TLV316-Q1: TLV316-Q1 Single-Pole, Low-Pass Filter Issue

Xiaoxiang,

"s" is a complex number: s = jω = j*2πf  (see below)

Thus, in the case of a low pass filter, fc (-3db frequency) may be derived as shown below: 

s*RC=1 where s=jω=j*2πf

 j*2πf*RC=1

fc=1/(2πRC) - a pole frequency

Hi Xiaoxiang,

The s in the equation is the complex variable "s" from the Laplace transform.

The transfer function VOUT/VIN shows the frequency response of the circuit in the picture.

1+RF/RG is the gain from the op-amp (assumed ideal) in the non-inverting configuration.

1/(1+sR1C1) is the frequency response of the low pass filter formed by R1 and C1. You can use this to evaluate the phase and gain at the non-inverting terminal of the op amp with respect to different VIN frequencies.

You can evaluate the frequency response on the imaginary axis (s = jω) and from (ω = 2πf), find the root of the denominator of 1/(1+sR1C1) to see that the your -3dB cutoff frequency is at is at 1/(2πR1C1).

You select R1 and C1 depending on the cut-off frequency that you desire.