Datasheet

"#$%&
SBOS316D − JULY 2005 − REVISED OCTOBER 2008
www.ti.com
20
Voltage amplification occurs when the input voltage is
converted to a current; this current in turn is converted
back to a voltage as amplifier A2 acts as a transimpedance
amplifier. The overall gain of the output amplifier A2 can be
altered by 6dB by the action of the H
/L signal. This enables
more optimum performance when the VCA interfaces with
either a 10-bit or 12-bit analog-to-digital converter (ADC).
An external capacitor (C) is required to provide a low
impedance connection to join the two sections of the
resistor network. Capacitor C could be replaced by a
short-circuit. By providing a DC connection, the output
offset will be a function of the gain setting. Typically, the
offset at this point is ±10mV; thus, if the gain varies from
1 to 100, the output offset would vary from ±10mV to
±100mV.
Clipping Program
Circuitry
Clipping Program
Circuitry
V
DD
V
DD
Q2
Q3
+IN
Q1 Q5 Q7 Q9
Q8
Q4 Q6
D1 D2
R1
H/L
R2
D3 D4
A1
A2
V
CM
Q27
Q28
−
IN
Q26
C
C
EXT
2
C
EXT
1
Q30
Q10 Q12 Q14 Q16 Q18 Q20 Q22 Q24
Q11 Q13 Q15 Q17 Q19 Q21 Q23 Q25
Q32
Q34
Q33Q29 Q31
D5 D6
R4
R3
D7 D8
A3
A4
V
CM
Control Signal
Voltage−Controlled
Resistor Network
External
Capacitor
V
CLMP
VCA
Program
Circuitry
V
CNTL
Figure 63. Block Diagram of VCA