Some big chipmakers have been looking to maintain an edge in the frenetic pace of the electronics industry partly by upgrading their online development tools beyond simple parametric device selectors. This has led to the creation of more comprehensive tools that link all design parts. In addition to these tool upgrades, they have begun moving from their own custom tool toward standardizing on National Instruments' LabVIEW as a common interface and engine.
National Semiconductor's Webench tool, for example, helps circuit designers select an analog-to-digital converter (ADC) and create any kind of anti-aliasing filter desired for the input signal path. It also assists them in creating the power supply needed to run the whole circuit.
Analog Devices' director of applications engineering, Dave Kress, provided the most cogent explanation of why companies are turning to these online tools. "Chip vendors vie with each other to get samples and eval boards to customers, because often, the first to get a chip into the engineer's hands wins the socket," he says. "These tools are a way to beat the 'sample wars' game." According to Kress, the tools also provide a way for field application engineers to kick-start customer engineers, who can then safely be left to their own devices (double entendre intended).
A HANDS-ON DEMO
I got to test-drive ADI's signal-path design tool with applications engineer Travis Harkness to see what the experience was like (Fig. 1). I used the tool's setup wizard to create a case in which we intended to use an op amp in non-inverting mode to condition a bipolar signal from a sensor and scale it to a 0- to 2.5-V input to an ADC.
When I clicked "Find Amplifiers," I got a long list of potential ADI parts. Some had notes, cautions, or alerts adjacent to the part number. A "Note" points out something the design engineer could do to make the circuit work better. A "Caution" indicates something sub-optimal that might dictate a circuit change. An "Alert" indicates that while the part meets the basic selection criteria, there are reasons it shouldn't be used.
From the list, Harkness first had me select the AD711 marked "Note" in the selection table and return to the evaluation tool. At this point, the circuit diagram showed the reference voltage and component values required.
After I hit the "run model" button, a graphic representation of input and output waveforms appeared. Also, under "log," a message said "Note: Typical Gain Error Exceeds 1%. Due to the amplifier's frequency dependent open loop gain, along with the selected closed loop gain and frequency, the calculated typical output error exceeds 1%. Possible solutions: Lower signal frequency or reduce closed loop gain."
Harkness noted that he had me select this amplifier precisely because it didn't have enough open-loop gain at higher frequencies to meet the design's required gain. Unlike SPICE and other simulators, in which you could see a problem but not necessarily understand where it came from, ADI wanted the tool to explain the underlying reasons why a part might prove unsatisfactory.
Gain error had a small effect at the first input frequency we chose—100 kHz. So Harkness had me increase the frequency to 3 MHz in the box in the GUI and rerun the simulation. This time, distortion was visible in the output waveform, and the "log" box message now read "Caution: Amplifier slew rate exceeded. Signal distortion and excessive errors may occur. Possible solutions: Reduce signal frequency, lower signal amplitude or reduce closed loop gain."
This illustrated the tool's value well, because the amount of distortion was still subtle. Harkness said it might not have been visually detectable in the waveform if we'd used 2.4 instead of 3 MHz, and using Spice, we may not have even noticed it.
While its ability to point out what won't work is useful, the tool's real benefit is in accelerating the search for the right answer. Next to the amplifier wizard box, there's a "suggest amplifier" option. Hitting that button sent me to a screen where I re-entered key parameters. Hitting "find amplifiers" returned a smaller set of acceptable part numbers (smaller because the input frequency remained at 3 MHz), which I could further evaluate.
THE WEBENCH SIGNAL PATH TOOL
National Semiconductor's Webench Signal Path Designer (signalpath.national.com) works somewhat differently, but it's equally user-friendly. A voice-over demo on the Web page provides a walk-through. The user can select an ADC first or design the response of the anti-aliasing filter. The demo takes the latter path.
The user first defines some ADC characteristics, operating voltage, number of channels, resolution, sample rate, maximum frequency, and operating temperature range. This produces a list of NSC's ADCs that satisfy those criteria, and the best-fit converter is selected.
The next step is to define the anti-aliasing filter's primary characteristics: input voltage, maximum permissible deviation within the passband, and attenuation at the ADC's Nyquist frequency. Once defined, an array of filter types is presented—Bessel, Butterworth, and a number of Chebyshev variants. Designers can select as many as they want, though the more they select, the longer it takes to produce a set of results.
These results consist of graphic presentations of the filters' response characteristics: frequency and phase response, group delay, and step response (Fig. 2). Here, the demo selects the Bessel filter design, for the sake of the relative lack of ripple in its step-input response.
Given the desired filter characteristics and type, Webench Signal Path Designer offers a selection of National op amps that can implement the filter. All characteristics, including price, are listed. Once the user selects one, Webench creates the design, listing all components and tabulating all the design's behaviors.
Currently, the Webench Signal Path tool handles conversion rates from 50 ksamples/s to 1 Msample/s. Its database contains 85 8-, 10-, and 12-bit data converters and 220 amplifiers. The tool's active filter designer handles third-order filters.
By January, Webench will be able to deal with speeds of up to 100 Msamples/s, Fourier transforms, and filters up to ninth-order, as well as provide design advice. By June of 2006, it will handle conversion speeds reaching 1.5 Gsamples/s, import and export netlists and other CAD data, and offer a database of roughly 150 converters.
Some big chipmakers have been looking to maintain an edge in the frenetic pace of the electronics industry partly by upgrading their online development tools beyond simple parametric device selectors. This has led to the creation of more comprehensive tools that link all design parts. In addition to these tool upgrades, they have begun moving from their own custom tool toward standardizing on National Instruments' LabVIEW as a common interface and engine.
National Semiconductor's Webench tool, for example, helps circuit designers select an analog-to-digital converter (ADC) and create any kind of anti-aliasing filter desired for the input signal path. It also assists them in creating the power supply needed to run the whole circuit.
Analog Devices' director of applications engineering, Dave Kress, provided the most cogent explanation of why companies are turning to these online tools. "Chip vendors vie with each other to get samples and eval boards to customers, because often, the first to get a chip into the engineer's hands wins the socket," he says. "These tools are a way to beat the 'sample wars' game." According to Kress, the tools also provide a way for field application engineers to kick-start customer engineers, who can then safely be left to their own devices (double entendre intended).
A HANDS-ON DEMO
I got to test-drive ADI's signal-path design tool with applications engineer Travis Harkness to see what the experience was like (Fig. 1). I used the tool's setup wizard to create a case in which we intended to use an op amp in non-inverting mode to condition a bipolar signal from a sensor and scale it to a 0- to 2.5-V input to an ADC.
When I clicked "Find Amplifiers," I got a long list of potential ADI parts. Some had notes, cautions, or alerts adjacent to the part number. A "Note" points out something the design engineer could do to make the circuit work better. A "Caution" indicates something sub-optimal that might dictate a circuit change. An "Alert" indicates that while the part meets the basic selection criteria, there are reasons it shouldn't be used.
From the list, Harkness first had me select the AD711 marked "Note" in the selection table and return to the evaluation tool. At this point, the circuit diagram showed the reference voltage and component values required.
After I hit the "run model" button, a graphic representation of input and output waveforms appeared. Also, under "log," a message said "Note: Typical Gain Error Exceeds 1%. Due to the amplifier's frequency dependent open loop gain, along with the selected closed loop gain and frequency, the calculated typical output error exceeds 1%. Possible solutions: Lower signal frequency or reduce closed loop gain."
Harkness noted that he had me select this amplifier precisely because it didn't have enough open-loop gain at higher frequencies to meet the design's required gain. Unlike SPICE and other simulators, in which you could see a problem but not necessarily understand where it came from, ADI wanted the tool to explain the underlying reasons why a part might prove unsatisfactory.
Gain error had a small effect at the first input frequency we chose—100 kHz. So Harkness had me increase the frequency to 3 MHz in the box in the GUI and rerun the simulation. This time, distortion was visible in the output waveform, and the "log" box message now read "Caution: Amplifier slew rate exceeded. Signal distortion and excessive errors may occur. Possible solutions: Reduce signal frequency, lower signal amplitude or reduce closed loop gain."
This illustrated the tool's value well, because the amount of distortion was still subtle. Harkness said it might not have been visually detectable in the waveform if we'd used 2.4 instead of 3 MHz, and using Spice, we may not have even noticed it.
While its ability to point out what won't work is useful, the tool's real benefit is in accelerating the search for the right answer. Next to the amplifier wizard box, there's a "suggest amplifier" option. Hitting that button sent me to a screen where I re-entered key parameters. Hitting "find amplifiers" returned a smaller set of acceptable part numbers (smaller because the input frequency remained at 3 MHz), which I could further evaluate.
THE WEBENCH SIGNAL PATH TOOL
National Semiconductor's Webench Signal Path Designer (signalpath.national.com) works somewhat differently, but it's equally user-friendly. A voice-over demo on the Web page provides a walk-through. The user can select an ADC first or design the response of the anti-aliasing filter. The demo takes the latter path.
The user first defines some ADC characteristics, operating voltage, number of channels, resolution, sample rate, maximum frequency, and operating temperature range. This produces a list of NSC's ADCs that satisfy those criteria, and the best-fit converter is selected.
The next step is to define the anti-aliasing filter's primary characteristics: input voltage, maximum permissible deviation within the passband, and attenuation at the ADC's Nyquist frequency. Once defined, an array of filter types is presented—Bessel, Butterworth, and a number of Chebyshev variants. Designers can select as many as they want, though the more they select, the longer it takes to produce a set of results.
These results consist of graphic presentations of the filters' response characteristics: frequency and phase response, group delay, and step response (Fig. 2). Here, the demo selects the Bessel filter design, for the sake of the relative lack of ripple in its step-input response.
Given the desired filter characteristics and type, Webench Signal Path Designer offers a selection of National op amps that can implement the filter. All characteristics, including price, are listed. Once the user selects one, Webench creates the design, listing all components and tabulating all the design's behaviors.
Currently, the Webench Signal Path tool handles conversion rates from 50 ksamples/s to 1 Msample/s. Its database contains 85 8-, 10-, and 12-bit data converters and 220 amplifiers. The tool's active filter designer handles third-order filters.
By January, Webench will be able to deal with speeds of up to 100 Msamples/s, Fourier transforms, and filters up to ninth-order, as well as provide design advice. By June of 2006, it will handle conversion speeds reaching 1.5 Gsamples/s, import and export netlists and other CAD data, and offer a database of roughly 150 converters.