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  1. 4018898 final gds oasis by Jeff DiCorpo · 1 year, 1 month ago main
  2. 130371c Merge pull request #1 from rohinthram/patch-1 by Nalinkumar S · 1 year, 1 month ago
  3. b9e973c Update caravan.spice by rohinthram · 1 year, 1 month ago
  4. a146ddd Update info.yaml by Nalinkumar S · 1 year, 1 month ago
  5. e078220 update by Nalinkumar S · 1 year, 1 month ago





Current Starved Voltage Controlled Oscillator (VCO)

This repository presents the design of an analog IP - avsdvco_1v8

It is a Current Starved Voltage Controlled Oscillator targerting 180nm tech for PLL based applications.

Table of Contents

Introduction

A VCO is the heart of the PLL and can be designed either by LC or RC. A LC VCOs have superior phase noise performance compared with ring VCO’S. However, an LC VCO has a small tuning range, large layout area and possibly higher power. The ring oscillators, however, do not have the complication of the on-chip inductors required for the LC oscillators. Thus the chip area is reduced and have a wide tuning range; ring oscillators with even number of delay cells can produce quadrature-phase outputs. “Current-Starved” means that the current through the circuit is indeed limited. Lowering Vn and increasing Vp increases the effective drive resistance Req of the inverter and thus increases the delay.The current in the first NMOS and PMOS are mirrored in each inverter/current source stage.Further tuning of oscillation frequency is done by adjusting the value of ID by changing size of bias stage transistors. Two buffer inverters are additionally used after inverter stages for preventing output loading(A large capacitive load may affect the Fosc and Kvco ).

The image shown below is a 5 stage - Current Starved VCO

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Block-Diagram

The block diagram of the proposed Current Starved VCO can be found below:

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Specifications

ParameterSymbolMin ValueTypical ValueMax ValueUnit
Technology--180-nm
Supply VoltageVDD1.51.82.0V
Operating Temperature RangeT-40+27+85°C
Control VoltageVCTRL0.40.91.6V
Output VCO FrequencyF_OUT174 K907 M1.75 GHz
Linearity--90.28-%
Power consumption--400-uW

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Open Source Tools Used

🌟 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.It can serve as an alternative to commercially available/licensed software tools like OrCAD, Xpedition and HSPICE.

    🔗 https://esim.fossee.in/home

🌟 Ngspice

  • Ngspice is a mixed-level/mixed-signal electronic circuit simulator.

  • Ngspice is based on three open-source free-software packages:

    • Spice3f5
    • Xspice
    • Cider1b1

    🔗 http://ngspice.sourceforge.net/

🌟 Sky130 PDK

  • The SKY130 is a mature 180nm-130nm hybrid technology originally developed internally by Cypress Semiconductor before being spun out into SkyWater Technology and made accessible to general industry. SkyWater and Google’s collaboration is now making this technology accessible to everyone.

  • The SKY130 Process Node is an extremely flexible offering, including many normally optional features as standard (features like the local interconnect, SONOS functionality, MiM capacitors, and more). This provides the designer with a wide range of flexibility in design choices.

    🔗 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. However, it is the well thought-out core algorithms which lend to magic the greatest part of its popularity.

  • Magic is widely cited as being the easiest tool to use for circuit layout, even for people who ultimately rely on commercial tools for their product design flow.

    🔗 http://opencircuitdesign.com/magic/

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Clone This Repository

  • Clone this repository using git clone command
$ git clone https://github.com/Nalinkumar2002/caravel_avsdvco_1v8_sky130.git

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Pre Layout Simulations

Tools And PDK Used For Pre-Layout Simulations

  • eSim
  • Ngspice
  • Skywater130 PDK

Installation Of Tools And PDK

📥 eSim:

📥 Ngspice :

📥 Sky130 PDK :

  • Use git clone method
$ git clone https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_pr

Place sky130_fd_pr folder in current working directory to avoid errors during simulations.

Pre-Layout Schematics And Simulations

Schematics

Current Starved VCO is designed using eSim and the screenshot of schematic file is shown below

Simulation

After creating the schematics, spice netlist was extracted with the help of esim and the necessary model files of sky130 tt transistors were included in the netlist and transient analysis was performed.

The result of transient analysis of VCO @ vctrl = 0.9 V is shown below

📢 Output frequency of VCO F_out = 937 MHz

🔶 Transient analysis is performed for different control voltages and output frequencies are tabulated for corresponding control voltage and graphs are plotted .

🔶 Similarly, transient analysis is performed for different plots

  • ✔️ AVSDVCO_1V8 BIAS CURRENT VS CONTROL VOLTAGE
  • ✔️ AVSDVCO_1V8 OUTPUT FREQUENCY VS BIAS VOLTAGE

💠 AVSDVCO_1V8 BIAS CURRENT VS CONTROL VOLTAGE

💠 AVSDVCO_1V8 OUTPUT FREQUENCY VS BIAS VOLTAGE

Executing The Pre-Layout Simulations

  • Change directory using command
 $ cd Pre_Layout_Simulations
  • Run the avsdvco_1v8_pre_layout.cir.out file in ngspice to perform simulations
$ ngpice avsdvco_1v8_pre_layout.cir.out
  • Output graphs are displayed on the screen after the execution .
  • To perform various transient analysis follow the README.txt given in that directory or please find it below by clicking README.txt
 ==================================== 
 IP Name :avsdvco_1V8
 PDK : Sky130 PDK by Google SkyWater
 ==================================== 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Name of the author : NALINKUMAR S 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 --------------------------------->
 To perform Pre-Layout Simulations 
 --------------------------------->
 	
 --> In file "avsdvco_1v8_pre_layout.cir.out" change the control voltage and transient command to get output for various control voltages.
 --> To get outputs at different control voltages change the transient command according to control voltages given below for perfect output graphs
 
 ---------------------------------------------------
  VCTRL (Control Voltage) |    Transient command
 ---------------------------------------------------
	0.4 V   	  |	tran 10ns 100us
	0.5 V		  |	tran 1ns 5us
	0.6 V		  |	tran 100ps 500ns
	0.7 V		  |	tran 10ps 50ns
	0.8 V		  |	tran 10ps 20ns
	0.9 V  		  |	tran 1ps 10ns
	1.0 V		  |	tran 1ps 5ns
	1.1 V		  |	tran 1ps 5ns
	1.2 V		  |	tran 1ps 5ns
	1.3 V		  |	tran 1ps 5ns
	1.4 V		  |	tran 1ps 5ns
	1.5 V		  |	tran 1ps 5ns
	1.6 V		  |	tran 1ps 5ns
	
 *Note: -> Before performing simulations keep the " sky130_fd_pr " folder in current working directory to avoid errors.
 	-> To get output frequency vs bias voltage plot varry VDD from 1.5 V to 2.0 V @ VCTRL = 0.9 V


 --> After performing all analysis the values are tabulated and output graphs are ploted :
	
	TABLES:
	-------
	-> AVSDVCO_1V8 OUTPUT FREQUENCY VS CONTROL VOLTAGE - avsdvco_1v8_pre_layout_table_1.png
	-> AVSDVCO_1V8 BIAS CURRENT VS CONTROL VOLTAGE - avsdvco_1v8_pre_layout_table_2.png	
	-> AVSDVCO_1V8 OUTPUT FREQUENCY VS BIAS VOLTAGE - avsdvco_1v8_pre_layout_table_3.png
	
	PLOTS:
	------
	-> AVSDVCO_1V8 OUTPUT FREQUENCY VS CONTROL VOLTAGE - avsdvco_1v8_pre_layout_output_1.png
	-> AVSDVCO_1V8 BIAS CURRENT VS CONTROL VOLTAGE - avsdvco_1v8_pre_layout_output_2.png	
	-> AVSDVCO_1V8 OUTPUT FREQUENCY VS BIAS VOLTAGE - avsdvco_1v8_pre_layout_output_3.png
	-> AVSDVCO_1V8 TRANSIENT ANALYSIS @ VCTRL = 0.9 V - avsdvco_1v8_pre_layout_output.png   
  

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Post Layout Simulations

Tools And PDK Used For Post-Layout Simulations

  • Magic
  • Ngspice
  • Skywater130 PDK
  • Sky130A Tech file

Installation Of Tools And PDK

📥 Magic :

  • To install magic follow the steps below
    $ 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

📥 Ngspice :

📥 Sky130A Tech file :

  • Download Sky130A Tech file in Layout_Files folder in this repository and place it in current working directory.

📥 Sky130 PDK :

  • Use git clone method
$ git clone https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_pr

Place sky130_fd_pr folder in current working directory to avoid errors during simulations.

Post-Layout Layout Implementation And Simulations

Layout

Layout of VCO is implemented using magic tool and screenshot of layout is shown below

5-Stage Ring Oscillator Layout

Simulation

After the layout implementation, spice netlist was extracted and the necessary model files of sky130 tt transistors were included in the netlist and transient analysis was performed.

The result of transient analysis of VCO @ vctrl = 0.9 V is shown below

📢 Output frequency of VCO F_out = 907 MHz

🔶 Transient analysis is performed for different control voltages and output frequencies are tabulated for corresponding control voltage and graphs are plotted .

🔶 Similarly, transient analysis is performed for different plots

  • ✔️ AVSDVCO_1V8 BIAS CURRENT VS CONTROL VOLTAGE
  • ✔️ AVSDVCO_1V8 OUTPUT FREQUENCY VS BIAS VOLTAGE

💠 AVSDVCO_1V8 BIAS CURRENT VS CONTROL VOLTAGE

💠 AVSDVCO_1V8 OUTPUT FREQUENCY VS BIAS VOLTAGE

Extracting The Spice File

  • To Change directory using command
 $ cd Layout_Files
  • To open magic tool
 $ magic -T sky130A.tech
  • To open avsdvco_1v8.mag file , Select File --> Open --> avsdvco_1v8.mag

  • To extract spice file , Type the following commands in magic commmand window

    % save <file-name>
    % extract all
    % ext2spice
  • Spice file will be created in current working directory and necessary changes are done to .spice file and saved as avsdvco_1v8_test.spice

Note: The avsdvco_1v8_test.spice file later renamed to avsdvco_1v8_post_layout.cir.out in Post_Layout_Simulations directory for easy access.

Executing The Post-Layout Simulations

  • To Change directory using command
 $ cd Post_Layout_Simulations
  • Run the avsdvco_1v8_post_layout.cir.out file in ngspice to perform simulations
$ ngpice avsdvco_1v8_post_layout.cir.out
  • Output graphs are displayed on the screen after the execution .
  • To perform various transient analysis follow the README.txt given in that directory or please find it below by clicking README.txt
 ==================================== 
 IP Name :avsdvco_1V8
 PDK : Sky130 PDK by Google SkyWater
 ==================================== 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Name of the author : NALINKUMAR S 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 --------------------------------->
 To perform Post-Layout Simulations 
 --------------------------------->
 	
 --> In file "avsdvco_1v8_post_layout.cir.out" change the control voltage and transient command to get output for various control voltages.
 --> To get outputs at different control voltages change the transient command according to control voltages given below for perfect output graphs
 
 ---------------------------------------------------
  VCTRL (Control Voltage) |    Transient command
 ---------------------------------------------------
	0.4 V   	  |	tran 10ns 100us
	0.5 V		  |	tran 1ns 5us
	0.6 V		  |	tran 100ps 500ns
	0.7 V		  |	tran 10ps 50ns
	0.8 V		  |	tran 10ps 20ns
	0.9 V  		  |	tran 1ps 10ns
	1.0 V		  |	tran 1ps 5ns
	1.1 V		  |	tran 1ps 5ns
	1.2 V		  |	tran 1ps 5ns
	1.3 V		  |	tran 1ps 5ns
	1.4 V		  |	tran 1ps 5ns
	1.5 V		  |	tran 1ps 5ns
	1.6 V		  |	tran 1ps 5ns
	
 *Note: -> Before performing simulations keep the " sky130_fd_pr " folder in current working directory to avoid errors.
 	-> To get output frequency vs bias voltage plot varry VDD from 1.5 V to 2.0 V @ VCTRL = 0.9 V

 --> After performing all analysis the values are tabulated and output graphs are ploted :
	
	TABLES:
	-------
	-> AVSDVCO_1V8 OUTPUT FREQUENCY VS CONTROL VOLTAGE - avsdvco_1v8_post_layout_table_1.png
	-> AVSDVCO_1V8 BIAS CURRENT VS CONTROL VOLTAGE - avsdvco_1v8_post_layout_table_2.png	
	-> AVSDVCO_1V8 OUTPUT FREQUENCY VS BIAS VOLTAGE - avsdvco_1v8_post_layout_table_3.png
	
	PLOTS:
	------
	-> AVSDVCO_1V8 OUTPUT FREQUENCY VS CONTROL VOLTAGE - avsdvco_1v8_post_layout_output_1.png
	-> AVSDVCO_1V8 BIAS CURRENT VS CONTROL VOLTAGE - avsdvco_1v8_post_layout_output_2.png	
	-> AVSDVCO_1V8 OUTPUT FREQUENCY VS BIAS VOLTAGE - avsdvco_1v8_post_layout_output_3.png
	-> AVSDVCO_1V8 TRANSIENT ANALYSIS @ VCTRL = 0.9 V - avsdvco_1v8_post_layout_output.png   
  

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Observations

🏷️ Maximum frequency of VCO achieved for pre-layout simulations F_OUT = 1.8 GHz @ vctrl= 1.6 V

🏷️ Maximum frequency of VCO achieved for post-layout simulations F_OUT = 1.75 GHz @ vctrl= 1.6 V

🏷️ VCO frequency increases (F_OUT) when control voltage (VCTRL) is being increased for both pre-layout and post-layout simulations.

🏷️ Bias current increases (I_BIAS) when control voltage (VCTRL) is being increased for both pre-layout and post-layout simulations.

🏷️ Vco output frequency (F_OUT) increases when Bias voltage (VDD) is being increased for both pre-layout and post-layout simulations.

🏷️ During pre-layout simulations, the output frequency of the VCO is dependent about 90.46 % linearly on control voltage.

🏷️ During post-layout simulations, the output frequency of the VCO is dependent about 90.28 % linearly on control voltage.

🏷️ Power consumption of circuit after layout implementation @ Frequency = 907 MHz with 50 ohm load = 400 uW

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Future Work

🏁 Linearity of the VCO can be increased.

🏁 Tuning range of VCO can be increased further.

Author

🖊️ Nalinkumar S , B.E (Electronics and Communication Engineering), Madras Institute of Technology, Anna University, Tamil Nadu

Acknowledgements

📖 Kunal Ghosh, Co-Founder of VLSI System Design (VSD) Corp. Pvt. Ltd. - kunalpghosh@gmail.com