“The second-order voltage-controlled low-pass filter circuit is shown in the figure. Two first-order low-pass filters are formed by R1, C1, R2, and C2, respectively. However, C1 is connected to the output terminal, and positive voltage feedback is introduced to form a voltage-controlled filter.
“
1 Second-order voltage-controlled low-pass filter
The second-order voltage-controlled low-pass filter circuit is shown in the figure. Two first-order low-pass filters are formed by R1, C1, R2, and C2, respectively. However, C1 is connected to the output terminal, and positive voltage feedback is introduced to form a voltage-controlled filter.
(1) Transfer function
(2) Frequency characteristics
It can be seen that the characteristic of this low-pass filter is that the damping coefficient ζ is determined by the ratio of the resistors R1, R2, C1, and C2; while the natural frequency ω0 is related to the specific values of R1, R2, C1, and C2, that is, ω0 and ζ are independently adjustable and independent of each other. influence.
(3) Parameter selection
In order to facilitate parameter matching, considering that there are few types of nominal capacitors, generally choose C1=C2=C. The specific natural frequencies ω0 and ζ can be satisfied by choosing different R1 and R2.
2 Unity Gain Second Order Voltage Controlled Low Pass Filter
For the second-order voltage-controlled low-pass filter, when the passband amplification factor Aup =1 (unity gain), the circuit shown in the figure becomes as shown in the figure, where RF=R1+R2.
(1) Basic relationship
(4) Parameter selection
When the natural frequency ω0 and the damping coefficient ζ are known, the design steps are as follows:
3 second order low pass filter
(1) Transfer function
(2) Frequency characteristics
4 Infinite Gain Multiple Feedback Low Pass Filters
(1) Transfer function
(2) Frequency characteristics
The Links: EL552256-Q1 M150XN07-V2