SSM2164

REV. 0

–10–

Single Supply Operation

The SSM2164 can easily be operated from a single power

supply as low as +8 V or as high as +36 V. The key to using a

single supply is to reference all ground connections to a voltage

midway between the supply and ground as shown in Figure 27.

The OP176 is used to create a pseudo-ground reference for the

SSM2164. Both the OP482 and OP176 are single supply

amplifiers and can easily operate over the same voltage range as

the SSM2164 with little or no change in performance.

GND

MODE

V+

V–

16

1

9

8

V+ = +8V

)

V+

2

500

Ω

560pF

30k

Ω

10µF

V+

1/4

OP482

OP176

V+

30k

Ω

10k

Ω

10k

Ω

V+

10µF

V+/2

TO ADDITIONAL

OP482 AMPLIFIERS

(1.8k

Ω FOR

CLASS A)

(OPEN FOR

CLASS B)

100pF

Figure 27. Single Supply Operation of the SSM2164

(One Channel Shown)

The reference voltage is set by the resistor divider from the

positive supply. Two 10 k

Ω resistors create a voltage equal to

the positive supply divided by 2. The 10

µF capacitor filters the

supply voltage, providing a low noise reference to the circuit.

This reference voltage is then connected to the GND pin of the

SSM2164 and the noninverting inputs of all the output amplifi-

ers. It is important to buffer the resistor divider with the OP176

to ensure a low impedance pseudo-ground connection for the

SSM2164.

The input can either be referenced to this same mid-supply

voltage or ac coupled as is done in this case. If the entire system

is single supply, then the input voltage will most likely already

be referenced to the midpoint; if this is the case, the 10

µF

input capacitor can be eliminated. Unity gain is set when V

C

equals the voltage on the GND pin. Thus, the control voltage

should also be referenced to the same midsupply voltage.

The value of the MODE setting resistor may also change

depending on the total supply voltage. Because the GND pin is

at a pseudo-ground potential, the equation to set the MODE

current now becomes:

I

(V

+) −V

R

B

The value of 1.8 k

Ω results in Class A biasing for the case of

using a +8 V supply.

Upgrading SSM2024 Sockets

The SSM2164 is intended to replace the SSM2024, an earlier

generation quad VCA. The improvements in the SSM2164

have resulted in a part that is not a drop-in replacement to the

SSM2024, but upgrading applications with the SSM2024 is a

simple task. The changes are shown in Figure 28. Both parts

have identical pinouts with one small exception. The MODE

input (Pin 1) does not exist on the SSM2024. It has fixed

internal biasing, whereas flexibility was designed into the

SSM2164. A MODE set resistor should be added for Class A

operation, but if the SSM2164 is going to be operated in Class

AB, no external resistor is needed.

V+

16

1

9

8

200

Ω

10k

Ω

NC

SSM2024

V–

10k

Ω

4

10k

Ω

3

2

V+

16

1

9

8

500

Ω

30k

Ω

SSM2164

V–

30k

Ω

4

3

2

560pF

Figure 28. Upgrading SSM2024 Sockets with SSM2164

Since both parts are current output devices, the output configu-

ration is nearly identical, except that the 10 k

Ω resistors should

be increased to 30 k

Ω to operate the SSM2164 in its optimum

range. The 10 k

Ω input resistor for the SSM2024 should also

be increased to 30 k

Ω to match the output resistor. Addition-

ally, the 200

Ω resistor should be replaced by a 500 Ω resistor in

series with 560 pF for the SSM2164 circuit.

One last change is the control port configuration. The

SSM2024’s control input is actually a current input. Thus, a

resistor was needed to change the control voltage to a current.

This resistor should be removed for the SSM2164 to provide a

direct voltage input. In addition, the SSM2024 has a log/log

control relationship in contrast to the SSM2164’s linear/log gain

constant. The linear input is actually much easier to control,

but the difference may necessitate adjusting a SSM2024 based

circuit’s control voltage gain curve. By making these relatively

simple changes, the superior performance of the SSM2164 can

easily be realized.