measurement applications.

• 1 kHz Audio Oscillator - This circuit consists of a CMOS square wave oscillator on a frequency of approximately 1 kHz. The RC filter, which has a roll-off frequency of 500 Hz, filters the harmonics, providing a sine-wave output. The oscillator has many uses, sidetone circuits in transmitters and signal injectors for audio tests are just two.
• 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
• 770 Hz Simple CPO - simple sinewave oscillator
• Amplitude-stable oscillator has low distortion, low cost - square wave and sinewave oscillator examples
• Audio signal (sinewave) generators - wien bridge oscillators, twin-t network oscillator and RC phase shift oscillator
• Audio Test Oscillator - Wein Bridge Basic Circuit
• 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
• Digital signals produce pure sine waves
• Gates provide low-cost sine-wave generator - simple device to generate 300 to 4000 Hz test signals
• 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.
• 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
• 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.
• Simple circuit generates clean sine waves - technique for generating a high-quality sine wave from a square-wave source
• 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.
• Voltage controls sine-wave frequency - generates a 50-Hz to 1-kHz sinusoidal waveform that exhibits lower than 60-dB THD

Square wave oscillators

Square wave oscillators are very commonly used as clock sources for digital electronics circuits and similar applications.

• 200-400MHz voltage controlled oscillator - produces clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz, pdf file
• 555 Tone Generator for 8 ohm speaker - used to produce a 1 Khz tone from an 8 ohm speaker
• Adjustable Duty-Cycle Oscillator - This circuit can be built with a single IC, two capacitors, three resistors, two trim-pots, and a diode.
• Amplitude-stable oscillator has low distortion, low cost - square wave and sinewave oscillator examples
• Clock Generators - crystal oscillators for 20 MHz and 3.5795 MHz
• Digital Clock Circuit - This circuit provides a digital square wave that can be viewed directly or used to drive other circuits. It uses the CMOS 4047 Low-Power Monostable/Astable Multivibrator.
• Generator has independent pulse width and frequency adjustments - modified 555 based circuit
• Inverters form three-phase VCO - You sometimes need an inexpensive VCO that can produce evenly spaced three-phase outputs over a wide frequency range. This application uses unbuffered U-type inverters for use in ring oscillator setup which generates relatively squarish somewhat sine-like waveforms. The range of frequencies over which the circuit can operate is more than 1000-to-1.
• Low frequeny oscillator draws only 500 nanoamperes - circuit draws only 0.5 microamps from a 6 volt supply, outpur frequency is 2 Hz but can be tuned up to 300 Hz, based on CD4007UB IC
• Multivibrators, relaxation oscillators and their allies - astable multivibrator, asymetrical multivibrator, complementary multivibrator, series multivibrator, emitter coupled multivibrator and more
• Precision ultra low power oscillator - works much like the classic 555 timer, but draws only about 1.5 microamps from a 3 volt battery, highly stable under varying temperature and supply voltages, pdf file
• Programmable Clock Oscillator - voltage controller oscillator that was designed as a wide range oscillator to generate clock pulses for a stepper motor drive system, frequency could be varied over 1,000,000:1
• Simple Square Wave Oscillator - This simple kit, based on the popular 555 timer IC, generates six preset frequencies - 1Hz, 10Hz, 100Hz, 1KHz, 10KHz and 100KHz. The output is selected by setting a jumper position. It has a wide operating voltage (5-18V) and even provides visual indication (LED) of the output.
• Use printer port as programmable frequency generator - A simple and inexpensive circuit and a simple C program are all you need to turn your PC's printer port into a programmable frequency generator. Using a few low-cost and readily available components, the circuit occupies little space and is easily attachable to the printer port. With this circuit you need only enter the desired frequency, and the PC does the rest. The circuit uses a MAX5130 low-power, programmable, 13-bit DAC, IC1; an OP07 buffer; and an AD537 VFC (voltage-to-frequency converter). The PC controls the DAC using a three-wire serial interface.

Pulse Width Modulation

The Pulse Width Modulator (PWM) is a very useful circuit that outputs a variable duty cycle at a fixed frequency (duty cycle is usually controlled using external control signal, potentiometer or using numerical control). The PWM is very useful in applications like wave generation, motor control and DC power controlling systems. With the aid of a filter, smooth analog waves can be generated usign PWM method.

• Circuits provide 4- to 20-mA PWM control - are useful when you use 4- to 20-mA current-loop signals to control a PWM signal
• Generator features programmable duty cycle - you can program the duty cycle of this simple pulse generator's output
• Pulse Width Modulators - generating PWM waveform is extremely simple with the circuits shown in this page, all circuits are DC control voltage in and PWM out
• PWM circuit uses one op amp - circuit delivers a rectangular signal with duty cycle varying between 0 and 100% in response to an input signal varying from 0 to 5V dc

Oscillators with other waveforms

• 20MHz Function Generator - This compact function generator provides sine, square and triangular waveforms up to 20MHz over three ranges using "course" and "fine" frequency adjustment controls. The output level is adjustable from 0 to 2Vp-p. A TTL output is also provided for connection to a frequency counter.
• Function Generator - Built around a single 8038 waveform generator IC, this circuit produces sine, square or triangle waves from 20Hz to 200kHz in four switched ranges.
• Générateur de fonction 0.1 Hz - 10 Mhz - funacion generator 0.1 Hz - 10 MHz, based on MAX038, text in French
• Low Cost Function Generator - low-cost function generator, based on the Maxim MAX038 high-frequency waveform generator, produces sine, triangle, and square waves from under 1 Hz to over 20 MHz
• Oscillators convert temperature to time - simple arrangement of active-R oscillators can generate an excellent triangular waveform
• Programmable ramp generator has 14-bit linearity - this linear ramp generator uses a DAC, a transistor array, MOSFET switches, and current-steering techniques to achieve 14-bit linearity
• Scheme yields frequency-locked triangle waves - circuit generates frequency-locked triangle waves of constant amplitude, uses readily available TTL and other older-technology parts
• SCR Oscillator - Silicon controlled rectifiers (SCR) can easily oscillate if there is an inductor (a speaker coil in this case) which gives just enough extra voltage to completely switch off the sustain current. In this way a new cycle may start and oscillations set in. It operates over a wide range of supply voltage and components values are not critical at all. Operational frequency in this circuit goes from 100Hz at 11V to 10KHz at 100V.
• Summer linearizes ramp and triangle generators - op-amp adder that sums a reference voltage with the voltage on C1 allows the ramp generator and the triangle-wave generator to charge capacitor linearly
• Transistor Organ - very simple electronic instrument
• Triangle and Squarewave Generator - uses common 1458 dual op-amp
• Tri-Waveform Generator - signal generator to test circuits, frequecy range is 20 to 20 kHz, outpus sinewave, triangle wave and square wave
• Versatile Waveform Generator Operates from 0.1Hz to 20MHz - a single-chip source of high-frequency waveforms, the MAX038 can serve both as the core of a moderate-performance waveform generator, and as a card-level waveform source for electronic systems
• Waveform Conversions: Sine to Square and Square to Sine
• Waveform generator circuits - ramp generator, phase oscillator, quadrature sine/cosine oscillator
• Zener Oscillators - These two circuits are interesting from an academic point of view. Their practical implementation is rather critical and it is not easy to get steady operation.

Multivibrators

Multivibrators are circuit which change their state contantly between different states (usually two states) at predefined rate. Multivibrators are usually used to generate square wave clock signals, but they can be used also for other applications.

• Circuit forms clockless, programmable one-shot - replace the timing resistor on a 74LS123 one-shot with a Howland current pump, drive the pump with a rail-to-rail voltage-output DAC, and you have a programmable one-shot with some unique features: single-supply operation, no clock required, a 25-to-1 pulse with adjustment range, and an "infinite" pulse-width capability
• D-flip/flop one shot circuits - you can use cheap D flip/flop logic circuits as nice one-shot pulse generators, this circuit shows how the popular CD4013 and the CD74HC74 can be used to generate pulses ranging from nanoseconds to seconds, pdf file
• LM555 timer chip datasheet - very popular timing IC used for monostable multivibrators and oscillators
• Basic IC MonoStable Multivibrator
• CMOS RC circuits - oscillator, one-shot and button debounche
• Discrete Multivibrator Schematic - astable multivibrator using discrete parts
• Long period computer watch dog timer - simple 4060 IC oscillator/timer which is reset periodically by a computer. Should the computer fail to send a pulse, the output changes state, time can easily be set from seconds to hours, pdf file
• One-shot and latch circuit using CD4013 - pdf file
• Retriggerable 555 Monostable Multivibrator
• Simple monovibrator uses three PLD pins - if you can afford just three spare PLD pins, this circuit is an alternative to using yet another 555
• Slow op amp makes fast multivibrator - improved version of classic one-shot multivibrator using an op amp, example circuit generates a pulse of approximately 700-µsec width with a 5-nsec, 2V triggering pulse
• Switch De-bouncer Using a 555

Flashing circuits

Most simple light flashing circuits are just multivibrators with enough output current/voltage capacity to drive a light bulb or a LED.

• Basic LM3909 Led Flasher - runs from 1.5V battery
• LED flasher - makes two LEDs alternately flash, two circuit examples

Noise generators

Noise generators are generally used in various measurements. The most common 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 sources in audio measurements are "white noise" and "pink noise". White noise is pure random noise, and the pink noise is specifically filtered white noise. In some digital telecommunication testing applications streams of random or semi-random bitstreans are needed. Those random or semi-random bitstreams are generated using a random-bit-sequence generator.

• Audio Frequency Digital Noide Generator - When you need to test an audio circuit with broadband noise, this circuit works great. It uses just three inexpensive C-MOS ICs that generate a series of output pulses whose widths vary randomly. This circuit includes a level control pot. The circuit is in pdf format.
• Circuit forms random-bit-sequence generator - A random-bit-sequence generator is basic equipment for prototyping and testing any data-transmission system. You use such a generator when measuring BER (bit-error rate) and pattern-dependent effects in a transmission system.
• Digital Generation of LFO's for Modulating Effects - pseudo-random signal generating circuit ideas
• Noise Generator - Sometimes there is a need for a noise generator: this will work well in the audio range and, without the 680pF capacitor, will extend in the radio frequency range up to 20-30MHz.
• Pseudonoise generator doubles its speed - you can double the speed of a standard pseudonoise (PN) generator by using additional exclusive-OR gates and a fast 2:1 multiplexer
• Random Noise Sources - Producing crypto-quality randomness in a computer is a perennial issue in cryptography, here are some ideas
• Single IC forms pseudorandom-noise source - Trying to find a single IC noise source can be frustrating. You could use a single-chip microcontroller, such as Microchip's 12C508 for this application. This article gives you idea and software how to do that.

Voltage controller oscillators

A voltage controlled oscillator or as more commonly known, a VCO, is an oscillator where the control voltage controls the oscillator output 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.

• CMOS inverter VCO tunes octave to UHF - robust and versatile vco provides a stable output to 300 MHz
• Voltage controller oscillators

Phase locked loops

Phase locked loop (PLL) is a system which consists of a voltage controlled oscillator, phase comparator and feedback circuit. PLL it's basic form takes in a reference frequency and tries to output the same frequency out (with a known phase shift). With a feedback circuit which contains a frequency divider it is possible to generate output frequencies which are N times the input frequency.

• Inverting latches make simple VCO - simple VCO circuit which is synthesized from inverting latch stages and is tunable to an integer multiple of the input frequency by selecting which output phases feed back to the input multiplexer, suitable to be usable as on-chip clock multiplication in ASICs
• Low-cost circuit biases VCOs for cable and TV - PLLs are useful in a variety of applications, most notably cable and TV tuners
• Software PLL locks VCXO to reference - provides a precisely controlled clock signal using voltage controlled crystal oscillator controlled by microcontroller
• Straightforward techniques cut jitter in PLL-based clock drivers - this article describes jitter and its causes and effects and shows you how to reduce it
• Synchronous oscillator outperforms the PLL - PLL has numerous limitations, including low input-signal sensitivity and contradictory design requirements, synchronous oscillator doesn't suffer from these problems and has many powerful properties
• Technique eases design of high-order PLLs - maintaining stability in high-order PLLs can be a chore unless you know exactly what you are doing
• Understanding VCO Concepts

Pulse circuits

Pulse circuits are circuits which generate a pulse with predetermined pulse width at constant predetermined rate or at on-need basis.

• 555 makes handy voltage-to-time converter - This circuit is a simple, low-cost voltage-to-time converter using the ubiquitous 555 timer chip.
• Circuit forms constant-current SCR - Resembling an SCR, this circuit provides a constant current of controlled pulse width and amplitude to a load.
• CMOS buffer delivers precise current pulses - this circuit delivers stable, fast-settling reference-current pulses
• Delay line aids in one-shot simulations - Many designers use small pulse generators to delay signals, open timing windows, drive sample/hold circuits, and other functions. Though the hardware implementation of these generators does not pose any problems, the lack of dedicated circuitry sometimes puzzles the Spice simulation of the system.
• High-speed pulse generator has programmable levels - This circuit can create fast rise time pulses whose high and low levels are programmable. Signal rise times in nanoseconds range. Pulse rate can be controlled with external circuit.
• Micropower pulse generator - produces clean 2mS logic pulses at rate of one per second while drawing only 1 microamp from a 9 volt battery, uses 2 transistor acting as programmable unijunction transistor, pdf file
• One-shot remembers input-pulse width
• Pulse discriminator excises narrow pulses - circuit deletes narrow pulses from fixed-frequency PWM waveforms
• Pulse-width trimmer outdoes one-shots - trims the trailing portion of a large-width input pulse to a size as narrow as 10 nsec irrespective of the input-pulse width, circuit doesn't require a capacitor to generate the timing pulse
• Repeating one-shot yields clean, stable pulses
• Time Domain Reflectometer (TDR) - produces very sharp pulses in range of 10 ns to 5 us
• µC squares input signal - converting a random-width pulse to a signal with the same frequency but with a 50% duty cycle isn't easy but a small microcontroller can do it

Timer circuits

Timer circuits are circuit which are trigged by input pulses. When they are triggered, they will wait for a predetermined time to change the output state. The most commonly used timer circuits are 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 monostable circuit deactivates itself and the output.

• A Technique For Forming Long Time-Constants
• LM555 timer chip datasheet - very popular timer IC for all kinds of applications, check also 555 Timer Design Tool
• Logic IC yields simple, wide-range timer - you can use a 4060B binary counter/oscillator to make a simple, accurate, long-delay timer for times between milliseconds and hours
• Long Delay Timer - A max. delay of 20 hours is achieved by this relatively simple circuit.
• One-shot circuit is programmable - digitally program the on-time of a one-shot multivibrator circuit based on NE555 timer and AD7524 DAC
• Simple timer exploits op-amp bias current - simple, low-cost analog timer exploits the parasitic input-bias current of op-amp to achieve long time delays even though it uses only low-value, inexpensive ceramic chip capacitors
• Timer provides power-off function - an interval from seconds to several minutes for automatic power-off switching in idle battery-powered systems
• µC-based one-shot has wide range - µC-based, digitally programmable, monostable multivibrator based on PIC16C54

Watchdog circuits for microcontroller and computer systems

The watchdog circuits used with microcontrollers are usually built in such way that the software running in the microcontroller periodically resets the watchdog circuit. If no watchdog circuit "reset" signal is received during a predetermined timeframe, the watchog circuit will activate it's alarm output (which is usually used to reset the microcontroller circuit to start all over). Watchdog circuit then causes an alarm when the software crashed (whn software crashes, it does not anymore give out watchdog reset pulses).

• Universal watchdog fully controls µ Preset
• Watchdog circuit uses leftover gates - extremely simple watchdog circuti to be used with microcontrollers
• Watchdog timer reboots PCs - watchdog timer reboot the computer if it runs astray, uses a PIC16C84 µC to provide the watchdog function

Other related circuits

• 300V peak-to-peak signal generator - converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times, pdf file
• Basic Missing Pulse Detector
• Circuit makes simple FSK modulator - The need for a compact telemetry system poses a challenge for designing a small, light, low-component-count system. Commercial FSK (frequency-shift-keying) modulators are bulky and need many passive components. This circuit uses a single NOT gate (inverter), an On Semiconductor NL27WZ14 in a surface-mount package, to generate continuous FSK data from TTL-level signals. This circuit is designed to provide 2400 Hz / 1200 Hz FSK, but can be adapted for other frequencies up to an operating frequency of approximately 80 kHz.
• Convert periodic waveforms to square waves - converts various waveforms to square wave with adjustable duty cycle
• Delay line implements clock doubler - using a 5-nsec delay unit, a 50- MHz, 50% duty-cycle square-wave input produces a 100-MHz, 50% duty-cycle output clock
• Frequency doubler operates on triangle waves
• Insect Repellant - a 22KHz oscillator with piezo output
• Line powered 60 Hz clock generator - optosolated circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit, provides 5000V isolation from line, pdf file
• Negatrons enrich filter, oscillator designs - atest wave of high-performance op amps allows you to incorporate "negatrons" (synthesized negative resistors) into your oscillators and filters
• PSpice tunes oscillator circuits - optimization technique to determine the impedance, ZB, that compensates for parasitic phase shifts that the real amplifier introduces in this high-frequency oscillator
• Ring oscillator measures cable length - ECL exclusive-NOR gate (F100107) and a length of cable form a simple ring oscillator, the delay from the cable and the gate determine the ring oscillators frequency, 100m cable yields approximately a 1 MHz oscillation frequency
• Self-powered Sine to Square wave Converter - Converts sine to square waves without a power-source
• Slew Rate Control - A circuit that limits the rate of change of a signal; a feature of this design is that the positive and negative rates can be different.
• Ultrasonic Dog Whistle
• Watchdog circuit uses ac triggering - A dc-triggered reset of a watchdog circuit is prone to failure. If the watchdog program hangs up, then the reset signal becomes activated continuously, and the microprocessor has no way to escape the situation. This simple solution uses an ac trigger to reset the watchdog circuit.

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