A fifth-order gm–c continuous-time Δ Σ modulator with process-insensitive input linear range

• Published in: IEEE journal of solid-state circuits 2009-09, Vol.44 (9), p.2381-2391
• Main Authors: Aiba, Yusuke, Tomioka, Koji, Nakashima, Yuta, Hamashita, Koichi, Song, Bang-Sup
• Format: Article
• Language: English
• Subjects: Adaptive common-mode control; Adaptive control; Area measurement; Bandwidth; continuous- time; Delta\Sigma modulator; Digital-analog conversion; Distortion measurement; Dynamic range; Gm-C filters; Harmonic distortion; over-sampling; Programmable control; switched-capacitor DAC; Temperature distribution; Temperature sensors; tri-level DAC
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2009.2025339

Continuous-time ¿¿ modulators (CT-DSMs) that use transistor-based G m -C integrators are simple but sensitive to process and temperature variations. Their performance depends heavily on the input linear range that varies widely. A CT-DSM is implemented using a triode G m -C integrator and a tri-level switched-capacitor digital-to-analog converter (SCDAC). A self-scaling SCDAC keeps the input signal range constant, and an adaptive input common-mode bias control enables the triode G m cell to operate always with its constant input linear range. The proposed G m cell exhibits a tuning range of ± 15% while maintaining its linear range over the temperature variation from -30°C to 85°C. A 2-MHz bandwidth, fifth-order CT-DSM in 0.18 ¿m CMOS samples at 128 MS/s with an over-sampling ratio of 32 (OSR = 32), occupies an active area of 0.4 mm 2 , and consumes 11 mW at 1.8 V. With a -3 dB input of the full scale (400 mV), the measured dynamic range, second harmonic distortion (HD2), and third harmonic distortion (HD3) are 71, -86, and -91 dB, respectively.