VCA810_16 Datasheet, PDF (21/40 Pages) Texas Instruments – VCA810 High Gain Adjust Range, Wideband and Variable Gain Amplifier

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9 Applications and Implementation
VCA810
SBOS275G – JUNE 2003 – REVISED DECEMBER 2015
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
9.1.1 VCA810 Operation
Figure 34 shows the circuit configuration used as the basis of the Electrical Characteristics and Typical
Characteristics. Voltage swings reported in the specifications are taken directly at the input and output pins. For
test purposes, the input impedance is set to 50 Ω with a resistance to ground. A 25-Ω resistance (R_T) is included
on the V− input to get bias current cancellation. Proper supply bypassing is shown in Figure 34, and consists of
two capacitors on each supply pin: one large electrolytic capacitor (2.2 μF to 6.8 μF), effective at lower
frequencies, and one small ceramic capacitor (0.1 μF) for high-frequency decoupling.
+5V -5V
0.1mF
0.1mF
6.8mF
+
6.8mF
+
V_I
50W
Source
6
1
7
2
R_S
VCA810
5
50W
3
8
R_T
25W
R_C
V_O
RL
500W
V_C
Figure 34. Variable Gain, Specification and Test Circuit
Notice that both inverting and noninverting inputs are connected to ground with a resistor (R_S and R_T). Matching
the DC source impedance looking out of each input will minimize input offset voltage error.
9.1.2 Range-Finding TGC Amplifier
The block diagram in Figure 35 illustrates the fundamental configuration common to pulse-echo range finding
systems. A photodiode preamp provides an initial gain stage to the photodiode.
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