NAND gate oscillator frequency calculation

[ukiceman]

Hi Guys

I’m just working my way through the “Electronic Circuits for the Evil Genius”, only been doing this for a little over 3 month. I’m in the middle of doing the NAND gate oscillator tutorial using the HEF4011BN CMOS Chip and, as usual, i’m stuck on the maths. Could somebody help me with the frequency calculation please?

I've been told to look at this link

fairchildsemi.com/an/AN/AN-118.pdf

I’ve had a look at the link and, the first formula I came across on page one I crunched into a calculator giving me the same answer

( 2 x 3 ) x ( 17 x 10-9) = 1 / answer = 9.8 Mhz

I've also been told that.... a general equation is

{2.1....2.4*R*C}

Why does the equation in the link above on page one, give the answer without anything to with RxC in the equation

I've included a graphic of the circuit i'm working on

C2 = .1uf
R4 = 2 megohms

The book is using

C2 = .1uf
R4 = 2.2 megohms, and suggests I should be seeing around 1Hz which is what i'm seeing on my scope. The book doesn’t mention the formula it’s just saying what I’m seeing on my scope which is 1hz using a .1uf cap and a 2megohm

I’m just looking for a calculator friendly way that gives me the answer I’m looking for but when i put my numbers in, i don't get 1hz

Thanks

 

[Resqueline]

Page one formula refers to page one diagram, which is a resistor- & capacitor-less oscillator, working on delay-time.
You'll want to use the formulas on page two. The diagram differs slightly from your circuit but is probably equal with regards to the calculations.
The last three simplified formulas might be what you're after.

 

[neon]

You just cannot calculate anything correctly since the gates threshold are not really set for it. Approximte yesor get a pot somewhere and tweeak