NI 5421/5422/5441 Analog Output

NI Signal Generator

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NI 5421/5422/5441
Analog Output


The following figure shows the NI 5421/5422/5441 Analog Output signal path.





Legend

NI 5421/5422/5441 Analog waveforms are generated as follows:

  1. The 16-bit digital waveform data from the Waveform Generation Engine or OSP is passed to a digital gain circuit and then high-speed DAC. This DAC also implements a portion of the Analog Output signal path attenuation with a range of 0 dB to 3 dB. Refer to the NI 5421, NI 5422, or the NI 5441 specifications for the exact resolution. You can adjust the amount of attenuation by configuring the Arbitrary Waveform Gain or Amplitude properties or the NIFGEN_ATTR_ARB_GAIN or NIFGEN_ATTR_FUNC_AMPLITUDE attributes. NI-FGEN calculates and sets the correct amount of attenuation required, corresponding to the gain setting.
  2. Following the DAC, the signal can take one of two paths: the Direct path or the Main path with High-Gain and Low-Gain amplifiers. NI-FGEN selects the Main path by default. To select the Direct path manually, refer to the Analog Path property or the NIFGEN_ATTR_ANALOG_PATH attribute.
    1. The Direct path bypasses the Analog Filter, the attenuation sections, and the amplifiers. Taking the amplifiers out of the signal path yields an output signal with the lowest distortion and a flat frequency response. Use the Direct path for communication signals. The Direct path can provide a maximum of 1 Vpk-pk output into 50 Ω with no offset and a maximum of 3 dB attenuation. A signal taking the Direct path skips steps 3 through 5 and continues at step 6.
    2. If the Low-Gain or High-Gain Amplifier path is selected, the signal passes through a switchable lowpass Analog Filter, attenuators, and amplifiers.
  3. The signal then passes through a switchable lowpass Analog Filter to remove Aliased Images. You can select whether to include the Analog Filter in the Analog Output path using either the niFgen Configure Analog Filter VI or the niFgen_EnableAnalogFilter or niFgen_DisableAnalogFilter functions.
  4. The signal then passes through the DC Offset Amplifier that adds the desired DC offset voltage. You can adjust the amount of DC offset added to the signal, up to one half the value of the NI-FGEN gain setting. Refer to either the Arbitrary Waveform Offset or DC Offset properties or the NIFGEN_ATTR_ARB_OFFSET or NIFGEN_ATTR_FUNC_DC_OFFSET attributes for more information.
  5. The signal then passes through the Pre-Amp Attenuation section, a set of selectable solid-state attenuators that provide 0 dB to 12 dB of attenuation in 3 dB increments. You can adjust the amount of attenuation by adjusting the Arbitrary Waveform Gain property or the NIFGEN_ATTR_ARB_GAIN attribute. NI-FGEN calculates and sets the correct amount of attenuation required, corresponding to the gain setting. Refer to either the Arbitrary Waveform Gain or Amplitude properties, or the NIFGEN_ATTR_ARB_GAIN or NIFGEN_ATTR_FUNC_AMPLITUDE attributes for more information.
  6. Following the Pre-Amp Attenuation section, the signal can take one of two paths: the High-Gain or Low-Gain Amplifier path. NI-FGEN automatically selects the best amplifier path between the High-Gain and Low-Gain amplifiers by default based on the gain or amplitude setting. Alternatively, you can set the signal path to remain constant regardless of the gain setting for applications requiring one path or the other. Refer to the Analog Path property or the NIFGEN_ATTR_ANALOG_PATH attribute for more information.
    1. The High-Gain Amplifier path is used for waveform output voltages greater than ±1.0 V into 50 Ω. The amplifier has a fixed gain and is included in the signal path to enable the AWG to provide the maximum Vpk-pk.
    2. The Low-Gain Amplifier path is used for waveforms that have all output voltages equal to or smaller than ±1.0 V into 50 Ω. The amplifier has a fixed gain.
  7. The signal passes through the Post Amp Attenuation section, a set of two passive attenuators 12 dB and 24 dB. You can adjust the amount of attenuation by configuring either the either the Arbitrary Waveform Gain or Amplitude properties, or the NIFGEN_ATTR_ARB_GAIN or NIFGEN_ATTR_FUNC_AMPLITUDE attributes . NI-FGEN calculates and sets the correct amount of attenuation required, corresponding to the gain setting.
  8. The signal then passes through the Output Enable relay. When the Output Enable relay is disabled, ground is connected to the output through a 50 Ω or a 75 Ω resistor. Intentionally, waveform generation continues while the output enable relay is disabled. When the relay is enabled, the analog waveform is seen at the CH 0 connector. You can enable or disable the output of the analog waveform generator, refer to the niFgen Output Enable VI or the niFgen_ConfigureOutputEnabled function for more information.
  9. The signal then passes through a 50 Ω/75 Ω selector to the CH 0 connector. You can configure the output impedance of the analog waveform generator, refer to the niFgen Configure Output Impedance VI or the niFgen_ConfigureOutputImpedance function.
Note  The NI 5421/5422/5441 uses mechanical relays to switch between the optional paths and sections in the Analog Output path. When you change a setting that results in a relay to switch, the bouncing of electromechanical relays on the NI 5421/5422/5441 distorts the output signal for about 10 ms.
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