Datasheet

OutputMeasured
HereWithHigh
Impedance
DifferentialProbe
THS4511
CM
V
IN
R
F
R
F
R
G
R
G
R
IT
R
IT
From
50 W
Source
5V
49.9 W
49.9 W
100 W
0.22 Fm
49.9 W
0.22 Fm
Open
THS4511
CM
From
50 W
Source
V
IN
0.22 Fm
49.9 W
V
OUT
Open
To50 W
Test
Equipment
R
G
R
IT
R
G
R
IT
R
F
5V
R
O
R
O
R
OT
0.22 Fm
1:1
R
F
THS4511
www.ti.com SLOS471E –SEPTEMBER 2005–REVISED NOVEMBER 2009
TEST CIRCUITS
The THS4511 is tested with the following test circuits
built on the evaluation module (EVM). For simplicity,
the power-supply decoupling is not shown—see
Layout in the Application Information section for
recommendations. Depending on the test conditions,
component values are changed per the following
tables, or as otherwise noted. The signal generators
used are ac-coupled 50-Ω sources, and a 0.22-µF
capacitor and 49.9-Ω resistor to ground are inserted
across R
IT
on the alternate input to balance the
Figure 38. Frequency Response Test Circuit
circuit.
Distortion and 1-dB Compression
Table 1. Gain Component Values
The circuit shown in Figure 39 is used to measure
GAIN R
F
R
G
R
IT
harmonic distortion, intermodulation distortion, and
0 dB 348 Ω 340 Ω 56.2 Ω
1-db compression point of the amplifier.
6 dB 348 Ω 165 Ω 61.9 Ω
A signal generator is used as the signal source and
Note the gain setting includes 50-Ω source
the output is measured with a spectrum analyzer. The
impedance. Components are chosen to achieve
output impedance of the signal generator is 50 Ω. R
IT
gain and 50-Ω input termination.
and R
G
are chosen to impedance-match to 50 Ω, and
to maintain the proper gain. To balance the amplifier,
Table 2. Load Component Values
a 0.22-µF capacitor and 49.9-Ω resistor to ground are
inserted across R
IT
on the alternate input.
R
L
R
O
R
OT
ATTEN.
100 Ω 25 Ω Open 6 dB
A low-pass filter is inserted in series with the input to
reduce harmonics generated at the signal source.
200 Ω 86.6 Ω 69.8 Ω 16.8 dB
The level of the fundamental is measured, then a
499 Ω 237 Ω 56.2 Ω 25.5 dB
high-pass filter is inserted at the output to reduce the
1 kΩ 487 Ω 52.3 Ω 31.8 dB
fundamental so that it does not generate distortion in
the input of the spectrum analyzer.
Note the total load includes 50-Ω termination by
the test equipment. Components are chosen to
The transformer used in the output to convert the
achieve load and 50-Ω line termination through a
signal from differential to single ended is an
1:1 transformer.
ADT1-1WT. It limits the frequency response of the
circuit so that measurements cannot be made below
Due to the voltage divider on the output formed by
approximately 1 MHz.
the load component values, the amplifier output is
attenuated. The column Atten in Table 2 shows the
attenuation expected from the resistor divider. When
using a transformer at the output as shown in
Figure 39, the signal will see slightly more loss, and
these numbers will be approximate.
Frequency Response
The circuit shown in Figure 38 is used to measure the
frequency response of the circuit.
A network analyzer is used as the signal source and
as the measurement device. The output impedance Figure 39. Distortion Test Circuit
of the network analyzer is 50 Ω. R
IT
and R
G
are
chosen to impedance match to 50 Ω, and to maintain
The 1-dB compression point is measured with a
the proper gain. To balance the amplifier, a 0.22-µF
spectrum analyzer with 50-Ω double termination or
capacitor and 49.9-Ω resistor to ground are inserted
100-Ω termination as shown in Table 2. The input
across R
IT
on the alternate input.
power is increased until the output is 1 dB lower than
expected. The number reported in the table data is
The output is probed using a high-impedance
the power delivered to the spectrum analyzer input.
differential probe across the 100-Ω resistor. The gain
Add 3 dB to refer to the amplifier output.
is referred to the amplifier output by adding back the
6-dB loss due to the voltage divider on the output.
Copyright © 2005–2009, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Link(s): THS4511