A T-filter is used when the input impedance is low. It is an alternative to the very popular Pi filter.
This calculator below requires
- Cutoff Frequency (Fc)
- Load Impedance (RL)
Example T Filter Calculation
For a source impedance of 50 Ω and a load Impedance of 1 kΩ, design a low pass filter with a cutoff frequency of 100 kHz.
Use the calculator above, the component values are as follows:
- L1 = 2.39 mH
- C2 = 2.12 nF
- L3 = 796 uH
We can also confirm that for the example in [1] where the source impedance is 50 Ω, load Impedance of 10 kΩ, cutoff frequency of 100 kHz, the calculator provides the following component values
- L1 = 23.9 mH
- C2 = 212 pF
- L3 = 7.96 mH
Advantages of a T-Filter
Used when either the input impedance is low or both input and output impedances are low
Disadvantages of a T-filter
Uses two inductors instead of one as in the case of the Pi Filter. Inductors are more expensive than capacitors and therefore the Pi filter is preferred. Note that a Pi filter can be used when
- the input impedance is high
- both input and output impedances are high
- input and output impedances are equal
References
[1] The Art of Electronics by Horowitz and Hill
[2] EMC Filter comparison – T and Pi Filters
Related Calculators
- Pi Filter – includes four different calculators for both low pass and hi pass filters
- Power supply pi filters – for both equal and unequal impedance
- Filter Bandwidth – compute the bandwidth and center frequency from the start and stop frequencies. Useful when you look at the data sheets for SAW filters that don’t provide this info up front.
- Pi Filter Cutoff Frequency – Use the component values from a schematic to find the cutoff frequencies for both low and high pass filters
- CLC Filter – provides component values for a desired low pass frequency response
- Inductor Impedance – calculate the reactance and impedance from the inductance