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A process-independent adaptive bandwidth spread-spectrum clock generator (SSCG) with digitally controlled self-calibration techniques is proposed. By adaptively calibrating the VCO gain (Kv) and charge-pump (CP) current over C (ICP/C), the SSCG can realize not only adaptive bandwidth but also process independence at each operating frequency. The innovative point is the adaptive bandwidth control using Kv and ICP/C calibration. This control enabled a test chip to keep a sharp triangular SSC profile while operating over a wide frequency range (125 to 1250 MHz). The variations of VCO gain and CP current are reduced to one third those of the conventional architecture. At 1250 Mbps (625 MHz) the reduction of spectrum peak amplitude is 18.6 dB which is 2.3 dB better than the reduction obtained without calibration.
Date of Publication: March 2009