# Design and Signal-Decoding Test Verification of Dual-Channel Round Inductsyn Decoding Circuit
## 1 Introduction  
As the demand for the rapid tracking and precise positioning of servo control systems on orbiting spacecraft continues to increase, especially for high-precision spacecraft, the minute vibrations introduced by moving components can have a significant impact on payload resolution [1]. Considering the significant cost of energy supply for spacecraft in orbit, high-efficiency energy conversion and stable permanent magnet synchronous motor drive-control systems are widely utilized [2]. To achieve the precise vector control of permanent magnet synchronous motors, in addition to excellent control algorithms, angle sensors that can provide rapid and accurate feedback of the motor rotor position are also crucial [3; 4; 5; 6]. Common angle sensors include circular grating, coding disk, encoders, resolvers, and inductsyn. Among them, encoders can directly output pulse signals containing angle information for communication with microprocessors, making them the simplest to apply, although their precision ceiling is lower compared to other sensor types [7]. Gratings and coding disks are typically used in servo control systems with high precision requirements, but have strict environmental requirements and complex assembly processes, leading to high maintenance costs [8]. The round inductsyn is a type of high-precisionangular displacement sensor based on the principle of electromagnetic induction [9; 10]. Its operation principle is similar to that of a resolver [11], but with more pole pairs, sometimes including coarse and fine channels. Its accuracy significantly surpasses that of a resolver. Meanwhile, the round inductsyn requires lower installation precision, exhibits resistance to shock and vibration, boasts excellent environmental adaptability [12], and offers a long operational lifespan. It can be utilized in scenarios where gratings are unsuitable, such as high-orbit weather satellites. As a result, the round inductsyn is increasingly being incorporated into high-precision servo control systems in aerospace applications [13]. The signals directly input/output by the round inductsyn are analog signals, which need to be decoded before being converted into digital angle quantities for reception by the subsequent system microprocessor, achieving angle acquisition for the control system [14; 15; 16; 17]. For the decoding-circuit design of the round inductsyn, the mainstream approach involves utilizing microprocessors such as FPGA (Field-Programmable Gate Array) and DSP (Digital Signal Processor) in conjunction with peripheral A/D sampling circuits to convert the output signals of the round inductsyn into digital quantities. In the software algorithm, trigonometric transformations such as inverse tangent are employed to calculate the angle information [18]. This method requires hardware design for the input/output signal processing circuitry of the round inductsyn, as well as software algorithm design for the microprocessor; even with the help of artificial intelligence technology [19; 20; 21], it is difficult to achieve a balance between software and hardware design. Due to the similarity in principles between the round inductsyn and resolvers, this paper draws inspiration from resolver decoding techniques to design the decoding circuit for the round inductsyn. Currently, RDC decoding chips are commonly used to decode resolvers in servo control systems [22; 23; 24]. However, the round inductsyn have certain driving capability requirements for excitation signals, and the induced signals mostly consist of dual-channel multi-output signals, with very small amplitudes typically in the range of tens of millivolts. Existing resolver decoding circuits are primarily designed for single-channel excitation and single-channel output modes, making it challenging to adapt the signal output/input specifications to the round inductsyn. Therefore, this paper proposes a decoding circuit design based on a dedicated resolver decoding chip, the AD2S1210, tailored to the signal characteristics of dual-channel round inductsyn.