LMH6401_16 Datasheet, PDF (17/48 Pages) Texas Instruments – LMH6401 DC to 4.5 GHz, Fully-Differential, Digital Variable-Gain Amplifier

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Setup Diagrams (continued)
LMH6401
SBOS730A – APRIL 2015 – REVISED MAY 2015
50
Agilent E4443A
with 50-Ÿ2XWSXWV
346B
Noise Source
LMH6401EVM
VS+
ZO = 50 Ÿ, 1:2
0º
180º
BAL-0010
LMH6401
INP
INM
PD
10
OUTP ⁴⁰
+
-
OUT_AMP
10
OUTM ₄₀
VOCM
SPI
VS-
USB
GND
2:1, ZO = 50 Ÿ
+
-
OUT_LOAD
0º
180º
BAL-0010
Figure 46. Noise Figure Test Setup
50
Agilent E4443A
with 50-Ÿ,QSXWV
8.2 Output Measurement Reference Points
The LMH6401 has two on-chip, 10-Ω output resistors. When matching the output to a 100-Ω load, the evaluation
module (EVM) uses an external 40-Ω resistor on each output leg to complete the output matching. Having on-
chip output resistors creates two potential reference points for measuring the output voltage. The first reference
point is at the internal amplifier output (OUT_AMP), and the second reference point is at the externally-matched
100-Ω load (OUT_LOAD). The measurements in the Electrical Characteristics table and in the Typical
Characteristics section are referred to the (OUT_AMP) reference point unless otherwise specified. The
conversion between reference points is a straightforward correction of 3 dB for power and 6 dB for voltage, as
shown in Equation 1 and Equation 2. The measurements are referenced to OUT_AMP when not specified.
VOUT_LOAD = (VOUT_AMP – 6 dB)
(1)
POUT_LOAD = (POUT_AMP – 3 dB)
(2)
8.3 ATE Testing and DC Measurements
All production testing and dc parameters are measured on automated test equipment capable of dc
measurements only. Some measurements (such as voltage gain) are referenced to the output of the internal
amplifier and do not include losses attributed to the on-chip output resistors. The Electrical Characteristics values
specify these conditions. When the measurement is referred to the amplifier output, the output resistors are not
included in the measurement. If the measurement is referred to the device pins, then the output resistor loss is
included in the measurement.
8.4 Frequency Response
This test is done by running an S-parameter sweep on a 4-port differential network analyzer using the standard
EVM with no baluns; see Figure 43. The inputs and outputs of the EVM are connected to the network analyzer
using 50-Ω coaxial cables with all the ports set to a characteristic impedance (Z_O) of 50 Ω.
The frequency response test with capacitive load is done by soldering the capacitor across the LMH6401 output
pins. In this configuration, the on-chip, 10-Ω resistors on each output leg isolate the capacitive load from the
amplifier output pins.
8.5 Distortion
The standard EVM is used for measuring both the single-tone harmonic distortion and two-tone intermodulation
distortion; see Figure 44 and Figure 45, respectively. The distortion is measured with differential input signals to
the LMH6401. In order to interface with single-ended test equipment, external baluns (1:2, Z_O = 50 Ω) are
required between the EVM output ports and the test equipment. The Typical Characteristics plots are created
with Marki™ baluns, model number BAL-0010. These baluns are used to combine two single tones in the two-
tone test plots as well as convert the single-ended input to differential output for harmonic distortion tests. The
use of 6-dB attenuator pads on both the inputs and outputs is recommended to provide a balanced match
between the external balun and the EVM.
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