USB interface digital-to-analog conversion system circuit design

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

This system uses the USB control chip PDIUSBD12 and D/A converter AD558 to implement DAC control. The computer can control the various analog signals required for the AD558 output via the USB interface. Since the USB interface of the computer has an external power supply function, the power supply of the USB interface is used to power the PDIUSBD12 chip. The circuit schematic of the USB interface section is shown in Figure 2.

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

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

This article explains how to use the USB interface chip to implement the host computer to control the D/A conversion output analog voltage. The D/A converter converts digital signals into analog signals, which can be controlled by sophisticated digital circuit technology and is widely used. Being proficient in this method is very useful for design work in related fields.