The very high-performance Advanced Filter Bank (AFB) Analog and Digital Converter architecture uses a parallel array of state-of-the-art analog-to-digital converters (ADCs) or digital-to-analog converters (DACs) to increase the speed of the conversion by up to six to eight times while maintaining very high resolution. This V-Corp proprietary and patented technology is capable of A/D conversion with, for example, 12-bit resolution and 1.3 GHz sample rate (six times the speed of state-of-the-art); it is capable of D/A conversion with 14-bit resolution and 1-2 GHz sample rate and direct digital upconversion up to 1 GHz. The AFB architecture is successful because the advanced filter bank signal processing significantly reduces the sensitivity to analog mismatches (e.g., gain mismatch, phase distortion, clock skew) which prohibit existing parallel architectures (such as Time-Interleaving or "Ping-Pong" methods) from achieving high-resolution. V-Corp has proven the technical viability of the technology with working prototype hardware with 12-bit resolution and 340 MHz sample rate (using a dual-channel Analog Devices AD10230 ADC part, which uses two 12-bit, 170 MSPS ADCs in parallel).

By eliminating much of the analog electronics, the high-performance AFB can significantly reduce the size, power, and cost of cellular basestation receivers, radar systems, adaptive array processing and digital beamforming, and other RF receivers by performing more of the processing digitally in reconfigurable software.

AFB Architecture Will Not Become Obsolete - Upgradeable - Scalable - Transportable

The AFB architecture will not become obsolete because the architecture can be applied to new higher performance ADC and DAC chips as they become available, thereby always maintaining a significant performance advantage over even the highest performing converters. The architecture was specifically designed to incorporate this feature and thereby it will always significantly exceed the performance of state-of-the-art commercial converters. The AFB architecture is amenable to a miniaturized multi-chip module (MCM) implementation. This unique technology is only available from V-Corp. (U.S. Patents 6,177,893, 6,339,390, and numerous patents pending)

AFB Overcomes the Critical A/D and D/A Conversion Bottleneck

High-speed, high-resolution analog-to-digital and digital-to-analog conversion is a critical technology in many modern electronic systems, such as radar systems and digital receivers for wireless communications. In general, high-speed, high-resolution converters enable wide bands of analog data to be converted to digital form to be processed more accurately and efficiently than is possible in analog form. Systems can be updated as requirements change and new standards arise by simply updating software to change the digital signal processing. A high-performance converter would significantly reduce the cost, size, and power consumption of systems by eliminating much of the analog circuitry while improving versatility and performance.

ADC performance is typically quantified by two parameters, speed (in samples per second) and resolution (in bits). Designers face the challenge of trading off the resolution of the conversion with its speed. Figure 1-1 illustrates the trade-off between speed and resolution of the most popular single-chip ADC architectures currently available. The thick line in Figure 1-1 indicates the state-of-the-art in single-chip ADCs.

Figure 1-1. Speed (bandwidth) versus resolution for analog-to-digital converter architectures. The V-Corp AFB technology surpasses state-of-the-art in speed (improves bandwidth by a factor of 6 - 8) while maintaining high resolution.

AFB Multi-Rate Filter Bank Processing Significantly Reduces Sensitivity to Analog Mismatches

Using a Filter Bank for analog-to-digital conversion is an unconventional application of the Filter Bank architecture that improves the speed and resolution of the conversion over the conventional Time-Interleaved array conversion technique (also called "Ping-Pong" or "Round-Robin" methods). The AFB uses a combination of time-division multiplexing and frequency-division multiplexing to split the input to each ADC in the array and multirate digital filters to reconstruct the digitized signal. This proprietary multirate digital filtering in the AFB significantly improves the speed and resolution of the conversion by attenuating the effects of analog mismatches (e.g., gain mismatch, phase distortion, and clock skew caused by imprecise analog component values, line length mismatches, and other variations in the analog front-end electronics) which otherwise severely limit the resolution of the system and which prohibit existing parallel architectures from achieving high-resolution. To achieve high-resolution (greater than 12 bits), conventional parallel approaches such as Time-Interleaving require phase matching on the order of a few picoseconds and gain matching to less than -80 dB, which is very difficult (if not impossible) to achieve. However, the AFB provides very high-resolution performance with phase distortion on the order of nanoseconds and gain mismatches of approximately -50 dB, which is relatively straightforward to achieve.

AFB Uses Parallel Processing to Achieve High-Speed, High-Resolution Performance and Direct IF Sampling

The AFB employs Decomposition splitters, Dk, to divide the wideband analog input signal into M channel signals. By using time-skewed channel clock signals for time-division multiplexing, the Decomposition splitter can simply be implemented as an RF splitter network. The channel signals are sampled at 1/M the effective sample rate of the system and converted to digital signals with n-bit ADCs. The digitized channel signals are upsampled by M and reconstructed via the digital Recombination Filters, Rk(z). The Recombination filters directly target the alias imaging errors caused by mismatches between converters in the array to insure that they do not limit the resolution of the system. The effective sample rate of the system is M times that of the channel ADCs in the array, and the resolution is n bits, the same as that of the channel ADCs in the array. The AFB architecture is illustrated in Figure 1-2. The AFB is well-suited for very high-resolution, very high-speed systems.

The AFB supports a combination of time-division multiplexing and frequency-division multiplexing. Decomposition processing can include bandpass filters to allocate a frequency band to each converter in the array. The stopband attenuation of the filters directly attenuates the effects of mismatches; for example, Decomposition filtering with 20 dB stopband attenuation will reduce the alias imaging errors caused by mismatches by approximately 20 dB. However, the multirate digital Recombination filters are so effective at reducing these alias imaging errors, that the additional attenuation afforded by using Decomposition filtering is usually not necessary. The reduction or elimination of this filtering greatly simplifies the analog circuitry in the AFB system.

ADC manufacturers such as Analog Devices have been incorporating high-precision sampling circuitry in their ADC chips which extends the sampling bandwidth of the device by up to six times the Nyquist bandwidth. Therefore, these commercially-available chips may be used in the AFB configuration to improve the speed of the conversion by up to six times without necessitating the use of additional sampling circuitry. V-Corp proprietary linearity error compensation techniques (LinComp) may be employed to extend the dynamic range at high IF even further.

Figure 1-2. Advanced Filter Bank (AFB) Analog-to-Digital Converter.

Enables Direct IF Sampling or Direct Digital Upconversion

The AFB technology enables direct IF sampling of wideband data at high IF frequency or direct synthesis of wideband data at high IF frequency, which dramatically reduces or eliminates much of the RF electronics in the system.

AFB is Ideally-Suited for RF Communications, Radar, Digital Beamforming

Achieving high-performance A/D conversion is currently the limiting factor in the cost, size, and power consumption of many electronic systems. For example, improving ADC performance in RF receivers can:

• · Eliminate racks of analog electronics by performing more of the processing digitally
• · Enable simultaneous support of multiple analog and digital signaling and protocols
• · Seamlessly support next generation standards with software updates
• · Reduce power, mass, volume and cost
• Conventional Time-Interleaving Approach is Very Sensitive to Mismatch Errors

For very high-speed conversion, manufacturers such as Hewlett-Packard and Tektronix have conventionally implemented Time-Interleaved (aka "Ping-Pong" or "Round-Robin") ADCs which consist of an array of M moderate speed ADCs which are triggered successively at 1/M the effective sample rate of the system. The speed and resolution of the system is limited because the system is extremely sensitive to ADC mismatches and clock timing errors. Time-Interleaving ADCs provide up to 8 bits resolution at gigasample per second (GSa/s) speeds, as shown in Figure 1-1. With signal preconditioning and compensation for linearity and timing errors, Hewlett-Packard has built an 8 GSa/s, 8-bit, Time-Interleaved ADC with a signal bandwidth of nearly 2 [GHz]. Effects of mismatches in converters in Time-Interleaved systems has been studied extensively.

Figure 1-3. Conventional Time-Interleaving Analog-to-Digital Converter.

V-Corp AFB Outperforms Time-Interleaving

The AFB architecture overcomes the Time-Interleaved architecture's extreme sensitivity to converter mismatches and the switched-capacitor architecture's speed and noise limitations. The multirate filter bank signal processing used in the AFB architecture isolates the converters in the array and attenuate the aliasing errors caused by gain and phase mismatches.

Wide Range of Commercial and Military Applications of the AFB Solution
Applications of high-resolution, high-speed data conversion include:

• · Multi-beam adaptive digital beamforming array transceivers
• · Advanced Radar systems
• · Smart radios for wireless communications (cellular and satellite)
• · Wideband electronic warfare transceivers
• · General test equipment such as oscilloscopes, spectrum analyzers, network analyzers
• · Special test equipment
• · Wide bandwidth modems
• · Software radios
• · Anti-Jam GPS Receivers

One particularly attractive application of AFB is the Software Radio, which can accommodate two or more RF modulation standards simultaneously by performing tuning and demodulation on the digital data in software. The Software Radio can seamlessly integrate new standards as they arise. The Software Radio promises lower power, smaller size, and lower cost by processing 50 or more channels in software instead of dedicated hardware. For military applications, the Software Radio is capable of understanding many different signalling protocols with a compact, low-power transceiver. For cellular telephone applications, the Software Radio allows for universal coverage without necessitating worldwide agreement on a single standard (which, due to politics and competition, has proven to be impossible) since it can understand signals from many different types of cellular telephones.

Enhances Adaptive Antenna Array Processing and Digital Beamforming

Space Division Multiple Access (SDMA) is used to improve communications capacity, reduce jamming and interference, and improve security by using spatial processing for intelligent beam steering (for both transmission and reception). Current systems are limited by converter bandwidth and precision; adaptive algorithms require wide dynamic range to accurately null interfering signals. AFB ADC overcomes the critical bandwidth and precision limitations.

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