NSC LMH2110 Evaluation board is designed to help the evaluation Datasheet

National Semiconductor
Application Note 2014
Gerrit de Wagt and Jaimy de Koning
May 4, 2010
General Description
tercept only, reducing calibration effort significantly. The device operates with a single supply from 2.7V to 5V. The
LMH2110 has an RF power detection range from -40 dBm to
5 dBm and is ideally suited for use in combination with a directional coupler. Alternatively a resistive divider can be used
as well.
The device is active for EN = High, otherwise it is in a low
power consumption shutdown mode. To save power and prevent discharge of an external filter capacitance, the output
(OUT) is high-impedance during shutdown.
The LMH2110 power detector is offered in a tiny 6-bump microSMD package.
Figure 1 shows the LMH2110 Evaluation Board.
The evaluation board is designed to help the evaluation of the
LMH2110, which is a 45 dB Logarithmic RMS power detector
particularly suited for accurate power measurement of modulated RF signals that exhibit large peak-to-average ratios,
i.e. large variations of the signal envelope. Such signals are
encountered in W-CDMA and LTE cell phones. The RMS
measurement topology inherently ensures a modulation insensitive measurement.
The device has an RF frequency range from 50 MHz to 8 GHz.
It provides an accurate, temperature and supply insensitive,
output voltage that relates linearly to the RF input power in
dBm. The LMH2110's excellent conformance to a logarithmic
response enables an easy integration by using slope and in-
LMH2110 Evaluation Board
LMH2110 Evaluation Board
30109716
FIGURE 1. LMH2110 Evaluation Board
Basic Operation
The circuit operates with a single supply form 2.7V to 5V and
has an RF power detection range from −40 dBm to 5 dBm.
The board consist of a single LMH2110 along with external
components soldered on a printed circuit board. External sup-
ply voltages and input signals can be applied to the on-board
connectors. The supply voltage is applied with connectors
P21 (VDD) and P22 (GND). The RF input signal is applied by
SMA connector P1. This RF signal is applied through an RF
generator and is connected with a 50Ω SMA cable. The detector output can be measured via BNC connector P3.
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301097
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To guarantee a correct operation a voltage divider formed by
R2 and R3 is present on the evaluation board. The absolute
maximum ratings are also exceeded when the enable (EN) is
switched to HIGH (from shutdown to active mode) while the
supply voltage is switched off. This situation should be prevented at all times. A solution to protect the device is the
resistor R1 of 1 kΩ in series with the enable input to limit the
current.
An overview of the various jumper positions on the board is
given in Figure 2. The settings of these jumpers and their
functions are listed in Table 1.
Configuration
The LMH2110 evaluation board can be configured via jumper
settings. The device is active when EN = High. This can be
accomplished by setting the jumper J4 to VDD or by using
external control on P4 by setting the jumper J4 to EN. Since
the device has an internal operating voltage of 2.5V, the voltage level on the enable should not be higher than 3V to
prevent damage to the device. Also enable voltage levels
lower than 400 mV below GND should be prevented. In both
cases the ESD devices start to conduct when the enable voltage range is exceeded and excessive current will be drawn.
30109710
FIGURE 2. Jumper Positions
TABLE 1. Jumper and Header Overview
Bold face jumper settings refer to the factory default configuration.
Jumper
J4
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Function
Enable
Jumper
Position
Description
1–2
Active, Connects Enable Pin to VDD
3–4
External Control, Connects Enable Pin to Enable P4
5-6
Shutdown, Connects Enable Pin to GND
2
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Measurement Setup
The performance of the LMH2110 can be measured with the
setup shown in Figure 3.
30109712
FIGURE 3. Measurement Setup
An external power supply provides a voltage of 2.7V to 5V to
the evaluation board. An accurate and stable RF Signal Generator is used to produce the test signal. It is recommended
to use low loss cables to ensure reliable measurement data.
The detected output voltage can be measured with a Digital
Voltage Meter (DVM).
Figure 4 depicts the output voltage versus frequency for various power levels on RFIN. The frequency range is from 10
MHz to 10 GHz. Figure 5 depicts the output voltage versus
RF input power for various frequencies.
30109709
FIGURE 5. Output Voltage vs. RF Input Power
30109708
FIGURE 4. Output Voltage vs. Freqency
3
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Schematic
30109705
FIGURE 6. Evaluation Board Schematic
Bill of Material
TP1
Test Point
GND
The Bill of Material (BOM) of the evaluation board is given in
Table 2.
U1
µSMD
LMH2110TM
Board Layout
TABLE 2. Bill of Material
Designator
Description
Comment
C1, C2
0603 Capacitor
10 nF
C3, C4, C6
0603 Capacitor
10 pF
C5
0603 Capacitor
1 pF
C7
0603 Capacitor
10 µF
J4
Header
2x3
P1
Connector
SMA
P21, P22
Connector
Banana
P3
Connector
BNC
P4
Connector
BNC
R1
0603 Resisitor
1 kΩ
R2, R3
0603 Resistor
100 kΩ
R4
0603 Resisitor
0Ω
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As with any other RF device, careful attention must me paid
to the board layout. If the board layout isn’t properly designed,
performance might be less than can be expected for the application. The LMH2110 is designed to be used in RF applications, having a characteristic impedance of 50Ω. To
achieve this impedance, the input of the LMH2110 needs to
be connected via a 50Ω transmission line. Transmission lines
can be created on PCBs using microstrip or (grounded) coplanar waveguide (GCPW) configurations. In order to minimize
injection of RF interference into the LMH2110 through the
supply lines, the PCB traces for VDD and GND should be
minimized for RF signals. This can be done by placing a small
decoupling capacitor between the VDD and GND. It should
be placed as close as possible to the VDD and GND pins of
the LMH2110.
Figure 7 shows the component locations of the LMH2110
evaluation board and Figure 8 shows the board layout of the
LMH2110 evaluation board.
4
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LMH2110 Evaluation Board
30109711
FIGURE 7. Component Locations of Evaluation Board
30109715
FIGURE 8. Board Layout of Evaluation Board
5
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LMH2110 Evaluation Board
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