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What is the simplest way of generating 42.8 [MHz] square (or sine) wave? I want to clock fast ADC for SDR purposes. I thought about wideband opamp and 10.7 [Mhz] cystal 4th harmonic. Is there any other solution?

Edit: I did search for specialized ic's but without success. I am looking for one piece device available for hobbyist. I live in EU and I don't want to import.

Edit2: For more clearance:

  1. Simple solution: power in, clock out
  2. Constant frequency
  3. Reasonable stability (for radio purposes)
  4. PLL is an alternative
  5. If you want to recommend device please do it only if it's available in mayor European retail distributor.
  6. Most companies do not send samples to Poland (unless you are a company which I am not) so samples are out of option :(
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Have you seen this chip from Texas Instruments?

http://www.ti.com/product/cdcs502

The CDCS502 is a crystal clock generator with built-in 4x clock multiplier.

The same 10.7 MHz crystal you mentioned above, plus one of these, will give you a nice stable 42.8MHz clock signal.

It also does spread-spectrum as an added bonus should that interest you at all.

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  • \$\begingroup\$ Cool, but not available where I live. \$\endgroup\$ – Maciej Kucia Sep 3 '11 at 11:32
  • \$\begingroup\$ Digikey ships to Poland, though I don't know how bad the shipping costs will be (for where I live, it's $8 flat rate, next day shipping...cant chose anything slower...). \$\endgroup\$ – Faken Sep 3 '11 at 23:04
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It's difficult to answer this without knowing exactly what may have access to or where you are willing to buy from - the other two answers are good examples of an easy solution to this, but were probably unaware of the conditions you seem to have added on. I have used a similar chip from TI (CDCE706) and it's a very easy solution for creating/manipulating high speed clocks of arbitrary frequencies.
FWIW, I also live in the EU and could have one of these (or the others mentioned, or plenty of cheaper options) next day delivery from e.g. Farnell or RS. You may want to look at ordering from somewhere like this to allow yourself more choice. The world is much smaller nowadays, I use Mouser like it was in the same country as the prices and delivery times are almost identical to local options.

However, you may want to look at a PLL like the 74HC4046, you are (maybe) more likely to find various types of this in a local electronics store. Since I have no idea what they may or may not stock, here is a list of possible options, also another list of clock synth ICs here.

Finding one capable of your required frequency in a DIP package will be harder nowadays, but there are plenty in reasonably friendly SOIC packages. You may have to relax your initial constraints on sourcing/packages to reach a decent solution.
You could roll your own RC/LC oscillator from discrete transistors/gates (e.g. hartley/colpitts/inverting gate, google will have loads of suggestions), but this would likely be far from ideal stability wise compared to a clock synth. The crystal harmonic oscillator would be an option, or indeed (if you can find one, I couldn't quickly) a ready rolled oscillator package at this frequency.

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  • \$\begingroup\$ I would even take BGA device if necessary :) CDCE706 is a first ic available in Farnell from the list of devices presented in this thread. I do know world is small nowadays but customs office seems not to understand that (I think it's different if you buy as company). PLL was an alternative to harmonic oscillator from the beginning, but such solution doesn't feel the simplest solution to me. Thanks for help! \$\endgroup\$ – Maciej Kucia Sep 3 '11 at 19:57
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The Si570 is a useful device for that sort of thing:

http://www.silabs.com/products/clocksoscillators/xo/Pages/default.aspx

Alternatively, you could design a simple 10.7 MHz crystal oscillator and use two doubler stages to get 42.80 MHz.

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  • \$\begingroup\$ Hard to get, high price. I am not looking for something universal but simple. \$\endgroup\$ – Maciej Kucia Sep 3 '11 at 11:43
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There are several options for you. Some of them will work for you, some won't. All of them apply to whatever frequency you need, not just 42.8 MHz. I'll list all of the options here, even if they probably don't apply to you, in order to help other folks with similar issues:

  1. Buy a standard crystal or oscillator with the exact frequency you want. How easy this is depends on your qty, and the frequency. I do notice that Digikey sells 42.8 MHz oscillators, but they are expensive and out of stock. If you need 50+ of them, or so, most manufacturers will custom make a batch with the exact frequency you want. For smaller qty you might be limited to the most standard frequencies.

  2. Get a "programmable standard oscillator". These are normal crystal or MEMS oscillators that can be programmed at the factory or in the lab for whatever frequency you want. Often the distributor/manufacturer/rep will program it for you, so getting qty 1-10 is possible. For the hobbyist, you should assume that you will probably program them yourself. There are many manufacturers of these, including Epson and SiTime.

  3. Use a Frequency Synthesizing PLL. These are chips that you put in a reference clock (which can be almost anything) and will output whatever frequency you want. Some store the settings in on-chip Flash, while others have to be reprogrammed on power-up. Most use an I2C interface for programming, but others use SPI or some sort of non-in-circuit device. I have used the Cypress Cy22150 on many boards, but there are many other companies that make similar products. These chips are nice because you are not limited to 42.8 MHz. You can select any clock frequency at any time.

Without knowing the details of your design or ability, I would recommend using option 3. It is the most flexible, relatively inexpensive, and is within the grasp of most hobbyists.

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  • \$\begingroup\$ Far too complex solutions. I want to make a simple board power input clock output. PLL synth is what I will probably try if 4th harmonic opamp generator will fail. \$\endgroup\$ – Maciej Kucia Sep 3 '11 at 19:46

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