VSD Intern - 10-bit DAC design using eSim and Sky130

Design 10-bit DAC from scratch using eSim - open source EDA tool for circuit design by FOSSEE IIT Bombay and Sky130 PDKs

Overview

Most of the signals around us, in the world we live in are not digital in nature, rather they are analog. The digital systems can understand only digital signals, not analog. Hence, it becomes important to interface the digital systems we the external analog world. The analog input signals are to be converted to digital signals using Analog to Digital Converters at the input end of the digital system. After the processing by the system, the digital signals are to be converted back into analog signals using Digital to Analog Converters.

A n-bit Digital to Analog Converter (DAC) takes a n-bit digital word and converts it into a proportional analog voltage with respect to the reference voltage. The potentiometric DAC uses the concept of Voltage Divider. In an N-bit DAC, the analog voltage range, i.e. the Vref (here 3.3 V) is equally divided into 2^N voltage values. This is achieved by a series on 2^N equal resistors and taps are provided across each R. The combination of switches to tap the values is designed using the N-bit digital word as input.

This circuit was designed using eSim

eSim (previously known as Oscad / FreeEDA) is a free/libre and opensource EDA tool for circuit design, simulation, analysis and PCB design. It is an integrated tool built using free/libre and opensource software such as KiCad, Ngspice and GHDL. eSim is released under GPL.

eSim offers similar capabilities and ease of use as any equivalent proprietary software for schematic creation, simulation and PCB design, without having to pay a huge amount of money to procure licenses. Hence it can be an affordable alternative to educational institutions and SMEs. It can serve as an alternative to commercially available/licensed software tools like OrCAD, Xpedition and HSPICE.

Objective:

Introduction
Basic 10-bit DAC Design
eSim Installation and basic Switch Circuit Design
Steps to label and simulate using eSim
DAC circuit design implementation using eSim
Implement 2-bit DAC using Swtich
2-bit DAC Working
From 2-bit DAC to 10-bit DAC using eSim symbols
DAC layout using eSim
Layout and post-layout introduction
Layout of Resistor
Design of Switch Layout
Labelling, extraction and post-layout simulations
Design of 2-bit DAC layout
10-bit DAC Layout
Conclusion

Audience Profile:

Beginner VLSI students curious to know about eSim and circuit design
Expert VLSI Physical designers curious to know about custom IP design using real foundry PDKs like Sky130