|NI-SCOPE (English | Japanese)|
The NI 5122/5142 offers two filters that limit the bandwidth of the signal path—a 20 MHz noise filter and a 35 MHz antialias filter.
|Note To change the filter type, call niScope Configure Chan Characteristics VI or the niScope_ConfigureChanCharacteristics function and set the Max Input Frequency parameter to the appropriate value.|
A 20 MHz input filter is available through both the 1 MΩ and 50 Ω signal paths. This filter is intended to reduce noise when the signal content is 20 MHz or less. A typical frequency response of the noise filter is shown in the following figure.
The noise filter provides over 20 dB of attenuation at 100 MHz, which is useful for rejecting out of band or background noise in lower frequency applications. An example application would be characterization of video waveforms in the presence of IF noise. Because most of the signal content is below the 8 MHz range, the 20 MHz noise filter is ideal. Many standard noise tests specify a 20 MHz noise bandwidth.
The NI 5122/5142 provides another bandwidth-limiting filter called an antialias filter. Although this filter can be used to limit out of band noise in many applications, its primary purpose is to minimize aliasing effects caused by signals greater than Nyquist applied to the 100 MS/s ADC. Refer to the hardware specifications document for more information on this filter.
A typical response with the antialias filter is shown in the following two figures.