Manufacturers of analog integrated circuits have long recognized that in many ways, analog design is as much art as it is science. Almost from the beginning, companies such as Burr-Brown and National Semiconductor (both now part of Texas Instruments) produced now-legendary books and collections of application notes to help working engineers understand and apply their products. These can be considered the first design tools.
Time (and technology) waits for no one. Although those old books offer valuable help and have even been updated and made available for download, the major producers of analog and mixed-signal devices are now, with few exceptions, also major manufacturers of microcontrollers. So it's not surprising that they offer a range of software-based analog design tools along with their editors, compilers and debuggers.
Simple software design tools for analog applications have been around for many years, beginning with sets of equations to be loaded into spreadsheets, followed by programs on floppy disks and CD. The advent of the Internet enabled downloadable code with regular updating.
It must be emphasized here that we’re only talking about tools that help engineers design with analog integrated circuits. The semiconductor manufacturers themselves have complete sets of tools that they use to design, validate and test their chips, but those are outside the scope of this discussion.
The Current State of the Art
These early programs mostly dealt with single-function devices such as op-amps. But analog designs are migrating to a subsystem approach where multiple formerly-separate components are integrated into one device. In addition, the number of available devices proliferated massively, with dozens of potential solutions to a particular design problem. This has led to online design tools that include a product selection tool to help the user with both designing the circuit and picking the best device.
The most recent shift, though, is towards a highly-interactive “Expert System” approach; beginning with the specification of key application parameters, the design tool not only suggests the best device, but lets the user fine-tune the design around such factors as BOM cost and circuit board footprint.
Figure 1: An example of an “Expert System”- based design tool, Texas Instruments’ WEBENCH Power Designer. (Source: Texas Instruments)
What benefits are offered by this new approach? Whereas older design tools use textbook formulas for calculating external component values, the new tools take advantage of their parametric search engine to pick suitable devices and then add device-specific parameters as inputs to the design algorithms.
For a voltage feedback amplifier circuit, say, the design benefits from the inclusion of op-amp parameters such as slew rate, parasitic input capacitance, noise and flicker-noise corners, in addition to the standard gain-bandwidth product. More subtle effects can also be incorporated, such as output-loading issues and how they interact with the amplifier’s frequency response.
After a circuit block is designed, many new design tools can then port that block into a more general simulation platform so that designers can combine several blocks together, add other required components, or perform thermal simulations; or they can download their circuit or PCB layout directly into a CAD program.
Examples of Analog Design Tools
WEBENCH – Texas Instruments offers a complete set of analog design tools under their WEBENCH platform, including tools for designers working with power supplies, FPGAs, LEDs, amplifiers, medical AFEs, and more. The tools are sensitive to real-world requirements. For example, the sensor tools provide optimized signal path performance, bill of materials, budgetary cost, and links to evaluation boards and other tools for testing and validating a simulated solution.
LTspice – from Linear Technology, LTspice version IV is a high-performance SPICE simulator, schematic capture and waveform viewer with enhancements and models for easing the simulation of switching regulators. The downloadable Windows application includes macro models for hundreds of LT's op-amps and switching regulators, as well as resistors, transistors and MOSFET models.
Filter Wizard – Analog Devices’ Filter Wizard helps you design low-pass, high-pass or band-pass filters. Begin by entering in the key parameters—passband and stopband frequency and gain, filter response time—then the program will pick a topology, generate a schematic and help you choose the best ADI component.
Figure 2: Filter Wizard screenshot. (Source: Analog Devices)
Analog Devices also offers a comprehensive suite of design tools in support of its broad RF portfolio. For example, ADIsimRF is a RF signal chain calculator that allows calculation of system parameters such as cascaded gain, noise figure, IP3 and P1dB as well as total power consumption. The number of stages can be varied up to a maximum of 15. The ADIsimRF design tool contains embedded data from many of ADI's RF ICs and data converters, which designers can easily access using pull-down menus to assist in component selection.
iSim – Intersil's iSim is an interactive web-based design tool for selecting and simulating devices from Intersil’s portfolio. Users follow a similar design procedure as in other tools:
1) Select the input and output specifications,
2) iSim will find suitable Intersil devices and calculate optimum components,
3) The design is displayed in an online schematic for testing of the application,
4) Once the design has been verified, iSim generates a BOM and a design report.
Currently iSim is only available for Intersil’s power management devices and operational amplifiers.
Mindi – This interactive design tool from Microchip is aimed at designers working with active filters, amplifiers, battery chargers, DC-DC converters, or digital power. The battery charger module, for example, helps with bi-directional power converter or multi-chemistry battery charger design with Li-Ion, NiMH or NiCd batteries. After choosing the basic parameters, the system generates an interactive schematic; users can change individual components, run simulations, view a Bode plot of circuit performance, or print out the schematic. The amplifier tool accommodates a variety of common op-amp circuits including inverting and non-inverting configurations, difference amplifier, integrator and differentiator. It offers similar functionality including transient analysis.
Power Supply WebDesigner (PSW) – Fairchild’s Power Supply WebDesigner (PSW) is a tool for designing and simulating a primary-side regulated (PSR) or secondary-side regulated (SSR) flyback converter. Like other tools, it produces a schematic, simulated verification, and bill of materials. With PSW, though, your BOM can include auto selection of parts from your preferred distributor's catalog. Fairchild offers similar design tools for other power supply applications, including buck-boost topologies, isolated and non-isolated designs, DC-DC converters, and power factor correction (PFC) circuits.
Design Tools from Arrow
We offer a large selection of digital design tools on our website. Just about all of the analog tools discussed, though, are free for the asking directly from the manufacturers’ websites. The components for the BOM, though..... ah, that's a completely different story.