Texas Instruments THS3062EVM, Руководство пользователя, Страница: 9 / 21

1-1 Introduction and Description
Introduction and Description
This chapter provides a description of the THS3062EVM dual high-speed
operational amplifier along with a schematic diagram.
1.1 Evaluation Schematic
As delivered, the EVM has a fully functional example circuit, requiring added
power supplies, a signal source, and a monitoring instrument. The default
schematic diagram is provided in Figure 1-1. The user can change the gain
by changing the ratios of the feedback and gain resistors (see the device data
sheet for recommended resistor values). The complete EVM
schematic—showing all components—is shown in this chapter.
EVM Channel 1:
The default configuration for EVM channel 1 is designed to provide a voltage
gain of -1 and a gain of about +2 depending on which input is connected to
the signal source. This voltage gain is the ratio of the voltage at the output pin
of the amplifier (pin 1) to the voltage at the input at J2 or J3 respectively.
For optimum frequency response and stability at either -1 or +2 gain, a
feedback resistor, R6 (562
Ω
), is chosen. R1 is set to the same value to provide
a gain in the inverting configuration of -1. To match the signal generator,
source impedance R2 was set to 54.9
Ω.
This is the closest value when placed
in parallel with R3 (562
Ω
) that terminates the inverting input to 50
Ω.
R4 is set
to 953
Ω
because when a high impedance instrument is connected to the
output connector, J1, the amplifier is loaded at about 1 k
Ω
.
When EVM channel 1 is used as an inverting amplifier in the default
configuration connected to a 50-
Ω
input device, R4 causes a slight gain error.
The total voltage gain is the negative ratio of the feedback resistor, R6, and the
gain resistor, R3, times the voltage divider created by R5, R4 and the
measurement device input termination resistance. This gain follows the
following equation:
V
O
V
I
+ *
R6
R1
ǒ
R4
ø
50
W
R4
ø
50
W )
R5
Ǔ
+ *
0.475
(1)
Chapter 1