A clock generating system for USB 2.0 with a high-PSR bandgap reference generator

A 48-MHz clock generating system for USB 2.0 with an improved bandgap reference generator is proposed to replace an external crystal oscillator. In order to comply with clock frequency and long term jitter specifications under severe supply noise, the power supply of the DCO is regulated by a low drop-out (LDO) regulator. The reference voltage for the LDO is generated by the bandgap reference generator with two bandgap cores to improve sup- ply rejection. The proposed clock generating system implemented in a 130 nm CMOS process shows ±2.5 ns jitter under ±400 mV supply noise.