In this paper, a calibration technique for Noise Transfer Function (NTF) optimization of Continuous-Time Bandpass Sigma Delta
(CT BP ΣΔ) modulators is presented. The proposed technique employs a test tone applied at the input of the quantizer to evaluate
the noise transfer function of the Analog-to-Digital Converter (ADC) using the capabilities of the Digital Signal Processing
(DSP) platform usually available in mixed-mode systems. Once the ADC output bit stream is captured, necessary information
to generate the control signals to tune the ADC parameters for best Signal-to-Quantization Noise Ratio (SQNR) performance
is extracted via an LMS software-based algorithm. Simulation results show that notch frequency of the NTF due to process variations
and temperature tolerances can be tuned using the proposed methodology. The proposed global calibration approach can be used
during the system start-up and the idle system time. The proposed approach uses a single in-band calibration tone, but it
can be expanded using out-of band test tones for background calibration schemes.
Keywords Bandpass sigma-delta modulators - ADC calibration techniques - Continuous-time - Bandpass modulators - Sigma-delta modulators