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1 MHz clock generation - need suggestion of oscillator

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donmarino

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1 MHz clock generation

I have to design a circuit for clock generation. Clock frequency is in the range of 1 - 10MHz and the special requirement is stability over temperature (lower then 2%) and tunability of oscillation frequency with 10 bits (step of 500Hz).
I think that these requirements are a little bit difficult to achieve with cmos ring oscillator. Probably a R-C oscillator is the best solution. Any suggestion?
thanks in advance for your support
 

1 MHz clock generation

too many potential solutions. but in general, sounds like you need a digitally controlled oscillator. there are many of them out there. one I recently saw is based on the si570 chip, and you can control it via a mcu.

temperature stability is more difficult. one approach is to use a power transistor as heating element, and a thermister as a temp sensor to control the current going through the power transistor. stick the power transistor to either the chip or the crystal to maintain temperature.
 

Re: 1 MHz clock generation

Sorry, I forgot to say that it has to be designed in full custom standard CMOS technology 0.18um
 

Re: 1 MHz clock generation

10 bits of control looks more like 9.7 KHz step size to me. What are the EXACT frequencies you are trying to hit, or do you not care, as long as it is tunable? Can you use external crystal resonator?
 

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    donmarino

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1 MHz clock generation

You are right, I don't care about exact central frequency (it has just to be in the range of 1MHz - 10MHz), what is important is that it is tunable around its value with 10 bits and step of about 500Hz (sorry but the first message of this topic was uncurrectly "step of 500KHz"). External resonator cannot be used for cost reduction, neither other external components
 

1 MHz clock generation

I think RC could achieve your goal.
You can use a switch res array or switch cap array to tune the frequency.
 

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