PRECISION FILTERS, INC.
Requires Adobe Reader (PDF) PFA-2 Flat/Pulse Low-Pass Filter Technology
You Want Your Analog Data to Come Clean Before Digital Conversion
The PFA-2 Filter/Amplifier has a flexible high performance 6-pole low-pass filter characteristic that can be optimized for time or frequency domain measurements.
Flat/Pulse Low-Pass Filters
The LP6F and LP6P 6-pole low-pass filters have the versatility to address applications in either the time or frequency domain. Simply program the filter characteristic to match your measurement requirements.
Flat Mode Low-Pass Filters
The LP6F FLAT mode characteristic has a pass-band amplitude response nearly identical to the 6-pole Butterworth yet has much sharper roll-off characteristics. This makes the LP6F a good choice for spectral analysis or for anti-aliasing applications.
Like the Butterworth low-pass filter, the LP6F has a non-linear phase response with 60 degrees of phase distortion at the cutoff frequency.
The non-linear phase characteristics of the LP6F result in an input to output time delay that is not constant versus frequency. Filters with linear phase, such as the LP6P, have constant delay for all frequencies in the pass-band.
Pulse Mode Low-Pass Filters
For the time domain, the LP6P PULSE mode low-pass filter has excellent transient response and phase linearity required for time domain applications such as transient (shock) measurements and time domain waveform analysis.
When compared to a 6-pole Bessel filter, the LP6P has similar pass-band characteristics yet has much sharper transition slope from pass-band to stop-band.
Anti-Aliasing Applications
When used for anti-aliasing applications, the LP6F provides more useable bandwidth for a given sampling frequency.
In exchange for linear phase and excellent transient response, the LP6P is less selective and thus requires a higher sampling frequency than the LP6F.
The chart below provides a comparison of attenuation of aliases versus sampling frequency for the LP6P, 6-pole Bessel (BE6), LP6F and the 6-pole Butterworth (BU6). It is clear that much lower sampling frequencies are required for the KSC-2 LP6P and LP6F when compared to traditional filter characteristics.
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Sampling Frequency for –3.01 dB Attenuation @ Fh |
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Alias Attenuation |
BE6 |
LP6P |
BU6 | LP6F |
20 |
3.4 Fc |
3.4 Fc |
2.5 Fc | 2.4 Fc |
40 |
4.6 Fc |
4.5 Fc |
3.2 Fc | 2.9 Fc |
60 |
6.4 Fc |
5.5 Fc |
4.2 Fc | 3.3 Fc |
80 |
9.0 Fc |
6.2 Fc |
5.6 Fc | 3.6 Fc |
