The embodiments of the invention disclose a signal processing circuit, which is applied to an Internet of Things terminal. The Internet of Things terminal comprises a main board. The circuit comprises: a PIFA antenna, a first filter circuit, an antenna switch circuit, a second filter circuit, a differential matching circuit, a low noise amplifying circuit and a mixing circuit; the PIFA antenna comprises an outer strip wire, a radiator, a grounding bending wire, a feeding plate, a grounding point and a short-circuit probe, the outer strip wire encircles a rectangle with an opening, the openingis located at the outer strip wire and the grounding point, the radiator is arranged inside the rectangle and connected to the grounding bending wire, the grounding bending wire is connected to the grounding point, the end of the grounding bending wire is connected to the short-circuit probe, and the feeding plate is arranged between the grounding point and the outer strip wire. By serially connecting the surface acoustic filter, the differential matching circuit and the low noise amplifier, secondary reflection signals can be reduced to enter the inside of a chip, so that the signal-to-noiseratio of useful signals is improved, and the sensitivity of a receiver is enhanced.