VCA2619 Datasheet, PDF (10/19 Pages) Burr-Brown (TI) – Dual, Variable Gain Amplifier with Input Buffer

VCA2619
SBOS276A − AUGUST 2003 − REVISED AUGUST 2003
VOLTAGE-CONTROLLED ATTENUATOR
The magnitude of the VCA input signal from the input
buffer is reduced by a programmable attenuation factor,
set by the analog VCA Control Voltage (VCA_CNTL) at pin
24. The maximum attenuation is programmable by using
the three MGS bits (pins 21, 22, and 23). Figure 2
illustrates this dual-adjust characteristic.
0
Minimum Attenuation
−41
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The MGS bits adjust the overall range of attenuation and
maximum gain while the VCA_CNTL voltage adjusts the
actual attenuation factor. Figure 3 is a simplified version of
the voltage control attenuator. Figure 4 illustrates the
piecewise approximation to the logarithmic control
characteristics. At any given maximum gain setting, the
analog variable gain characteristic is linear in dB as a
function of the control voltage, and is created as a
piecewise approximation of an ideal dB-linear transfer
function. The VCA control circuitry is common to both
channels of the VCA2619. The range for the VCA_CNTL
input spans from 0V to 3V. Although overdriving the
VCA_CNTL input above the recommended 3V maximum will
not damage the part, this condition should be avoided.
−52.3
0
Maximum Attenuation
Control Voltage
3.0V
Figure 2. Swept Attenuator Characteristic.
R_S
Input
V_CM
Q_1A
Q_1B
Q_2A
Q_2B
Q_3A
Q_3B
Q_4A
Q_4B
Q_5A
A1
B1
B2
A2
A3
A4
A5
Figure 3. Simplified Attenuator Diagram.
Output
Q_5B
10