Three ICs Produce Pure Sine Wa
a ttl counter, an 8-channel analog multiplexer, and a 4th-order lowpass filter can generate 1khz to 25khz sine waves with a thd better than -80db (figure 1). the circuit cascades the two 2nd-order, continuous-time sallen-key filters within ic3 to implement the 4th-order lowpass filter. two resistive dividers connected from ground to vdd and ground to vss provide bipolar dc input to the multiplexer.
figure 1. this circuit produces a pure, -80db thd sine wave whose frequency equals fc of the ic3 filter.
to operate the circuit, you must first choose the filter's cutoff frequency, fc, by tying ic3's d0 through d6 inputs to 5v or ground. the cutoff frequency can be at 128 possible levels between 1khz and 25khz depending on those seven digital input levels. because figure 1 ties d0 through d6 to ground, fc equals 1khz. the 100kω potentiometer adjusts the output leve between vdd -1.5v and vss +1.5v.
the clock's input frequency must be eight times higher than the filter's fc. the multiplexer then produces and eight-times oversampled staircase approximation of a sine wave. eight-times oversampling greatly simplifies the smoothing requirements of the lowpass filter by pushing the first significant harmonic out to seven times the fundamental. all higher-order harmonics are removed by ic3, which includes an uncommitted amplifier for setting the output level.
the frequency domain offers a view of filter's operation. smaller harmonics in the multiplexer's output spectrum (figure 2a), caused by inaccuracies in the voltage dividers, are significant with respect to the larger-amplitude harmonics associated with the staircase approximation. in the filtered output (figure 2b), all harmomnics are lost in the noise floor of the spectrum analyzer.
figure 2. the circuit's approximation process generates large harmonics in the multiplexer's output spectum (a), which the filter attenuates to a level below the spectrum analyzer's noise floor (b).
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figure 1. this circuit produces a pure, -80db thd sine wave whose frequency equals fc of the ic3 filter.
to operate the circuit, you must first choose the filter's cutoff frequency, fc, by tying ic3's d0 through d6 inputs to 5v or ground. the cutoff frequency can be at 128 possible levels between 1khz and 25khz depending on those seven digital input levels. because figure 1 ties d0 through d6 to ground, fc equals 1khz. the 100kω potentiometer adjusts the output leve between vdd -1.5v and vss +1.5v.
the clock's input frequency must be eight times higher than the filter's fc. the multiplexer then produces and eight-times oversampled staircase approximation of a sine wave. eight-times oversampling greatly simplifies the smoothing requirements of the lowpass filter by pushing the first significant harmonic out to seven times the fundamental. all higher-order harmonics are removed by ic3, which includes an uncommitted amplifier for setting the output level.
the frequency domain offers a view of filter's operation. smaller harmonics in the multiplexer's output spectrum (figure 2a), caused by inaccuracies in the voltage dividers, are significant with respect to the larger-amplitude harmonics associated with the staircase approximation. in the filtered output (figure 2b), all harmomnics are lost in the noise floor of the spectrum analyzer.
figure 2. the circuit's approximation process generates large harmonics in the multiplexer's output spectum (a), which the filter attenuates to a level below the spectrum analyzer's noise floor (b).
ups电源有几种_ups电源分类
我国首条压敏传感芯片产线落户湖南
预计:2021年半导体市场将实现两位数增长
数字实现过程中的惯性延迟和传输延迟
华为路由H6开启预售 一加9R全新顶配版开售
Three ICs Produce Pure Sine Wa
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未来触控屏是否会完全取代传统的物理按键？
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国芯思辰｜地芯科技16位8通道SAR型模数转换器GAD7689(替代AD7689)用于锂电池化成分容设备
有哪些智能手表既好看，又能独立通信功能？
NVMe-oF E-JBOF设计解析
传特斯拉使用不良零件组装，官方回应
AI时代的到来衍生了上千种AI从业方向！