dspZONE Products for the week of September 24, 2007
Quickfilter Technologies Says…
Programmable Digital Filter Can Be Configured To Provide Complete Two-Way Audio Crossover Network
High-quality sound usually available only in high-end audio systems now possible with low-cost Quickfilter device
Quickfilter Technologies Inc. has announced a reference design to allow a single QF1D512 Simple and versatile FIR engine (SavFIRe) IC to be configured to provide the complete digital filtering for a two-way audio crossover network. Using this solution, designers can now achieve exceptionally high-quality filtering that is generally seen only in high-end audio systems with a programmable digital filter device that costs less than 1/3 the cost of an equivalent DSP previously used to perform these functions.
“The QF1D512 SavFIRe chip gives designers an incredibly easy-to-use solution with world-class quality. When paired with just an inexpensive codec, the device provides a complete two-way audio crossover network at a very low cost,” said Don DiDonato, Vice President of Worldwide Sales for Quickfilter Technologies. “The QF1D512 device can be configured in minutes to support the user’s choice of sampling and crossover frequencies.”
In the two-way audio crossover network configuration, the QF1D512 SavFIRe chip enables 100dB attenuation in stop band and better than 24dB per octave attenuation in transition band based on 48 kHz sampling and a 1500 Hz crossover. The combined response is perfectly flat over the entire frequency band.
This configuration can be applied to both wired and wireless audio systems including wireless speakers, devices which plug into iPods and audio systems for stereo networks.
Announced in September 2006, the QF1D512 SavFIRe chip allows systems designers to quickly and easily add precision digital filtering to an application. The chip can simply be added between an existing analog-to-digital converter (ADC) and the host controller (microcontroller, microprocessor, digital signal processor or field programmable gate array), or can be connected as a co-processor device for controllers with embedded ADCs. “Using the Quickfilter Design Software, the QF1D512 SavFIRe chip can be easily programmed to support virtually any FIR digital filter configuration,” DiDonato continued.
“With design-wins at key high-volume players, the costs for the QF1D512 chip continue to move down. At Quickfilter Technologies, we are aggressively passing those savings on to customers to secure more high-volume design wins,” DiDonato concluded. “The Quickfilter management team sees this as a big trend for the company going forward.”
EN-Genius Says…
Reviewing the evaluation kit for this clever little hardware processor is going to get me into lots of trouble. My colleague Paul (analog guru and guardian of the audio/videoZONE) is going to give me hell because he feels that it’s usually simpler and better to do audio processing in the analog domain. I also expect some hate mail from my friends selling DSPs for audio applications who will say that the Quickfilter device doesn’t have the flexibility or processing power that their chips are capable of delivering. But, even tough I agree with them (at least to a point), there are many applications where the low cost, low power and ease of development that this configurable fixed-function device delivers makes it an excellent choice for handling specific signal processing tasks in or around the audio band.
Quickfilter achieves its processing efficiency by using a configurable pipeline rather than a traditional DSP (see Fig. 1). The QF1D512 can be configured to accept a serial bit stream containing sample widths between 12 and 24 bits with your choice of input and output format or bit orientation (LSB first/MSB first). Configuration data for the 256-tap-FIR filter and other functions can be loaded as needed via the SPI port. Depending on how much processing power you need (and your power budget) data can be clocked through the QF1D512 at speeds of up to 500 kbit/s. Besides actual signal processing, the filter has the ability to read and process headers or tags attached to the data packet. Among other things, this allows you to create two (or more) filter channels by splitting the taps into groups and creating multiple data streams using header tags on the data.
 The filter can be configured with as many as 256 taps in an asymmetrical FIR. If you are using a symmetrical configuration the taps can be re-used to produce an effective single-channel filter with up to 512 taps. Of course this cuts the filter’s effective throughput in half but a 250 kbit/s bit rate is more than acceptable for many applications.
If you really need more processing power, Quickfilter’s serial pipeline allows you to cascade multiple chips to add filter depth or concatenate algorithms. At somewhere a little under $3 apiece, the cost of cascading two or three Quickfilters starts to grow past the price tag of a low-end DSP from Microchip or TI, but their low power consumption and short development time (Quickfilter claims novices can have working prototypes in 10 - 20 minutes with their own algorithms and less when using modified reference designs) may still make it an attractive option.
This ease of programming is very evident in the development kit described in the release above which includes firmware templates for seven different algorithms including basic Parks-McClellan, multi-band Parks-McClellan, and several flavors of Windowed Sinc Blackman. If that’s not enough for you, the development tool allows you to import any other algorithm you like from popular algorithm development packages like MathCAD and Mathworks. You can even hand-draw the curve you’re looking for using the Freeform feature of Quickfilter’s QFPro design software.
 All this talk about easy filter design sounded very nice but the ripples I saw in the passband region of a sample filter response (see Fig. 2) raised some question about whether it was too noisy for precision audio applications. QuicLogic answered that the ripples were artifacts caused by the basic mathematics of the algorithms they use and not the filter itself. They also explained that you can tune the algorithm’s response to produce less ripple in the passband but, just like with analog filters, it would be at the expense of less control over the shape and slope of the roll off curves.
I did not have time to come up with a calculation that would provide a fair comparison between the Quickfilter power consumption and a programmable DSP that would provide an equivalent amount of processing power but a first glance shows the Quickfilter should at lest be competitive. Of course the Quickfilter’s power consumption is a function of how fast you clock it, and how many taps you turn on in its FIR pipeline but, even with all gates blazing at its maximum 500 kHz clock rate, it only consumes 16.5 mA at 1.8 V power. Running only 256 taps consumes around 9.5 mA and dropping the clock rate to 64 kHz drops a maximum-sized filter’s consumption to only 2 mA.
Being able to deliver a substantial chunk of signal processing power for under $3 opens the Quickfilter for use in some interesting applications including equalizing the response of headsets, handsets, and speakers as well as in digital microphones. Quickfilter says it’s currently involved with several more unusual products such as smart digital stethoscopes and providing digital crossover in wireless surround sound speakers. This versatile little chip is also finding lots of use in non-audio applications such as processing signals from detectors used in remote sensing to detect acceleration, vibration, or acoustic signatures. Other creative customers are using the QF1D512 to filter out noise in the strain gauges used in ultra-precise scales. I also see some significant potential for using it in things like digital IF processing and down-sampling.
The QF1D512 is packaged in a 3x3 mm QFN package, is characterized over the industrial temperature range and is in production with pricing at $2.98 in 1000-piece lots.
Data Sheet
|
