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ROHM Semiconductor |
Video ICs
Stereo microphone amplifier for cam-
corders
BA7781K
The BA7781K allows construction of a stereo-microphone amplifier for camcorder use with a minimum number of
external components. The IC has a built-in wind-noise detection circuit, and wind-noise rejection filter. The filter cir-
cuit is controlled automatically. The IC can operate off a 3.0V power supply.
•Applications
Camcorders
•Features
1) Operates off a 3.0V to 5.25V power supply.
2) Automatic wind-noise rejection circuit.
3) Matrix circuit for stereo emphasis.
4) Automatic switching circuit for external micro-
phones, built-in external monaural decision circuit,
and input switch mode decision circuit.
•Block diagram
24 23 22 21 20 19 18 17
EXT IN L 25 EXT
BG 26 INT
13dB
–
+
15dB
16 DET OUT
15 DET IN
INT IN L 27
GND 28
VREG 29
INT IN R 30
+– MIX
10dB
EXT
EXT
14 BIAS
BIAS
VCC
13 VCC
12 LPF INV OUT
+–
11 LPF INV IN
RIPL 31
INT
13dB
10 MIX OUT
+
EXT IN R 32 EXT
–
15dB
09 MIC MONO
01 02 03 04 05 06 07 08
1
Video ICs
BA7781K
•Absolute maximum ratings (Ta = 25°C)
Parameter
Symbol
Limits
Unit
Power supply voltage VCC 7.0
Power dissipation
Pd 400∗
Operating temperature
Topr
– 10 ~ +70
Storage temperature
Tstg – 55 ~ +125
∗ Reduced by 4mW for each increase in Ta of 1°C over 25°C.
•Recommended operating conditions (Ta = 25°C)
V
mW
°C
°C
Parameter
Symbol Min. Typ. Max.
Unit
Power supply voltage
VCCS 3.0 — 5.25
V
•Electrical characteristics (unless otherwise noted, Ta = 25°C and VCC = 3.3V)
Parameter
Current dissipation 1
Current dissipation 2
Preamplifier gain
Output amplifier gain
Distortion
Maximum output voltage
Output noise voltage
Input switch separation
Interchannel separation
Symbol Min. Typ. Max. Unit
Conditions
IINT
—
5.0
8.0
mA
INT MIC IN, L / Rch
No dissipation by mic
IEXT
—
4.8
8.0
mA
EXT MIC IN, L / Rch
No dissipation by mic
VGPR
12
13
14
dB
30 / 32pin→2pin GAIN
27 / 25pin→23pin GAIN
VGOA
14
15
16
dB
3 / 6 / 7pin→8pin GAIN
22 / 19 / 18pin→17pin GAIN
THD
— 0.05 0.3
% INT / EXT, Vo = 300mVrms, L / Rch∗2
Vom
0.85 1.1
—
Vrms
INT / EXT MIC IN, L / Rch
f = 1kHz (distortion 1%∗2 )
VNO
— – 90 – 80
dBV
INT / EXT, L / Rch, Rg = 1kΩ
When gain is 28dB∗1
CTI→E
— – 88 – 70
dB
INT→EXT MIC IN, Rg = 1kΩ, L / Rch
(distortion 1%∗2 ) , when gain is 28dB∗1
CTL← →R — – 61 – 50
dB
INT / EXT MIC, Lch→Rch, Rg = 1kΩ
(distortion 1%∗2 ) , when gain is 28dB∗1
Internal microphone power supply voltage VREG
2.3 2.5 2.75
V Pin 27 output voltage for 30kΩ load
Input switch control voltage
High-pass filter switching
attenuation characteristic
High-pass filter control voltage
∗1 JIS-A filter used.
∗2 400Hz to 30kHz filter used.
2
VHSWH
VHSWL
1.6
0
VGHON
—
VGHOFF
—
VHON
VHOFF
2.5
0
— VCC
— 0.6
— – 30
— – 30
— VCC
— 0.3
V “H”level, 1 / 24 pin DC
V “L” level, 1 / 24 pin DC
Input 80Hz signal to pin 15, and
measure gain at switch off side.∗1
15pin – 29.0dBV IN (80Hz)
dB 6 / 19pin – 25.5dBV IN (1kHz)
6→8pin / 19→17pin GAIN
15pin – 45.0dBV IN (80Hz)
dB 7 / 18pin – 25.5dBV IN (1kHz)
7→8pin / 18→17pin GAIN
V HPF on holding voltage (pin 16)
V HPF off holding voltage (pin 16)
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