INA163UASLASH2K5.A datasheet(8/16 Pages) TI2

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INA163

SBOS177D

www.ti.com

2.2k

(2)

(3)

INA163

47 F

47k

6.8k

Phantom Power

+48V

2.2k

(1)

47 F 60V

(1)

47 F 60V

OPA134

0.1 F

+15V

0.1 F

15V

Optional DC

Output Control Loop

Female XLR

Connector

NOTES: (1) Use non-polar capacitors if phantom

power is to be turned off. (2) R

6 sets maximum gain.

(3) R

7 sets minimum gain.

1N4148

15V

1N4148

FIGURE 5. Phantom-Powered Microphone Preamplifier.

MICROPHONE AMPLIFIER

Figure 5 shows a typical circuit for a professional

microphone input amplifier. R1 and R2 provide a cur-

rent path for conventional 48V phantom power source

for a remotely located microphone. An optional switch

allows phantom power to be disabled. C1 and C2 block

the phantom power voltage from the INA163 input

circuitry. Non-polarized capacitors should be used for

C1 and C2 if phantom power is to be disabled. For

additional input protection against ESD and hot-plug-

ging, four INA4148 diodes may be connected from the

input to supply lines.

R4 and R5 provide a path for input bias current of the

INA163. Input offset current (typically 100nA) creates a

DC differential input voltage that will produce an output

offset voltage. This is generally the dominant source of

output offset voltage in this application. With a maxi-

mum gain of 1000 (60dB), the output offset voltage can

be several volts. This may be entirely acceptable if the

output is AC-coupled into the subsequent stage. An

alternate technique is shown in Figure 5. An inexpen-

sive FET-input op amp in a feedback loop drives the

DC output voltage to 0V. A2 is not in the audio signal

path and does not affect signal quality.

Gain is set with a variable resistor, R7, in series with

R6. R6 determines the maximum gain. The total resis-

tance, R6 + R7, determines the lowest gain. A special

reverse-log taper potentiometer for R7 can be used to

create a linear change (in dB) with rotation.

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