VCA2615 Datasheet, PDF (20/29 Pages) Texas Instruments – Dual, Low-Noise Variable-Gain Amplifier with Preamp

VCA2615
SBOS316C − JULY 2005 − REVISED SEPTEMBER 2005
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
www.ti.com
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
V_DD
H/L
R1
Q1
Q5
Q7
Q9
+IN
Q2
A1
Q3
R2
D1
D2
D3
D4
A2
V_CM
Q4
Q6
Q8
External
Capacitor
C
C_EXT2
C_EXT1
Voltage−Controlled
Resistor Network
Q26
Q10
Q12 Q14 Q16 Q18
Q20
Q22
Q24
Q11
Q13 Q15 Q17 Q19
Q21
Q23
Q25
Q30
Q32
Control Signal
A3
−IN
Q27
Q28
V_CM
D5
D6
A4
R3
D7
D8
R4
Q29
Q31
Q33
Q34
V_DD
Clipping Program
Circuitry
V_CLMP
V_CNTL
VCA
Program
Circuitry
Figure 63. Block Diagram of VCA
20