Mid-infrared laser sources with broad instantaneous-bandwidth are critical for many applications, including infrared micro-spectroscopy, environmental monitoring, medical diagnosis, and ultra-short pulse generation. In this article, the output spectrum bandwidth from synchronously pumped optical parametric oscillator (SPOPO) was focused on and a scheme, chirped-pulse optical parametric oscillator (CPOPO) was proposed to achieve broadband output beyond the limitation of pump pulse width. The CPOPO with self-phase modulation (SPM) or chirped quasi-phase matching (CQPM) were studied and achieved through period-poled lithium niobate (PPLN) based SPOPO. The outputs covered 2.9-3.9 μm (~27 THz) with power up to 92 mW and 2.9-5.0 μm (~44 THz) with 64 mw, respectively.