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(dǎo)體技術(shù)的發(fā)展，模數(shù)轉(zhuǎn)換器（Analog to Digital Converter，ADC）作為模擬與數(shù)字接口電路的關(guān)鍵模塊，對(duì)性能的要求越來越高。為了滿足這些要求，模數(shù)轉(zhuǎn)換器正朝著低功耗、高分辨率和高速度方向快速發(fā)展。在磁盤驅(qū)動(dòng)器讀取通道、測(cè)試設(shè)備、纖維光接收器前端和日期通信鏈路等高性能系統(tǒng)中，高速模數(shù)轉(zhuǎn)換器是最重要的結(jié)構(gòu)單元。因此，對(duì)模數(shù)轉(zhuǎn)換器的性能，尤其是速度的要求與日俱增，甚至是決定系統(tǒng)性能的關(guān)鍵因素。在分析各種結(jié)構(gòu)的高速模數(shù)轉(zhuǎn)換器的基礎(chǔ)上，本文設(shè)計(jì)了一個(gè)分辨率為6位，采樣時(shí)鐘為1GS/s的超高速模數(shù)轉(zhuǎn)換器。本設(shè)計(jì)采用的是最適合應(yīng)用于超高速A/D轉(zhuǎn)換器的全并行結(jié)構(gòu)，整個(gè)結(jié)構(gòu)是由分壓電阻階梯，電壓比較器，數(shù)字編碼電路三部分組成。在電路設(shè)計(jì)過程中，主要從以下幾個(gè)方面進(jìn)行分析和改進(jìn)：采用了無采樣/保持電路的全并行結(jié)構(gòu)；在預(yù)放大電路中，使用交叉耦合對(duì)晶體管作為負(fù)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(shí)鐘控制的自偏置差分放大器作為輸出緩沖級(jí)，使得比較輸出結(jié)果能快速轉(zhuǎn)換為數(shù)字電平，以此來提高ADC的轉(zhuǎn)換速度；在編碼電路上，先將比較器輸出的溫度計(jì)碼轉(zhuǎn)換成格雷碼，再把格雷碼轉(zhuǎn)換成二進(jìn)制碼，這樣進(jìn)一步提高ADC的轉(zhuǎn)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(yīng)用筆記介紹一種采用dsPIC數(shù)字信號(hào)控制器（Digital Signal Controller，DSC）或PIC24單片機(jī)來實(shí)現(xiàn)無刷直流（Brushless Direct Current，BLDC）電機(jī)無傳感器控制的算法。該算法利用對(duì)反電動(dòng)勢(shì)（Back-Electromotive Force，BEMF）進(jìn)行數(shù)字濾波的擇多函數(shù)來實(shí)現(xiàn)。通過對(duì)電機(jī)的每一相進(jìn)行濾波來確定電機(jī)驅(qū)動(dòng)電壓換相的時(shí)刻。這一控制技術(shù)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(nèi)容及應(yīng)用軟件，都是假定使用三相電機(jī)。該電機(jī)控制算法包括四個(gè)主要部分：·利用DSC或單片機(jī)的模數(shù)轉(zhuǎn)換器（Analog-to-Digital Converter，ADC）來采樣梯形波BEMF信號(hào)·PWM導(dǎo)通側(cè)ADC采樣，以降低噪聲并解決低電感問題·將梯形波BEMF信號(hào)與VBUS/2進(jìn)行比較，以檢測(cè)過零點(diǎn)·用擇多函數(shù)濾波器對(duì)比較結(jié)果信號(hào)進(jìn)行濾波·以三種不同模式對(duì)電機(jī)驅(qū)動(dòng)電壓進(jìn)行換相：-傳統(tǒng)開環(huán)控制器·傳統(tǒng)閉環(huán)控制器比例-積分（Proportional-Integral，Pl）閉環(huán)控制器
