generating a 32Mhz clock
generating a 32Mhz clock
(OP)
Hi,
I am trying to build a 32MHz clock signal from a ring oscillator circuit. I used 74HC04 CMOS inverters [five of them] but the maximum frequency i could get was only 20Mhz. I reduced the number of inverters to 3, but i could get only 23MHz. I found the 74HC04 was rated to operate for 75MHz. My guess is that the Tr and Tf for the inverter [6ns] are too high.
Could anyone suggest me on this? I want to build the circuit from simple components [without using VCOs and frequency doubling circuits]. I would appreciate any help and advice in this matter.
thanks.
I am trying to build a 32MHz clock signal from a ring oscillator circuit. I used 74HC04 CMOS inverters [five of them] but the maximum frequency i could get was only 20Mhz. I reduced the number of inverters to 3, but i could get only 23MHz. I found the 74HC04 was rated to operate for 75MHz. My guess is that the Tr and Tf for the inverter [6ns] are too high.
Could anyone suggest me on this? I want to build the circuit from simple components [without using VCOs and frequency doubling circuits]. I would appreciate any help and advice in this matter.
thanks.





RE: generating a 32Mhz clock
RE: generating a 32Mhz clock
RE: generating a 32Mhz clock
As for your circuit, you could also have delays caused by stray capacitance forming an RC delay with the output resistance of the previous stage. If I am not mistaken, most 74HC04 devices actually have several stanges internally with the final stage being a buffer. To drive this buffer, two input stages are needed thus three inverters. A five stage ring is actually 15 stages!
RE: generating a 32Mhz clock
That's why most ring oscillators used to measure propagation delay are generally built with dozens of stages to ensure that sufficient settling of the gates has occurred before the next transition shows up.
TTFN