AD73411 datasheet(33/36 Pages) AD

33 / 36 page

REV. 0

AD73411

–33–

CONTINUOUS

TIME

LOW-PASS

FILTER

REFOUT

REFERENCE

0/38dB

PGA

VREF

REFCAP

0.1 F

VINN

VINP

0.047

100

0.1 F

VOUTP

VOUTN

10k

AD73411

+6/–15dB

PGA

Figure 28. Analog Input (AC-Coupled) Single-Ended

CONTINUOUS

TIME

LOW-PASS

FILTER

REFOUT

REFERENCE

0/38dB

PGA

VREF

REFCAP

0.1 F

VINN

VINP

VOUTP

VOUTN

AD73411

+6/–15dB

PGA

0.047

100

0.1 F

10k

Figure 29. Analog Input (AC-Coupled) Single-Ended

(Alternate Input)

Interfacing to an Electret Microphone

Figure 30 details an interface for an electret microphone which

may be used in some voice applications. Electret microphones

typically feature a FET ampliﬁer whose output is accessed on

the same lead that supplies power to the microphone; therefore,

this output signal must be capacitively coupled to remove the

power supply (dc) component. In this circuit the AD73411

input channel is being used in single-ended mode where the

inverting ampliﬁer provides suitable gain to scale the input

signal relative to the ADC’s full-scale input range. The buffered

internal reference level at REFOUT is used via an external

buffer to provide power to the electret microphone. This pro-

vides a quiet, stable supply for the microphone. If this is not a

concern, the microphone can be powered from the system

power supply.

VINN

VINP

VOUTP

VOUTN

ELECTRET

MICROPHONE

10 F

CONTINUOUS

TIME

LOW-PASS

FILTER

REFCAP

REFOUT

REFERENCE

VREF

0/38dB

PGA

CREFCAP

+6/–15dB

PGA

Figure 30. Electret Microphone Interface Circuit

Analog Output

The AD73411’s differential analog output (VOUT) is produced

by an on-chip differential ampliﬁer. The differential output can

be ac-coupled or dc-coupled directly to a load that can be a

headset or the input of an external ampliﬁer. It is possible to

connect the outputs in either a differential or a single-ended

conﬁguration, but please note that the effective maximum output

voltage swing (peak-to-peak) is halved in the case of single-ended

connection. Figure 31 shows a simple circuit providing a differ-

ential output with ac coupling. The capacitors in this circuit

(COUT) are optional; if used, their value can be chosen as follows:

OUT

LOAD

where fC = desired cutoff frequency.

CONTINUOUS

TIME

LOW-PASS

FILTER

REFCAP

REFOUT

REFERENCE

CREFCAP

COUT

RLOAD

COUT

VINN

VINP

VOUTP

VOUTN

AD73411

+6/–15dB

PGA

Figure 31. Example Circuit for Differential Output

Figure 32 shows an example circuit for providing a single-ended

output with ac coupling. The capacitor of this circuit (COUT) is

not optional if dc current drain is to be avoided.

RLOAD

COUT

CONTINUOUS

TIME

LOW-PASS

FILTER

REFCAP

REFOUT

REFERENCE

CREFCAP

VINN

VINP

VOUTP

VOUTN

AD73411

+6/–15dB

PGA

Figure 32. Example Circuit for Single-Ended Output

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