A GmC filter design methodology for high-speed continuous time-delta A/D converters in 90 nm standard CMOS
A GmC filter design methodology for high-speed continuous time-delta A/D converters in 90 nm standard CMOS
- Author(s): R. Schoofs ; M. Steyaert ; W. Sansen
- DOI: 10.1049/cp:20050145
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- Author(s): R. Schoofs ; M. Steyaert ; W. Sansen Source: 5th IEE International Conference on ADDA 2005. Advanced A/D and D/A Conversion Techniques and their Applications, 2005 p. 129 – 133
- Conference: 5th IEE International Conference on ADDA 2005. Advanced A/D and D/A Conversion Techniques and their Applications
- DOI: 10.1049/cp:20050145
- ISBN: 0 86341 542 3
- Location: Limerick, Ireland
- Conference date: 25-27 July 2005
- Format: PDF
This paper presents a design methodology for a GmC filters in continuous-time sigma-delta A/D converters. It focuses on the challenges the designer faces when a deep sub-micron technology is used. According to the proposed methodology, a single-bit, 3rd order modulator is designed. The modulator achieves an accuracy of 10 bits within a signal band of 10 MHz. The design is made in a 90 nm standard CMOS process. The small transistor dimensions enable a clock rate of 1 GHz. An analytical comparison between RC filters and GmC filters is presented based on their power consumption. It is shown that a RC filter requires an integrator closed loop gain-bandwidth equal to the sampling rate. This puts a severe limitation on the minimal power consumption for this type of filter. Therefore, a GmC filter implementation is chosen because it consumes the lowest power in order to meet the design specifications. Mathematical expressions for harmonic distortion and thermal noise generation are derived. They are interpreted in terms of a low power design approach. Since the input signal swing scales down with the supply voltage, harmonic distortion becomes less important in a deep sub-micron technology. Therefore, the thermal noise requirements determine the overall power consumption of the continuous-time modulator. All proposed design choices are verified by numerical simulations.
Inspec keywords: modulators; RC circuits; sigma-delta modulation; low-pass filters; continuous time filters; thermal noise; CMOS integrated circuits; harmonic distortion; power consumption
Subjects: A/D and D/A convertors; CMOS integrated circuits; Other topics in statistics; Filtering methods in signal processing; Modulators, demodulators, discriminators and mixers
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