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Chapter 6 Theory of Analog Operation
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National Instruments Corporation 6-13 PCI-4451/4452 User Manual
Mute Feature
The two-channel DAC chip on the PCI-4451 goes into mute mode if the
chip receives at least 4,096 consecutive zero values on both channels at
once. In mute mode, the outputs clamp to ground and the noise floor drops
from about 92 dB below full-scale to about 120 dB below full-scale. Upon
receiving any nonzero data, the DAC instantly reverts to normal mode.
Mute mode is designed to quiet the background noise to extremely low
levels when no waveforms are being generated. Mute mode has a slightly
different offset from the normal offset when zeros are being sent. As a
result, the DAC has one offset for the first 4,096 zero samples and another
offset in mute mode for as long as zeros are sent. This difference is usually
less than 1 mV.
User.book Page 13 Tuesday, April 14, 1998 10:20 AM