NI PXI/PCI-5401/5411/5431
Output Attenuation

The following figure shows the output attenuator chain for the NI signal generators.

Resistor networks make up output attenuators and you can switch them in any combination. The maximum attenuation possible for NI PXI/PCI-5401/5411/5431 is 73 dB.

Note  You can switch an additional 10 dB attenuator in the Analog path that is not shown in the previous figure.

By attenuating the output signal, you keep the dynamic range of the DAC; that is, you do not lose any bits from the digital representation of the signal because the attenuation is done after the DAC and not before it.

attenuation (in decibels) = -20 log¹⁰ (V_o /V_i)

where

V_o = desired voltage level for the output signal

V_i = input voltage level

Note  For the NI PXI/PCI-5401/5411/5431, Vi = ±5 V for a terminated load and ±10 V for an unterminated load.

NI-FGEN calculates the value of the output attenuation chain, which you can control by changing the peak-to-peak amplitude parameter. Attenuation of 0 dB corresponds to an amplitude of 10 V_pk-pk. The maximum attenuation of 73 dB corresponds to an amplitude of 2.24 mV_pk-pk. Any amplitude less than 2.4 mV_pk-pk is coerced to this value.