Author Topic: Cheapest way to generate 100Mhz sine wave  (Read 12164 times)

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Offline freebilTopic starter

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Cheapest way to generate 100Mhz sine wave
« on: August 11, 2016, 03:56:20 pm »
Hello. Is there any cheap way to generate 100Mhz sine wave? I have 2 ad9850 dds. Is it possible to add the frequencies of each 9850 sine wave and see the result to the oscilloscope?
« Last Edit: August 11, 2016, 06:28:11 pm by freebil »
 

Offline Fungus

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Re: Cheapest way to generate 100Mhz sine wave
« Reply #1 on: August 11, 2016, 07:03:27 pm »
I understand your AD9850 has some frequency limitation though I am not sure what that is. 

The cheapo eBay modules go up to about 25MHz before they start falling apart.

 

Offline joeqsmith

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Re: Cheapest way to generate 100Mhz sine wave
« Reply #2 on: August 12, 2016, 01:05:08 am »
A 100 MHz oscillator can be made with about $0.1 of parts, a single transistor and a few passive components could be used to make
a Colpitts type oscillator or Hartley type oscillator which produce sine waves when adjusted properly.

Agree with evb149.  Really depends what you need.    Here's a simple 80 - 100MHz single 2n4401 transistor oscillator I stuck on some protoboard.   Cheap.
 
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Offline joeqsmith

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Re: Cheapest way to generate 100Mhz sine wave
« Reply #3 on: August 12, 2016, 11:45:32 am »
You could also build a 100 MHz signal generator with logic gates (perhaps some kind of ring oscillator or crystal controlled one) and then buffer that and apply the signal to a series LC filter tuned to 100 MHz to get something like a sine wave from the fundamental frequency of the input square wave.

Again I agree with evb149's comment.  I had to search for it but I had posted a fair amount of data using 7400 logic.   

https://www.eevblog.com/forum/projects/waveforms-in-a-74ls04-ring-oscillator/
 
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Offline bobaruni

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Re: Cheapest way to generate 100Mhz sine wave
« Reply #4 on: August 12, 2016, 12:05:52 pm »
You could put the ad9850's output through a frequency multiplier with a tuned output for ~100Mhz.
A single transistor amplifier with a tank in the collector tuned to 100Mhz should do the trick.
Just feed a sub-harmonic of the desired exact frequency (near to or on 100Mhz) on the input and the tank will resonate at an integer multiple of the input.
If you want to combine the outputs of both ad9850's, you will need preferably a double balanced mixer with a similarly tuned output.
« Last Edit: August 12, 2016, 12:17:42 pm by bobaruni »
 
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Offline KE5FX

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Re: Cheapest way to generate 100Mhz sine wave
« Reply #5 on: August 13, 2016, 05:52:34 am »
All you need is a filter of some sort.  Your AD9850 will put out a healthy signal at 100 MHz in its second or third Nyquist zone. 
 

Offline freebilTopic starter

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Re: Cheapest way to generate 100Mhz sine wave
« Reply #6 on: August 13, 2016, 07:48:28 am »
Thanks for the answers. Is it possible to use the built in ds1054z filters?
 

Offline Kalvin

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Re: Cheapest way to generate 100Mhz sine wave
« Reply #7 on: August 13, 2016, 01:25:58 pm »
If you need a better frequency accuracy, you can add a simple and cheap PLL which will keep your $0.10 oscillator stable.

You can use the AD9850 as the reference oscillator for the PLL so you can fine-tune or adjust the output frequency easily.
« Last Edit: August 13, 2016, 01:31:43 pm by Kalvin »
 

Offline ADT123

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Re: Cheapest way to generate 100Mhz sine wave
« Reply #8 on: August 13, 2016, 03:25:39 pm »
If you are more worried about the frequency accuracy than purity of the sine wave then a quick way would be to buy a 100MHz CMOS crystal oscillator (couple of dollars/pounds/euros).  They are available in 4 pin DIP packages (power, ground and output).

It will output a square wave in theory but in practice the output driver will not be fast enough to produce the 3rd, 5th and above harmonics so it will be pretty sine wave like anyway.  To improve check the output impedance from the datasheet and then choose a capacitor value to make a low pass filter (cap between the output and ground) with a corner frequency of about 80MHz.  That will attenuate the 100MHz signal a bit but will get rid of most of the 200MHz and above frequency components.  On a scope it will look like a sinewave, you might see small harmonics if you FFT it but for many applications its not an issue.
Disclaimer: I have worked for Pico Technology for over 30 years and designed some of their early oscilloscopes. 

We are always recruiting talented hardware and software engineers! Happy to answer Pico related questions when time permits but here as electronics is a hobby
 


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