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1
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
04
05
06
24
23
22
18
17
16
15
14
12
11
09
25
26
27
28
29
30
31
32
13
10
01
02
03
07
08
21
20
19
EXT IN L
BG
INT IN L
GND
VREG
INT IN R
RIPL
EXT IN R
DET OUT
DET IN
BIAS
V
CC
LPF INV OUT
LPF INV IN
MIX OUT
MIC MONO
MODE 24
PRE OUT L
INV IN L
INV OUT L
MTX IN L
MTX OUT L
HPF IN L
OUT L
MODE 1
PRE OUT R
INV IN R
INV OUT R
MTX IN R
MTX OUT R
HPF IN R
OUT R
EXT
INT
13dB
13dB
GND
REG
BIAS
INT
EXT
+
NOR
WND
NOR
WND
15dB
EXT
EXT
BIAS
V
CC
MIX
+
10dB
15dB
+
DET
+
2
Video ICs
BA7781K
Absolute maximum ratings (Ta = 25C)
Parameter
Symbol
Limits
Unit
V
CC
7.0
V
Pd
mW
Topr
C
Tstg
C
400
10 ~ +70
55 ~ +125
Reduced by 4mW for each increase in Ta of 1
C over 25
C.
Power supply voltage
Power dissipation
Operating temperature
Storage temperature
Recommended operating conditions (Ta = 25C)
Parameter
Symbol
Min.
Typ.
Max.
Unit
V
CCS
3.0
--
5.25
V
Power supply voltage
Electrical characteristics (unless otherwise noted, Ta = 25C and V
CC
= 3.3V)
Parameter
Symbol
Min.
Typ.
Max.
Unit
I
INT
--
5.0
8.0
mA
I
EXT
--
4.8
8.0
mA
VG
PR
12
13
14
dB
VG
OA
14
15
16
dB
THD
--
0.05
0.3
%
V
om
0.85
1.1
--
V
rms
VNO
--
90
80
dBV
CT
I
E
--
88
70
dB
--
61
50
dB
V
REG
2.3
2.5
2.75
V
V
HSWH
1.6
--
V
CC
V
V
HSWL
0
--
0.6
V
VG
HON
--
--
30
dB
VG
HOFF
--
--
30
dB
V
HON
2.5
--
V
V
HOFF
0
--
0.3
V
CT
L
R
Conditions
V
CC
INT MIC IN, L / Rch
EXT MIC IN, L / Rch
30 / 32pin
2pin GAIN
27 / 25pin
23pin GAIN
3 / 6 / 7pin
8pin GAIN
22 / 19 / 18pin
17pin GAIN
INT / EXT, Vo = 300mV
rms
, L / Rch
2
INT / EXT MIC IN, L / Rch
INT / EXT, L / Rch, R
g
= 1k
INT / EXT MIC, Lch
Rch, R
g
= 1k
15pin 29.0dBV IN (80Hz)
6 / 19pin 25.5dBV IN (1kHz)
6
8pin / 19
17pin GAIN
15pin 45.0dBV IN (80Hz)
7 / 18pin 25.5dBV IN (1kHz)
7
8pin / 18
17pin GAIN
INT
EXT MIC IN, R
g
= 1k
, L / Rch
Current dissipation 1
Current dissipation 2
Preamplifier gain
Output amplifier gain
Distortion
Maximum output voltage
Output noise voltage
Input switch separation
Interchannel separation
Internal microphone power supply voltage
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.
No dissipation by mic
No dissipation by mic
f = 1kHz (distortion 1%
2
)
When gain is 28dB
1
(distortion 1%
2
) , when gain is 28dB
1
(distortion 1%
2
) , when gain is 28dB
1
Pin 27 output voltage for 30k
load
"H"level, 1 / 24 pin DC
"L" level, 1 / 24 pin DC
Input 80Hz signal to pin 15, and
measure gain at switch off side.
1
HPF on holding voltage (pin 16)
HPF off holding voltage (pin 16)
3
Video ICs
BA7781K
1
MODE 1
--
25k
2
PRE OUT R
1.65
3
INV IN R
1.65
100k
4
INV OUT R
1.65
5
MTX IN R
1.65
B
6
MTX OUT R
1.65
7
HPF IN R
1.65
100k
8
OUT R
1.65
9
MIC MONO
--
C
10
MIX OUT
1.65
11
LPF INV IN
--
B
12
LPF INV OUT
--
13
V
CC
3.3
--
14
BIAS
1.65
15
DET IN
1.65
2k
16
DET OUT
--
22k
17
OUT L
1.65
18
HPF IN L
1.65
100k
19
MTX OUT L
1.65
20
MTX IN L
1.65
B
21
INV OUT L
1.65
22
INV IN L
1.65
100k
23
PRE OUT L
1.65
24
MODE 24
--
25k
25
EXT IN L
1.65
75k
26
BG
1.25
10k
27
INT IN L
1.65
75k
28
GND
--
--
29
VREG
2.5
C
30
INT IN R
1.65
75k
31
RIPL
1.65
50k
32
EXT IN R
1.65
75k
EF (P - P)
EF (P - P)
EF (P - P)
C (P - P)
EF (P - P)
EF (P - P)
EF (P - P)
C (P - P)
EF (P - P)
EF (P - P)
EF (P - P)
Pin name
Function
Pin No.
Voltage (V)
EF: emitter follower, P-P: push pull, B: base, and C: collector.
Circuit
Mode control 1 input
Preamplifier output
Inverter input
Inverter output
Matrix amplifier input
Matrix amplifier output
High-pass filter input
Signal output
External microphone monaural decision signal output
Mix Output
Low-pass filter block inverter input
Low-pass filter block inverter output
V
CC
Bias voltage
Detector circuit input
Detector circuit output
Signal output
High-pass filter input
Matrix amplifier output
Matrix amplifier input
Inverter output
Inverter input
Preamplifier output
Mode control 24 input
External microphone input
For regulator ripple filter capacitor
Internal microphone input
GND
Regulator output
Internal microphone input
For bias ripple filter capacitor
External microphone input
All numerical values are standardized values.
Pin descriptions
4
Video ICs
BA7781K
Measurement circuit
2
1
3
4
5
6
7
8
24
23
22
21
20
19
18
17
16
15
14
13
11
10
9
25
27
28
29
30
31
32
EXT
INT
13dB
13dB
GND
REG
BIAS
INT
EXT
+
NOR
WND
NOR
WND
15dB
+
EXT
EXT
BIAS
V
CC
MIX
+
10dB
15dB
+
DET
0.1
10k 10.5k
0.1
0.1
1
2
1
2
2200p
0.1
0.1
0.1
2200p
SW2
HPF IN
2.2
+
1M
0.1
0.1
200k
200k
10
+
10k 10.5k
1
2
MODE 24
SW1
MODE 1
HPF IN
L OUT
V
CC
INV (11) IN
R OUT
EXT IN
INT IN
INT IN
EXT IN
GND
0.1
10
0.1
30k
0.1
10
0.1
Lch
Rch
+
+
UNITS
RESISTOR:
CAPACITOR: F
26
12
Fig. 1
5
Video ICs
BA7781K
Application example
12
EXT
INT
13dB
13dB
GND
REG
BIAS
INT
EXT
+
NOR
WND
NOR
WND
15dB
+
EXT
EXT
BIAS
V
CC
MIX
+
10dB
15dB
+
DET
0.1
10k
10.5k
100k
0.1
0.022
2200p
0.1
0.1
2200p
2.2
+
1M
100k
220k
150k
10
+
1
+
10k 10.5k
100k
A
B
L OUT
V
CC
MIC-MONO
R OUT
EXT IN
INT IN
INT IN
EXT IN
0.1
10
0.1
0.1
10
0.1
+
+
0.022
24k
15k
15k
A'
B'
2200p
0.01
0.01
24k
0.022
0.022
GND
R ch
L ch
UNITS
RESISTOR:
CAPACITOR: F
Additional components INT / EXT monitoring
INT / EXT
L OPEN
100k
29
1
2
3
4
5
24
23
22
21
20
19
18
17
16
13
12
11
10
9
26
27
28
30
31
32
6
7
25
15
8
14
100k
1) When using the matrix circuit connect A-A' and B-B'.
2) The pin 10 and 12 low-pass filter components are for fc = 150Hz, Gain = 0dB, 18dB / oct.
Fig. 2
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