Datasheet SSM2164 (Analog Devices) - 10

SSM2164 Single Supply Operation Upgrading SSM2024 Sockets
The SSM2164 can easily be operated from a single power The SSM2164 is intended to replace the SSM2024, an earlier supply as low as +8 V or as high as +36 V. The key to using a generation quad VCA. The improvements in the SSM2164 single supply is to reference all ground connections to a voltage have resulted in a part that is not a drop-in replacement to the midway between the supply and ground as shown in Figure 27. SSM2024, but upgrading applications with the SSM2024 is a The OP176 is used to create a pseudo-ground reference for the simple task. The changes are shown in Figure 28. Both parts SSM2164. Both the OP482 and OP176 are single supply have identical pinouts with one small exception. The MODE amplifiers and can easily operate over the same voltage range as input (Pin 1) does not exist on the SSM2024. It has fixed the SSM2164 with little or no change in performance. 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
V+ = +8V
AB, no external resistor is needed.
(1.8k
Ω
FOR CLASS A) RB (OPEN FOR CLASS B) 100pF 10k
Ω
VC1 V+ 16 30k
Ω
3 NC V+ 1 16 10k
Ω
V+ 10µF 1 30k
Ω
MODE 10k
Ω
V 2 4 IN VIN1 SSM2024 GND 1/4 500
Ω
OP482 VOUT VOUT1 V– 200
Ω
8 560pF 8 9 9 V+ V+ V– VC V+ (0dB GAIN AT VC = ) 2 V+/2 10k
Ω
OP176 V+ VC1 3 10k
Ω
10µF R TO ADDITIONAL 16 B OP482 AMPLIFIERS 30k
Ω
1 30k
Ω
2 4 VIN1 SSM2164 VOUT1 8 500
Ω Figure 27. Single Supply Operation of the SSM2164
9 560pF
(One Channel Shown)
V–
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 Figure 28. Upgrading SSM2024 Sockets with SSM2164 supply voltage, providing a low noise reference to the circuit. This reference voltage is then connected to the GND pin of the Since both parts are current output devices, the output configu- SSM2164 and the noninverting inputs of all the output amplifi- ration is nearly identical, except that the 10 kΩ resistors should ers. It is important to buffer the resistor divider with the OP176 be increased to 30 kΩ to operate the SSM2164 in its optimum to ensure a low impedance pseudo-ground connection for the range. The 10 kΩ input resistor for the SSM2024 should also SSM2164. be increased to 30 kΩ to match the output resistor. Addition- The input can either be referenced to this same mid-supply ally, the 200 Ω resistor should be replaced by a 500 Ω resistor in voltage or ac coupled as is done in this case. If the entire system series with 560 pF for the SSM2164 circuit.
OBSOLETE
is single supply, then the input voltage will most likely already One last change is the control port configuration. The be referenced to the midpoint; if this is the case, the 10 µF SSM2024’s control input is actually a current input. Thus, a input capacitor can be eliminated. Unity gain is set when VC resistor was needed to change the control voltage to a current. equals the voltage on the GND pin. Thus, the control voltage This resistor should be removed for the SSM2164 to provide a should also be referenced to the same midsupply voltage. direct voltage input. In addition, the SSM2024 has a log/log The value of the MODE setting resistor may also change control relationship in contrast to the SSM2164’s linear/log gain depending on the total supply voltage. Because the GND pin is constant. The linear input is actually much easier to control, at a pseudo-ground potential, the equation to set the MODE but the difference may necessitate adjusting a SSM2024 based current now becomes: circuit’s control voltage gain curve. By making these relatively simple changes, the superior performance of the SSM2164 can − 0.6V easily be realized. I = (V +) −VGND MODE R B The value of 1.8 kΩ results in Class A biasing for the case of using a +8 V supply. –10– REV. 0