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图中所示电路为一个非线性高通滤波器,可用作基线恢复电路。基线恢复电路在脉冲信号及交流信号测量中,可以减小由于放大器漂移或电磁噪声而叠加的直流信号,提高了信噪比。这一电路特别适用于象人体这样高阻抗信号源。与标准的频域滤波器不同,本电路对输入信号的变化率起作用,而不是对输入信号的频率起作用。在V_(OUT)端,该电路将输入脉冲信号的基线电平恢复到由V_(REF)设置的任意电平上。调节V_(PROGRAM)可以改变滤波器的截止频率,并决定I_1和I_2的大小。(如在模拟自适应滤波器应用中,可以用一个电压输出的D/A转换器来设置V_(PROGRAM)值,或者去掉R_(PROGRAM),用电流输出的D/A转换器来设置电流值)。要了解电路的工作原理,首先应注意到三极管镜象电流源作用。Q_2的集电极电流为Q_1的
The circuit shown in the figure is a non-linear high-pass filter that can be used as a baseline recovery circuit. The baseline recovery circuit improves the signal-to-noise ratio by reducing DC signals superimposed by amplifier drift or electromagnetic noise in both pulse and AC signal measurements. This circuit is particularly suitable for high impedance signal sources such as the human body. Unlike standard frequency domain filters, this circuit works on the rate of change of the input signal, not on the frequency of the input signal. At the V OUT terminal, the circuit recovers the baseline level of the input pulse signal to any level set by V REF. Adjusting the V_ (PROGRAM) can change the cut-off frequency of the filter and determine the size of I_1 and I_2. (For analog adaptive filter applications, a voltage output D / A converter can be used to set the value of the V_ (PROGRAM), or R_ (PROGRAM) can be removed. The current output can be set by a D / A converter ). To understand the working principle of the circuit, we should first notice the role of the transistor mirror current source. The collector current of Q_2 is Q_1