BA7781 データシートの表示（PDF） - ROHM Semiconductor

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BA7781

Stereo microphone amplifier for camcorders

ROHM Semiconductor 

Video ICs

BA7781K

•Measurement circuit switch table (blank cells: no spesification)

Parameter

SW1 SW2

Current dissipation 1

1

1

Current dissipation 2

1

1

Preamplifier gain

1

1

Output amplifier gain

1

1

Distortion

1

1

Maximum output

1

1

Output noise voltage

1

1

MODE1

MODE24

H

L

Conditions other than No. 1

Signal input pin

Input switch separation (INT→ EXT)

1

1

L

L

INT

Interchannel separation

INT

1

1

H

EXT

1

1

L

Internal microphone power supply voltage

1

1

Input switch control voltage

1

1

H

1

1

Vth

2

2

H

High-pass filter switching attenuation characteristic

1

1

H

High-pass filter control voltage

1

1

H

2

2

H

∗ H and L are VCC and GND levels.

Measure the voltage range that maintains the mode for Vth.

L

INT

L

EXT

Vth

INT, EXT

L

INT, EXT

L

INV (11) , HPF

L

INV (11) , INT

L

INV, 16pin of Vth

L

HPF, 16pin of Vth

•Operation notes

(1) Automatic wind-noise rejection circuit

The MAX OUT (pin 10) signal passes through the

three-stage low-pass filter connected between pins 10

and 12, and the DC level of the low-frequency signal

component is detected. This DC voltage (pin 16 DC

voltage) automatically controls the on / off switching of

the high-pass filter. The components connected to pins

11 and 12 set the gain of a multiple-feedback-type two-

stage low-pass filter constructed around an inverting

amplifier, and by changing the gain of the circuit you

can adjust the detection sensitivity.

It is also possible to switch the high-pass filter manually

by applying a DC voltage to pin 16 (see Fig 2).

(2) Additional compornents for INT / EXT monitor use

An internal circuit sets pin 12 to roughly the bias poten-

tial in INT mode, and to GND for EXT mode. This

switches the external transistor on and off for INT and

EXT modes respectively. This can be used to indicate

whether the microphone amplifier is operating with the

INT or EXT input. In the case of a camcorder, this can

be used to display a massage such as “EXT MIC ON”

in the EVF.

6

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