INTRODUCTION In the past, adding speech recording and playback capability to a product meant using a digital signal processor or a specialized audio chip. Now, using a simplified Adaptive Differential Pulse Code Modulation(ADPCM) algorithm, these audio capabilities can be added to any PICmicro device. This application note will cover the ADPCM compression and decompression algorithms, performance comparison of all PICmicro devices, and an application using a PIC16C72 micro-controller.DEFINITION OF TERMS step size -value of the step used for quantization of ana-log signals and inverse quantization of a number of steps.quantization -the digital form of an analog input signal is represented by a finite number of steps.adaptive quantization -the step size of a quantizer is dramatically changed with time in order to adapt to a changing input signal.inverse quantizer -a finite number of steps is converted into a digital representation of an analog signal.
隨著半導體技術的發展,模數轉換器(Analog to Digital Converter,ADC)作為模擬與數字接口電路的關鍵模塊,對性能的要求越來越高。為了滿足這些要求,模數轉換器正朝著低功耗、高分辨率和高速度方向快速發展。在磁盤驅動器讀取通道、測試設備、纖維光接收器前端和日期通信鏈路等高性能系統中,高速模數轉換器是最重要的結構單元。因此,對模數轉換器的性能,尤其是速度的要求與日俱增,甚至是決定系統性能的關鍵因素。在分析各種結構的高速模數轉換器的基礎上,本文設計了一個分辨率為6位,采樣時鐘為1GS/s的超高速模數轉換器。本設計采用的是最適合應用于超高速A/D轉換器的全并行結構,整個結構是由分壓電阻階梯,電壓比較器,數字編碼電路三部分組成。在電路設計過程中,主要從以下幾個方面進行分析和改進:采用了無采樣/保持電路的全并行結構;在預放大電路中,使用交叉耦合對晶體管作為負載來降低輸入電容和增加放大電路的帶寬,從而提高比較器的比較速度和信噪比;在比較器的輸出端采用時鐘控制的自偏置差分放大器作為輸出緩沖級,使得比較輸出結果能快速轉換為數字電平,以此來提高ADC的轉換速度;在編碼電路上,先將比較器輸出的溫度計碼轉換成格雷碼,再把格雷碼轉換成二進制碼,這樣進一步提高ADC的轉換速度和減少誤碼率。
This example shows how you can use signal functions in the Visiondebugger to simulate a signal that is coming into one of the analog inputs of the LPC21xx.The Measure example is described in detail in the Getting StartedUser's Guide.The MEASURE example program is available for several targets:Simulator: uVision Simulator for LPC2129MCB2100: Keil MCB2100 evaluation board with ULINK debugger - Application is loaded to internal Flash. - Switch S2 (INT1) is used as GPIO and sampled (jumper positions: J1= off, J7= on) - potentiometer POT1 is sampled as AIN0 (jumper position: J2= on) - serial port COM1 parameters: 9600 baud, no parity, 8-bits, 1 stop bit, flow control noneMCB2130: Keil MCB2130 evaluation board with ULINK debugger - Application is loaded to internal Flash. - Switch S2 (INT1) is used as GPIO and sampled (jumper positions: J1= off, J7= on) - potentiometer POT1 is sampled as AIN1 (jumper position: J2= on) - serial port COM1 parameters: 9600 baud, no parity, 8-bits, 1 stop bit, flow control none
本應用筆記介紹一種采用dsPIC數字信號控制器(Digital Signal Controller,DSC)或PIC24單片機來實現無刷直流(Brushless Direct Current,BLDC)電機無傳感器控制的算法。該算法利用對反電動勢(Back-Electromotive Force,BEMF)進行數字濾波的擇多函數來實現。通過對電機的每一相進行濾波來確定電機驅動電壓換相的時刻。這一控制技術省卻了分立的低通濾波硬件和片外比較器。需指出,這里論述的所有內容及應用軟件,都是假定使用三相電機。該電機控制算法包括四個主要部分:·利用DSC或單片機的模數轉換器(Analog-to-Digital Converter,ADC)來采樣梯形波BEMF信號·PWM導通側ADC采樣,以降低噪聲并解決低電感問題·將梯形波BEMF信號與VBUS/2進行比較,以檢測過零點·用擇多函數濾波器對比較結果信號進行濾波·以三種不同模式對電機驅動電壓進行換相:-傳統開環控制器·傳統閉環控制器比例-積分(Proportional-Integral,Pl)閉環控制器