A 125–1250 MHz Process-Independent Adaptive Bandwidth Spread Spectrum Clock Generator With Digital Controlled Self-Calibration

A process-independent adaptive bandwidth spread-spectrum clock generator (SSCG) with digitally controlled self-calibration techniques is proposed. By adaptively calibrating the VCO gain ($K_v$) and charge-pump (CP) current over C ($I_{CP}/C$), 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 $K_v$ and $I_{CP}/C$ 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.