Designer’s Guide Community

mixed_signal

Senior Member

Offline

Posts: 183

low power current starved ring oscillator
Jun 30^th, 2012, 2:07am

Hi,
I am designing a low power current starved ring oscillator as shown in attachment. The bias current for each inverters is in the range of 50n to 100nA.
M1 M4 are in strong inversion saturation and act as current sources. i have made w/l very small like 1/40 to put them in strong inversion.

How do i size M2 M3? If i size for general inverter like 4/1 and 2/1 then they will be in weak inversion during switching at such low currents. Is that OK?
OR should i size them with w/L small so that the are in strong inversion?

Back to top

ringosc.jpg

IP Logged

AnalogDE Senior Member Offline Posts: 137	Re: low power current starved �ring oscillator Reply #1 - Jun 30^th, 2012, 11:43am M2 and M3 are just switches. They will be in linear operation region of operation for the most part. Start with min-L and wide enough so the voltage drop across them is small enough to keep the outer devices in saturation.
Back to top	IP Logged

mixed_signal Senior Member Offline Posts: 183	Re: low power current starved �ring oscillator Reply #2 - Jun 30^th, 2012, 8:14pm If w/l of M2, M3 is made greater than 1 then at current =40nA they will be in weak inversion. Isnt it a problem? To put them in strong inversion w/l of all transistors have to be <<1
Back to top	IP Logged

AnalogDE Senior Member Offline Posts: 137	Re: low power current starved �ring oscillator Reply #3 - Jul 1^st, 2012, 10:09am The goal in sizing the switches is to minimize Vds. You may also want to minimize the gate cap of the switches (minimize loading). All this necessitates a min L device with the smallest W that works for you.
Back to top	IP Logged

loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: low power current starved �ring oscillator Reply #4 - Jul 3^rd, 2012, 2:57pm what is this for? THis type of architecture is very noise sensitive (power and ground) and full of jitter problems in a VCO ring oscillator PLL.
Back to top	Jerry Twomey www.effectiveelectrons.com Read My Electronic Design Column Here Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical IP Logged

mixed_signal Senior Member Offline Posts: 183	Re: low power current starved �ring oscillator Reply #5 - Jul 3^rd, 2012, 10:16pm Hi loose-electron, This is for an ultra low power temperature sensor. I found this vco frequenc to be highly linear wrt bias current. I like it!!!! I want to do a transient simulation for the vco and at the same time sweep temperature during the transient. How can it be done in cadence?
Back to top	IP Logged

ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: low power current starved �ring oscillator Reply #6 - Jul 4^th, 2012, 7:36am Hi mixed-signal, Please look at http://www.designers-guide.org/Forum/YaBB.pl?num=1275773203/1#1 for changing temperature during a transient analysis. Yawei
Back to top	IP Logged

loose-electron

Senior Fellow

Offline

Best Design Tool =
Capable Designers

Posts: 1638
San Diego California

Re: low power current starved �ring oscillator
Reply #7 - Jul 7^th, 2012, 8:58pm

mixed_signal wrote on Jul 3^rd, 2012, 10:16pm:

Hi loose-electron,

This is for an ultra low power temperature sensor. I found this vco frequenc to be highly linear wrt bias current. I like it!!!!

I want to do a transient simulation for the vco and at the same time sweep temperature during the transient. How can it be done in cadence?

Put some impedance in the power and ground, and put some noise on both.

You may not like it so much after that.

Back to top

Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

IP Logged

mixed_signal Senior Member Offline Posts: 183	Re: low power current starved �ring oscillator Reply #8 - Jul 8^th, 2012, 9:02am Hi loose electron, I m interested in the simulations suggested. But how do u put impedance & noise in cadence? Can u explain ?
Back to top	IP Logged