[SOLVED] Clock Voltage and Shape questions

Hi,

How could I determine the required clock characteristics for a particular IC?

Many datasheets list only frequency requirements. However, there are also important factors including:
1. Voltage.
2. Shape, which can be either sinusoid or square wave

For standard I/O pins, there are widely-adopted conventions that logic low is below 30% of DVDD_IO, and logic high is above 70% of DVDD_IO.

But does this apply to clock input? There can be several groups of power supply, including analog and digital at different voltages. So how can voltage and shape characteristics of input clock be known given these information?

Is there any convention here, or different chips has different specification?

Bob

Hi,

Perhaps I'm missing some point of your question, but clock signals is respect of micros and typical digital / ttl circuitry etc must be square wave* and conform the standards and voltages shown in the manufactures datasheets.
* assuming you are referring to standard oscillators for clocks , things like pwm pulses can have different widths.


Why you would think a sinusoid signal would be used in digital clock circuity I'm not sure ..??

wp100,

I was new to this. Now it is solved, thanks.

Bob

bobsun said:

wp100,

I was new to this. Now it is solved, thanks.

Bob

Click to expand...

Just to give some typical examples, most micros run off an oscillator, crystal or RC that derives its power from the host micro, so supply voltage is not an issue. Many newer micros have inbuilt oscillators anyway.

If you want to connect to other ciruitry, say your own oscillator etc then it must be either on the same Vdd as the micro or use some form of voltage converter when sending its signal to the micro.

This is becoming a problem as the old micros and associate devices were all running at 5v, but today many micros and new style devices are designed for 3v3, so creating a headache as its not always practacible, for the hobbyist, to find and use all the devices needed that run at the same voltage, hence the need for some form of voltage level shifter.

The power supply, can be digital or linear , no difference in practice.

hth

wp100,

I got it, thanks for the advices.

Bob