SSM2163

REV. 0

–13–

The circuit of Figure 26 illustrates dc coupling of the inputs.

DC coupling is practical with dual supplies and ground-

referenced inputs, because the dc offsets associated with single-

supply operation are reduced. However, ac coupling could also

be used, and employing both ac- and dc-coupled signals in one

mixer is also possible. In addition, this circuit illustrates the

connections for

±5 V power supplies. Note that the negative

supply, as well as the positive supply, should be bypassed to

ground.

Implementing a Software-Controlled Pan-Pot

Pan and fade effects are important attributes of modern multi-

media presentations and similar applications. One way to

achieve these effects is to apply the input signal to two input

channels of the SSM2163, as shown in Figure 27. Since any

input channel can be mixed into either or both outputs,

sophisticated pan and fade effects are easily accomplished in

software. For example, Input 1 can be connected to the left

channel with 0 dB attenuation, while Input 2 is applied to the

right channel with –10 dB of attenuation. This configuration

will produce the effect of having the audio source “located” to

the left of center line of the speakers. Another possible option

would be to attenuate the left channel while boosting the right,

which would produce an effect of movement of the audio source.

Since any input can be connected to either output, very flexible

and sophisticated effects can be produced without hardware

changes.

SSM2163

TO INPUTS

Σ

Σ

Figure 27. Connecting the SSM2163 for Pan-Pot

Operation

Driving Headphones

A high speed, high output current amplifier, such as the OP279,

can be added to drive headphones directly. A typical connection

is shown in Figure 28. Single +5 V operation is maintained,

since the OP279 offers rail-to-rail inputs and outputs. The

OP279’s high current output stage can drive a 48

Ω load to

4 V p-p while maintaining less than 1% THD.

Mixing Additional Channels

Some mixing applications require more than four inputs for

each stereo channel. To meet the requirements of these systems,

two or more SSM2163s can be paralleled to provide additional

channels. A typical circuit is shown in Figure 26, which combines

two SSM2163s to form a 16-input, 2-output mixer. An SSM2135

dual audio op amp sums the outputs of each of the SSM2163s.

With this system, any of the 16 inputs can be mixed into either

or both of the output channels.

5

22

7

20

9

18

11

16

27

26

25

24

28

14

15

3

NC

4

10

+5V

+

10µF

0.1µF

DATA OUT

SHIELD

SHIELD

SHIELD

SHIELD

SHIELD

AGND

ACOM

DGND

212

1

6

8

19

21

23

17

13

10µF

0.1µF

+

DATA IN

CLK

WRITE

LD

SYSMUTE

SSM2163

DATA IN

CLOCK

CHIP SELECT

SYSTEM MUTE

5

22

7

20

9

18

11

16

27

26

25

24

28

14

15

3

NC

4

10

+5V

+

10µF

0.1µF

DATA OUT

SHIELD

SHIELD

SHIELD

SHIELD

SHIELD

AGND

ACOM

DGND

2

12

1

6

8

19

21

23

17

13

DATA IN

CLK

WRITE

LD

SYSMUTE

SSM2163

–5V

#1

#2

10µF

0.1µF

+

–5V

NC

20k

+5V

0.1µF

0.1µF

–5V

20k

20k

1/2 SSM2135

20k

1/2 SSM2135

20k

20k

Figure 26. A 16-Input, 2-Output Mixer

This circuit utilizes the DATA OUT feature of the SSM2163 to

transfer data from the first SSM2163 to the second. In the

daisy-chain mode, the DATA OUT pin of the first SSM2163 is

connected to the DATA IN pin of the second device. The

advantage of this “daisy chain” connection is that it allows a

3-wire serial interface, as was used in the previous 8-input

mixer, to control two or more SSM2163s.

The serial data format for the daisy chain circuit is similar to the

8-channel application, except that the SSM2163s are loaded in

tandem. After setting WRITE and LOAD low, two bytes (16 bits)

are clocked into the first SSM2163. When WRITE and

LOAD return high, data will be latched into both SSM2163s

simultaneously.