One of the most critical blocks in a wide-band continuous time sigma delta (CTSD) analog-to-digital converter (ADC) is the loop filter. For most loop filter topologies, the performance of the filter depends largely on the performance of the operational amplifiers (op-amps) used in the filter. The op-amps need to have high linearity, low noise and large gain over a wide bandwidth.
In this work, the impact of op-amp parameters like noise and linearity on system level performance of the CTSD ADC is studied, and the design specifications are derived for the op-amps. A new class-AB bias scheme, which is more robust to process variations and has an improved high frequency response over the conventional Monticelli bias scheme, is proposed. A biquadratic filter which forms the input stage of a 5th order low pass CTSD ADC is used as a test bench to characterize the op-amp performance. The proposed class-AB output stage is compared with the class-AB output stage with Monticelli bias scheme and a class-A output stage with bias current reuse. The filter using the new op-amp architecture has lower power consumption than the other two architectures. The proposed class AB bias scheme has better process variation and mismatch tolerance compared to the op-amp that uses conventional bias scheme.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2011-08-9896 |
| Date | 2011 August 1900 |
| Creators | Krishnan, Lakshminarasimhan |
| Contributors | Silva-Martinez, Jose |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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