Datasheet

DeviceOnboard
MICBIAS.GND
MIC.SUB.P/MIC.MAIN.P
MICBIAS1/2.OUT
R /R
MM.BP MS.SP
C /C
MM.B MS.B
MIC.SUB.M/MIC.MAIN.M
47pF
Closeto
device
Closeto
device
032-034
C /C
MM.P MS.P
C /C
MM.PM MS.PM
C /C
MM.M MS.M
R /2orR /2
MM.GM MS.GM
C orC
MM.GM MS.GM
C orC
MM.GP MS.GP
R /2orR /2
MM.GM MS.GM
TPS65950
www.ti.com SWCS032E–OCTOBER 2008–REVISED JANUARY 2011
NOTE
For other component values, see Table 15-1.
Figure 6-21. Analog Microphone Differential
NOTE
For other component values, see Table 15-1.
NOTE
To improve the rejection, it is highly recommended to ensure that MICBIAS_GND is as clean
as possible. This ground must be shared with AGND of TPS65950 and must not share with
AVSS4, which is the ground used by RX class-AB output stages.
In differential mode, adding a low-pass filter (made by R
SB
and C
B
) is highly recommended if
coupling between RX output stages and the microphone is too high (and there is not enough
attenuation by the echo cancellation algorithm). The coupling can come from:
• The internal TPS65950 coupling between MICBIAS.OUT voltage and RX output stages
• Coupling noise between MICBIAS.GND and AVSS4
In pseudodifferential mode, the dynamic resistance of the microphone improves the rejection
versus MICBIAS.OUT:
PSRR = 20*log((R
B
+ R
Dyn_mic
)/R
B
)
6.2.1.3 Digital Microphone Bias Module Characteristics
Figure 6-22 is a block diagram of the digital microphone bias module.
Copyright © 2008–2011, Texas Instruments Incorporated Audio/Voice Module 87
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