Datasheet BA7725S, BA7725FS Datasheet (ROHM)

1

Multimedia ICs

Analog compander for KARAOKE
echo systems

BA7725S / BA7725FS

The BA7725S and BA7725FS are analog companders designed for KARAOKE echo systems, and logarithmically
compress the signal level by 1 / 2 and then logarithmically expand it by a factor of 2. These ICs can be used in com­bination with the BU9252S or BU9252F to create a digital echo system. These ICs have an internal line mixer ampli­fier for mixing line input and echo signals. The internal electronic volume control makes it possible to adjust the mixer
level and loop level mixer with an external DC voltage.

•

Applications

Circuits that require analog signal compression and expansion

•

Features

1) Internal logarithmic 1 / 2 compression circuit and 2 ×
expansion circuit

2) Internal 2-channel buffer amplifier used as a tertiary
low pass filter

3) Internal mixer amplifier that mixes line input and
microphone input

4) Internal electronic volume control allows for adjust­ment of the echo mixer level and loop mixer level
using an external DC voltage.

5) Internal microphone amplifier and microphone input
ON / OFF switch

•

Absolute maximum ratings (Ta = 25°C)

Parameter Symbol Limits Unit

Power supply voltage V

CC 13 V

Power
dissipation

BA7725S 1000

∗

1

mW

600

∗

2

BA7725FS
Storage temperature °C
Operating temperature °C

– 55 ~ + 125
– 10 ~ + 70

Pd

Tstg
Topr

∗

1 Reduced by 10mW for each increase in Ta of 1°C over 25°C.

∗

2 Reduced by 6.0mW for each increase in Ta of 1°C over 25°C.

•

Recommended operating conditions

Parameter Symbol Limits Unit

Power supply voltage VV

CC 6.5 ∼ 12.0

2

Multimedia ICs BA7725S / BA7725FS

•

Block diagram

BA7725S BA7725FS

22

21

20

19

18

17

16

15

14

13

12

10

9

8

7

6

5

4

3

2

1

20

19

18

17

16

15

14

13

12

11

11

1

2

3

4

5

6

7

8

9

10

SW VR

VR

BF

EXPAND

BF

BF

BF

BF

EXPAND

VR

VRSW

MIC AMP IN

MIC AMP OUT

N.C.N.C.

GND

GND

DLY BF OUT

EXP BF IN

EXP BF OUT

EXP DET CT

EXP DET

LOOP GAIN CTRL

ECHO LEV CTRL

LINE IN

LINE OUT

COMPRESS

COMPRESS

RIPPLE FILTER

CMP DET

CMP DET CT

CMP OUT

CMP BF IN

CMP BF OUT

DLY BF IN

LINE OUT

LINE IN

ECHO LEV CTRL

LOOP GAIN CTRL

EXP DET

EXP DET CT

EXP BF OUT

EXP BF IN

DLY BF OUT

MIC AMP IN

MIC AMP OUT

RIPPLE FILTER

CMP DET

CMP DET CT

CMP OUT

CMP BF IN

CMP BF OUT

DLY BF IN

VCC

+

+

+

+

+

+

VCC

BF

3

Multimedia ICs BA7725S / BA7725FS

•

Pin descriptions

Pin name Function

BA7725S BA7725FS

1 1 LINE OUT Line output
2 2 LINE IN Line input
3— —

—

N.C.

4 3 ECHO LEV CTRL

Microphone turns off when voltage drops below 1V.
Set echo signal damping ratio between 2-9V (Vcc = 9.0V).

5 4 GND Ground

6 5 LOOP GAIN CTRL

Setting the loop damping ratio. Set between
2-9V (Vcc = 9.0V).

7 6 EXP DET Expand detection
8 7 EXP DET CT

9 8 EXP BF OUT LPF BF output (expansion)
10 9 EXP BF IN LPF BF input (expansion)
11 10 DLY BF OUT Echo signal input BF output
12 11 DLY BF IN Echo signal input BF input
13 12 CMP BF OUT LPF BF output (compression)
14 13 CMP BF IN LPF BF input (compression)
15 14 CMP OUT Compression output

16 15 CMP DET CT
17 16 CMP DET Compression detection

18 17 RIPPLE FITER Attached ripple rejection capacitor
19 18
20 — N.C.
21 19 MIC AMP OUT Microphone amplifier output
22 20 MIC AMP IN Microphone amplifier input

Setting expand attack / recovery time
Attack (R) = 5.6kΩ, recovery (R) = 85.6kΩ

Setting the compression attack / recovery time
Attack (R) = 5.6kΩ, recovery (R) = 85.6kΩ

V

CCVCC

Pin No.

4

Multimedia ICs BA7725S / BA7725FS

•

Input / output circuits

Pin name Pin No. Equivalent circuit

ECHO LEVEL

CTRL

4

LOOP GAIN

CTRL

6

Note: The BA7725FS is mounted on a 20-pin SSOP-A package with a different pin number than the BA7725S.

On the BA7725FS, the ECHO LEVEL CTRL pin is pin 3, and the LOOP GAIN CTRL pin is pin 5.

4

6

5

Multimedia ICs BA7725S / BA7725FS

•

Electrical characteristics (unless otherwise noted, Ta = 25°C, Vcc = 9V)

Parameter Symbol Min. Typ. Max. Unit Conditions

Supply current I

CC

4.3 5.7 7.6 mA No input

Line through output level V

OLL

– 9.0 – 8.0 – 7.0 dBV VIN = – 26.0dBV

Line through output distortion THD

LL

— 0.15 0.5 %

Line through maximum output level V

OML

+ 5.0 + 7.2 — dBV

Line through noise level V

ONL

— – 92 – 77 dBV

Microphone through output level V

OML

– 10.5 – 8.5 – 6.5 dBV VIN = – 52dBV

Microphone through output distortion THD

ML

— 0.2 0.5 %

Microphone through input conversion noise V

ONM

— – 114 – 104 dBV Input shorted

Microphone through crosstalk CT

ML

— – 91 – 75 dBV

Compress output level V

OMC

– 6.5 – 4.5 – 2.5 dBV VIN = – 52dBV

Compress output distortion THD

MC

— 0.5 2.0 %

Compress noise level V

ONC

— – 55 – 45 dBV

Compress characteristics CMP — – 11.0 — dB

V

ODL1

– 11.7 – 9.7 — dBV VIN = – 5.0dBV, V4 = 9.0V

Expand output distortion THD

DL

— 0.25 2.0 %

Expand characteristic EXP — – 19.5 — dB

V

ODL2

— – 54 – 44 dB

V

ODC1

– 7.5 – 5.5 — dBV VIN = – 5.0dBV, V6 = 9.0V

V

ODC2

— – 42 – 32 dBV

MIC OFF holding voltage V

4OFF

0.0 — —
—

1.0 V

MIC ON holding voltage V

4ON

2.0 — 9.0 V

V

IN

= – 42dBV → – 62dBV

Output level differential

Expand output level 1

Expand output level 2

V

IN

= 0dBV → – 10.0dBV

Output level differential
V

IN

= – 5.0dBV,

Output level differential relative to Vo

DL1

VIN = – 5.0dBV,

Output level differential relative to Vo

DC1

Loop output level 1

Loop output level 2

〈

LINE THROUGH〉 INPUT : LINE IN, OUTPUT : LINE OUT

〈

MIC THROUGH〉 INPUT : MIC AMP IN, OUTPUT : LINE OUT

〈

COMPRESS〉 INPUT : MIC AMP IN, OUTPUT : CMP BF OUT

〈

EXPAND〉 INPUT : DLY BF IN, OUTPUT : LINE OUT

〈

Loop〉 INPUT : DLY BF IN, OUTPUT : CMP BF OUT

〈

Mode holding voltage

〉

Unless otherwise noted, V4 = 9.0V (MIC ON), V6 = 9.0V (Max. LOOP GAIN)

∗

1 BW = 0.4-30kHz

∗

2 DIN AUDIO

V6 = 2.0V (VR = Min. time)

V

4

= 2.0V (VR = Min. time)

V

IN

= – 26.0dBV, MIC OFF,

∗

1

MIC OFF, Rg = 600Ω,

∗

2

VIN = – 52dBV,

∗

1

V

IN

= – 44dBV, MIC OFF,

∗

2

V

IN

= – 52dBV,

∗

1

Rg = 600Ω,

∗

2

V

IN

= – 5.0dBV, V

4

= 9.0V,

∗

1

THD = 1%,

∗

1

6

Multimedia ICs BA7725S / BA7725FS

•

Measurement circuit

BF

BF

BF

VR

VRSW

EXPAND

12345 78910116

17 12131415161819202122

V4 V6

+

+

R17

C15

R13

C14

R16

C18

R34
1k

C33

R11

C10

R9

C12

R8

+++

COMPRESS

0.1µ

MIC AMP IN

R2

2.2kR382k

C1
1µ

C4

22µ

C5

0.1µC60.47µ

C32

0.1µ

R35

10k

DLY BF IN

CMP BF OUT

+

C30

2.2µ

C20

0.1µ

R31
10k

R33
1k

LINE
OUT

LINE

IN

C20

0.1µ

C19

0.47µ

++

VCC 9V

Fig.1

The above measurement circuit applies to a BA7725S mount­ed to a 22-pin SDIP package. A BA7725FS mounted to a 20­pin SSOP-A package lacks N.C. pins 3 and 20; other than this
difference, the above circuit diagram applies.

•

Circuit operation
(1) MIC AMP IN / LINE OUT gain
Microphone amplifier gain (determined by R9 and R10) + line
amplifier gain (+12dB)
The audio signal is input via pin 22 (BA7725S) or pin 20
(BA7725FS) and amplified by the internal microphone amplifi­er, whose gain can be set with (attached) R9 and R10.

Note: Microphone amplifier gain must be set above +15dB.

Microphone amplifier frequency
characteristic measurement circuit

–
+

Fig.2

1.5k 12k

22 21

BA7725S

VoutVIN

60
50
40
30
20
10

0
– 10
–20
–30
– 40

1M

10M

24681 1864218642

Open loop gain

10k 100k

Frequency characteristic (Hz)

Voltage (dB)

Microphone amplifier frequency
characteristics

Fig.3

++

+

+ 18dB

+

Fig.4

21

2122

MIC AMP IN

R9 R10

SW

LINE OUT LINE IN

7

Multimedia ICs BA7725S / BA7725FS

105

– 100

–50

0

Secondary echo

Sound source

Primary echo

0

ATT (dB)

V

4 = 9.0V

LOOP GAIN CTRL pin voltage : (V)

Line output attenuation vs.
loop gain control pin voltage

Line output attenuation : A

TT

(dB)

Fig.7

0

– 50

– 100

0510

Primary echo

Sound source

ATT (dB)

ECHO LEVEL CTRL pin voltage : (V)

Line output attenuation vs.
echo level control pin voltage

Line output attenuation : A

TT

(dB)

Fig.6

(2) LINE IN / LINE OUT gain
Line amplifier gain is fixed at +18dB.

+

+

+

+

+12dB

Fig.5

21

2122

MIC AMP IN

R9 R10

SW

LINE OUT LINE IN

After being amplified by the internal microphone amplifier, the audio signal is log­arithmically compressed by 1 / 2 then input to the tertiary low pass filter, which
comprises an internal BF and attached capacitor and resistor.

(3) Echo level control
The DC voltage supplied to pin 4 (BA7725S) or pin 3 (BA7725FS) determines
when the microphone switch is turned on and off and controls the echo level.

Line input and level-controlled microphone input are mixed and output.

Mode Threshold voltage Operation

L (1.0V Max.) Only line audio is output.MIC OFF
H (2.0V Min.)MIC ON

Microphone switch control

Echo level control
Attenuation of the primary echo signals from sound
source can be controlled by changing the DC voltage
impressed on pin 4 (BA7725S) or pin 3 (BA7725FS)
between 2V and 9V.

Attenuation of primary echo signals can be controlled
by changing the DC voltage impressed on pin 6
(BA7725S) or pin 5 (BA7725FS) .

8

Multimedia ICs BA7725S / BA7725FS

A : Echo signal attenuation
B : Loop signal attenuation
C : Delay time

CCC

B

B

A

(dB)

(t)

Fig.8

Relationship between echo gain and loop gain

(4) Echo signal frequency characteristicis
The figure below shows the attenuation of signals out­put from pin 1 when the audio signal is input to pin 22
(BA7725S) or pin 20 (BA7725FS). (This is the attenua­tion when the input signal is output without being
passed through the BU9252S / F, and when the prima­ry and secondary echo signals are passed through an
attached low pass filter with the same constant shown
in "Application example," and then processed by the
BU9252S / F delay circuit.)

Note: These are the values when using the constant shown in "Application

example."

0

–10

–20

–30

– 40

– 50

100 1k 10k 100k

Sound source

Secondary echo signal

SIGNAL FREQUENCY : f (Hz)

—

3pin, 5pin = VCC (VR : Max.)

Echo signal frequency
characteristics

LINE OUTPUT ATTENUATION : A

TT

(dB)

Fig.9

Primary echo signal

•

External dimensions (Units: mm)

SDIP22 SSOP-A20

3.95 ± 0.3

0.51Min.

19.4 ± 0.3

3.4 ± 0.2

0.5 ± 0.1

6.5 ± 0.3

1

11

1222

0.3

± 0.1

0° ~ 15°

1.778

7.62

BA7725S BA7725FS

11

10

20

1

0.11

7.8 ± 0.3

5.4 ± 0.2

8.7 ± 0.2

0.15 ± 0.1

0.36 ± 0.10.8

1.8 ± 0.1

0.3Min.

0.15