Hi all


Could you help me please to design a ring oscillator circuit using MOSFET inverters ( 5 stages ) to get a frequency about 20 MHz ?

- recommended software is LTspice or Multisim


Thanks in advance for your help

 

Welcome to AAC!
Is this a school/college project?

 

no

 

Hello,

Have a look at this wiki page:
http://en.wikipedia.org/wiki/Ring_oscillator

Bertus

 

If this is not homework, who recommended LTspice or Multisim?

 

I need to work on these two programs

 

Google for application notes from National Semiconductors. I recall at least two of them explaining the basics.

 

The problem with the ring oscillator is that it is critically dependent on device factors that are not critically controlled during manufacture. Beyond the obvious suggestion of an integrated or discrete crystal oscillator, there are other non-resonant oscillator structures that give you more control over its design and operation. 20 MHz might be a bit high for a classic phase-shift oscillator, but you could do one with ECL gates.

ak

 

Yes that is right. Actually I have to use MOSFET in order to save power and in the meanwhile I got 25 Mhz using 3 stages inverters and supply voltage of 8v. This voltage is considered high and I need to reduce it but the problem is that there no output waveform when the voltage reduced below 8v. do you have suggestion about what type of MOSFET I have to use with low voltage needed?

 

Can you post your schematic?

ak

 

Hello,

For a 5 gate ring oscillator wich should produce 20 Mhz, you would need a propagation delay of total 50 nS.
This will yield to a propagation delay of 10 nS for one gate.
This can be found in TTL chips, but cmos will be most likely to slow.

Bertus

 

Please find the attached schematic

 

Yes that is right. Actually I have to use MOSFET in order to save power and in the meanwhile I got 25 Mhz using 3 stages inverters and supply voltage of 8v. This voltage is considered high and I need to reduce it but the problem is that there no output waveform when the voltage reduced below 8v. do you have suggestion about what type of MOSFET I have to use with low voltage needed?

Are you trying to design with 5 stages, or 3? What is your desired operating voltage? Any reason why you're using high current devices?

 

dear Dennis,
'' Are you trying to design with 5 stages, or 3?'' ....... I need to design both of them.

''What is your desired operating voltage?'' ................ the desired voltage is 3.3 v .

''Any reason why you're using high current devices?'' ............. no, please advise me if you have suggestion about type and serial number of the MOSFET transistor.

thanks

 

Look for some low threshold voltage devices. I think it's going to be difficult to get 5 stages to work at 3.3V; even 3 stages may be difficult. Don't use power devices; larger devices mean more parasitics and you don't need the drive capability.

 

With all of its amplitude and frequency stability issues, why are you focused on a ring architecture?

ak

 

I need it in a specific application