SSM2164 View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
SSM2164 Datasheet PDF : 12 Pages
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SSM2164
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.
10µF 30kΩ
VIN
500Ω
560pF
VC
(0dB GAIN AT VC =
V+ )
2
V+ = +8V
(1.8kΩ FOR
RB
CLASS A)
(OPEN FOR
CLASS B)
100pF
16
V+ 1
MODE
GND
V– 8
9
30kΩ
V+
1/4
OP482
VOUT
V+
V+
V+/2
OP176
10kΩ
TO ADDITIONAL
OP482 AMPLIFIERS
10kΩ
10µF
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 kΩ 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 VC
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:
IMODE = (V + ) −VGND − 0.6V
RB
The value of 1.8 kΩ 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.
10kΩ
VC1
3
VIN1
10kΩ
2
200Ω
VC1
3
VIN1
30kΩ
2
500Ω
560pF
V+
NC
16
1
SSM2024 4
8
9
V–
V+
16
RB
1
SSM2164 4
8
9
V–
10kΩ
30kΩ
VOUT1
VOUT1
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 kΩ resistors should
be increased to 30 kΩ to operate the SSM2164 in its optimum
range. The 10 kΩ input resistor for the SSM2024 should also
be increased to 30 kΩ 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.
–10–
REV. 0
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