Design Analog Mixed Signal blocks Using Open Source Tools©

Objectives

• The main aim of the lab is to propose an open source framework for a full-custom Integrated Circuit (IC) design, as shown in Figure 1. The framework relies on the cooperation of open resources; Xschem for schematic editing,NGspice for circuit netlisting/simulating,Python for data analysis. As a result, the proposed open-source framework facilitates freely sharing and commercialization of the Integrated circuits design.

• A part of the presented framework is an xray tool which provides several benefits; It provides a deep automated analysis,a fully characterization of analog IP blocks,improvementof productivity time, assessment of maturity design.

• Herein, a practical example for xray tool is xray4ota.

Figure 1. Open-Source Framework for Full-Custom IC Design.

Tools/Packages Installation

• Since the proposed framework relies on open-source tools, they can be installed freely on MS Windows or Linux operating system. In practice, the tools have been installed on a Linux server, and users can log in remotely.

Next, a short note about each used tool.

• XSCHEM is a schematic capture program. It provides a graphical method to draw an electronic schematic circuit, easily. XSCHEM can support main four netlist formats; SPICE netlist, VHDL netlist, VERILOG netlist, and tEDAx netlist. Consequently, once drawing the schematic circuit, a circuit netlist can be generated for simulation. Noted, the schematic circuit is saved with an extension of “.sch”.

• NGSPICE is an open-source spice simulator for electric and electronic circuits. It contains existing SPICE features with some extra analyses such as modeling methods and device simulation features. NGSPICE is mainly used for computer-based circuit simulations (Analog, Digital, and Mixed-mode simulations). Noted that, NGSPICE can be executed using two different ways: batch mode or interactive mode. The latter model is preferred because it allows for running a script. The NGSPICE can be saved with an extension of “.cir”. Moreover, a file including the netlist and NGSPICE is saved with an extension of “.spice”

• SkyWater Open Source Physical Design Kit (PDK) is a collaboration between Google and SkyWater technology foundry to provide fully open-source PDK and related resources, which can be used to create manufacturable designs at SkyWater’s facility.

• Python is widely powerful programming. It can be integrated with NGSPICE simulator for data manipulation/analysis and visualization. Python makes NGSPICE more powerful. Noted, the python script is saved with an extension of “.py”. You have to import the following modules; import os, sys, import spice_read, import NumPy, and import matplotlib for well-data analysis and visualization.

Open source tools

Before starting, You should double ckeck the required tools/packages if they were installed.

SkyWater Technology

• SkyWater open-source PDK provides a 130 nm CMOS process, SKY130, suitable for analog, digital, and mixed designs. As depicted in Figure 2, the SKY130 layer stack consists of 5 metal layers (metal 1 to metal 5) with a local interconnect layer. The process includes deep n-well, Metal-insulator-Metal (MiM) capacitors, high and ultra-high sheet resistors, and isolated gate flash memory transistors. Moreover, SkyWater open-source PDK includes several libraries to serve the design of analog, digital, and mixed circuits

Figure 2. SKY130 layer stackup.

SkyWater SKY130 Libraries

Category	Libraries	Comment
Digital standard cells	sky130_fd_sc_hd	High Density
	sky130_fd_sc_hdll	High Density, Low Leakage
	sky130_fd_sc_hs	High Speed
	sky130_fd_sc_ms	Medium Speed
	sky130_fd_sc_ls	Low Speed
	sky130_fd_sc_lp	Low power
	sky130_fd_sc_hvl	High Voltage
Primitive devices/analog	sky130_fd_pr	Primitive Cells
I/O cells	sky130_fd_io	IO and Peripheral Cells