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SSM2164S Datasheet(PDF) 7 Page - Analog Devices |
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SSM2164S Datasheet(HTML) 7 Page - Analog Devices |
7 / 12 page SSM2164 REV. 0 –7– 0 –20 –100 10 100 1M 100K 10k 1k –40 –60 –80 FREQUENCY – Hz VS = ±15V TA = +25°C +PSRR –PSRR Figure 20. PSRR vs. Frequency 25 20 0 1k 10k 1M 100k 15 10 5 RBIAS – Ω +ISY –ISY VS = ±15V TA = +25°C Figure 21. Supply Current vs. R BIAS –45 –20 100 –35 –25 –25 –30 –50 –40 75 50 25 0 TEMPERATURE – °C CLASS A AND CLASS AB VS = ±15V Figure 22. Gain Constant vs. Temperature APPLICATIONS INFORMATION Circuit Description The SSM2164 is a quad Voltage Controlled Amplifier (VCA) with 120 dB of gain control range. Each VCA is a current-in, current-out device with a separate –33 mV/dB voltage input control port. The class of operation (either Class A or Class AB) is set by a single external resistor allowing optimization of the distortion versus noise tradeoff for a particular application. The four independent VCAs in a single 16-pin package make the SSM2164 ideal for applications where multiple volume control elements are needed. Figure 23. Simplified Schematic (One Channel) The simplified schematic in Figure 23 shows the basic structure of one of the four VCAs in the device. The gain core is com- prised of the matched differential pairs Q1-Q4 and the current mirrors of Q5, Q6 and Q7, Q8. The current input pin, I IN, is connected to the collectors of Q1 and Q7, and the difference in current between these two transistors is equivalent to I IN. For example, if 100 µA is flowing into the input, Q1’s collector current will be 100 µA higher than Q7’s collector current. Varying the control voltage V C, steers the signal current from one side of each differential pair to the other, resulting in either gain or attenuation. For example, a positive voltage on V C steers more current through Q1 and Q4 and decreases the current in Q2 and Q3. The current output pin, I OUT, is con- nected to the collector of Q3 and the current mirror (Q6) from Q2. With less current flowing through these two transistors, less current is available at the output. Thus, a positive V C attenuates the input and a negative V C amplifies the input. The VCA has unity gain for a control voltage of 0.0 V where the signal current is divided equally between the gain core differential pairs. The MODE pin allows the setting of the quiescent current in the gain core of the VCA to trade off the SSM2164’s THD and noise performance to an optimal level for a particular applica- tion. Higher current through the core results in lower distortion Q6 Q5 Q8 Q7 Q2 Q1 Q4 Q3 IIN IOUT VC 4.5k Ω 500 Ω 450 Ω MODE V– V+ |
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