Linsley hoods wienbridge oscillator with low harmonic distortion from may 1981 pp. Design considerations for lowdistortion filter and oscillator ics for. Low distortion, crystal stabilized oscillator circuit. The design of low noise oscillators offers a new timevariant phase noise model. Since if is at dc, all even order distortion now plagues the system, because the distortion at dc can easily swamp the desired signal. When the current at the input node goes high and the current at the output node. Low distortion crystal oscillator crystal this crystal oscillator is designed to operate with fundamental crystals with less than 1 mw dissipated in the crystal. The circuit of figure 1 generates sinusoids down to very low frequencies with distortion in the region of 3% or less, yet has no feedback or gainstabilizing components because none are needed.
The resulting sinewave has low distortion and phase noise. Distortion the instrument is classified as an ultra low distortion generator since its sinewave output typically has less than 0. Simple generator provides verylowfrequencydistortion sine. Distortion is a direct result of excess gain overdriving the amplifier. Lowdistortion sine wave oscillator with precise rms amplitude stability. The wien bridge oscillator in the simulation is not a low distortion design with amplitude stabilization. Availability of high quality capacitors with higher values up to 1 uf.
Low noise oscillator design and performance michael m. It is well known that sinusoidal signals can be conventionally used as test waveform or references by certain electronic circuits and systems, such as frequency. The transmission gate circuit includes two mosfets connected between input and output nodes of the inverter circuit. Ring oscillator design in 32nm cmos with frequency and. The frequency of oscillation can be calculated in the same way as any parallel resonant circuit, using. Design and implementation of opamprc sine wave oscillator diyala journal of engineering sciences, vol. A lowdistortion oscillator with fast amplitude stabilization.
As adjuster also explained, the designer takes steps of varying complexity according to the required output signal purity specification to reduce the effects of the distortion. There are some lower distortion examples using different types of oscillator, the best i was aware of back in 1982 was one designed by john linsley hood using a twint oscillator with r54 thermistor level stabilisation. By using decade resistance boxes, the frequency range can be selected easily. The frequency of the output wave may be fixed or variable, depending on the oscillator design. January 1948, theory of amplitudestabilized oscillators, proceedings of the ire, 36 1. A wien bridge oscillator with harmonic distortion in the parts per billion is shown in figure 36. Pdf lowdistortion sine wave generation using a novel.
Because the total harmonic distortion of both waves is so low, its hard to visually see the effect on the waves. The output of the last inverter is connected to the first inverter. Ultra low distortion an op amp sine wave generator 6 likewise, the output from the sine tap point can be seen in figure 9. Producing low distortion sine waves, this oscillator operates over the range 16 to 22000 hz. This firstgeneration design has several weak points for example the chosen compensation of the amplitude control loop results in slow settling and parasitic oscillation of. A ring oscillator is a type of relaxation oscillator that contains an odd number of inverters creating a nonsinusoidal signal alternating between a high and low voltage 2. For intermodulation distortion measurements the instrument provides an smpte im output. Variation on the classic sinewave wienbridge oscillator. Adc circuits that resolve signal into 20 or more bits need a lownoise signal source for measuring parameters such as harmonic distortion or effective number of bits. Ultra low distortion 0 00001 1khz sine generator assembled. A low total harmonic distortion sinusoidal oscillator based. A novel technique is proposed to generate robust, low distortion sine waves. A full oscillator design using the new low distortion design methodologies is discussed.
Wein bridge oscillator is an electronic oscillator that is used in many applications. A disadvantage is that higher order harmonics are increased somewhat, but these are still generally at a fairly low level. The basic circuit for an oscillator of this form, using a single operational amplifier as the gain block, is shown in fig. Before we ignored this source of noise becuase it occurs at low frequency.
Lowdistortion sine wave oscillator with precise rms amplitude. The oscillator circuit incorporates an inverter circuit in combination with a diode connected transmission gate circuit. The circuit is based on two articles that have appeared earlier in wireless world roger rosens phase shifting oscillator, february 1982 pp. If the oscillator fails to start, the loading capacitors may need adjustment, a higher gain oscillator mode may need to be selected or a 1 to 2 m. How to build lowdistortion audiorange oscillator circuit. There is a related, very popular scheme the state variable oscillator, chiefly, svo. The op amp to the left forces a symmetric signal to develop across the bridge, while the negative tempco of the lamp filament stabilizes the amplitude of oscillation by the rightside section. Although both these oscillators oscillator use an lc tuned tank circuit to control the oscillator frequency, the hartley design can be recognised by its use of a tapped inductor l1 and l2 in fig. An ultra lowdistortion oscillator with thd below 140 db vojtech janasek. A crystal oscillator circuit that provides a low distortion clocking signal. In this method, outputs of a phase shift oscillator pso are weighted and summed to obtain multiple outputs with very. An ultra lowdistortion oscillator with thd below 140 db janascard. Lowdistortion sine wave oscillator with precise rms. My thesis from may 2010 that covers the design of a low distortion oscillator with a frequency range of 3 hz to.
The wien bridge has been used since the vacuum tube era. The bubba oscillator an op amp sine wave generator 6 likewise, the output from the sine tap point can be seen in figure 9. The colpitts oscillator is a particularly good circuit for producing fairly low distortion sine wave signals in the rf range, 30khz to 30mhz. This greatly simplifies the design and analysis of the wienbridge oscillator. Many applications require a frequency andor amplitudestable sine wave as a reference for calibration or measurement. Generate highvoltage sine waves using ic based circuits by driving a transformer in a stepup. An ultra low distortion oscillator described in ref 1 can be easily modified to work in range 100 hz to 20 khz but at lower frequencies, two main problems appear. An949, making your oscillator work microchip technology. From these results it slowly became clear i would need to generate an extremely low distortion 1 khz sinewave. Image reject filter in our example, rf mhz, and if 1mhz. Adc circuits that resolve signal into 20 or more bits need a lownoise signal source for measuring parameters such as harmonic distortion or effective. Phaseshift oscillators have distortion, but they achieve low distortion output voltages because cascaded rc sections act as distortion filters. The colpitts configuration can be recognized by its use of a tapped capacitor divider c 1 and c 2 in figure 1.
Because the total harmonic distortion of both waves is so low, its hard to. Schematic of the sine wave oscillator, consisting of a lowdistortion lt1632based wien bridge oscillator core and an. A good oscillator should exhibit 2nd harmonic levels on the order of 40dbc. Over a wide range of frequency, it provides a stable low distortion sinusoidal output. For some oscillator topologies, it is easy to predict the amplitude of the oscillator output. Circuit design for crystal oscillator peripheral circuits. Phase shift oscillators have less distortion than the wien bridge oscillator. Using these i tested a number of capacitors but with only partial success.
Its also important to make the right choice of op amp for the oscillator, but now this seems to be not a problem because a good modern op amp easily ensures its own distortion being. Us5450042a low distortion crystal oscillator circuit. Note that the output is taken between the two outputs of s1 and s2. Wien bridge oscillator an overview sciencedirect topics.
For example, the differential oscillator described in the first note set is biased by a current source, so the maximum current into the tank is known. Sine output waveform from second stage of bubba oscillator. The jfet local oscillator is excellent when a low harmonic content is required for a good mixer circuit. The design methodology has been used to design oscillators meeting quite di. The notch filter is a passive twint circuit, which rejectsthe oscillators fundamental frequency, but it also attenuates the second andthird harmonics by about 9 db and 5 db. As adjuster explained, it is an inherent property of the oscillator design topology, rather than something attributable to any particular component or components. Generating low distortion sine waves is actually, down to about 80 db, not really a challenge. May 03, 2012 a low distortion notch filter lets youmeasure residual distortion much more simply than a spectrum analyzer. Capacitor sounds 1 low distortion sub 1ppm 1 khz test. It may be surprising to note that the sampling pulse can be as wide as 0. Figure 3 shows a tunable notch filterwith an amplifier.
If the rp is also well controlled not necessarily easy to do, then vtank ic rp. The implemented prototype of the oscillator operates at 683. Low distortion sine wave oscillator with precise rms amplitude stability. The wien bridge oscillator is a twostage rc coupled amplifier circuit that has good stability at its resonant frequency, low distortion and is very easy to tune making it a popular circuit as an audio frequency oscillator but the phase shift of the output signal is considerably different from the previous phase shift rc oscillator. Capacitor sounds 1 low distortion sub 1ppm 1 khz test oscillator.
This crystal oscillator is designed to operate with fundamental crystals with less than 1 mw dissipated in the crystal. Adc circuits that resolve signal into 20 or more bits need a low noise signal source for measuring parameters such as harmonic distortion or effective number of bits. Another useful indicator of good oscillator design is the change in oscillation frequency versus dc bias reduction. Producing lowdistortion sine waves, this oscillator operates over the range 16 to 22000 hz. The notch filter is a passive twint circuit, which rejectsthe oscillator s fundamental frequency, but it also attenuates the second andthird harmonics by about 9 db and 5 db. Design of op amp sine wave oscillators texas instruments. A lowdistortion notch filter lets youmeasure residual distortion much more simply than a spectrum analyzer. Analog circuit design samuel groner resources low distortion. Pdf a novel technique is proposed to generate robust, low distortion. The super op amps s1 and s2 are the previously described composite amplifiers as shown in figure 36. The signal current is filtered by the crystal and develops a voltage across a capacitor with about 500 ohm of reactance. Edn low distortion oscillator tests measurement circuits.
Phaseshift oscillators have distortion, but they achieve lowdistortion output voltages because cascaded rc sections act as distortion filters. The wave shape and amplitude are determined by the design of the oscillator circuit and choice of component values. An263 sine wave generation techniques texas instruments. Distortion the waveforms on the osc1 and osc2 oscillator pins are checked at the same 4 or 5 combinations of vdd and. By discarding the implicit assumption of time invariance underlying many other approaches, this model is capable of making quantitative predictions of the phase noise and jitter of different types of oscillators.
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