THS4520_14 Datasheet, PDF (19/37 Pages) Texas Instruments – WIDEBAND, LOW NOISE, LOW DISTORTION FULLY DIFFERENTIAL AMPLIFIER

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THS4520
SLOS503B – SEPTEMBER 2006 – REVISED JULY 2007
CM SMALL SIGNAL FREQUENCY RESPONSE
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
R_F = 499 W
-12
-13
-14
-15
R_L = 200 W
Gain = 0 dB
V_O = 100 mV_PP
-16
-17
V_S = ±1.65 V
-18
-19
-20
0.1
1
10
100
f - Frequency - MHz
1000
Figure 54.
TEST CIRCUITS
GAIN
20 dB
R_F
499 Ω
R_G
34.8 Ω
R_IT
115 Ω
The THS4520 is tested with the following test circuits
built on the EVM. For simplicity, power supply
decoupling is not shown – see layout in the
applications section for recommendations.
V_IN
From
R_G
50 W
Source
R_IT
R_F
V_S+
THS4520
R_O
1:1
V_OUT
To 50 W
R_O
R_OT
Test
Equipment
0.22 mF
R_IT
CM
49.9 W
V_S-
R_F
Open
Figure 55. General Test Circuit for Device Testing
and Characterization
Note: The gain setting includes 50-Ω source
impedance. Components are chosen to achieve gain
and 50-Ω input termination.
Table 2. Load Component Values
R_L
100 Ω
200 Ω
499 Ω
1 kΩ
2k
R_O
25 Ω
86.6 Ω
237 Ω
487 Ω
976
R_OT
open
69.8 Ω
56.2 Ω
52.3 Ω
51.1
Atten.
6 dB
16.8 dB
25.5 dB
31.8 dB
–37.86
Note: The total load includes 50-Ω termination by the
test equipment. Components are chosen to achieve
load and 50-Ω line termination through a 1:1
transformer.
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 a 49.9-Ω
resistor to ground are inserted across R_IT on the
alternate input to balance the circuit. A split power
supply is used to ease the interface to common test
equipment, but the amplifier can be operated
single-supply as described in the applications section
with no impact on performance.
Table 1. Gain Component Values
GAIN
0 dB
6 dB
10 dB
14 dB
R_F
499 Ω
499 Ω
499 Ω
499 Ω
R_G
487 Ω
243 Ω
147 Ω
88.7 Ω
R_IT
53.6 Ω
57.6 Ω
63.4 Ω
71.5 Ω
Due to the voltage divider on the output formed by
the load component values, the amplifier's output is
attenuated in test. The column Atten in Table 2
shows the attenuation expected from the resistor
divider. When using a transformer at the output the
signal will have slightly more loss, and the numbers
will be approximate.
Frequency Response
The general circit shown in Figure 55 is modified as
shown in Figure 56, and is used to measure the
frequency response of the device.
A network analyzer is used as the signal source and
as the measurement device. The output impedance
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