Low Power Design Techniques

Sizing a n-input standard gate (where n≠1)

Load Capacitance = C_LOAD

Input Capacitance of the n-input NAND gate = C_N

Beta ratio of n-input NAND gate = β_N

Input Capacitance of equivalent inverter = C_INV

Beta ratio of equivalent Inverter = β_INV

(a) Logical Effort:

(b) Assume an inverter in place of the n-input NAND gate:

Now, the equivalent pull-down strength of the n-input NAND gate is:

Hence, adding WN_N and WP_N we get C_N:

E.g. for ND2, β_N = 1 and for INV β_INV = 2:

Wire resistive shielding

With a very long wire, the net RC for calculations is assumed to be 50% of the actual RC. This is because of resistive shielding of the long wire. The driver can only see 50% of the actual RC and increasing the drive-strength by more than that required for a 0.5RC won't give us any more benefit.

Sizing the bit-line pre-charge device

Margins

Slopes

Better Tracking

Sizing the bit-line keeper

The bit-line keeper should be sized so that the following criterion are met:

1. Writability

2. Keeper Leaker Ratio

Design Margins in SRAM Design

To basic types:

• Self Timed: Does not vary with frequency, process, temperature, voltage
• Frequency Dependent: Varies with each timing, process corner

Self-Timed Margin (STM) can be of two sub-types:

• STM(Functional): Not meeting this margin breaks your functionality and the design is broken. For Example: Setup and Hold Violations.
  Typically 15% pre-layout and 10% post-layout

• STM(Crowbar): Not meeting this margin, causes a crow-bar current. You lose performance and power, but the design is correct functionally. For Example: Turning off pre-charge clock after the word-line turns on, causes the bit-line to discharge very slowly and there is a huge crow-bar current flowing through it. This impacts your clk2q and also is a huge power drain.
  Typically 0-10% pre-layout and 10% post-layout

Sorting in a huge data file

Instead of writing a perl code that uses Bubble Sort/Quick Sort/or any other sorting algorithm, simply use "sort" command in unix.

## unix sort
## sort -gk 4,4 inputfile -o outputfile
## -g :general, handles scientific notation
## -k 4,4 :start and end on 4th field