|Figure 1: Using a band stop filter to remove a 5-MHz sine|
wave from a 4-MHz square wave
Ultimately, the answer most likely lies in improved decoupling, shielding, and other signal integrity approaches. For now, though, you just want to see what your square wave looks like. In that case, the answer is to apply digital filtering on your oscilloscope.
|Figure 2: Using a high pass filter to eliminate 60-Hz pickup|
from a 63-kHz PWM signal
If your oscilloscope happens to be one of ours, the Digital Filter Package 2 (DFP2) option is compatible with most Teledyne LeCroy instruments. It offers a selection of several standard infinite impulse response or finite impulse response filters, including such types as low pass, high pass, band pass, or band stop filters. Users can also apply a custom filter configuration where needed.
|Figure 3: Removing baseline shaping by separating and|
subtracting the low-frequency content of a waveform
Another example is the use of a high pass filter to eliminate 60-Hz pickup from a 63-kHz pulse-width-modulated signal (Figure 2). The high pass filter is set to attenuate signals lower than 200 Hz, thereby removing the 60-Hz hum.
|Figure 4: Using peak detection and filtering to|
demodulate an AM signal
Finally, another spectral separation example shows the use of a low pass filter in a detector simulation (Figure 4). Modulation from an amplitude-modulated signal is extracted by peak detection and filtering. The absolute-value function performs full-wave peak detection. The DFP 2 option provides the necessary low pass filtering to remove the residual carrier from the detected waveform.
These are just a few examples of how digital filters can aid in signal analysis. Let us know what you've come up with.