簡單低通濾波器：Simple Low-pass Filter

The simple low-pass filter is shown in Figure 11. This circuit has a 6 dB per octave roll-off after a closed-loop 3 dB point defined by fc. Gain below this corner frequency is defined by the ratio of R3 to R1. The circuit may be considered as an AC integrator at frequencies well above fc; however, the time domain response is that of a single RC rather than an integral. R2 should be chosen equal to the parallel combination of R1 and R3 to minimize errors due to bias current. The amplifier should be compensated for unity-gain or an internally compensated amplifier can be used. A gain frequency plot of circuit response is shown in Figure 12 to illustrate the difference between this circuit and the true integrator.

簡單低通濾波器的電路如圖11。本電路在閉環(huán)3dB轉(zhuǎn)折點為fc，對高于fc的信號有6dB/2倍頻程的衰減。低于fc頻率的信號的增益由R3/R1決定，在輸入信號頻率遠大于fc的情況下，電路可以看成是對交流信號的積分器；可以認(rèn)為，在此時，從時域響應(yīng)上看，比起積分來說，RC（的時間延遲特性）更明顯。R2的阻值應(yīng)選為R1和R3的并聯(lián)阻值，以減小輸入偏置電流帶來的誤差。在這里可以選擇帶內(nèi)部頻率補償?shù)腛P或者在外部對單位增益的頻率特性進行補償。電路的增益波特圖見圖12，本圖說明了LPF和真正的積分器之間在頻率特性上的區(qū)別。