SSM2018

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Voltage Controlled Amplifier Data Sheet SSM2018 Rev. C Document Feedback Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. Tel: 781.329.4700 ©2002–2013 Analog Devices, Inc. All rights reserved. Technical Support www.analog.com

FEATURES

0.006% typical THD+N (@ 1 kHz, unity gain) 140 dB gain range No external trimming required Differential inputs Complementary gain outputs Buffered control port I–V converter on-chip Low external parts count Low cost FUNCTIONAL BLOCK DIAGRAM Figure 1. GENERAL DESCRIPTION The SSM2018 represents the continuing evolution of the Frey Operational Voltage Controlled Element (OVCE) topology that permits flexibility in the design of high performance volume control systems. The SSM2018 is laser trimmed for gain core symmetry and offset. As a result, the SSM2018 is the first professional audio quality VCA to offer trimless operation. Due to careful gain core layout, the SSM2018 combines the low noise of Class AB topologies with the low distortion of Class A circuits to offer an unprecedented level of sonic transparency. Additional features include differential inputs, a 140 dB (−100 dB to +40 dB) gain range, and a high impedance control port. The SSM2018 provides an internal current-to-voltage converter. Thus, no external active components are required. This device is offered in 16-lead, plastic DIP package and guaranteed for operation over the extended industrial temperature range of −40°C to +85°C. SSM2018 VC G GAIN CORE 1–G VG –IG V1–G –I1–G +IN –IN 00345-001

Rev. C | Page 2 of 16 TABLE OF CONTENTS

REVISION HISTORY

2/13—Rev. B to Rev. C Changed Theory of Operation of the SSM2018T Section to Changed Applications Section to Applications Information Changes to Output Drive Section, Upgrading SSM2018 Sockets Section, Temperature Compensation of the Gain Constant 7/02—Rev. A to Rev. B Deleted 16-Lewad Plastic DIP and SOL from Deleted section Basic VCA Configuration For

Rev. C | Page 3 of 16 SPECIFICATIONS ELECTRICAL SPECIFICATIONS VS = ±15 V , AV = 0 dB, RL = 100 kΩ, f = 1 kHz, 0 dBu = 0.775 V rms, simple VCA application circuit with 18 kΩ resistors, −VIN floating, and Class AB gain core bias (RB = 150 kΩ), −40°C < TA < +85°C, unless otherwise noted. Typical specifications apply at TA = 25°C. Table 1. Parameter Conditions Min Typ Max Max (E Grade) Unit AUDIO PERFORMANCE Noise VIN = GND, 20 kHz Bandwidth –95 –93 dBu Headroom Clip Point = 1% THD + N 22 dBu Total Harmonic Distortion plus Noise 2nd and 3rd Harmonics Only (25°C to 85°C) AV = 0 dB, VIN = +10 dBu 0.006 0.020 0.01 % AV = +20 dB, VIN = −10 dBu 0.013 0.03 0.02 % AV = −20 dB, VIN = +10 dBu 0.013 0.03 0.02 % INPUT AMPLIFIER Bias Current VCM = 0 V 0.25 1 µA Offset Voltage VCM = 0 V 1 15 mV Offset Current VCM = 0 V 10 100 nA Input Impedance 4 MΩ Common-Mode Range ±13 V Gain Bandwidth VCA Configuration 0.7 MHz VCP Configuration 14 MHz Slew Rate 5 V/µs OUTPUT AMPLIFIER Offset Voltage VIN = 0 V, VC = 4 V 1.0 15 mV Output Voltage Swing IOUT = 1.5 mA Positive 10 13 V Negative −10 −14 V Minimum Load Resistance For Full Output Swing 9 kΩ CONTROL PORT Bias Current 0.36 1 µA Input Impedance 1 MΩ Gain Constant Device Powered in Socket > 60 sec −30 mV/dB Gain Constant Temperature Coefficient −3500 ppm/°C Control Feedthrough 0 dB to –40 dB Gain Range ±1 ±4 ±3 mV Maximum Gain VC = −1.3 V 40 mV Maximum Attenuation VC = 4 V 100 dB POWER SUPPLIES Supply Voltage Range ±5 ±18 V Supply Current 11 15 mA Power Supply Rejection Ratio 80 dB

for device in socket for P-D I P. Table 3. Thermal Resistance Figure 2. Typical Application Circuit

Table 4. Pin Function Descriptions 1 +I1−G Positive Current Feedback Input for V1-G. 2 V+ Positive Power Supply. Connect this pin directly to the positive power rail. 3 −IG Negative Current Feedback Input for VG. 4 −I1−G Negative Current Feedback Input for V1-G. 6 +IN Non-Inverting Current Input. 7 −IN Inverting Current Input. 10 V− Negative Power Supply. Connect this pin directly to negative power rail. 11 VC Control Voltage Input Port. Apply voltage to control VCA according to the Control Section. Operating Mode for the SSM2018 section. 14 VG Output Voltage at Gain of G. 15 BAL Symmetry Trim Input for Older Version. Do not connect for SSM2108T operation. 16 V1−G Output Voltage at Gain of 1-G.

Figure 4. THD + N Frequency (80 kHz Low-Pass Filter, for Figure 5. Distortion Distribution Figure 6. THD + N vs. Amplitude (Gain = 0 dB, fIN = 1 kHz, 80 kHz Low-Pass Figure 7. THD + N vs. Amplitude (Gain = +20 dB, fIN =1 kHz, Figure 8. THD + N vs. Gain (fIN = 1 kHz; for –60 dB ≤ AV ≤ –20 dB, VIN = 10 V Figure 9. THD + N vs. Supply Voltage (AV = 0 dB, VIN = 1 V rms, fIN = 1 kHz, 80

300 UNITS

Figure 16. Gain vs. Frequency Figure 17. Distortion vs. Temperature Figure 18. Output Noise vs. Gain (VIN = GND, 20 kHz Bandwidth) Figure 19. Control Feedthrough Distribution Figure 20. Control Feedthrough vs. Frequency Figure 21. Control Feedthrough vs. Temperature

gain core, which comprises two differential pairs (Q1–Q4). opposite is true for a negative input. the external 18 kΩ feedback resistor around amplifier A3. When this current is reduced, the output voltage is also reduced. input signal, which explains why the gain constant is negative. The collector currents of Q2 and Q3 produce the output voltage. of Q1 and Q4 are used for feedback to the differential inputs. input resistors is balanced by the collector currents in Q1 and Q4. the OVCE circuit, COMP3 should be left open. Figure 28. Detailed Functional Diagram

Rev. C | Page 11 of 16 A compensation capacitor must be added between COMP1 and COMP2. Because the VCA operates over such a wide gain range, the compensation should ideally be optimized for each gain. When the VCA is in high attenuation, there is very high loop gain, and the part needs to have high compensation. On the other hand, at high gain, the same compensation capacitor would overcompensate the part and roll off the high frequency performance. Thus, the SSM2018 employs a patented adaptive compensation circuit. The compensation capacitor is Miller connected between the base and collector of an internal transistor. By changing the gain of this transistor via the control voltage, the compensation is changed. Increasing the compensation capacitor causes the frequency response and slew rate to decrease, which tends to cause high frequency distortion to increase. For the basic VCA circuit, 47 pF was chosen as the optimal value. The OVCE circuit described later uses a 220 pF capacitor. The reason for the increase is to compensate for the extra phase shift from the additional output amplifier used in the OVCE configuration. The compensation capacitor can be adjusted over a practical range from 47 pF to 220 pF if desired. Below 47 pF , the parts may oscillate; above 220 pF the frequency response is significantly degraded. CONTROL SECTION As noted above, the control voltage on Pin 11 steers the current through the gain core transistors to set the gain. The unity gain (0 dB) condition occurs at V C = 0. Attenuation occurs in the VCA for positive voltages (0 V to 3 V , typ), and gain occurs for negative voltage (0 V to −1.3 V , typ). From –1.3 V to +3.0 V, 140 dB of gain range is obtainable. The output gain formula is as follows: V OUT = VIN × e(−aVC) (1) The exponential term arises from the standard Ebers-Moll equation describing the relationship of a transistor’s collector current as a function of the base-emitter voltage: I C = IS × e(VBE /VT) (2) The factor a is a function not only of VT but also the scaling due to the resistor divider of the 200 Ω and 1.8 kΩ resistors shown in Figure 2. The resulting expression for a is as follows: a = 1/(10 × V T), which is approximately equal to 4 at room temperature. Substituting a = 4 in the above equation results in a −28.8 mV/dB control law at room temperature. The −28.8 mV/dB number is slightly different from the data sheet specification of −30 mV/dB. The difference arises from the temperature dependency of the control law. The term V T is known as the thermal voltage, and it has a direct dependency on temperature: V T = kT/q where k = Boltzmann’s constant = 1.38 E − 23 q = electron charge = 1.6 E − 19 T = absolute temperature in Kelvin) This temperature dependency leads to the −3500 ppm/°C drift of the control law. It also means that the control law changes as the part warms up. Thus, our specification for the control law states that the part has been powered up for 60 seconds. When the part is initially turned on, the temperature of the die is still at the ambient temperature (25°C for example), but the power dissipation causes the die to warm up. With ±15 V supplies and a supply current of 11 mA, 330 mW is dissipated. This number is multiplied by θ JA to determine the rise in the die’s temperature. In this case, the die increases from 25°C to approximately 50°C. A 25°C temperature change causes a 8.25% increase in the gain constant, resulting in a gain constant of 30 mV/dB. The graph in Figure 22 shows how the gain constant varies over the full temperature range.

Figure 37. 16-Lead Plastic Dual In-Line Package [PDIP] REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. CORNER LEADS MAY BE CONFIGURED AS WHOLE OR HALF LEADS. registered trademarks are the property of their respective owners.