A glance at avsdbgp_3v3 IP

avsdbgp_3v3 is a Bandgap Reference circuit, which is used to generate a constant voltage reference in analog domain which is independent of temperatarure and supply voltage variations.

The objective was to achieve some specifications using only open-source tools with the Flow/FreePDKs provided by VLSI Computer Architecture Research Group (VLSIARCH) at Oklahoma State University (OSU).

To get an basic idea about this IP, the working principle, basic implementation, applications and significance, kindly go thru this

Symbol and Pin descriptions

Parameters

To view the specifications, go through this

Below is the compiled list of parameters according to specifications

Parameter	Description	Min	Type	Max	Unit	Condition
RL	Load resistance	100			Mohm	T=-40 to 125C
CL	Load capacitance			1	pF	T=40 to 85C
Vbgp	Output Reference voltage	1.28464	1.28	1.28627	V	T=-40 to 140C
TC_Vbgp	Temperature Coefficient of Vbgp	-25	5	2	ppm/C	T=-40 to 125C
VC_Vbgp	Voltage Coefficient of Vbgp	0.065	0.07	0.08	V	V=2.1 to 6.6, T=-40 to 125C
V_Noise	Noise at Vbgp Terminal				uV rms	Vdd= 3.3V T=27C, f=0.1 to 10Khz
T_start	Start up time				uS	Vdd=27c, T=27C, Cl=50pF
VDD	Supply Voltage	2.1	3.3	3.6	V	T=-40C to 125C

Future work and limitations

• The reference voltage needs to be more accurate with specifications.
• A working Enable circuitry needs to implemented for easy switching of IP.
• The post layout spice file has parasitic BJTs. Their origin shall be studied and tried to get rid off.
• The Bipolar models are imported from LTspice.
• The futurework involves working/obtaining on a compatible Bipolar model with osu180nm tech, Which is not included in OSU libraries.

IP usage

Tools needed to view and simulate this IP

1. Ngspice

Ngspice is the open source spice simulator for electric and electronic circuits. Ngspice is an open project, there is no closed group of developers.

Installing Ngspice in Ubuntu 20.04

Open the terminal and type the following to install Ngspice

$  sudo apt-get install ngspice

2. Magic

Magic is a VLSI layout tool.

Installing Magic in Ubuntu 20.04

Open the terminal and type the following to install Magic

$  wget http://opencircuitdesign.com/magic/archive/magic-8.3.32.tgz
$  tar xvfz magic-8.3.32.tgz
$  cd magic-8.3.32
$  ./configure
$  sudo make
$  sudo make install

Steps to clone this git repository in Unix based systems for simulating waveforms.

Open the terminal and type the following

$  sudo apt install -y git
$  git clone https://github.com/ankursah5/avsdbgp_3v3

Pre-Layout simulations

• To run and view the waveforms, type the following commands after cloning in above step.

$  cd avsdbgp_3v3/Prelayout/Cir/
$  ngspice

• This opens ngspice shell.
• To plot Vref vs Temperature (-40 to 140C) at Rload = 100Mohms, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 1bgr_tv.cir

• To Plot Vref vs Vdd (2V to 4V) at Rload=100Mohms, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 2bgr_vv.cir

• To plot Temperature Co-efficient of Vref vs Temperature (-40 to 125C) at Rload=100Mohms, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 3bgr_tc.cir

• To plot Voltage Co-efficient of Vref vs VDD(2.1V to 3.6V) at Rload=100Mohms, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 4bgr_vc.cir

• To plot Start-up Votage variation with time using ramp signal, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 5bgr_su.cir

Post-Layout simulations

• To view the layout, type the following comand in continuation with pre-layout simulations,

ngspice 1 -> exit

• This exits the ngspice shell.
• In the terminal, type the following commands.

$  cd ..
$  cd ..
$  cd Postlayout2/Mags
$  magic -T osu018.tech bgr1.mag

• To run and view the post- layout waveforms, type the following commands after above steps in terminal.

$  cd ..
$  cd spice \files/
$  ngspice

• This opens ngspice shell.
• To plot Vref vs Temperature (-40 to 140C) at Rload = 100Mohms, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 1pl_tv.spice

• To Plot Vref vs Vdd (2V to 4V) at Rload=100Mohms, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 2pl_vv.spice

• To plot Temperature Co-efficient of Vref vs Temperature (-40 to 125C) at Rload=100Mohms, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 3pl_tc.spice

• To plot Voltage Co-efficient of Vref vs VDD(2.1V to 3.6V) at Rload=100Mohms, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 4pl_vc.spice

• To plot Start-up Votage variation with time using ramp signal, Type the following in Ngspice shell and press enter.

ngspice 1 -> source 5pl_su.spice

Author

Ankur Sah

Acknowledgments

• Kunal Ghosh, Director, VSD Corp. Pvt. Ltd.
• Philipp Gühring, Software Architect, LibreSilicon Assocation
• Saroj Rout, Associate Professor & Chief Mentor of VLSI Center of Excellence SIT, Bhubaneswar, India
• Santunu Sarangi, Asst. Professor, SIT, Bhubaneswar, India
• Tim Edwards, Senior Vice President of Analog and Design at efabless corporation
• Sheryl Serrao, Undergraduate Student, Mumbai University
• YALAMANCHILI VAHINI M.tech Embedded Systems, NIT Jamshedpur

Contact Information

• ANKUR SAH, M.tech Embedded Systems, NIT Jamshedpur [email protected]
• KUNAL GHOSH, Director, VSD Corp. Pvt. Ltd. [email protected]
• PHILIPP GÜHRING, Software Architect at LibreSilicon Association [email protected]
• Dr. GAURAV TRIVEDI, Co-Principal Investigator, EICT Academy, IIT Guwahati [email protected]