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Delta-Sigma Modulator with Multi-level (RZ) Return to Zero Analog to Digital Converter

IP.com Disclosure Number: IPCOM000013847D
Original Publication Date: 2002-Jul-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 1 page(s) / 42K

Publishing Venue

IBM

Abstract

Continuous-Time Delta-Sigma Modulator is a solution for high-speed, high-resolution A/D (Analog to Digital) converters. Excess loop delay [1] (delay between the quantizer clock edge and the time when a change in output bit us seen at the feedback point in the modulator) degrades the performance of Delta-Sigma modulator since it’s unpredictable and the right parameters can’t be determined before manufacturing. The way to make the circuit unaffected by the unknown excess loop delay is to use RZ (Return to Zero DAC (Digital to Analog Converter) [1]. The implementation of 2-levels ADC is quite simple to implement with differential logic. The implementation of multilevel ADC, which can help the implementation of modulator with lower sampling rate and lower OSR (Over Sampling Ratio), is harder task. In this invention I give a solution for RZ multilevel ADC implementation. The invention is a way to implement Delta-Sigma Modulator with RZ multilevel DAC, assuming that we have RZ 2-level DAC. A block diagram of the architecture is followed: The output of the A/D is the input to a LUT (Look-Up-Table). According to the A/D output (every sampling period) the LUT will divide the RZ DACs into 3 sets: Set #1 all the RZ DACs that will output negative RZ pulse. Set #2 all the RZ DACs that will output positive RZ pulse. Set #3 all the RZ DACs that will output zero pulse (this set is optional). The LUT will choose those 3 sets (or 2 sets) such that the output of the header will give the desired RZ multilevel pulse. The alternative solution is multilevel DAC which is made zero at some point. Implementation of such DAC is hard to make, especially if accuracy is needed. The technical advantages are the accuracy that can be achieved and the simplicity of implementation. There are lot of effort to implement high-speed, high resolution Bandpass Delta-Sigma Modulators. RZ DAC is necessary for the implementation of such modulators. Multilevel RZ DACs afford to use a lower sampling rate. This way of implementation can help the implementation of such Multilevel RZ DACs. The commercial benefits are the ability to have high performance Bandpass Delta-Sigma Modulator on time. The invention makes the commercial implementation easier. Continuous Bandpass Delta-Sigma Modulators are of lot of interest for the communication market (3rd generation software radio). 3rd generation software radios is one of the targets for the invention. References: [1] “Excess Loop Delay in Continuous-Time Delta-Sigma Modulators”, James A. Cherry and W. Martin Snelgrove, IEEE Trans on Circuits and Systems-II, Vol. 46, No. 4, April

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  Delta-Sigma Modulator with Multi-level (RZ) Return to Zero Analog to Digital Converter

Continuous-Time Delta-Sigma Modulator is a solution for high-speed, high-resolution A/D (Analog to Digital) converters. Excess loop delay [1] (delay between the quantizer clock edge and the time when a change in output bit us seen at the feedback point in the modulator) degrades the performance of Delta-Sigma modulator since it's unpredictable and the right parameters can't be determined before manufacturing. The way to make the circuit unaffected by the unknown excess loop delay is to use RZ (Return to Zero DAC (Digital to Analog Converter) [1]. The implementation of 2-levels ADC is quite simple to implement with differential logic. The implementation of multilevel ADC, which can help the implementation of modulator with lower sampling rate and lower OSR (Over Sampling Ratio), is harder task. In this invention I give a solution for RZ multilevel ADC implementation. The invention is a way to implement Delta-Sigma Modulator with RZ multilevel DAC, assuming that we have RZ 2-level DAC. A block diagram of the architecture is followed: The output of the A/D is the input to a LUT (Look-Up-Table). According to the A/D output (every sampling period) the LUT will divide the RZ DACs into 3 sets: Set #1 - all the RZ DACs that will output negative RZ pulse. Set #2 - all the RZ DACs that will output positive RZ pulse. Set #3 - all the RZ DACs that will output zero pulse (this set is option...