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Low-Pass Filter Using Operational Transconductance Amplifiers

This example shows how to model a second-order active low-pass filter. The filter is characterized by the transfer function H(s) = 1 / ( (s/w1)^2 + (1/Q)*(s/w1) + 1 ) where w1 = 2*pi*f1, f1 is the cut-off frequency and Q is the quality factor. Parameters f1 and Q are specified by the Design parameters block. To check the filter frequency response, double-click the Plot frequency response block after running the simulation. In the ideal case, the gain should be zero dB at DC, -20*log10(1/Q) dB at frequency f1, and should attenuate at -12dB/octave at high frequency. The model can be used to determine the impact of impairments, such as finite transconductance gain, on the filter frequency response. Using an operational transconductance amplifier permits digital control of the filter by varying the values of the two current sources.

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