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Filters for simulation.

Contents


Introduction.

These are a number of different filters as LTSpice sub-circuits.
There is nothing special about them, I just find it a convenient collection.
Most are just Laplace transforms.
If you use a SPICE other than LTSPICE, you can copy the Laplace transforms from the *.asc files. They are in ASCII format and should work in most SPICE simulators.
To use them, simply unpack the zip file in your working directory and you can select them like any other component.
Most of the filters have a 1 TΩ resistor from input to ground, so be aware that the input impedance is not infinite.


Schematic Symbols.

LT Spice filter symbols.
Fig.1: Filter symbols

Fig. 1 shows how most of the symbols look when they are opened in a schematic (clearly showing my lack of artistic skills).
Right click the symbol to edit the parameters. For symbols with more than one parameter, enter all parameters in the PARAMS box separated by a space.
The editable parameters are generally displayed on the symbol (K, f0, t3, t4, t5) in fig. 1, although for some of the filters it does not make any sense to change them. All parameters are in absolute units (i.e. Hz, seconds, etc.). Gain is entered as a factor.


General purpose filters.

FI_GP_LP1: 1. order low-pass filter.
Parameters: f0 (corner frequency), K (gain).

FI_GP_LP2: 2. order low-pass filter.
Parameters: f0 (corner frequency), Q (quality factor), K (gain).

FI_GP_HP1: 1. order high-pass filter.
Parameters: f0 (corner frequency), K (gain).

FI_GP_HP2: 2. order high-pass filter.
Parameters: f0 (corner frequency), Q (quality factor), K (gain).

FI_GP_BP2: 2. order band-pass filter.
Parameters: f0 (corner frequency), Q (quality factor), K (gain).

FI_GP_BR2: 2. order band-reject filter.
Parameters: f0 (corner frequency), Q (quality factor), K (gain).

FI_GP_AP1: 1. order all-pass filter (non-inverting at DC).
Parameters: f0 (corner frequency), K (gain).

FI_GP_AP1I: 1. order all-pass filter, (inverting at DC).
Parameters: f0 (corner frequency), K (gain).

FI_GP_AP2: 2. order all-pass filter.
Parameters: f0 (corner frequency), Q (quality factor), K (gain).


Noise weighting filters.

Noise-weighting filters. These allow you to correlate your simulations with measurements.
The different filters are shown in the following plot:

Noise weighting filters.
Fig.2: Noise weighting filters.

FI_WTD_A (V(a)): A-weighting filter.
Parameters: None.

FI_WTD_B (V(b)): B-weighting filter.
Parameters: None.

FI_WTD_C (V(c)): C-weighting filter.
Parameters: None.

FI_WTD_D (V(d)): D-weighting filter.
Parameters: None.

FI_WTD_ITU_R_468 (V(468)): ITU-R 468 filter. Also called CCIR-468 filter or CCIR-468-1K filter.
Parameters: None.

FI_WTD_ITU_R_468_ARM (V(468a)): Same as FI_WTD_ITU_R_468, but with 0 dB at 2 kHz instead of 1 kHz.
Parameters: None.

FI_WTD_NBW_20kHz (V(20k)): Filter with 20 kHz noise-bandwidth. It is a 8.order Butterworth filter with f0 at 19854 Hz.
Parameters: f0 (corner frequency).


RIAA filters.

A number of RIAA emphasis/de-emphasis filters with 3 or more of the following time constants (see Stanley P. Lipshitz "On RIAA Equalization Networks", Journal of the Audio Engineering Society, 1979 June, Volume 27, Number 6, Page 458 for a detailed explanation).

RIAA emphasis and de-emphasis filters.

FI_RIAA_EMP: RIAA emphasis filter with t3, t4, t5.
Parameters (defaults in ()): t3 (3180 µs), t4 (318 µs), t5 (75 µs), K (gain at 1 kHz).

FI_RIAA_EMP_HF0: RIAA emphasis filter with t3, t4, t5, t6.
Parameters (defaults in ()): t3 (3180 µs), t4 (318 µs), t5 (75 µs), t6 (3.18 µs), K (gain at 1 kHz).

FI_RIAAIEC_EMP_HF0: RIAA emphasis filter with t1, t2, t3, t4, t5, t6.
Parameters (defaults in ()): t1 (10 s), t2 (7950 µs), t3 (3180 µs), t4 (318 µs), t5 (75 µs), t6 (3.18 µs), K (gain at 1 kHz).

FI_RIAA_DEEMP: RIAA de-emphasis filter with t3, t4, t5.
Parameters (defaults in ()): t3 (3180 µs), t4 (318 µs), t5 (75 µs), K (gain at 1 kHz).

FI_RIAA_DEEMP_HF0: RIAA de-emphasis filter with t3, t4, t5, t6.
Parameters (defaults in ()): t3 (3180 µs), t4 (318 µs), t5 (75 µs), t6 (3.18 µs), K (gain at 1 kHz).

FI_RIAAIEC_DEEMP: RIAA de-emphasis filter with t2, t3, t4, t5.
Parameters (defaults in ()): t2 (7950 µs), t3 (3180 µs), t4 (318 µs), t5 (75 µs), K (gain at 1 kHz).

FI_RIAAIEC_DEEMP_HF0: RIAA de-emphasis filter with t2, t3, t4, t5, t6.
Parameters (defaults in ()): t2 (7950 µs), t3 (3180 µs), t4 (318 µs), t5 (75 µs), t6 (3.18 µs), K (gain at 1 kHz).


Other filters.

FI_SP_LP05: Pink-noise weighting filter.
This is a low-pass filter with 10 dB / decade roll-off.
Parameters: f0 (corner frequency), K (gain).


Download.

Download all filters (zip file).


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