Digitally-Based Calibration Techniques for RF Sigma Delta Modulators
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A calibration technique for Noise Transfer Function (NTF) optimization of Continuous-Time Sigma Delta (CT $$ Upsigma Updelta $$ ) modulators is presented. This technique employs a test tone applied at the input of the quantizer to evaluate the noise transfer function of the $$ Upsigma Updelta $$ modulator using the capabilities of the Digital Signal Processing (DSP) platform usually available in mixed-mode systems. Once the modulators 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. This approach uses a simple test signature to measure both in-band and out-of-band loop behavior.