Implementation of bandgap reference circuit on Skywater's open-source 130nm pdk.
Table of Contents
A bandgap reference circuit implementation on Skywater’s open-source 130nm process design kit (pdk) is proposed here. A simple bandgap topology is valuated with a set of simulations and then implemented in open-source EDA tools. In the design, a current mirror without operational amplifier is used to keep the topology simple. For more information, please check here.
Design specifications and requirements are listed here.
Parameter | Description | Min | Type | Max | Unit | Condition |
---|---|---|---|---|---|---|
Technology | 130 nm CMOS Process | |||||
RL | Load resistance at Vbgp terminal | 100 | Mohm | VDD=3.3V, T=27C | ||
Vbgp | Output Reference voltage | 1.197642 | 1.201057 | 1.212476 | V | T=-40 to 140C, VDD=3.3V |
Vbgp | Output Reference voltage | 1.178285 | 1.201057 | 1.211677 | V | VDD=2.7V to VDD=3.6V, T=27C |
TC_vbgp | Temperature Coefficient of Vbgp | 6.8717 | ppm/C | T=-40 to 140C, VDD=3.3V | ||
VC_vbgp | Voltage Coefficient of Vbgp | 2.7802 | %/V | VDD=2.7V to 3.6, T=27C | ||
VDD | Supply Voltage | 3.2 | 3.3 | 3.6 | V | T=-40C to 140C |
IDD | Supply Current | 3.954 | uA | EN=1 | ||
IDD | Supply Current | 607.836 | nA | EN=0 |
Open-source tools are used to design and simulate bandgap reference circuit.
XSCHEM is a schematic capture and netlisting EDA tool. In addition to Xschem, a version named Xschem_sky130 which is optimised to work with Skywater's 130nm pdk is used. For more information, please check this link.
Although XSCHEM is not required to run simulation files in this repository, it can be installed with built-in ngspice tool and support for sky130 pdk. Please follow set up steps mentioned in this video.
ngspice offers a spice simulator to model active, passive, analog and digital elements of a device according to parameters provided by semiconductor manufacturer. For more information, please check this link.
Installation on Ubuntu
sudo apt-get install -y ngspice
Magic is a opensource VLSI layout tool. Please check link.
Installation on Ubuntu
sudo wget "http://opencircuitdesign.com/magic/archive/magic-8.3.122.tgz"
tar -xvzf magic-8.3.122.tgz
cd magic-8.3.122
sudo ./configure
sudo make
sudo make install
A simple current mirror topology is implemented to achieve stable reference voltage output.
Here are the steps to run simulation files,
git clone https://github.com/swarup-p/bandgap-ref-on-sky130.git
cd avsdbgp_3v3_sky130_v1/pre-layout/spice-deck/
ngspice
Run below commands in ngspice terminal to get the simulation results.
Reference voltage (vbgp) vs variations in supply voltage Vdd (2V to 4V)
source pre_vv_check.spice
Reference voltage (vbgp) vs variations in temperature (-40 to 140) degree
source pre_tv_check.spice
source pre_vc_check.spice
source pre_tc_check.spice
source pre_startup_check.spice
Check the current values when enable terminal is at logic 1 and when enable terminal is at logic 0.
source pre_enable_check.spice
Check the layout file in magic,
cd avsdbgp_3v3_sky130_v1/layout/
magic -T ../lib/sky130A.tech avsdbgp_3V3.mag &
Here are the steps to run simulation files,
git clone https://github.com/swarup-p/bandgap-ref-on-sky130.git
cd avsdbgp_3v3_sky130_v1/post-layout/spice-deck/
ngspice
Run below commands in ngspice terminal to get the simulation results.
Reference voltage (vbgp) vs variations in supply voltage Vdd (2V to 4V)
source post_vv_check.spice
Reference voltage (vbgp) vs variations in temperature (-40 to 140) degree
source post_tv_check.spice
source post_vc_check.spice
source post_tc_check.spice
source post_startup_check.PNG
Check the current values when enable terminal is at logic 1 and when enable terminal is at logic 0.
source post_enable_check.spice
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Add cascode transistors in the design to improve stability of output reference voltage.
-
Add a resistor at the gate terminal of enable transistor.
-
Improve enable logic to consume low current when enable logic is 0.
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Perform PNR of the design using openLANE flow.
Here are some reference links used to learn to design in open source EDA tools and about bandgap reference circuit design.
1. https://github.com/nickson-jose/vsdstdcelldesign
2. https://github.com/praharshapm/vsdmixedsignalflow
3. https://github.com/sherylcorina/avsdbgp_3v3
4. https://github.com/an3ol/General-purpose-Bandgap-Reference-avsdbgp_3v3
5. https://www.udemy.com/course/vlsi-academy-custom-layout/
- Kunal Ghosh - Co-founder (VSD Corp. Pvt. Ltd)
- Tim Edwards - Senior Vice President of Analog and Design at efabless corporation
- Anmol Purty - VSD Intern
- Sheryl Serrao - VSD Intern