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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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LM4671 Fiches technique(PDF) 16 Page - National Semiconductor (TI) |
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LM4671 Fiches technique(HTML) 16 Page - National Semiconductor (TI) |
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16 / 18 page  Application Information (Continued) 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 300 Ω (see schematic). 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 com- ponent on the outputs. The grounded capacitive filter ele- ments 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 differ- ential, necessitating a differential input on any analysis in- strument connected to it. Most lab instruments that feature BNC connectors on their inputs are NOT differential re- sponding because the ring of the BNC is usually grounded. The commonly used Audio Precision analyzer is differential, but its ability to accurately reject high frequency signals is questionable necessitating the on board measurement filter. When in doubt or when the signal needs to be single-ended, use an audio signal transformer to convert the differential output to a single ended output. Depending on the audio transformer’s characteristics, there may be some attenua- tion of the audio signal which needs to be taken into account for correct measurement of performance. Measurements made at the output of the measurement filter suffer attenuation relative to the primary, unfiltered outputs even at audio frequencies. This is due to the resistance of the inductors interacting with the termination resistor (300 Ω) and is typically about -0.25dB (3%). In other words, the voltage levels (and corresponding power levels) indicated through the measurement filter are slightly lower than those that actually occur at the load placed on the unfiltered out- puts. This small loss in the filter for measurement gives a lower output power reading than what is really occurring on the unfiltered outputs and its load. 201073J4 FIGURE 8. www.national.com 16 |
Numéro de pièce similaire - LM4671 |
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Description similaire - LM4671 |
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