Circuit Design of USB Interface Digital-to-Analog Conversion System

　　Some analog signals are often used in control systems, and a digital-to-analog converter is usually used to output the required analog signals. Computer control of the digital-to-analog converter requires the use of an external bus interface. The USB interface is a commonly used external bus interface, which is very convenient for controlling the digital-to-analog converter. Taking a typical USB interface chip and a D/A converter chip as an example, the circuit design method of the digital-to-analog conversion system based on the USB interface is described in detail.

　　This system uses the USB control chip PDIUSBD12 and the D/A converter AD558 to realize DAC control. The computer can control the AD558 to output various analog signals required through the USB interface. Since the computer's USB interface has the function of supplying power to the outside, the power supply of the USB interface is used here to power the PDIUSBD12 chip. The circuit schematic diagram of the USB interface part is shown in Figure 2.

　　The data bus of AD558 is connected to PDIUSBD12. AD558 works in 0~+10V analog voltage output mode. Capacitors C9 and C10 are used to improve the output waveform. AD558 uses a single 12V power supply and does not require an external reference voltage source. The circuit schematic of the digital-to-analog conversion part is shown in Figure 3.

　　The D+ and D- in the USB interface are used for high-speed USB data transmission. Therefore, these two signal lines directly affect the stability of the USB interface circuit and need to be carefully arranged when PCB wiring. The routing of D+ and D- should be as short and equal as possible, and the wire width and spacing of D+ and D- should be set reasonably. The differential impedance between D+ and D- should be 90W±10%. Ensure that there is a complete GND layer under the D+ and D- signals. A disconnected GND layer in the middle will cause differential impedance mismatch and increase signal interference.

　　This article explains how to use the USB interface chip to achieve host computer control D/A conversion output analog voltage. D/A converter converts digital signals into analog signals, and can be controlled using mature digital circuit technology. It has a wide range of applications. Mastering this method is very useful for design work in related fields.