Digital based calibration technique for continuous-time bandpass sigma-delta analog-to-digital converters

Abstract

In this paper, a calibration technique for Noise Transfer Function (NTF) optimization of Continuous-Time Bandpass Sigma Delta (CT BP RD) 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 softwarebased 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.

Main defects of LC-based ΣΔ modulators

“…Trimming is needed to correct or compensate the drift in circuit components to obtain the optimum performance from the modulator. There are some publications that discuss calibration of CT Σ∆ modulators, but they are limited to calibration of the modulator notch frequency [4]- [6]. In this paper, it is shown that there are more parameters to calibrate other than the notch frequency.…”

“…One of the main issues in BP CT Σ∆ modulators is the poor accuracy and sensitivity to process variations [4]. Trimming is needed to correct or compensate the drift in circuit components to obtain the optimum performance from the modulator.…”