示波器系统参考设计

本文介绍了一个基于PC的示波器参考设计。重点介绍了MAX1393 ADC和MAX1396 EV (评估)板，文中给出了电路图、软件及软件功能说明。

引言

本参考设计提供了构建一个示波器所需的全部电路(图1)，设计采用MAX1396EVKIT (参考设计要求用MAX1393ETB ADC替代MAX1396ETB ADC)和一台PC，并提供了电路图、Windows®软件和微控制器固件。固件示例程序采用C语言编写，利用IAR Embedded Workbench®平台针对MAXQ2000进行编译，可免费下载MAXQ® 1.13C，4K KickStart版本的IAR Embedded Workbench。


图1. 基于PC的示波器

MAX1393简介

MAX1393为单通道、312.5ksps、真差分、12位SAR ADC。本参考设计采用MAX1393对输入波形进行采样。

硬件简介

MAX1396EVKIT包括MAX1396 ADC (本设计中将其替换为MAX1393)、MAXQ2000微控制器、所有必需的无源元件以及经过验证的PCB布局。MAX1396EVKIT原理图如图2所示。

MAX1396EVKIT的电路板上没有安装MAX1393，可通过Maxim网站订购MAX1393ETB的样品，替换评估板上的MAX1396ETB。表1列出了所需的跳线设置。


详细电路图(PDF, 19kB)
图2. MAX1396EVKIT原理图

表1. 跳线设置

固件简介

AN4530-firmware.zip文件包含的C程序可以使MAXQ2000的SPI™外设与MAX1393通信。当MAXQ2000采用20MHz系统时钟时，SPI串行时钟为5MHz。MAXQ2000从PC机收到命令后，微控制器即刻开始从MAX1393获取数据。存储512个采样数据后，MAXQ2000将数据发送给PC。

Windows程序简介

将MAX1396EVKIT通过USB电缆连接到PC机后，固件将等待接收Windows程序命令，如图3所示。按下Convert键接收评估板采集的输入信号数据，然后显示数据波形(图4)。当鼠标光标放置在波形区域时，将在屏幕顶端显示相应的时间(Time)和电压(Voltage)，如图5所示。表2给出了其它软件功能。

图3. MAX1393参考设计的Windows程序启动


图4. 显示波形


图5. 在屏幕顶端显示时间和电压
表2. 软件功能

Button	Description
	Vertically scales the waveform.
	Horizontally scales the waveform.
	Shifts the waveform horizontally.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the starting time at the left of the screen.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the ending time at the right of the screen.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the sampling time.
	Enter a proper trigger-level value into this edit box.
	Click on one of the two radio buttons to choose either rising-edge triggering or falling-edge triggering.
	Press this button to receive input-signal data from the EV kit board and display the waveform on the screen.
	Select this checkbox to receive continuous data from the EV kit and continuous updates to the waveform on the screen.
	Press this button to redraw the waveform on the screen.
	Press this button to exit the program.

Button	Description
	Vertically scales the waveform.
	Horizontally scales the waveform.
	Shifts the waveform horizontally.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the starting time at the left of the screen.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the ending time at the right of the screen.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the sampling time.
	Enter a proper trigger-level value into this edit box.
	Click on one of the two radio buttons to choose either rising-edge triggering or falling-edge triggering.
	Press this button to receive input-signal data from the EV kit board and display the waveform on the screen.
	Select this checkbox to receive continuous data from the EV kit and continuous updates to the waveform on the screen.
	Press this button to redraw the waveform on the screen.
	Press this button to exit the program.