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CMOS analog delay circuit help

Donatello

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

Parents

  • Hi Andrew,

     

    Thanks for your response. I obviously don't want to put you in under any demand, any help on this forum is much appreciated.

     Can you tell me what parameters you used for your design? I mean, this BBD has been done before and that too on CMOS, so i don't see why i shouldn't be able to do it. There were chips like Panasonic MN3xxx series and Reticon TDA1022, they work very well and their schematics show the same concept which i have tried.

    I understand the transistor capacitance thing, but at the moment i am looking for some delay. As you can see my output signals are just clock glitches, no delay. My clocks are out of phase, i have shown the clock setting in the image. One clock is DC voltage 1 while other one has dc voltage 2. 

     

    Also, what do you mean by complementary switches? 

Reply

  • Hi Andrew,

     

    Thanks for your response. I obviously don't want to put you in under any demand, any help on this forum is much appreciated.

     Can you tell me what parameters you used for your design? I mean, this BBD has been done before and that too on CMOS, so i don't see why i shouldn't be able to do it. There were chips like Panasonic MN3xxx series and Reticon TDA1022, they work very well and their schematics show the same concept which i have tried.

    I understand the transistor capacitance thing, but at the moment i am looking for some delay. As you can see my output signals are just clock glitches, no delay. My clocks are out of phase, i have shown the clock setting in the image. One clock is DC voltage 1 while other one has dc voltage 2. 

     

    Also, what do you mean by complementary switches? 

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