A broadband terahertz （THz） detector chip supporting both direct detection and heterodyne detection modes is designed and fabricated using a 180 nm CMOS process. The detector consists of a loop antenna， a differential detection circuit based on NMOS transistors， and an impedance matching network， with a chip area of 200×200 μm2. Based on the bidirectional radiation characteristic of the loop antenna， a layout scheme that places the radio frequency （RF） signal and local oscillator （LO） signal on opposite sides of the detector is proposed.This scheme eliminates the need for a beam splitter for signal coupling， thereby avoiding signal attenuation. The LO signal is generated by an external independent THz source， which offers advantages in frequency stability and output power compared with on-chip integrated LO sources. To suppress the surface wave loss of the silicon substrate， a high-resistivity silicon lens with a diameter of 12 mm and a thickness of 8 mm is integrated on the backside of the chip. The measured results demonstrate that the detector operates over a broadband frequency range of 75-325 GHz. The noise equivalent power （NEP） under heterodyne detection is more than three orders of magnitude better than that under direct detection. The detector achieves its optimal performance at 220 GHz， with a heterodyne NEP of 6.26 fW/Hz and a direct detection NEP of 18.42 pW/Hz^1/2.