How Do You Design and Troubleshoot a Ring Oscillator in PSpice?

In summary, you designed a digital ring oscillator that uses logic inverters that have propagation delay times of tPLH = 28ns and tPHL = 42ns. However, the oscillator does not work in Pspice Capture. You may have to adjust the pmos bulk connection to vdd in order to get the oscillator to work.
  • #1
snoggerT
186
0
Design a digital ring oscillator using logic inverters that have propagation delay times of tPLH = 28ns and tPHL = 42ns.




The Attempt at a Solution



I'm using a general ring oscillator design using 3 CMOS inverters like this:

http://upload.wikimedia.org/wikipedia/commons/7/75/Ring_osc_5.png

I can't get this to work in Capture (Pspice) though. All I'm getting on the ouput is a DC signal. Can somebody explain to me how to get an oscillator to work in Capture? Also, how would you measure the tPLH and tPHL values?
 
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  • #2
Sounds like you didn't set an initial condition for one of your gate voltages...
I tried a simulation in both multisim and cadence orcad w/pspice.

For OrCAD, choose the part "IC1" from the SPECIAL menu then enter an initial voltage (I used 0V).
Connect this to any gate input of your inverters - then simulation should work.
FWIW, I chose ON_MOS parts for simulation (MbreakN/P will not converge for simulation... at least for me)

Same idea for Multisim, except you can add the initial conditions by editing the properties of the net.
 
  • #3
terranpro said:
Sounds like you didn't set an initial condition for one of your gate voltages...
I tried a simulation in both multisim and cadence orcad w/pspice.

For OrCAD, choose the part "IC1" from the SPECIAL menu then enter an initial voltage (I used 0V).
Connect this to any gate input of your inverters - then simulation should work.
FWIW, I chose ON_MOS parts for simulation (MbreakN/P will not converge for simulation... at least for me)

Same idea for Multisim, except you can add the initial conditions by editing the properties of the net.

- I'm actually using an older version of Pspice Capture (v. 9.1 student edition) since it's free. So I made my logic inverters with the EVAL parts IRF150 and IRF9140. I tried adding the IC1 part to the gate and it would only give me the first rise and then it would stay high endlessly. Is there maybe something wrong with using those MOSFETS?
 
  • #4
Could you post a screenshot / printout of your OrCAD schematic? I found your IRF150 under PWRMOS and the simulation worked fine for me.

One thing to note, are you sure your pmos bulk is correctly connected to vdd? For me, the part initially is 'upside down' according to how I usually layout my digital transistor schematics; and my first mistake was not noticing this - had to mirror the pmos vertically to correct this issue. This misalignment produces a simulation result similar to what you mention...

If that doesn't help I'll be glad to post my schematic/plots.
 

1. What is Pspice and how is it used in circuit design?

Pspice is a computer software program used for simulating electronic circuits. It allows users to create and analyze circuit designs, test their functionality, and determine the performance of different components.

2. What is a Ring Oscillator and how does it work?

A Ring Oscillator is a type of electronic oscillator circuit that generates a continuous output signal without the use of an external input signal. It consists of an odd number of inverters connected in a loop, with the output of the last inverter connected back to the input of the first. The oscillation is created by the continuous switching between logic high and logic low states of the inverters.

3. How is Pspice used to simulate a Ring Oscillator circuit?

Pspice allows users to create a schematic of the Ring Oscillator circuit, specify the necessary parameters such as power supply voltage and component values, and simulate the circuit to obtain the desired output waveform. Users can also modify the circuit and simulate it again to see the effects of different changes on the output signal.

4. What are the advantages of using a Ring Oscillator in circuit design?

Ring Oscillators are simple and compact circuits that do not require external components or an external input signal. They also have a wide frequency range and can be easily adjusted by changing the number of inverters in the loop. They are commonly used in digital systems for clock generation and timing applications.

5. Are there any limitations or drawbacks to using Pspice and Ring Oscillators in circuit design?

One limitation of using Pspice is that it relies on the accuracy of the input parameters and component models. If these are not accurately specified, the simulation results may not reflect the actual performance of the circuit. In terms of Ring Oscillators, they can be susceptible to noise and variations in supply voltage, which can affect the stability and accuracy of the output signal.

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