# Setup¶

## Setup PySpice¶

We use own compiled version of ngspice and set NGPSICE_LIBRARY_PATH accordingly. Reason is to use more recent version (>= 35) that speeds up the simulation wirh the ngspice decks. Also the provided .spiceinit file in the running directory is needed to get this speed up.

We use l of 2µm

# Bandgap design¶

This is a quick design for a working bandgap design. Better optimization for sensitivity to process and voltage variations are left for a follow-up exercise.

## bipolar ratio¶

We use 9 bipolar transistor in the design in a common centroid design: 1 in the first branch; 4 in the second and third branch. This results in a ratio for the bipolars for 1:4

## Transistor sizing¶

We assume a supply voltage of 3.3V nominal and design to optimize the temperature sensitivity for this nominal voltage. If we assume a voltage over the bipolars of around 0.7V we can design the circuit for 20µA for a l of 2.0µm. As Vt for nmos is lower than for pmos to compute the w of the transistors we use Vds of 1.25V for nmos and 1.35V for pmos. This gives values for w of 3.7µm for nmos and 18µm for the pmos.

## Resistor sizing¶

### Resistor 1 sizing¶

We size resistor 1 to get the 20µA current used for sizing the transistors