4093 NAND GATE, different responses on OSCILLATOR

I was making a high noise immunity divide by two for square wave. I didn't even chose to use the D type edge triggered CMOS flip flop 4013, for the sake of best noise immunity in noisy enviornment. I was getting stuck in the responses from the circuit.The schmitt trigger NAND gate 4093 was used in divide by two circuit. The circuit wasn't behaving as it should and even I had made the final circuit in the first shot.When I checked it was not functioning as it should So I decided to do simple test on those IC, like I did the test of oscillation. I get abnormal results. Even though ICs are fresh,brand new and I have hundreds. I have 4093 from different manufacturers and their responses are different.

I made the simple circuit as shown in the 2nd figure. Just NAND gate two inputs are short and positive feedback of resistor with capacitor is given. I actually forget to show the complete input pins of the NAND gate, you can see only one input, actually there are two and both are short.
You can also see two 4093 IC, they both are of different manufacturers.

I use the formula f=1/RC, I choosed R=82K and C=0.22uF and I get the frequency of somewhere around f=55Hz.
IC which is from RS is given 55Hz
IC which is from SGS is given 221Hz

Why is this happening, i have new IC stocks and none had been used before.I used to believe before that I must always pays attention on the IC number and never give importance to whether the IC is from RS,SGS,Hitachi, Motorola,etc


Added after 1 hours 58 minutes:

I'm still working at this moment, trying to understand. I have investigate the datasheet of the two IC manufacturer. It's science as we all know. It's no magic going on. I have seen little bit changes in transition time from LOW->HIGH and from HIGH->LOW and maybe a little change in hysterisis voltage might be doing that. I don't know which factor would be doing this? I think that, I better find 4011 non-schmitt trigger NAND gate and put it and see the difference.

According to the datasheet, the 4093 hysteresis voltage can vary about a 1:4 range. In so far you should be aware of more than just a "small change", although most devices are probably near the typical values. But there's no guarantee.

The ST oscillator circuit doesn't work with a non-ST device, by the way. A resistor across an inverting gate actually provides negative rather than positive feedback, the circuit can only work as an oscillator by it's hysteresis. There are however RC-oscillator circuits for standard gates, that can be found in application notes and datasheets.

The ST oscillator circuit doesn't work with a non-ST device, by the way.

Click to expand...

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What are ST and non-st, I try to google it first, but I didn't come across anything related to electronics.One IC is from SGS and not ST. Other is from RS. Am I into correct direction.

ST -- Schmitt trigger

srizbf
26thjune2010