Continue to Site

# What is "Worst Case Simulation"?

Status
Not open for further replies.

#### 020170

##### Full Member level 4
When I want to do Worst Case Simulation through simulation tool like spice,

What do I do?

I Know I have to consider many conditions voltage variation, coner simulation.

however I don't know exactly What do I do and What do I observe as power supply variation happens.

thanks.

worst case simulation depends on the spec of the devices you use... if you want to operate the device in a particular region of operation then calculate the value in the edge of that region and simulate to find the value of other parameters at that point....

worst case simulation depends on your design. you can use corner analysis.

Depending on your design and conditions of operation, the worst case simulation can be a corner case simulation.

My way: First, do simulation sperately at different temp, process corner and power supplies. Second, accumulate all the worst(min. or max.) conditions. At last do the worst simulation at all worst conditions(temp, power supplies and process corner).

B/R
Edwin

### 020170

Points: 2
worst case simulation means, for eg when you simulate an opamp you are interested in its phase margin so that the opamp is stable.so you look for the corner at which the phase margin is least.So the designer should try meeting the spec at this worst case corner, thus ensuring that the design works even at the worst possible operating conditions.

amarnath

but if every time use simulate to find the worst case,it's troublesome

I don't remember exactly but in cadence, you can choose 3 cases of simulations: worst case, normal case, and best case. You can use the two latter for principle simualtion meanwhile the first one for real operation. Of course you can add a margin to the worst case to make sure it works. Is it what you wonder about?

you must meet all corner in your simulation, first of all, consider TT, then FF and SS, as a product, you must make sure all condition your IC can works properly.

### 020170

Points: 2
The worst/best corner condition has to be evaluated by the designer for each spec he is interested in. e.g lets say we are interested in delay of an inverter and that it shouldnt give more than 1 ns delay under any condition. the way we go about is we have to find P(process),V(supplyvoltage),T(temperature) at which delay is worst. we know that Slow process is defined as max. VTH which causes max delay condition. in a similar was min voltage and max temperature is also the worst case for delay. hence we have to ensure that delay is below 1ns at Slow,max temp and min supply voltage. similarly worst case PVT can be derived for any spec like UGB of a amplifier to phase noise of a oscillator. so this helps.

HI,Why the MAX temperature is the worst case when calculate the delay time ?
As we kouw ,the VTH reduce when temperature increase.So, in my opinion ,the worst case should been ss process ,min voltage and min temp.
Correct me if mistake.

docini said:
The worst/best corner condition has to be evaluated by the designer for each spec he is interested in. e.g lets say we are interested in delay of an inverter and that it shouldnt give more than 1 ns delay under any condition. the way we go about is we have to find P(process),V(supplyvoltage),T(temperature) at which delay is worst. we know that Slow process is defined as max. VTH which causes max delay condition. in a similar was min voltage and max temperature is also the worst case for delay. hence we have to ensure that delay is below 1ns at Slow,max temp and min supply voltage. similarly worst case PVT can be derived for any spec like UGB of a amplifier to phase noise of a oscillator. so this helps.

I usually simulate the circuits for the following corners:
Process:tt,ff,fs,sf,ss
Voltage:min,type,max
Temperature:min,type,max

### 020170

Points: 2
Worst case simulation is where your simulation results is below than the specification of your products that you design for. So, after seeing the worst case corner simulation results as others mentioned, you need to optimize your design again in order to meet the least design specs.

worst case is the case your simulation result is worst to fit your design spec. In general it is "ss" 125°C corner.

holddreams said:
I usually simulate the circuits for the following corners:
Process:tt,ff,fs,sf,ss
Voltage:min,type,max
Temperature:min,type,max

Processes: tt, ff, fs, sf, ss are what I know when working with Cadence. Is there any equivalent thing in ADS?

Status
Not open for further replies.