Texas Instruments THS3062EVM, Руководство пользователя, Страница: 16 / 21

Noninverting Gain Stage
3-2
3.2 Noninverting Gain Stage
For a noninverting stage in EVM channel 1, the EVM can be modified to
eliminate the gain error imposed by R2 by replacing R2 with a 0-
Ω
resistor. This
is shown in Figure 3-2. R4 has been removed as shown in the inverting gain
stage example above. The following equation indicates the voltage gain from
J3 to J1:
V
O
V
I
+
ǒ
1
)
R6
R1
Ǔ
ǒ
50
W
50
W )
R5
Ǔ
+
1
(5)
Figure 3-2. Noninverting Gain Stage
R2
0
R5
R3
-
+
U1A
THS3062
2
3
6
7
4
Vs-
R6
J1
1 out
Vs+
R1
J3
1 in+
562
W
49.9
W
562
W
49.9
W
This is a common amplifier configuration used to drive a transmission line. The
49.9-
Ω
resistor in series with the output matches the effective output
impedance of the amplifier to the line impedance. In test and measurement
instruments the nominal line impedance is assumed to be 50
Ω
, for video the
nominal line impedance is assumed to be 75
Ω
. If testing this device as a video
linear driver we recommend changing the value of R5 to 75
Ω
.
Due to the nature of current feedback high speed amplifiers the gain of the
THS3062 can be increased by decreasing the values of R1 and R8 with little
change in bandwidth. R6 should be reduced to maintain optimum
compensation. Refer to the data sheet for recommended resistor values.
3.3 Applications for EVM Channel 2
Since the board layout of EVM channel 2 is identical to EVM channel 1, the
applications above can be applied identically. The only physical difference is
that different values have been installed in the default configuration for
different EVM channels. In addition, the components are labeled differently for
each EVM channel. Refer to complete schematic and board silkscreen to
resolve these issues.