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ADMP621ACEZ-RL7 Fiches technique(PDF) 9 Page - Analog Devices |
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ADMP621ACEZ-RL7 Fiches technique(HTML) 9 Page - Analog Devices |
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9 / 16 page  Data Sheet ADMP621 DYNAMIC RANGE CONSIDERATIONS The full-scale digital output (0 dBFS) of the ADMP621 is mapped to an acoustic input of 140 dB SPL. The microphone clips (THD = 10%) at 133 dB SPL (see Figure 9); however, it continues to output an increasingly distorted signal above that point. The peak output level, which is controlled by the modulator, limits at about −3 dBFS (see Figure 10). To fully use the 111 dB digital dynamic range of the output data of the ADMP621 in a design, the digital signal processor (DSP), analog-to-digital converter (ADC), or codec circuit following it must be chosen carefully. The decimation filter that inputs the PDM signal from the ADMP621 must have a dynamic range sufficiently better than the dynamic range of the microphone so that the overall noise performance of the system is not degraded. If the decimation filter has a dynamic range of 10 dB better than the microphone (121 dB), the overall system noise only degrades by 0.4 dB. CONNECTING PDM MICROPHONES A PDM output microphone is typically connected to a codec with a dedicated PDM input. This codec separately decodes the left and right channels and filters the high sample rate modulated data back to the audio frequency band. This codec also generates the clock for the PDM microphones or is synchronous with the source that is generating the clock. See the Applications Information section for additional details on connecting the ADMP621 to Analog Devices, Inc., audio codecs with a PDM input. Figure 15 and Figure 16 show mono and stereo connections of the ADMP621 to a codec. The mono connection shows an ADMP621 set to output data on the right channel. To output on the left channel, tie the L/R SELECT pin to VDD instead of tying it to GND. CLOCK OUTPUT CODEC 0.1µF 1.8V TO 3.3V GND L/R SELECT DATA ADMP621 CLK VDD DATA INPUT Figure 15. Mono PDM Microphone (Right Channel) Connection to Codec CLOCK OUTPUT CODEC 0.1µF 1.8V TO 3.3V GND L/R SELECT DATA ADMP621 CLK VDD DATA INPUT 0.1µF 1.8V TO 3.3V GND L/R SELECT DATA ADMP621 CLK VDD Figure 16. Stereo PDM Microphone Connection to Codec Decouple the VDD pin of the ADMP621 to GND with a 0.1 µF capacitor. Place this capacitor as close to VDD as the printed circuit board (PCB) layout allows. Do not use a pull-up or pull-down resistor on the PDM data signal line because it can pull the signal to an incorrect state during the period that the signal line is tristated. The DATA signal does not need to be buffered in normal use when the ADMP621 microphone(s) is placed close to the codec on the PCB. If the DATA signal must be driven over a long cable (>15 cm) or other large capacitive load, a digital buffer may be required. Only use a signal buffer on the DATA line when one microphone is in use or after the point where two microphones are connected (see Figure 17). The DATA output of each microphone in a stereo configuration cannot be individually buffered because the two buffer outputs cannot drive a single signal line. If a buffer is used, take care to select one with low propagation delay so that the timing of the data connected to the codec is not corrupted. CLOCK OUTPUT CODEC DATA ADMP621 ADMP621 CLK DATA INPUT DATA CLK Figure 17. Buffered Connection Between Stereo ADMP621s and a Codec Rev. 0 | Page 9 of 16 |
Numéro de pièce similaire - ADMP621ACEZ-RL7 |
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Description similaire - ADMP621ACEZ-RL7 |
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