Datasheet BA7781K Datasheet (ROHM)

1

Video ICs

Stereo microphone amplifier for cam­corders

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 cir­cuit 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 micro­phones, 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 = 25°C)

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 = 25°C)

Parameter Symbol Min. Typ. Max. Unit

V

CCS

3.0 — 5.25 VPower supply voltage

•

Electrical characteristics (unless otherwise noted, Ta = 25°C and VCC = 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 — Vrms

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 — VCC 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 = 1kΩ

INT / EXT MIC, Lch→Rch, R

g = 1kΩ

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 = 1kΩ, 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 30kΩ 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

—

25kΩ
2 PRE OUT R 1.65
3 INV IN R 1.65 100kΩ
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 100kΩ
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 2kΩ
16 DET OUT — 22kΩ
17 OUT L 1.65
18 HPF IN L 1.65 100kΩ
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 100kΩ
23 PRE OUT L 1.65
24 MODE 24 — 25kΩ
25 EXT IN L 1.65 75kΩ
26 BG 1.25 10kΩ
27 INT IN L 1.65 75kΩ
28 GND ——
29 VREG 2.5 C
30 INT IN R 1.65 75kΩ
31 RIPL 1.65 50kΩ
32 EXT IN R 1.65 75kΩ

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 FunctionPin 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

21 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

0.1µ

10k 10.5k

0.1µ

0.1µ

1212

2200p

0.1µ

0.1

µ

0.1

µ

2200p

SW2

HPF IN

2.2µ

+

1M

0.1µ

0.1µ

200k

200k

10µ

+

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

0.1µ

10µ

0.1µ

30k

0.1µ

10µ

0.1µ

Lch

Rch

+

+

UNITS
RESISTOR: Ω
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

0.1µ

10k 10.5k

100k

0.1µ

0.022µ

2200p

0.1µ

0.1µ

2200p

2.2µ

+

1M

100k

220k

150k

10µ

+

1µ

+

10k

10.5k

100k

A

B

L OUT

V

CC

MIC-MONO

R OUT

EXT IN

INT IN

INT IN

EXT IN

0.1µ

10µ

0.1µ

0.1µ

10µ

0.1µ

+

+

0.022µ

24k

15k

15k

A'B'

2200p

0.01µ

0.01µ

24k

0.022µ

0.022µ

GND

R ch

L ch

UNITS
RESISTOR: Ω
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

67

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

6

Video ICs BA7781K

•

Measurement circuit switch table (blank cells: no spesification)

SW1 SW2 MODE1 MODE24

11 H L
11
11
11
11
11
11

1 1 L L INT

1 1 H L INT
1 1 L L EXT
11
1 1 H Vth
1 1 Vth L
2 2 H L INV (11) , HPF
1 1 H L INV (11) , INT
11 H L
2 2 H L HPF, 16pin of Vth

INV, 16pin of Vth

INT, EXT
INT, EXT

EXT

INT

Signal input pin

Parameter
Current dissipation 1
Current dissipation 2
Preamplifier gain
Output amplifier gain
Distortion
Maximum output
Output noise voltage

Input switch separation (INT

→ EXT)

Interchannel separation

Internal microphone power supply voltage

Input switch control voltage

High-pass filter switching attenuation characteristic

High-pass filter control voltage

Conditions other than No. 1

∗

H and L are VCC and GND levels.

Measure the voltage range that maintains the mode for 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 two­stage 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 poten­tial 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.

7

Video ICs BA7781K

•

Electrical characteristic curves

OUTPUT LEVEL: VROUT (dBV)

15PIN INPUT SIGNAL LEVEL: VDETIN (dBV)

VCC = 3.3V
Ta = 25°C

– 60

– 40

– 20

0

– 60 – 50 – 40 – 30 – 20 – 10

Input: 80Hz

NOR side output

6

→

8pin

HPF side output

7

→

8pin

Fig. 3 HPF switching characteristics

16PIN DETECT OUTPUT: VDETOUT (V)

15PIN INPUT SIGNAL LEVEL: VDETIN (dBV)

VCC = 3.3V
Ta = 25°C

0

0.5

1.0

1.5

2.0

2.5

– 60 – 50 – 40 – 30 – 20 – 10

Input: 80Hz

Fig. 4 Detector voltage characteristis

•

External dimensions (Units: mm)

0.15

0.4 ± 0.1

24

17

16

9

8

1

25

32

7.0 ± 0.2

9.0 ± 0.3

7.0 ± 0.2

9.0 ± 0.3

0.4

0.05

1.45 ± 0.1

0.15 ± 0.1

0.8

QFP32