inventory + variety = success

[mstechca]

On a more electronics theme, an 8 bit R2R ladder still needs better than 0.5% tolerance resistors.

Actually, my PLL is 20 times more picky with me than my DAC!

For my DAC, I used 62K and 120K resistors, both at 5% tolerance, and the DAC works well for me. (at least the output of my circuit shows it).

I decided against 240K because the range of '"tolerable" resistances were from 228K to 252K, and for the 62K resistor, the range is only 58.9K to 65.1K. Big difference. Audioguru's Error rate (whatever the heck it's called) didn't even come into play because my resistors were well over 10K.

My PLL is so picky, because I have to get the two frequencies in comparison, spot-on without one trace of interference in order for it to work, or it will keep searching and searching.

My on-board oscillator is a 555 timer with two 120K resistors and a 0.1uF capacitor (5% tolerance, because they are cheaper).

The oscillator that is to be detected is exactly the same.
I bet anything its the tolerance! I'm going to have to pot each resistor! (add a potentiometer in series with it), just to compensate for the tolerances. and I think I will drop each one to 10K.

BUT, before I go to 10K, I was wondering, what is the absolute maximum speed a CMOS chip can operate at? I'm using the 4001 (Cmos NOR gates), 4077 (Cmos XOR gates), and the 4024 (Cmos counter).

I'm afraid if my clock runs too fast for the IC's, the PLL won't work.

In the meantime, I'll go and use POTS.

 

[audioguru]

For my DAC, I used 62K and 120K resistors, both at 5% tolerance, and the DAC works well for me. (at least the output of my circuit shows it).

I decided against 240K because the range of '"tolerable" resistances were from 228K to 252K, and for the 62K resistor, the range is only 58.9K to 65.1K. Big difference.

The difference is the same. 5% is 5%.

My on-board oscillator is a 555 timer with two 120K resistors and a 0.1uF capacitor.

Then its frequency is about only 60Hz.

I was wondering, what is the absolute maximum speed a CMOS chip can operate at? I'm using the 4001 (Cmos NOR gates), 4077 (Cmos XOR gates), and the 4024 (Cmos counter).

It's on their datasheets and depends on their supply voltage. A few MHz. You can't modulate your transmitter anywhere near that high.

I'm afraid if my clock runs too fast for the IC's, the PLL won't work.

You're darn right! The entire system won't work.