Effects of Offset on Waveform Resolution Using NI-5401 Function Generator Hardware: Signal Sources (AWG/FG/AO)>>Arbitrary Waveform and Function Generators>>PXI-5401
Problem: How does adding an offset affect the resolution of a waveform generated with the NI-5401 Function Generator? Solution: When generating waveforms with the NI-5401 Function Generator, all waveforms are generated with a Digital to Analog Converter (DAC) with a fixed range of -1 to 1 V. That generated signal is then amplified/attenuated in hardware in order to output the waveform of the specified offset and amplitude. Both the offset and amplitude are factored into the waveform generation prior to the amplification/attenuation. The result is that generating a small waveform with a large offset will decrease the resolution of the waveform being generated. As an example, take a waveform with a peak-to-peak amplitude of 0.2V. With no offset added to the waveform, the waveform will be centered around 0V. The waveform will be generated using the full range of the +/-1V DAC on the device, and attenuated by a factor of 10 in the analog hardware to an actual amplitude of +/-0.1V. This results in a high-resolution representation of the waveform. As another example, take this same waveform with a peak-to-peak amplitude of 0.2V, and add an offset of 0.9V. This results in a waveform with a maximum of 1.0V and a minimum of 0.8V. Since the waveform and offset must be generated by the single +/-1V DAC on the device, the waveform is directly generated using only the top 10% of the available resolution of the ADC. The amplification/attenuation circuitry is set to apply a gain of 1 to the signal. This results in a low-resolution representation of the waveform. Related Links: Product Page: NI 5401 Function Generator Attachments:
Report Date: 09/29/2006 Last Updated: 10/18/2006 Document ID: 41SFN8X1 |
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