Conventional mechanical angle measurement sensors are utilized in order to solve the problems caused by increasing system size, weight, cost and installing sensors that lead in errors and unreliability in frame servo systems. Based on TMS320F28335 as main controller and A3PE3000 as slave controller, we have designed the hardware circuit for electrical signal acquisition and operation. Meanwhile, a sliding mode observer is proposed for angle estimation to replace mechanical sensors. In this method, the relevant electrical signals in the motor windings are measured by hardware circuits. The rotor position and velocity estimation are implemented by establishing a sliding mode observer and a phase-locked loop algorithm. The simulation model is built in Simulink. The simulation results show that the values of position and velocity estimated by the sliding mode observer are convergent to real value after the system runs for 0.2 s.