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Programmable signal converter provides sensor interface

Allen, Texas — Recent start-up Quickfilter Technologies Inc. unveiled its first product — a four-channel programmable signal converter (PSC) that it said will enable complete four-channel signal processing and filtering in minutes.

The QF4A512 PSC features a 16-bit analog-to-digital (A/D) converter with four differential or single ended inputs. Each channel can be individually programmed for gain, anti-aliasing filter cutoff frequency, A/D converter sampling frequency, and the filtering requirements unique to that input (up to 512 taps per channel). The four independent finite impulse response (FIR) filters are capable of generating brick wall filters. As an example, a lowpass filter with a 1-kHz cutoff frequency, 80 dB of rejection, and a total transition band of only 5 Hz can be designed in minutes, said Bob Silco, CEO of the fabless IC company. Each channel can have a different signal bandwidth, A/D sample rate, and filter function design.

 
 
See Functional Block Diagram

Quickfilter's QF4A512 signal converter product line allows engineers to design and implement a custom circuit for signal conditioning, conversion and processing — without the cost and complexity of designing a circuit board containing discrete components in addition to programming a digital signal processing (DSP), Silco said.

Quickfilter's design software has been created for rapid configuration and filter design, according to Silco. Filter templates are selectable in Quickfilter's design software for a variety of applications. “By making it extremely easy to program and re-program at any time, we are enabling our customers to personalize their products, implement just-in-time manufacturing and create new products,” he said.

The QF4A512 PSC is suited for industrial control, machine monitoring, medical monitoring and diagnostics, industrial smart sensors, homeland security monitoring, and a variety of other applications.

The Quickfilter development kit includes a Windows-based graphical user interface (GUI) that prompts engineers for all the relevant filter specifications of any common digital filter type (lowpass, notched lowpass, highpass, bandpass, dual bandpass, bandstop, and dual bandstop). The user configures the rest of the chip for parameters such as gain, A/D converter sampling rate, power consumption, output speeds, and run configurations. The software then loads the information into the chip and using the included white noise file, or other signal source, the engineer views the signal output on his computer screen as a fast Fourier transform (FFT) graph.

A complete development kit for the QF4A512 PSC is available for $199. The kit includes all hardware and software necessary to design, implement, and test a complete filter design, including a development card, input and output cables, software and sample signal input files.

Click here to see the software demo slideshow.

Samples of the QF4A512 PSC are available now and production quantities are slated for March. The QF4A512 is priced at $9.89 in 1,000-piece quantities. Click here for the QF4A512 PSC data sheet.

Quickfilter Technologies Inc. , 1-214-547-0460, www.QuickfilterTech.com.

Quickfilter is a new venture that was incorporated in 2003. The company's programmable signal converter, which combines A/D functionality and digital filtering, is their very first product. “The converter acts like an analog front end board with digital processing in it,” said Chris Phipps, Quickfilter's vice president of sales and marketing. “It enables fast design time, high filter performance, conserves board space, is easily configurable and there is no code to write,” he added.

Without this device, designers can use other approaches to achieve the same result. The designer can do the filtering using conventional analog techniques prior to the A/D converter, Phipps said. “In the analog domain, there is no programmable aspect so it's hard to achieve precision responses this way,” he said.

Another technique would be to do a quick conversion with an anti-aliasing filter and DSP block. Doing the filtering this way eliminates temperature drift and provides flexibility, but this approach means you have to write code, purchase the DSP, RAM, flash memory, etc., Phipps said.

Programmable filters have been used before also but they aren't usually powerful enough and can cost double or triple the cost of traditional discrete component solutions, according to Phipps. Quickfilter's single chip offers the functionality of between 13 to 19 components for half or a third of the cost of a discrete hardware solution, he said (see cost chart below).

 
 
See related cost chart

Quickfilter has several patents filed and pending — each with a number of claims, for the QF4A512 PSC. One of the most interesting patents is for the technology that enables the device to convert analog input signals from below 1 Hz up to 2.5 MHz to a digital signal. Without this technology, the anti-aliasing filter would have to be changed to prevent anti-aliasing errors, Phipps said.

The A/D converter, which utilizes the pipeline architecture, runs up to 100 MHz. Each of the four filters is programmable. The 512 tap filters can produce very sharp roll offs, Phipps said. “You can combine two filters like a notched lowpass filter for very sharp notch filtering. This would be useful in medical applications with a frequency of a couple hundred hertz,” he said.

Regarding the microcontroller, Quickfilter made a deliberate decision not to include the MCU core on-chip. “Because customers have equity in specific cores, the feedback from them was that they didn't want us to integrate the MCU core. We do the signal conditioning, filtering and analog portion, and they choose the microcontroller, DSP or FPGA,” he said.

The device is so flexible that customers building low volume designs can wait till the end of the production line to tailor the devices to specific customer requirements, Phipps said. “They can be customized at the last minute, which is particularly attractive to industrial control and monitoring equipment that use technicians in the field with sliding interface cards. Our device eliminates these cards since the applications can now be configured remotely in the field,” he said.

Quickfilter's software allows you to display the actual frequency response of the filter you create in real time right on your PC screen — without a separate power supply, and without going near a lab. As long as it's within the audio range of your laptop or PC, you can verify the filter response you need, Phipps said.

 
 
Filter Design Screen (notched lowpass filter)

Some engineers that Quickfilter visited recently used the software for analog filtering conversion. They kept tightening the specs to see how sharp of a filter they could get, Phipps said. “Their existing design only required 20 odd taps so they kept tightening the specs until they used up all 512 taps. They made a really tight bandpass filter — only 10 Hz wide. The engineers couldn't believe how much they could sharpen the slopes of the filter in just five minutes. This would normally take a lot of money and time,” he said.

Next year, the company plans to follow up with additional devices utilizing different types of A/D converters for faster and higher resolution (20 or 24 bits) versions. “Later on we may target wireless sensor networks,” Phipps said.

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