SSM2164 Ver la hoja de datos (PDF) - Analog Devices
Número de pieza
componentes Descripción
Fabricante
SSM2164 Datasheet PDF : 12 Pages
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0
–20
VS = ±15V
TA = +25°C
–40
+PSRR
–60
–PSRR
–80
–100
10
100
1k
10k
100K
1M
FREQUENCY – Hz
Figure 20. PSRR vs. Frequency
25
20
+ISY
15
–ISY
10
VS = ±15V
TA = +25°C
5
0
1k
10k
100k
1M
RBIAS – Ω
Figure 21. Supply Current vs. RBIAS
–45
–40
VS = ±15V
–35
CLASS A AND
CLASS AB
–30
–25
–20
–50
–25
0
25
50
TEMPERATURE – °C
75
100
Figure 22. Gain Constant vs. Temperature
SSM2164
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.
V+
IIN
Q5
Q6 Q7
Q8
MODE
Q1 Q2
Q3 Q4
450Ω
4.5kΩ
500Ω
IOUT
VC
V–
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, IIN, is
connected to the collectors of Q1 and Q7, and the difference in
current between these two transistors is equivalent to IIN. 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 VC, 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 VC
steers more current through Q1 and Q4 and decreases the
current in Q2 and Q3. The current output pin, IOUT, 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 VC attenuates
the input and a negative VC 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
REV. 0
–7–
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