RC oscillator - your opinion on choosing component values

rc oscillator using 74hc04

Hello,

I need to use the 4046 PLL, and i don't know how to choose RC values that are optimum to minimize jitter&noise of the VCO?

In general, should I use a high C value, thus charging/discharging the cap with higher current, or use a lower C ?
Because I need a narrow VCO domain, offset should be used so the VCO range doesn't start from very low frequency?

Thanks

74hc4046 oscillator

If 4046 is too bad regarding jitter, i want to ask about another type.
A ring VCO based on inverters (74HC04) would give a lower jitter than 4046?
Or in general, ring VCOs are cleaner than RC VCOs?
It's something for hobby, and i thought of using 3 or 5 inverters from 74HC04, and controlling frequency from the 74HC04 supply. The datasheet says propagation delay varies a lot with supply voltage.

rc delay 74hc04

Well on the other wayyou can use R's metal film resistors and the C's NPO capacitors.
Good luck.

74hc04 rc osc

What are your jitter and frequency range specifications?

Re: RC oscillator - your opinion on choosing component valu

Thanks for reply.

Frequency 14-16MHz. Jitter should be minimized, as it is for a ham radio receiver - I know it will be bad anyway, but at least minimized.
I need to get quadrature outputs, so the 14-16MHz signal is divided by 4. Maybe the division will improve jitter a bit.
I use the PLL with a reference of 1-10kHz, not decided already.


Regarding 74HC4046

This document says increasing current reduces jitter
www.eecg.toronto.edu/~kphang/papers/2001/wilkin_vco.pdf , page 8.
I thought to use a large capacitor, use offset resistor, to increase the current, and reduce VCO range to the minimum needed.

Also I would try to decouple to ground R1 and R2 pins with 100n caps - these pins drive the internal current source. Is this good or bad?

I know it's not right, but I try to use this rather than an LC osc in an HF receiver. I've seen this https://groups.yahoo.com/group/softrock40/files/fracturedrock/fr80.pdf and now i have a bit of "courage"