This project includes the simulation of two stage Operational Amplifier design and postlayout simulation of different parameters of the Op-Amp.

• Overview of LV Op-Amp IP
• Block Diagram of Low Power Operational Amplifer IP
• Circuit Diagram of Low Power Operational Amplifer IP
• Specifications
• Performance Parameters
• Open Source Tools Used
• Installation in Ubuntu
  • eSim Installation
  • Ngspice Installation
  • SkyWater PDK Installation
• Installation in Windows
  • eSim Installation
• Pre Layout Schematic and Simulations
• Contributors
• Acknowledgmentsg
• Contact Information

The low power operational amplifier consists of two stages and operates at 1.8V power. It is designed to meet a set of provided specification such as high gain and low power consumption.

This two-stage op-amp is designed using the Skywater 130nm technology library. The proposed two stage op-amp consists of NMOS current mirror as bias circuit, differential amplifier as the first stage and common source amplifier as the second stage.

The first stage of an op-amp contributed high gain while the second stage contributes a moderate gain. The results show that the circuit is able to work at 1.8V power supply voltage (VDD)

• eSim

  • eSim (previously known as Oscad / FreeEDA) is a free/libre and open source EDA tool for circuit design, simulation, analysis and PCB design. It is an integrated tool built using free/libre and open source software such as KiCad, Ngspice and GHDL. eSim is released under GPL.
  • https://esim.fossee.in/home

• Ngspice

  • ngspice is the open source spice simulator for electric and electronic circuits.
  • http://ngspice.sourceforge.net/

• SkyWater Open Source PDK

  • The SkyWater Open Source PDK is a collaboration between Google and SkyWater Technology Foundry to provide a fully open source Process Design Kit and related resources, which can be used to create manufacturable designs at SkyWater’s facility.
  • https://github.com/google/skywater-pdk

• Magic

  • Magic is a venerable VLSI layout tool, written in the 1980's at Berkeley by John Ousterhout, now famous primarily for writing the scripting interpreter language Tcl. Due largely in part to its liberal Berkeley open-source license, magic has remained popular with universities and small companies. The open-source license has allowed VLSI engineers with a bent toward programming to implement clever ideas and help magic stay abreast of fabrication technology.
  • http://opencircuitdesign.com/magic/

• The eSim Software is currently available for Windows 7, 8 and 10 and Ubuntu 16.04 LTS and above

• The Magic Design Tool is available for Ubuntu

• Ngspice is installed when eSim is installed, but if any other version is needed please follow the steps mentioned

• The Pre-requisites for installing the following in Ubuntu are

  • git
  • make

• Install them using

  To make sure that you install the latest version of the software(that is the package information is up to date)

  $ sudo apt-get update
  

  $ sudo apt install git
  
  $ sudo apt install make
  

Please refer to the following links for proper installation of eSim

• https://static.fossee.in/esim/installation-files/Install_eSim_on_Windows.pdf

• https://github.com/FOSSEE/eSim/blob/master/INSTALL

Please refer to the following links for proper installation of Ngspice

• http://ngspice.sourceforge.net/download.html

• In Windows

  • Download the GitHub Repository : https://github.com/google/skywater-pdk

• In Ubuntu In terminal, execute the following commands

• To download the repository into the current working directory

  $ git clone git://opencircuitdesign.com/open_pdks
  

• Go to open_pks directory

  $ cd open_pdks
  

• Configure and install

  $ ./configure --enable-sky130-pdk
  
  $ make
  
  $ sudo make install
  

• The eSim Software is currently available for Windows 7, 8 and 10 and Ubuntu 16.04 LTS and above

• Ngspice and SkyWater PDK are installed when eSim is installed in Windows OS.

Please refer to the following links for proper installation of eSim

• https://static.fossee.in/esim/installation-files/Install_eSim_on_Windows.pdf
• https://static.fossee.in/esim/installation-files/eSim-2.3_installer.exe

Note: In windows there is no need to install ngspice and sky130nm PDK saperately. They will be installed when you install eSim directely.

Create the schematic of your circuit withh mos transistors and extract the netlist file and by using kicad to ngspice converter in eSim convert the spice file into ngspice file and follow the below steps.

• Step1. Please download sky130 from this link and unzip : https://static.fossee.in/esim/installation-files/sky130_fd_pr.zip
• Step2. Save the .cir.out file in the sky_fd_pr folder as .cir file.
• Step3. Open with notepad and add the path .lib "models/sky130.lib.spice" tt at the top.
• Step4. Replace with CMOSP, mos_p with sky130_fd_pr__pfet_01v8 and CMOSN, mos_n with sky130_fd_pr__nfet_01v8.
• Step5. To replace an inductor, capacitor, or resistor do it this way for example: L1 out gnd 1m by x1 out gnd mid 0 sky130_fd_pr__ind_03_90.
• Note: For more details go to the cells folder in sky_fd_pr. Open the specific component folder which you want to use. Then open the test folder and check the SPICE file. The SPICE file is an example of implementation of that component. You will get to know how to use the component in your ckt.
• Step6. Now Run the ckt with ngspice

• Step1. Right click on the .cir file.
• Step2. Click on Open With
• Step3. Browse for the ngspice.
• Step4. If ngspice is not present scroll down click on More Apps.
• Steps5. Go to the FOSSEE folder search for Ngspice. Run it.

Run the following commands in ngspice run command window after setting the location of the .cir file.

source differential_mode_gain.cir

Run the following commands in ngspice run command window after setting the location of the .cir file.

source common_mode_gain.cir

Run the following commands in ngspice run command window after setting the location of the .cir file.

source offset_voltage.cir

Run the following commands in ngspice run command window after setting the location of the .cir file.

source input_noise_spectrum.cir

To obtain Noise Spectrum

• Please run the following commands in the ngspice window for obtaining the plot

• Use setplot to see all plots available

  ngspice-> setplot
  

• select the plot which has "Noise Spectral Density Curves".For example,

  ngspice-> setplot noise1
  

• Then plot the graph using the command

  ngspice-> plot inoise_spectrum
  

source power_dissipation.cir

Note:

• The above simulation is done for 1Kohm load with 2mV p-p sine input

source slew_rate.cir

A much easier plot to see slew rate could be obtained by changing the analysis as

.tran 0.5f 10ns

The Transient Anlysis when the inputs are vin1=sine(0 1m 60) and vin2=sine(0 -1m 60).

source transient_analysis.cir

The Transient Analysis when the inputs are vin1=sine(0 5m 60) and vin2=0V

source temp_differential_mode_gain.cir

source temp_common_mode_gain.cir

source temp_offset_voltage.cir

Note:

• For performing any of the simulation mentioned in this repository the sky130_fd_pr folder is necessary.
• All simulation given in this repository are properly linked to the sky130_fd_pr library. Hence files execute with no error if the folders are kept as such
• For any external simulation using SkyWater Models, it is a must to properly include the library

• Velugoti Ashok kumar

• Kunal Ghosh, Director, VSD Corp. Pvt. Ltd.
• Sumanto kar, Assistant Project Manager, FOSSEE
• Dr.K.Babulu, Professor, Department of ECE, UCEV, JNTUK, DWARAPUDI Post, VIZIANAGARAM, A.P, 53500

• Velugoti Ashok kumar, Student, JNTU-GV CEV [email protected]
• Dr.K.Babulu, Professor, Department of ECE, UCEV, JNTUK [email protected]
• Kunal Ghosh, Director, VSD Corp. Pvt. Ltd. [email protected]
• Sumanto kar, Assistant Project Manager, FOSSEE