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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 off a 3.0V to 5.25V power supply. 1) Operates
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
MTX OUT L PRE OUT L INV OUT L MTX IN L MODE 24 HPF IN L 18 WND 15dB DET NOR INV IN L 24 EXT IN L 25 EXT BG 26 INT IN L 27 GND REG GND 28 VREG 29
INT
23
22
21
20
19
17 16 DET OUT 15 DET IN 14 BIAS BIAS VCC 13 VCC 12 LPF INV OUT
- +
13dB
+ MIX -
10dB
EXT
+-
BIAS INT IN R 30 RIPL 31
INT
OUT L 11 LPF INV IN 10 MIX OUT 09 MIC MONO 08 OUT R
EXT
13dB NOR WND 06 MTX OUT R
EXT IN R 32 EXT 01 MODE 1 02 PRE OUT R 03 INV IN R 04 INV OUT R
+ -
05 MTX IN R
15dB
07 HPF IN R
1
Video ICs
BA7781K
*Absolute maximum ratings (Ta = 25C)
Parameter Power supply voltage Power dissipation Operating temperature Storage temperature Symbol VCC Pd Topr Tstg Limits 7.0 400 - 10 ~ +70 - 55 ~ +125 Unit V mW C C
*Recommended operating conditions (Ta = 25C)
Parameter Power supply voltage Symbol VCCS Min. 3.0 Typ. -- Max. 5.25 Unit V
Reduced by 4mW for each increase in Ta of 1C over 25C.
*Electrical characteristics (unless otherwise noted, Ta = 25C 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 Internal microphone power supply voltage Input switch control voltage Symbol IINT IEXT VGPR VGOA THD Vom VNO CTIE CTL
R
Min. -- -- 12 14 -- 0.85 -- -- -- 2.3 1.6 0
Typ. 5.0 4.8 13 15 0.05 1.1 - 90 - 88 - 61 2.5 -- --
Max. 8.0 8.0 14 16 0.3 -- - 80 - 70 - 50 2.75 VCC 0.6
Unit mA mA dB dB % Vrms dBV dB dB V V V
Conditions INT MIC IN, L / Rch No dissipation by mic EXT MIC IN, L / Rch No dissipation by mic 30 / 32pin2pin GAIN 27 / 25pin23pin GAIN 3 / 6 / 7pin8pin GAIN 22 / 19 / 18pin17pin GAIN INT / EXT, Vo = 300mVrms, L / Rch2 INT / EXT MIC IN, L / Rch f = 1kHz (distortion 1%2 ) INT / EXT, L / Rch, Rg = 1k When gain is 28dB1 INTEXT MIC IN, Rg = 1k, L / Rch (distortion 1%2 ) , when gain is 28dB1 INT / EXT MIC, LchRch, Rg = 1k (distortion 1%2 ) , when gain is 28dB1 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
VREG VHSWH VHSWL
High-pass filter switching attenuation characteristic
VGHON
--
--
- 30
dB
VGHOFF VHON High-pass filter control voltage VHOFF
-- 2.5 0
-- -- --
- 30 VCC 0.3
dB V V
15pin - 29.0dBV IN (80Hz) 6 / 19pin - 25.5dBV IN (1kHz) 68pin / 1917pin GAIN 15pin - 45.0dBV IN (80Hz) 7 / 18pin - 25.5dBV IN (1kHz) 78pin / 1817pin GAIN HPF on holding voltage (pin 16) HPF off holding voltage (pin 16)
1 JIS-A filter used. 2 400Hz to 30kHz filter used. 2
Video ICs
BA7781K
*Pin descriptions
Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Pin name MODE 1 PRE OUT R INV IN R INV OUT R MTX IN R MTX OUT R HPF IN R OUT R MIC MONO MIX OUT LPF INV IN LPF INV OUT VCC BIAS DET IN DET OUT OUT L HPF IN L MTX OUT L MTX IN L INV OUT L INV IN L PRE OUT L MODE 24 EXT IN L BG INT IN L GND VREG INT IN R RIPL EXT IN R Function 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 VCC 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 Voltage (V) -- 1.65 1.65 1.65 1.65 1.65 1.65 1.65 -- 1.65 -- -- 3.3 1.65 1.65 -- 1.65 1.65 1.65 1.65 1.65 1.65 1.65 -- 1.65 1.25 1.65 -- 2.5 1.65 1.65 1.65 Circuit 25k EF (P - P) 100k EF (P - P) B EF (P - P) 100k C (P - P) C EF (P - P) B EF (P - P) -- EF (P - P) 2k 22k C (P - P) 100k EF (P - P) B EF (P - P) 100k EF (P - P) 25k 75k 10k 75k -- C 75k 50k 75k
EF: emitter follower, P-P: push pull, B: base, and C: collector.
All numerical values are standardized values.
3
Video ICs
BA7781K
*Measurement circuit
MODE 24 HPF IN SW2 10k 10.5k 0.1
0.1
24 25
+
EXT
1 0.1
2 2200p
18 17 16
DET
+
0.1 EXT IN Lch INT IN 0.1
28
23
22
21
20
19 NOR
2.2 1M
L OUT
- +
13dB
26 27
INT
WND
15dB
15 14
10 GND
+ MIX -
REG
+
10 0.1
EXT
10dB
GND
BIAS VCC
13 12
VCC
30k 0.1
29
BIAS
INT IN Rch EXT IN 0.1
+
+ -
200k
11
30 31
EXT
INV (11) IN
200k 0.1
10
INT 32 EXT 1
13dB
NOR WND
10
+ -
2 3 4 5 6
15dB
7 8
9
0.1 0.1 10k 10.5k
0.1 2200p 1 SW1 2
R OUT
MODE 1
HPF IN
UNITS RESISTOR: CAPACITOR: F
Fig. 1
4
Video ICs
BA7781K
*Application example
UNITS RESISTOR: CAPACITOR: F
B' A' 15k 2200p
10k 10.5k 0.022 100k
0.1
24 25
+
EXT
L OUT 2.2
0.1 21 20 19
NOR
0.022 18
WND
15dB
0.1 EXT IN L ch INT IN 0.1
28
23
22
17 16
24k
+
- +
13dB
1M
DET
26 27
INT
15 14
+
10
GND
+ MIX -
REG
EXT
10 VCC 2200p 220k
10dB
GND
29
BIAS VCC
+ -
13 12
0.1
BIAS
INT IN R ch EXT IN 0.1
+
30 31 32
EXT
11
100k
13dB
NOR WND
150k
0.01
10
INT
EXT
10
+ -
2 3 4 5 6
100k
15dB 7 8 0.022 9
0.01 MIC-MONO
1
24k
0.1
0.1
10k 10.5k 0.022 100k
R OUT 2200p
A
B 15k
Additional components INT / EXT monitoring INT / EXT L OPEN 100k
12
1
+
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
5
Video ICs
BA7781K
*Measurement circuit switch table (blank cells: no spesification)
Parameter Current dissipation 1 Current dissipation 2 Preamplifier gain Output amplifier gain Distortion Maximum output Output noise voltage Input switch separation (INT EXT) INT EXT Internal microphone power supply voltage Input switch control voltage SW1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 High-pass filter control voltage 1 2 SW2 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 2 H Vth H H H H Vth L L L L L INT, EXT INT, EXT INV (11) , HPF INV (11) , INT INV, 16pin of Vth HPF, 16pin of Vth L H L L L L INT INT EXT MODE1 H MODE24 L Signal input pin Conditions other than No. 1
Interchannel separation
High-pass filter switching attenuation characteristic
H and L are VCC and GND levels. Measure the voltage range that maintains the mode for Vth.
*Operation notes rejection circuit (1) Automatic wind-noise
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.
6
Video ICs
BA7781K
*Electrical characteristic curves
16PIN DETECT OUTPUT: VDETOUT (V) OUTPUT LEVEL: VROUT (dBV) VCC = 3.3V Input: 80Hz Ta = 25C 0 2.5 2.0
VCC = 3.3V Input: 80Hz Ta = 25C
- 20
NOR side output 68pin
HPF side output 78pin
1.5
- 40
1.0
0.5
- 60 - 60 - 50 - 40 - 30 - 20 - 10
0 - 60
- 50
- 40
- 30
- 20
- 10
15PIN INPUT SIGNAL LEVEL: VDETIN (dBV)
15PIN INPUT SIGNAL LEVEL: VDETIN (dBV)
Fig. 3 HPF switching characteristics
Fig. 4 Detector voltage characteristis
*External dimensions (Units: mm)
9.0 0.3 7.0 0.2 24 9.0 0.3 7.0 0.2 25 17 16 0.4 0.15 0.1 0.15
32 1 8
9
1.45 0.1
0.05
0.8
0.4 0.1
QFP32
7

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