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  3. CMOS analog delay circuit help

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CMOS analog delay circuit help

Donatello
Donatello over 12 years ago

Hello Everyone!

 So i am designing this analog circuit, basically which can delay a singal (ac signal) by about 1ms. I am looking into the bucket brigade concept as invented by F.L.J.Sansgter back in the 1960s and 70s.

The circuit and basic topology can be found on these web pages:

(2.1 from here) 

http://www.electrosmash.com/mn3007-bucket-brigade-devices

http://www.google.com/patents?id=mJF8AAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q&f=false

Basically, you have a row of Nmos or Pmos transistors turning on and off with two out of phase clock pulses at their gate. The source/drain is connected to a capacitor which stores the charges. So after a number of such stages, the signal gets delayed.

However, i am having trouble with Cadence simulating it. I have tried LTspice and Multisim, which show the simulation as a delay, but Cadence does not. This is important as for my custom IC i have to simulate and get it working in Cadence first and then do the LVS as well.

I am attaching the images from my design and simulation run.

I am using VPulse to generate the clocks.

I am using Vsin to generate a sine wave. The signal can be arbitrary as right now the aim is to get some sort of delay.

Transistors are the standard NMOS from the XH035 PRIMLIB family, as we are going to run for 350nm process.

The capacitors, resistors and ground are from the analogLib.

I have put in a filter at the end and on the simulation you can see the signal out with and without the filter.

Please help me analyze this. The weird thing is that it seems to be working in LTspice but not in Cadence. I have tried adding a source-follower at the signal out, but it still doesn't help.

Is there anything special i need to do? 

Oh yes, i am using Cadence Virtuoso IC6.1.3.500.13

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  • Donatello
    Donatello over 12 years ago
    Can i not upload images from my PC?
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  • Andrew Beckett
    Andrew Beckett over 12 years ago

    First of all, there is no such tool "Cadence" (that's the Company name, not the name of any tool) - so which simulator are you trying to use?

    Secondly, you can update pictures (one per post) by using the Options tab that you'll see at the top when you Reply to an Existing message (it's just under the words "Reply to an Existing message").

    Almost impossible to help you without more details.

    Regards,

    Andrew.

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  • Donatello
    Donatello over 12 years ago
    The bucket brigade circuit
    • bucketbrigade.png
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  • Donatello
    Donatello over 12 years ago
    Simulation run
    • newBBD_simulationrun.png
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  • Donatello
    Donatello over 12 years ago
    Clock properties
    • clock_properties.png
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  • Donatello
    Donatello over 12 years ago
    NMOS properties
    • nmos.png
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  • Donatello
    Donatello over 12 years ago
    VSin for the signal in
    • vsin.png
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  • Andrew Beckett
    Andrew Beckett over 12 years ago

    Did you really mean to have a 12.5 milliFarad capacitor on the output? That's enormous!

    I didn't check the rest of the circuit, but that looks clearly wrong to me... 

    Andrew

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  • Donatello
    Donatello over 12 years ago
    I am using Virtuoso Analog design environment IC6.1.3.500.13 and using Spectre that comes in the ADE L/XL package.
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  • Donatello
    Donatello over 12 years ago

    Hi Andrew, That's just for the filter, but i have also shown the signal before going into the filter.

     

    When Spectre runs the simulation, does it assume the capacitance values in real time?

     

     

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