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THAT Alternatives to the Analog Devices SSM2164

Analog Devices has discontinued their SSM2164 quad VCA. Our THAT 2162 dual VCA is comparable in many respects.

To replace a 2164 with (two) 2162 ICs, see below for some of the issues which you will need to consider. Please contact applications support for specific assistance with the 2162.  And, if you want to find out more about the possibility of a THAT equivalent to the SSM2164, please contact our sales department.

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fillerKey Specifications
fillerParameter
SSM2164
THAT2162
  Conditions
fillerDynamic Range
116 dB
> 118 dB
 
fillerGain Range
120 dB
> 130 dB
 
fillerTHD + N
0.16 %
0.05 %
  Class A-B, Typical, 0 V control voltage
0.02 %
N/A
  Class A, Typical, 0 V control voltage
fillerNoise
-94 dBu
-97.5 dBu
  Class A-B, Typical, 20 kHz BW, 0 dB gain
-83 dBu
N/A
  Class A, Typical, 20 kHz BW, 0 dB gain
fillerC-V Feedthrough
1.5 mV
1.0 mV
  Class A-B, 0 ~ -40 dB
fillerGain Matching
0.07 dB
0.2 dB
  Typical, Channel to channel
fillerSupply Voltage
±4 V to ±18 V
±2.25 V to ±16 V
 
fillerSupply Current
±2 mA / VCA
±3.5 mA / VCA
  Maximum, ± 15 V supplies
fillerPackaging
Quad
Dual
 
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fillerPackaging / Layout
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The THAT2162 IC contains two VCAs, while the SSM2164 has four. So, two 2162s are needed to replace one 2164. However, the 2162 comes in a QSOP16 package, which occupies only 30 square mm of PCB space – about half the space required by the SOIC version of the 2164. Thus, the board space required is a toss up.
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SSM2164
THAT 2162
SSM2164 block diagram
2162 block diagram
DIP16, 20mm x 6mm (approx.) = 140 sq mm
SOIC16, 10mm x 6mm (approx.) = 60 sq mm
QSOP16, 5mm x 6mm (approx), x2 = 60 sq mm
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Control Ports
The 2164 has a single control port for each VCA, the 2162 has two ports of opposing polarities.  The control constants are different (see table below), so adapting the 2162 to a 2164 application will require circuit changes.  Both parts offer 120dB of gain range, but differences in symmetry of that range will be important for some applications.  Again, see the table below.
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Parameter SSM2164 THAT2162

Control Port(s)

One (negative sense)

One (negative-sense),
One (positive-sense)
When used single-ended, ground the unused port

Control Constant

-33mV/dB

-6.4mV/dB (negative port)
+6.4mV/dB (positive port)

0 dB Gain Point

0 V

0 V

Gain Range

+20 to -100dB

+60 to -60dB (single-ended)
+60 to -120dB (differential)

Temperature Coefficient

3300ppm/ °C

3300ppm/ °C


The 2162 can support the assymetrical gain range of the 2164 in single-ended control mode if the unused control port is connected to a suitable offset.  Contact THAT's applications engineering for details.
Parameter SSM2164 THAT2162
Control Port Input Impedance 5 kΩ Direct to a transistor base

Each 2162 control port (Ec+ & Ec-) connects directly to the base of a transistor. Each 2164 control port has a resistive divider between it and the equivalent internal transistor base. (This is partly responsible for the 2162's superior distortion performance.)

To achieve the lowest possible THD, we recommend that the 2162's Ec port be driven from a source impedance of less than 100 ohms. To scale up the control constant to equal that of the 2164 (-6.4 to -33mV/dB), use the resistive divider in the figure below, which yields the same control constant, though a lower control input impedance of -6.4 mV/dB.

Parameter SSM2164 THAT2162
Suggested low impedance control voltage divider network
2162 resistor divider
To minimize THD, we recommend driving the 2162 control port directly from the output of a low noise opamp, with appropriate scaling of the control sensitivity before or within the opamp driver.
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Inputs and Outputs
Parameter SSM2164 THAT2162
Input / Output Current Flow Current In / Current Out Current In / Current In

Current in to the input terminal of the 2164 produces current out of the output terminal. As a result, the voltage at the output of the current to voltage converter stage is out of phase with the input voltage.

Current in to the input terminal of the 2162 produces current in to the output terminal. As a result, the voltage at the output of the current to voltage converter stage is in phase with the input voltage. 

This is a significant difference. In some applications, this may necessitate the adding (or removing) an inverter stage when replacing the 2164 with the 2162.
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Parameter SSM2164 THAT2162
Input Resistor Value 30 kΩ 20 kΩ
Current to Voltage Feedback Resistor Value 30 kΩ 20 kΩ
For best noise performance with the 2162, we recommend 20 kΩ for the input resistor (Rin) and for the output (Rout) resistor in the current-to-voltage converter. Note also the difference in the current to voltage converter frequency compensating capacitor (Cout). Also note the difference in the input snubber network values.
Parameter SSM2164 THAT2162

Input Network
Recommended Component Values

SSM2164 input snubber circuit
2162 input snubber circuit
Current to Voltage Converter
Recommended Component Values
SSM2164 current to voltage converter
THAT2162 current to voltage converter

It is OK to use 30 kΩ resistors with the 2162, but the noise performance will be increased by approximately 3.5 dB (at unity gain).

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Operating Mode
Parameter SSM2164 THAT2162
Operating Mode Biasing Class A or Class A-B, selectable via external resisitor Class A-B only
In class A operation, the 2164 provides better THD performance (at unity gain), but it comes at significant expense in noise. Noise increases from -94 dBu to approximately -83 dBu using ADI's recommended circuit for Class A operation. As well, dc feedthrough is worse -- unspecified. THAT believes that class A-B operation offers a better tradeoff in VCA design, so the 2162, like all other THAT VCAs, operates only in class A-B mode.
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