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Review of Texas Instruments: AN263 Sine Wave Generation Techniques

Download AN263 Sine Wave Generation Techniques from Texas Instruments (1999, 18 pages, 350KB)

If you scroll through this app note, you might become confused by a little formality: It has “Texas Instruments” on the cover and on the last page, but all the other pages make it clear that it is a National Semiconductor app note. The solution to this riddle is, that National was acquired by Texas Instruments in September 2011, and now TI is merging National’s app notes with their own documents – this app note got the TI literature number SNOA665B.

In this app note you will find a nice overview of several sine wave generation techniques. Please take a look at the table on page 3 for a comparison of the techniques that are discussed, regarding frequency range, distortion and amplitude stability.

If you are looking for a low distortion sine wave oscillator and the ability to change the frequency quickly is not so important, a very interesting type is the Wien bridge oscillator (incorrectly called “Wein” bridge throughout the app note. This is a very common error, if you are searching for Wien bridge anywhere, please make sure you search for Wein bridge too, or you might miss some documents). The very simple circuit in figure 2 a) on page 3 that uses a little light bulb to stabilize the amplitude reaches a distortion level of 100ppm. You can do even better if you are willing to put some more effort in – please see AN43 Bridge Circuits page 29 - 33 for an in depth discussion, with a 3ppm Wien bridge oscillator !

Other types of oscillators that directly generate a sine wave are the phase shift oscillator on page 1 and a negative resistance oscillator using a LC combination on page 5. For even more sine wave oscillators, including the Bubba oscillator, take a look at Op Amps For Everyone chapter 15. On page 3 of the app note a high voltage sine oscillator is discussed, which can reach up to 542 Vpp. I would advise to stay away from this unless you already have experience with higher voltages. At least take a look at this introduction to Electrical Safety before you try to build anything.

If you are most interested in frequency stability, using a quartz crystal oscillator is a good choice. On page 7 a 100 kHz Colpitts oscillator is discussed, together with the circuit of a little temperature controlled oven. By using this you can even get rid of the (small) temperature dependency of the quartz. If you have access to Analog Circuit Design, you can find a discussion of some more crystal oscillator circuits on page 333 – 347. Page 6 of the app note shows an interesting circuit that uses a tuning fork to achieve a 1 kHz output, and claims that it has good frequency stability too, but is more robust against mechanical shock than a quartz crystal.

If you are looking for a circuit where you can quickly sweep the frequency over a desired range, take a look at pages 9 -12 of the app note. What these circuits have in common is that they do not start with a sine wave generator, but with a triangle or similar wave that is then “beaten into shape” by various methods so that it more or less looks like a sine wave. You can change the frequency very quickly, but even if you put in considerable effort into the design of the wave shaping part of the circuit, you cannot expect such low distortion as in the Wien bridge circuits discussed above.

On page 13 starts the discussion of digital methods. Page 14 shows a 10-bit D-A converter that is driven by a chain of up/down counters to produce a triangle wave which is then converted into a sine wave, as discussed in the paragraph above. An even better method (if the desired frequencies are not too high) would be to substitute the up/down counters by a microcontroller (which might even include the D-A converter) and use a look-up table to generate the sine wave. Then you do not need the wave shaping network but just a little low-pass filter after the D-A converter. And you have the flexibility to change the sine wave to any waveform you can imagine with a minimum amount of effort.

You may also be interested in the other free E-books and Application Notes from Texas Instruments.

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