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ICs for Sine wave signal generation (Any PDIP left?)

jdlui

I've been looking into ICs for sine wave signal generation and find that most ICs only generate square waves, and are sold as clock generators. I notice that the difference between square wave Clock Generators and true sine wave function generators is poorly delimited on RS Electronics. Both on RS and digikey, it seems Analog Devices is the only true supplier of something that can generate a sine wave, with something like the AD5932. Other companies like Silicon Labs or Linear Technology are just offering up oscillators and square wave clock generators.

 

Wondering if the market is truly this small. Are there other manufacturers of these chips? Any that still create PDIP chips? All we could find was the Exar XR2206 but is obsolete so my only options seems to be buying it from ebay or alibaba, which I'd like to avoid if possible. I looked a little further; it seems that all other function generator PDIP chips (MAX038, ICL8038) are going obsolete. Guess I may just have to up my soldering game!

 

I realize it's better to move to this SMD ICs but for basic prototyping and my beginner skill set, it's a lot easier to look for PDIP components. I'm trying to get into some Visual Light Communication and Li-Fi stuff, and learn how to transmit and receive a signal through an LED photodiode pair. I'd prefer to work with sine waves for now instead of an on-off keying system so that I have less noise, harmonics, and interference to worry about.

 

Any advice people can lend is appreciated. Any alternate websites or manufacturers that you could suggest?

 

Thanks!

Jordan

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  • 0 in reply to clem57

    Thanks for the link Clem.

     

    This indeed seems to be one of the major routes I can take. I need to analyze my project needs a bit more and understand the signal quality that would come out of a method like this. Other method I'm considering is using a square wave clock generator and trying to bandpass filter just the main signal to reconstruct a sine wave.

     

    However I'm honestly not sure which one would give me a better signal.

  • 0 in reply to jdlui

    This would be easier if you explained a little more what you are trying to achieve.

     

    My cheap function generator gets its sine wave (about 1% distortion) by shaping the triangular wave [using the non-linear characteristics of diodes]. The chips you mention above do something similar, only better because of the closer control they have over the semiconductor characteristics.

     

    If you try and do it by low-pass filtering of a square wave, the filter needs a steep cut-off to get the third harmonic down to an acceptable level [try it with a simulator and different orders of filter]. That will also have implications if the phase of the sine wave coming out relative to the square wave is important to you. If the frequency is variable, you'd need to accurately track it with the filter. You're getting into quite a lot of involved analogue design.

     

    If you need low harmonic content, then generating it with a wein bridge oscillator might be one way to go, but you can't move the frequency quickly and it takes time for the amplitude to settle.

     

    If you want it as simple as possible and aren't too concerned about frequency stability, traditional oscillators like the Colpitts and Hartley are possibles. At high frequencies you can move the frequency around using varactor diodes. At low frequencies, you might be able to do it crudely by switching capacitors into circuit with processor IO pins (just a thought I'm throwing in - don't ask me how to actually do it).

     

    A crystal oscillator should be capable of producing a good sinewave - the crystal is a good filter - but you won't be able to move the frequency by very much.

     

    If the frequencies are low, you'd probably be better off doing what Clem suggests and generating it from a microcontroller. If you massively oversample, the reconstruction filter on the output can be quite simple. If the frequencies are higher, you could do the same with programmable logic of some sort. The great advantage of this approach is that you might find you don't even want a sine wave - perhaps adjusting the waveform might improve the received waveform at the far end (preemphasis).

     

    Is it a high power LED you're driving? If so, by working linearly like this, you'll need a power amplifier. It's a lot more involved than just modulating the LED with PWM, which a simple LED driver will do for you as long as the frequencies aren't too high.

     

    Perhaps you should look at an old book on rf design for ideas. At one time, radio transmitters were basically a sine oscillator, a modulator of some sort, and then an amplifier stage.

Reply
  • 0 in reply to jdlui

    This would be easier if you explained a little more what you are trying to achieve.

     

    My cheap function generator gets its sine wave (about 1% distortion) by shaping the triangular wave [using the non-linear characteristics of diodes]. The chips you mention above do something similar, only better because of the closer control they have over the semiconductor characteristics.

     

    If you try and do it by low-pass filtering of a square wave, the filter needs a steep cut-off to get the third harmonic down to an acceptable level [try it with a simulator and different orders of filter]. That will also have implications if the phase of the sine wave coming out relative to the square wave is important to you. If the frequency is variable, you'd need to accurately track it with the filter. You're getting into quite a lot of involved analogue design.

     

    If you need low harmonic content, then generating it with a wein bridge oscillator might be one way to go, but you can't move the frequency quickly and it takes time for the amplitude to settle.

     

    If you want it as simple as possible and aren't too concerned about frequency stability, traditional oscillators like the Colpitts and Hartley are possibles. At high frequencies you can move the frequency around using varactor diodes. At low frequencies, you might be able to do it crudely by switching capacitors into circuit with processor IO pins (just a thought I'm throwing in - don't ask me how to actually do it).

     

    A crystal oscillator should be capable of producing a good sinewave - the crystal is a good filter - but you won't be able to move the frequency by very much.

     

    If the frequencies are low, you'd probably be better off doing what Clem suggests and generating it from a microcontroller. If you massively oversample, the reconstruction filter on the output can be quite simple. If the frequencies are higher, you could do the same with programmable logic of some sort. The great advantage of this approach is that you might find you don't even want a sine wave - perhaps adjusting the waveform might improve the received waveform at the far end (preemphasis).

     

    Is it a high power LED you're driving? If so, by working linearly like this, you'll need a power amplifier. It's a lot more involved than just modulating the LED with PWM, which a simple LED driver will do for you as long as the frequencies aren't too high.

     

    Perhaps you should look at an old book on rf design for ideas. At one time, radio transmitters were basically a sine oscillator, a modulator of some sort, and then an amplifier stage.

Children
  • 0 in reply to jc2048

    Jon,

    Thank you for the detailed and insightful reply! It has given me many things to think of.

     

    To succinctly summarize my goals with this hardware project: I'm trying to record received signal strength from multiple light sources which are modulating at different frequencies. Applications are for communications and localizing with visual light spectrum sources, aka LiFi and VLC Positioning.

     

    I realize that square waves are more practical and seems other researchers are indeed using square waves and OOK type modulation schemes. However for my initial steps into this topic, I was told that I may want to consider sine waves for my initial testing, simply to limit noise and harmonics.

     

    I realize going forward that I'll need to just use oscillators and modulate a square wave, so I will probably switch to square waves when I start building a multi light source system.

     

    My current research plan is to modulate 4 light sources, each one at a different frequency. I intend to receive the signal on a single photodiode and then use a transimpedance amplifier to convert to a voltage signal. From there I will use a bandpass filter to split each of the signals, and then use an RMS-DC converter to read the RMS, which is proportional to my Received Signal Strength. I read that other papers use fairly large frequency separations (like 1, 3, 5, and 9 kHz) so I believe that the BPF is fairly reasonable to realize. However it's my first time with all of this so I'm sure I'll hit some gritty realities as I move forward image. The design of this system would have each light using a unique but fixed modulation frequency. As a result I should only have to configure my BPF once, although I will have to spend some time tuning it well, especially if I'm using square waves and dealing with the harmonics. I've chosen a MAX274 PDIP BPF where I can implement multiple BPF in one package by just choosing the right resistors.

     

    I believe my frequencies at 1-100 kHz are relatively low so I'll indeed look into microcontrollers. Long term I'd like to realize a solution which I can retrofit into existing light fixtures so I've also ordered some small oscillators which I believe should suit my needs.

     

    For now I am using very small little LEDs, so I believe I do not need a power amp yet. However long term I want to be able to implement this modulation in a light source which can actually light a room. Maybe I'll leave this as a goal for later though image

     

    Thanks for the tip on the RF design book as well. I'm very new to this field so I think that a book would be a great idea for ideas and inspiration.

     

    Thanks again for the great insights and ideas!

     

    Jordan