IC clock source

[John Gutmann]

does any one know of a single IC that i can use as a clock source that requires no other components, if i have to connect pins that is alright

i know of the 555 but that requires a capacitor and resistors and that is really in convienent

what i am looking for is like a decade counter with a built in clock and optional frequecies are optional

i dont know if any of you follow me on this but any questions just pm or post

thx

[Jeff Pahl]

The DS1099 from Maxim (Dallas Semi) is pretty cool if it covers the frequency range you need: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4226/ln/

Maxim has a whole line of programmable oscillators at http://www.maxim-ic.com/products/tim...oscillator.cfm , they are pretty much all surface mount but don't require any external components. We use them at work for various test related circuits, a lot of them are field programmable so we can set them for whatever specific weird frequency we need.

[Al Skierkiewicz]

Sparks,
You didn't specify the frequency and that is really important. If it is in the MHz range, a few CMOS inverters and a crystal will get you what you need. For that matter an RC network and a few inverters get you the same thing with temperature induced frequency drift. For low frequency, ease of use, wide power supply and adjustability you can't beat a 555 and you can pick them up anywhere.

[John Gutmann]

how would that cmos inverter and crystal thing work?

[Al Skierkiewicz]

Any oscillator has a few requirements to operate. One is that the loop must have 360 degrees of phase shift (or multiples of 360) and the loop must have unity gain or better to begin and sustain oscillation. An inverter has 180 degree phase shift already, input to output. Adding a feedback network from the output back to the input that adds an additional 180 phase shift will cause the circuit to oscillate since an inverter is (by definition) a unity gain device. A simple crystal connected from the output of an inverter back to the input will cause the crystal to start osciallating and produces the required phase shift. There are other methods that insure that the oscillator will start, run without temperature or capacitive influences changing the output frequency or stability. There are several resources on these designs both on the internet and the library. This type of oscillator produces a square wave if that is what you need. Crystal oscillators generally are high frequency types, i.e. >100kHz. If you are looking for something lower, then the 555 or one of the other IC timers would be your best bet. There are a few cheap crystal modules that are designed to be used for timing applicataions. They have a crystal running at 32kHz and divide down to an accurate 1Hz pulse. Digital watches use this method to keep accurate time over several days-weeks.