Slow-Slow (Ss) Corner
Slow-Slow (SS) corner represents the slowest possible transistor performance — combining slow process, low voltage, and high temperature to create worst-case delay conditions, the critical corner for setup timing verification.
What Is SS Corner?
- Definition: Slow process + low voltage + high temperature.
- Characteristics: Maximum threshold voltage, minimum mobility, lowest drive current.
- Purpose: Verify setup timing, worst-case delays, minimum performance.
SS Corner Parameters
Process: Slow transistors (high Vth, low mobility).
Voltage: Minimum supply (e.g., 0.9V for 1.0V nominal).
Temperature: Maximum (e.g., 125°C or 150°C).
Result: Slowest possible transistor switching.
Why SS Corner Matters?
- Setup Time: Critical paths must meet timing at slowest corner.
- Functionality: Chip must work even with slowest transistors.
- Yield: Determines which chips pass timing requirements.
- Guardbanding: Defines safety margins for manufacturing.
What Gets Verified
Setup Time: Ensure data arrives before clock edge.
Critical Paths: Identify and fix slowest timing paths.
Frequency: Determine maximum operating frequency.
Functionality: Verify correct operation at slow corner.
Margins: Ensure adequate timing slack.
Applications: Setup timing analysis, frequency binning, yield prediction, timing closure.
Typical Values: 30-50% slower than typical corner, 10-100× lower leakage than FF.
SS corner is the slowest marathon runner — if design meets timing here, it will work for all manufactured chips.