Frequency Translating Sigma-Delta Modulator
Lead Inventors: John KhouryProblem or Unmet Need:Analog to digital conversion at intermediate frequencies (IF) provides an optimal performance to the digital radio receivers, however this technique is riddled with several problems. Conventional homodyne receivers suffer from interference by local oscillator frequency, DC offsets in signal path, low dynamic range of bandpass filters as well as mismatches in the in-phase/quadrature (I/Q) path that limit image frequency separation.Another common approach for such conversions is to use a heterodyne receiver. The difficulty with these receivers is obtaining a high quality factor band pass filter and amplifier at IF frequencies. Also mismatches in analog signal path remains problematic.One promising technology for IF A/D conversion is discrete time sigma-delta modulators. They have been successfully used for digitization narrow band input signals centered at one fourth of the sampling frequencies. Conventional continuous-time band pass sigma-delta converters can operate at very high sample rates without front hand sample and hold (S/H) circuitry. However, accurately controlling the center frequency and quality factor (Q) of these converters can be very difficult. A high-Q resonator is very important for quantization error rejection and dead zone avoidance in these converters. Current invention provides a sigma-delta modulator having a decreased band pass quantization noise due to resonant center frequency errors. It also provides a continuous time resonator with moderate Q and center frequency requirements. Such a modulator can directly convert radio or intermediate frequencies to base band or other low or intermediate frequencies for use in wireless communication systems and other digital receiver systems. The electronic device consists of a summing device, an analog filter, analog mixer, a quantizer coupled to the analog mixer and a feed back branch coupled between quantizer and summing device for providing the feed back analog signal to the summing device.
Better A/D conversion will result in improved manufacturability of chips that have both analog and digital circuits due to an increase in overall digital circuitry. It will also cause less power dissipation. Early stage digital processing permits a high degree of programmability in the filtering and demodulation processes, thus easing compatibility with various wireless standards. For I/Q receivers, as compare to analog, digital demodulation does not suffer degradation due to mismatches in in-phase and quadrature channels High sample rates without front end sample and hold (S/H) circuitryOpportunities: Licensing
Wireless communication systems Digital receiver systems for analog to digital conversions at radio and IF frequencies
Current invention provides a sigma-delta modulator having a decreased band pass quantization noise due to resonant center frequency errors. It also provides a continuous time resonator with moderate Q and center frequency requirements. Such a modulat...
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