Sigma delta modulator with SAW filter
AssigneeInternational Business Machines Corporation
InventorsMiaochen Wu, Aria Eshraghi, Theodore Tewksbury
Life of this patent
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Abstract
A sigma delta modulation device and method for filtering high frequency intermediate frequency signals. A summing amplifier receives the analog intermediate frequency signal, and provides to a surface acoustic wave filter (SAW) an analog signal which is to be converted to a digital quantity. A quantizer digitizes the signal to produce a digitized intermediate frequency signal. A digital to analog converter provides a feedback signal from the quantizer output signal, to the summing amplifier to form a sigma delta modulation device. The SAW filter provides for high stop band attenuation of signal images within the intermediate frequency signal, and produces a low noise signal with substantially no intermodulation products.
Claims10
A sigma delta modulation device for filtering high frequency intermediate signals, comprising:
- a summing amplifier for receiving an analog intermediate frequency signal;
- a SAW filter connected to receive a signal from said summing amplifier of at least 25 MHz, a center frequency of 109 MHz and a stop band of 60 db, said SAW filter providing a bandwidth for eliminating image frequencies contained in said analog intermediate frequency signal;
- a buffer amplification circuit for amplifying a signal produced from said SAW filter;
- a quantizer for digitizing a signal from said buffer to produce a digitized intermediate frequency signal;
- and
- a digital to analog converter connected to received said digitized intermediate frequency signal, and to apply an analog output voltage as a feedback signal to said summing amplifier.
A method for converting high frequency analog intermediate frequency signals to digital signals, comprising:
- amplifying said intermediate frequency analog signal;
- filtering said analog signal in a SAW filter having a center frequency rater than 100 MHz, and a bandwidth of 25 MHz to remove image signals contained in said analog signal, wherein said filtering of said analog signal through said SAW filter produces a band pass signal which is attenuated outside of a bandpass frequency range which is at least 60 db below signals within said bandpass frequency range;
- amplifying said filtered analog signal;
- quantizing said amplified analog signal;
- decimating the quantized digital signal wherein a filtered digital intermediate frequency signal is produced;
- converting said quantized signal into an analog signal;
- and
- combining said converted quantized signal with said intermediate frequency signal.
A sigma delta modulation device for filtering high frequency intermediate signals, comprising:
- a summing amplifier for receiving an analog intermediate frequency signal;
- a SAW filter connected to receive a signal from said summing amplifier, said SAW filter providing a bandwidth for eliminating image frequencies contained in said analog intermediate frequency signal, said SAW filter having a stop band attenuation of greater than 60 db;
- a buffer amplification circuit for amplifying a signal produced from said SAW filter;
- a quantizer for digitizing a signal from said buffer to produce a digitized intermediate frequency signal;
- and
- a digital to analog converter connected to receive said digitized intermediate frequency signal, and to apply an analog output voltage as a feedback signal to said summing amplifier.
Dependencies are inferred from the claim text.