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本文介绍并比较了三种低成本的D/A变换器(DAC)。这些设计很容易采用集成电路实现:传统的脉冲—宽度调制(PWM)DAC;新的脉冲—计数调制(PCM)DAC以及一阶噪声整形(FONS)DAC。这三种方法都控制脉冲宽度的总和与恒定的转换周期比率,由于脉冲宽度是单位脉冲的整数倍,故三种方法都可归为脉冲—计数调制。 本文给出了由简单的数字电路和低通滤波器构成的三种DAC的框图。对一个固定的数字输入值,滤波器输出最坏情况下的纹波被用来计算低通滤波器的截止频率,本文给出了一阶、二阶和四阶巴特沃斯低通滤波器3dB截止频率的近似值。在时域(建立时间)和频域(一个满度正弦波输入的非滤波输出谱)分析了动态特性及对静态精度的主要影响并举例说明了PCM和FONS的性能。
This article describes and compares three low-cost D / A converters (DACs). These designs are easy to implement with integrated circuits: traditional pulse-width modulated (PWM) DACs; new pulse-count modulation (PCM) DACs and first-order noise shaping (FONS) DACs. Each of these three methods controls the ratio of the sum of the pulse widths to the constant conversion period. Since the pulse width is an integer multiple of the unit pulse, all three methods are classified as pulse-count modulation. This article presents a block diagram of three DACs consisting of a simple digital circuit and a low-pass filter. For a fixed digital input value, the worst-case filter output ripple is used to calculate the cut-off frequency of the low-pass filter. In this paper, the first-order, second-order, and fourth-order Butterworth low- Cutoff frequency approximation. The dynamic characteristics and the main effects on the static accuracy are analyzed in the time domain (settling time) and the frequency domain (a non-filtered output spectrum of a full-scale sinusoidal input) and exemplify the performance of PCM and FONS.