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Texas Instruments AN-1806 LMV232 Evaluation Board (Rev. A) User guides
User's Guide
SNWA009A – March 2008 – Revised April 2013
AN-1806 LMV232 Evaluation Board
1
General Description
This board, the LMV232TLEVAL, can be used to evaluate the Texas Instruments LMV232 dual-channel
mean square power detector. The LMV232 mean square power detector is particularly suited for accurate
power measurement of RF modulated signals that exhibit large peak to average ratios, that is, large
variations of the signal envelope. Such noise-like signals are encountered in applications such as CDMA
and wideband CDMA cellphones.
2
Basic Operation
The LMV232 power detector provides an accurate power measurement for arbitrary input signals, low and
high peak-to-average ratios and crest factors. This is because its operation is not based on peak
detection, but on direct determination of the mean square value. The single supply, ranging from 2.5V to
3.3V, can be applied through connectors P5 and P6 of the evaluation board. The device has two digital
interfaces. The signal connected to P3 (SD) puts the device in an active mode or a shutdown mode. When
SD = HIGH, the device is in shutdown, if SD = LOW the device is active. The signal connected to P4 (BS)
selects the active RF input signal. When BS = HIGH, RFIN1 is active (P1). When BS = LOW, RFIN2 is
active (P2). The output voltage is measured through connector P8. Connector P7 can be used to monitor
the voltage on the FB pin of the LMV232 when a 0Ω resistor is placed in R2. Further details can be found
in the Application Notes section of LMV232 Dual-Channel Integrated Mean Square Power Detector for
CDMA & WCDMA (SNWS017).
The LMV232 conversion gain and bandwidth can be configured by a resistor and a capacitor. Resistor R1
sets the conversion gain from RFIN to the output voltage. A higher resistor value will result in a higher
conversion gain. The maximum dynamic range is achieved when the resistor value is as high as possible,
i.e. the output signal just doesn’t clip and the voltage stays within the baseband ADC input range. The
filter bandwidth is adjusted by capacitor C4. The capacitor value should be chosen such that the response
time of the device is fast enough and modulation on the RF input signal is not visible at the output (ripple
suppression). The -3 dB filter bandwidth of the output filter is determined by the time constant R1*C4.
Generally a capacitor value of 1.5 nF is a good choice.
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SNWA009A – March 2008 – Revised April 2013
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AN-1806 LMV232 Evaluation Board
1
Schematics
3
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Schematics
The schematic of the evaluation board is shown in Figure 1.
VDD
R2
N/C
U1
P1
B3
RFIN1
RFIN1
RFIN2
P2
RFIN2
A1
A2
A3
C3
SD
VDD
C2
R1
6.2 k:
C4
1.5 nF
OUT
P8
OUT
B1
BS
GND
P3
J1
SD
R3
100 k:
C5
10 nF
P5
VDD
VDD
P4
FB
FB
LMV232
C1
P7
P6
+ C3
100 µF
GND
J2
U1 ± pin B3
C2
10 nF
U1 ± pin B1
BS
R4
100 k:
C1
10 nF
Figure 1. Schematic of the Evaluation Board
4
Bill of Materials
The bill of material (BOM) of the evaluation board is listed in Table 1.
Table 1. Bill of Materials of the Evaluation Board
2
Designator
Description
Comment
C1, C2, C5
0603 Capacitor
10 nF
C3
Case_C Capacitor
100 µF
C4
0603 Capacitor
1.5 nF
J1, J2
Header 1 × 3
For Jumper
P1, P2
Connector
SMA
P3, P4, P7, P8
Connector
BNC
P5, P6
Connector
Banana
R1
0603 Resistor
6.2 kΩ
R2
0603 Resistor
Not Connected
R3, R4
0603 Resistor
100 kΩ
U1
DSBGA
LMV232
AN-1806 LMV232 Evaluation Board
SNWA009A – March 2008 – Revised April 2013
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Copyright © 2008–2013, Texas Instruments Incorporated
Layout
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5
Layout
The layout of the evaluation board is shown in Figure 2.
All Layers
Silk Screen
Figure 2. Layout of the Evaluation Board
SNWA009A – March 2008 – Revised April 2013
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Copyright © 2008–2013, Texas Instruments Incorporated
AN-1806 LMV232 Evaluation Board
3
Measurement Procedure
6
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Measurement Procedure
The performance of the LMV232 can be measured with the setup given in Figure 3.
In this measurement example a supply voltage of 2.7V is applied by the power supply. The LMV232 is set
in active mode by connecting SD (P3) to GND, while RFIN1 is selected by connecting BS (P4) to 2.7V. Both
RFIN2 (P2) and FB (P7) can be left unconnected. The resulting DC output voltage is measured with a
multimeter connected to OUT (P8).
VDD
Power
Supply
VDD
BS
P4
RFIN1
RF Signal
Generator
RFIN2
P5
Evaluation Board
LMV232
P1
OUT
P8
Digital
Volt
Meter
FB
P7
P2
P3
SD
P6
GND
Figure 3. Measurement Setup
7
Measurement Results
Figure 4 and Figure 5 show the measurement results for the LMV232. The power is swept at 900 MHz for
different temperatures (Figure 4). The resulting error with respect to an ideal fitted curve is shown in
Figure 5.
Figure 4. VOUT - VPEDESTAL vs. RF Input Power
at 900 MHz
4
AN-1806 LMV232 Evaluation Board
Figure 5. Input Referred Error vs. RF Input Power
at 900 MHz
SNWA009A – March 2008 – Revised April 2013
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Copyright © 2008–2013, Texas Instruments Incorporated
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