CD4093 oscillator frequency

Thot so. I couldn't believe what I was reading. :)

joe

See "MonolithicOscCMOS.pdf" on the S.E.D/Schematics Page of my website. ...Jim Thompson

I'm having a lot of senior moments lately. It's got me a little worried frankly, but worrying about things might be the reason.

A tablespoon of coconut oil a day keeps Alzheimer away[1][2][3].

joe

Darn, I was fixed to jump all over that one.

The bigger question is why the waveform at the cap is such a nice triangle.

If only you can remember to take it! Now what was it we were talking about?

Sounds to me the coconut business is slowing.

Jamie

Maybe the migrating swallows will bring more.

The other guys have already straightened you out on not loading 4000 CMOS with 200 ohms.

As far as depending on hysteresis, you can make the oscillator largely independent of hysteresis and thresholds by greatly increasing the voltage swing across the timing cap.

I solved that problem from scratch a few months ago, only to find I'd been beaten by, um, thirty years or so...

This oscillator...

Fig. 1 ====== |\ .----| >o--+--> | |/ | | Rt | | '----------+ | --- Ct --- | ---

has a timing swing across timing cap Ct equal to merely the hysteresis voltage, a small and highly variable quantity that varies with Vdd.

Fig. 2 ====== If you drive Ct's "cold" end with a buffer, though, you increase the swing by Vdd in each direction, making the timing dramatically less dependent on threshold or hysteresis.

R1 is a high value resistor to prevent the CMOS gate's input diodes from conducting and spoiling the R*C time constant. For accuracy, most of the timing current should flow thru Rt, thus, R1 >= 3 or 4*Rt.

|\ |\ .-- R1 --| >o--+---| >o--+--> | |/ | |/ | | Rt | | | Ct | '--------------+----||---'

The resulting behavior is surprisingly close to ideal.

Cheers, James Arthur

African or European swallows?

Barn.

Hmmm..data sheet curves indicate what you said, but those i worked with were all rather close to one half CMOS supply. Maybe because they all were RCA and "wanted" to be contrary to those data curves?

Nah, that's all conspiracy. :)

joe

Only an African swallow could possibly carry the weight.

If anybody ever asks you for the capital of Abyssinia, don't sweat. Just say, "What do you mean? The modern capital or one of the many ancient capitals."

It's a shame that guy didn't think of this.