Clock Circuit help

Hello, I need help in building a on chip clock for a Digital to Analog Converter, I am using a Successive Approximation chip DM74LS503, the circuit will be designed with a 100khz input analog signal, the sampling frequency will be 200khz according to nyquist sampling theorem( or so I have estimated)
200Khz * 8 bits * Needing a clock of 1.6Mhz. I can only use cmos parts like, inverters , and resistors and capacitors. How do I do this should I do this.?

CMOS gates like the 4049, 4011 and 4001 will work for an oscillator, with two resistors and a capacitor, or you can use an MM5369 to reduce parts count.

10 Oct 2008 17:41 HEEEEEEEEEEEEEEEEEEELP


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i need the code and circulate of this system

i have to devise a plan the its a digital clock with this form : hours:min:sec
and it should have and LCD with two rows

mail it to me plz

tears_love_2(at)yahoo.com

Code for what microcontroller? Is it a school assignment?

mario279 said:

with a 100khz input analog signal, the sampling frequency will be 200khz according to nyquist sampling theorem( or so I have estimated)

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The Nyquist theorem gives the absolute theoretial minimum for the sample frequency. You actually need a sampling frequency somewhat higher than 200kHz if you want to reproduce a 100kHz signal. For example if the input frequency were exactly 100kHz with a 200kHz sampling frequency, each sample would occur at exactly the same point on the 100kHz signal and the sampled output would be a DC level. You also need some room with practical filters to avoid aliasing (see https://en.wikipedia.org/wiki/Nyquist_frequency for more info).

answer

blueroomelectronics said:

Code for what microcontroller? Is it a school assignment?

Click to expand...

ts should be written by 8051
i forgot to tell you
thansk for ur help

ok so based on carl's comment, I made to adjustments to the sampling rate and decided to have a sampling frequency of 300khz for a input frequency of 100khz and a clock circuit of 2.4Mhz. Thanks. Shockjok, I researched on your idea of creating an oscillator with cmos inverters setup as an oscillator, but my problem was, how do you get a specific frequency? I know that you can work with the propagation delay, but is that exact? according to some specs the average propagation delay of the cd4007 cmos inverters is 50ns. Thanks for the chip 5369, that should work like a charm, hopefully they will take that, but they told me I have to build it from inverters, caps and resistors though....

A variable frequency can be obtained with 2 CMOS inverters, a capacitor and a potentiometer. Experiment with different component values until you get the required frequency. A CMOS databook should have a suitable circuit you can use.