Datasheet

LM4671
www.ti.com SNAS258D –MARCH 2005–REVISED MAY 2013
Figure 27. Dual input with a single-ended input and a differential input
REFERENCE DESIGN BOARD SCHEMATIC
Figure 28. Reference Design Board Schematic
In addition to the minimal parts required for the application circuit, a measurement filter is provided on the
evaluation circuit board so that conventional audio measurements can be conveniently made without additional
equipment. This is a balanced input, grounded differential output low pass filter with a 3dB frequency of
approximately 35kHz and an on board termination resistor of 300Ω (see Figure 28). Note that the capacitive load
elements are returned to ground. This is not optimal for common mode rejection purposes, but due to the
independent pulse format at each output there is a significant amount of high frequency common mode
component on the outputs. The grounded capacitive filter elements attenuate this component at the board to
reduce the high frequency CMRR requirement placed on the analysis instruments.
Even with the grounded filter the audio signal is still differential, necessitating a differential input on any analysis
instrument connected to it. Most lab instruments that feature BNC connectors on their inputs are NOT differential
responding because the ring of the BNC is usually grounded.
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