示波器系統(tǒng)參考設(shè)計(jì)
本文介紹了一個(gè)基于PC的示波器參考設(shè)計(jì)。重點(diǎn)介紹了MAX1393 ADC和MAX1396 EV (評(píng)估)板，文中給出了電路圖、軟件及軟件功能說(shuō)明。
引言
本參考設(shè)計(jì)提供了構(gòu)建一個(gè)示波器所需的全部電路(圖1)，設(shè)計(jì)采用MAX1396EVKIT (參考設(shè)計(jì)要求用MAX1393ETB ADC替代MAX1396ETB ADC)和一臺(tái)PC，并提供了電路圖、Windows®軟件和微控制器固件。固件示例程序采用C語(yǔ)言編寫，利用IAR Embedded Workbench®平臺(tái)針對(duì)MAXQ2000進(jìn)行編譯，可免費(fèi)下載MAXQ® 1.13C，4K KickStart版本的IAR Embedded Workbench。
圖1. 基于PC的示波器
MAX1393簡(jiǎn)介
MAX1393為單通道、312.5ksps、真差分、12位SAR ADC。本參考設(shè)計(jì)采用MAX1393對(duì)輸入波形進(jìn)行采樣。
硬件簡(jiǎn)介
MAX1396EVKIT包括MAX1396 ADC (本設(shè)計(jì)中將其替換為MAX1393)、MAXQ2000微控制器、所有必需的無(wú)源元件以及經(jīng)過(guò)驗(yàn)證的PCB布局。MAX1396EVKIT原理圖如圖2所示。
MAX1396EVKIT的電路板上沒有安裝MAX1393，可通過(guò)Maxim網(wǎng)站訂購(gòu)MAX1393ETB的樣品，替換評(píng)估板上的MAX1396ETB。表1列出了所需的跳線設(shè)置。
詳細(xì)電路圖(PDF, 19kB)
圖2. MAX1396EVKIT原理圖
表1. 跳線設(shè)置
| Jumper | Position |
| JU1 | 1-2 |
| JU2 | 1-2 |
| JU3 | 1-2 |
| JU4 | 1-2 |
| JU5 | 1-2 |
| JU6 | 1-2 |
| JU7 | 1-2 |
固件簡(jiǎn)介
AN4530-firmware.zip文件包含的C程序可以使MAXQ2000的SPI™外設(shè)與MAX1393通信。當(dāng)MAXQ2000采用20MHz系統(tǒng)時(shí)鐘時(shí)，SPI串行時(shí)鐘為5MHz。MAXQ2000從PC機(jī)收到命令后，微控制器即刻開始從MAX1393獲取數(shù)據(jù)。存儲(chǔ)512個(gè)采樣數(shù)據(jù)后，MAXQ2000將數(shù)據(jù)發(fā)送給PC。
Windows程序簡(jiǎn)介
將MAX1396EVKIT通過(guò)USB電纜連接到PC機(jī)后，固件將等待接收Windows程序命令，如圖3所示。按下Convert鍵接收評(píng)估板采集的輸入信號(hào)數(shù)據(jù)，然后顯示數(shù)據(jù)波形(圖4)。當(dāng)鼠標(biāo)光標(biāo)放置在波形區(qū)域時(shí)，將在屏幕頂端顯示相應(yīng)的時(shí)間(Time)和電壓(Voltage)，如圖5所示。表2給出了其它軟件功能。
圖3. MAX1393參考設(shè)計(jì)的Windows程序啟動(dòng)
圖4. 顯示波形
圖5. 在屏幕頂端顯示時(shí)間和電壓
表2. 軟件功能
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. |
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