Signal simulator circuit diagram

Power supply design

Because the DSP chip uses two different voltages, the core 1.8 V voltage and the IO port 3.3 V voltage, dual power supplies are generally used to power the DSP system. In this design, the TPS767 D301 power supply chip specially provided by TI for DSP is used. Provide power. This chip is a linear DC/DC conversion chip. If you provide 5 V DC power to TPS767 D301, it can generate voltages of 3.3 V and 1.8 V that meet the requirements of F2812, and directly provide power to the DSP. In addition, the maximum output of this power chip The current can reach 1 A, which can power the DSP chip and a small number of peripheral circuits at the same time.

Clock and reset circuit

The clock of the DSP2812 chip has two pin connection methods. One is to use the crystal oscillator circuit provided internally and connect a crystal between its X1/XCLKIN and X2 pins to start the internal oscillator; the other is to directly connect the The external clock source is directly input to the X1/XCLKIN pin, and the X2 pin is left floating. The first method is used in this design, as shown in Figure 1.

The DSP2812 chip has a phase-locked loop clock module (PLL), which can input the clock for frequency multiplication, so a 30 MHz external crystal oscillator is used. After the phase-locked loop frequency multiplication, the system's 150 MHz requirement can be achieved. Since the power module TPS767D301 chip itself can generate a reset signal, and this reset signal can be directly used by the DSP chip, there is no special reset chip in this design.

Working principle of conversion chip and its interface design with DSP

The 12SXZ conversion chip consists of the following five parts: reference transformer, quadrant selection switch, sine and cosine multiplier, power amplifier, and output transformer. After the digital full-angle and reference signal inputs are passed through the sine and cosine multipliers, they are converted into sine and cosine signals representing the angle. After being amplified by the power amplifier, they have a load capacity of 1.3VA. After being isolated and boosted by the output transformer, It becomes a three-wire or four-wire analog signal output in the form of an auto-rectifier/resolver.

The left side of the equation is the output voltage, θ is the input digital angle, K is the proportional coefficient, and URH-RL is the reference voltage. The working principle block diagram of the converter is shown in Figure 2.

The core of the simulator is DSP 2812, which can generate the required attitude signal through software control, and the system has a self-check function. In the system design, the DSP controls the I/O port to directly operate the 12SXZ to generate analog signals. We know above that DSP has two voltages. The voltage of the I/O port is 3.3 V. The conversion chip we use is TTL level 5 V voltage. Considering the driving capability of the DSP to generate signals, we first need to level conversion to convert the DSP The 3.3 V level of the port output is converted to 5 V. The level conversion chip used is SN74ALVC164245 ($0.8750). This chip is a 16-way bidirectional level conversion chip, and its conversion direction is controlled by the pin DIR. The conversion chip SXZ is a 12-bit converter. The data ports D0~D11 of the DSP are connected to the 12 channels in the level conversion chip. The converted 12-bit level is then connected to the 12-bit digital input terminal of SXZ. The interface circuit between DSP and 12SXZ converter is shown in Figure 3.

This article introduces the hardware design circuit of the attitude signal simulator based on DSP technology. This method overcomes the shortcomings of traditional simulation technology such as complex structure, low accuracy, and poor reliability. The heading and attitude signal can be realized through software programming. Through the development, debugging and application of this simulator, the simulator has the advantages of low power consumption, small size, etc., which is convenient for on-site debugging, can be used in a variety of environments, and can eliminate aircraft There will be significant improvements in aspects such as malfunction and maintenance of aircraft safety and improvement of flight quality.

The core control chip selected for the design is TMS320F2812 ($18.5250), but basic peripheral circuits must be provided to play the role of the core control circuit. A typical minimum DSP system should include a DSP chip, a power circuit that provides appropriate power to the DSP chip, a reset circuit that triggers DSP initialization, a clock circuit, and a JTAG interface circuit for online simulation and downloading. In addition, considering the need to communicate with the host computer and complete the transmission of data and control signals, a serial communication circuit was added on this basis. The basic system block diagram of DSP is shown in Figure 2. The external RAM is used to store a large amount of signal data, and the external FLASH is used to store the control program.