Analog designers — 'artists' respected by the majority

Electronic News, March 2, 1998 by Bill Altonen

Design of analog circuits is an engineering art practiced by a minority of engineers. They are tasked with solving real world interface problems that involve the sensing, conversion, regulation, conditioning, and processing of signals based upon stimuli related to temperature, sound, pressure, light, or motion. Like an artist, the analog designer often becomes an expert who focuses on one specialty, like audio signal processing, RF power, or process control systems. While specializing, the analog artist can become extremely creative and proficient, and can create circuits that range from simple amplifiers to highly complex transceiver integrated circuits or modules. However, no matter how simple or complicated the design task is, the design of an analog circuit is always a challenge.

When vacuum tubes were invented, analog circuit design was very popular. Even the first computers were analog. But the invention of the bipolar transistor changed everything. Analog vacuum tube designs were converted to discrete semiconductor transistor designs, and analog computers gave way to digital computers as simple semiconductor logic gates became available. Designs implemented with discrete transistors moved to linear integrated circuits (op amps, comparators, regulators, etc.), and the complexity of the designs moved to even higher levels of integration, sophistication and performance. This technology migration put an even larger burden on the analog designer, and forced many to use CAD tools and simulation models to get the job done.

Unlike digital design, which involves the grouping, storage and processing of digital packets of data, analog designers are tasked with understanding the idiosyncrasies of the input and output interfaces. They must also control the preservation, processing and protection of signals once received and observed in either the frequency or time domain. These signals, which can be sampled data as well, involve voltages that can have a wide variation in level, dynamic range, bandwidth and linearity whose accuracy and precision is greatly affected by system level parasitics and noise. No wonder we have so few analog designers....

To address the myriad of analog interface and circuit design problems, designers solve their application problems in their own way, relative to interface, system environment, performance, space, time, and cost. These solutions range from the simplest circuit to the most complex integrated circuit or hybrid. At one end of the spectrum, designs can be implemented on a single layer PWB where each component is carefully selected and critically placed relative to signal routing, power, ground and noise to yield a circuit that meets the system objective. Any alteration of a signal trace or component value affects the design's performance, and the designer is aware of all variations, including parasitics. These designs are really 'designed-in,' and difficult to displace. They are often migrated to newer generations of equipment that have minor enhancements. Based on experience, the analog 'artist' adapts to address the idiosyncrasies associated with any specific design. Also, the analog designer in an enviable position as the 'artist' is able to play a major role in new product development.

On the other end of the spectrum (e.g. a custom analog integrated circuit, an RF module, or a power hybrid module), the design task becomes more complex and abstract. These designs cannot be totally migrated since the applications that require them are new or require higher levels of performance, integration, mixed-signal, smaller space, lower cost or must conform to tight time-to-market windows. These designs can only be addressed with CAD tools that force the analog artist into the world of manufacturing data, process variations, models (if available), simulators, physical layout rules, hand-crafting and six-sigma design methodologies.

Analog design has been and will continue to be an engineering art. Real-world signals will have to be dealt with. They will need to be detected, converted, regulated and processed no matter how complicated the systems become. The signal waveforms can vary from complex low level high frequency RF to simple high level DC. All signals need to be preserved and protected from system level parasitics and noise and all signals must be received from and transmitted to an analog interface. That is the job of the analog circuit designer.

Practitioners of the art will be tasked to apply their knowledge and experience as they have done in the past. They will be also tasked to look at new and better ways to solve their problems using new models, simulators, CAD tools, and products like field programmable analog arrays, analog ASICs and analog compilers. The role of the analog designer cannot be underestimated. They may be in the minority, but they command the respect of the majority.

Mr. Altonen is director for field programmable analog and mixed-signal array products at Motorola SPS in Phoenix.