Anti-aliasing Filter (Analogue Low-Pass Filter)

posted in: Technical | 0

Schematic of the analogue low-pass filter (LPF) used for data acquisition process is shown in Figure 1. The LPF design was based on Sallen-Key LPF circuit (2-pole Butterworth filter).

LPF Filter circuit

Design procedures (Carter, 2001) §

  • Choose a cut-off frequency fo (Hz).
  • In this research fo = 10 kHz.
  • Select C1 value between 100 pF and 0.1 uF.
  • C1 was chosen to be 1000 pF.
  • Make C2 = 2 x C1
  • C2 = 2 x C1 = 2000 pF
  • Calculate R1 = R2 = 0.707 / (2 · π · fo · C1)
  • R1 = R2 = 0.707 / (2 · π · 10kHz · 1000 pF) = 11.2 K Ohms

§ Carter, B. 2001, Filter Design in Thirty Seconds – Application Report SLOA093, Texas Instruments

Test Result
input-output of the LPF