LMV225/LMV226/LMV228
RF Power Detector for CDMA and WCDMA
General Description
The LMV225/LMV226/LMV228 are 30 dB RF power detec-
tors intended for use in CDMA and WCDMA applications.
The device has an RF frequency range from 450 MHz to 2
GHz. It provides an accurate temperature and supply com-
pensated output voltage that relates linearly to the RF input
power in dBm. The circuit operates with a single supply from
2.7V to 5.5V. The LMV225/LMV226/LMV228 have an inte-
grated filter for low-ripple average power detection of CDMA
signals with 30 dB dynamic range. Additional filtering can be
applied using a single external capacitor.
The LMV225 has an RF power detection range from –30
dBm to 0 dBm and is ideally suited for direct use in combi-
nation with resistive taps. The LMV226/LMV228 have a de-
tection range from –15 dBm to 15 dBm and are intended for
use in combination with a directional coupler. The LMV226 is
equipped with a buffered output which makes it suitable for
GSM, EDGE, GPRS and TDMA applications.
The device is active for Enable = HI, otherwise it is in a low
power consumption shutdown mode. During shutdown the
output will be LOW. The output voltage ranges from 0.2V to
2V and can be scaled down to meet ADC input range re-
quirements.
The LMV225/LMV226/LMV228 power detectors are offered
in the thin 1.0 mm x 1.0 mm x 0.6 mm micro SMD package
and the ultra thin 1.0 mm x 1.0 mm x 0.35 mm micro SMD
package. The LMV225 and the LMV228 are also offered in
the 2.2 mm x 2.5 mm x 0.8 mm LLP package.
Features
n30 dB linear in dB power detection range
nOutput voltage range 0.2 to 2V
nLogic low shutdown
nMulti-band operation from 450 MHz to 2000 MHz
nAccurate temperature compensation
nPackages:
— micro SMD thin 1.0 mm x 1.0 mm x 0.6 mm
— micro SMD ultra thin 1.0 mm x 1.0 mm x 0.35 mm
— LLP 2.2 mm x 2.5 mm x 0.8 mm
(LMV225 and LMV228)
Applications
nCDMA RF power control
nWCDMA RF power control
nCDMA2000 RF power control
nPA modules
Typical Application
LMV225
20076001
LMV226/LMV228
20076046
October 2006
LMV225/LMV226/LMV228 RF Power Detector for CDMA and WCDMA
© 2006 National Semiconductor Corporation DS200760 www.national.com
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage
V
DD
- GND 6.0V Max
ESD Tolerance (Note 2)
Human Body Model 2000V
Machine Model 200V
Storage Temperature Range −65˚C to 150˚C
Junction Temperature (Note 3) 150˚C Max
Mounting Temperature, Infrared or convection (20 sec)
Tin/Lead 235˚C
Lead-Free 260˚C
Operating Ratings (Note 1)
Supply Voltage 2.7V to 5.5V
Temperature Range −40˚C to +85˚C
RF Frequency Range 450 MHz to 2 GHz
2.7 DC and AC Electrical Characteristics
Unless otherwise specified, all limits are guaranteed to V
DD
= 2.7V; T
J
= 25˚C. Boldface limits apply at temperature extremes.
(Note 4)
Symbol Parameter Condition Min Typ Max Units
I
DD
Supply Current Active Mode: RF
IN
/E
N
=
V
DD
(DC), No RF Input
Power Present
LMV225 4.8 7
8
mA
LMV226 4.9 6.2
8
LMV228 4.9 6.2
8
Shutdown: RF
IN
/E
N
= GND (DC), No RF
Input Power Present
0.44 4.5 µA
V
LOW
E
N
Logic Low Input Level
(Note 6)
0.8 V
V
HIGH
E
N
Logic High Input Level
(Note 6)
1.8 V
t
on
Turn-on-Time (Note 9) No RF Input Power
Present, Output Loaded
with 10 pF
LMV225 2.1
µsLMV226 1.2
LMV228 1.7
t
r
Rise Time (Note 7) Step from no Power to
0 dBm Applied, Output
Loaded with 10 pF
LMV225 4.5
µs
Step from no Power to
15 dBm Applied, Output
Loaded with 10 pF
LMV226 1.8
LMV228 4.8
I
EN
Current into RF
IN
/E
N
Pin 1µA
P
IN
Input Power Range (Note 5) LMV225 −30
0
dBm
−43
−13
dBV
LMV226 −15
15
dBm
−28
2
dBV
LMV228 −15
15
dBm
−28
2
dBV
LMV225/LMV226/LMV228
www.national.com 2
2.7 DC and AC Electrical Characteristics (Continued)
Unless otherwise specified, all limits are guaranteed to V
DD
= 2.7V; T
J
= 25˚C. Boldface limits apply at temperature extremes.
(Note 4)
Symbol Parameter Condition Min Typ Max Units
Logarithmic Slope (Note 8) 900 MHz LMV225 44.0
mV/dB
LMV226 44.5
LMV228 uSMD 44.0
LMV228 LLP 48.5
1800 MHz LMV225 39.4
LMV226 41.6
LMV228 uSMD 41.9
LMV228 LLP 47.4
1900 MHz LMV225 38.5
LMV226 41.2
LMV228 uSMD 41.6
LMV228 LLP 46.6
2000 MHz LMV225 38.5
LMV226 41.0
LMV228 uSMD 41.2
LMV228 LLP 45.4
Logarithmic Intercept (Note 8) 900 MHz LMV225 −45.5
dBm
LMV226 −24.5
LMV228 uSMD −27.2
LMV228 LLP −23.7
1800 MHz LMV225 −46.6
LMV226 −25.1
LMV228 uSMD −28.2
LMV228 LLP −23.8
1900 MHz LMV225 −46.3
LMV226 −24.9
LMV228 uSMD −28.0
LMV228 LLP −23.7
2000 MHz LMV225 −46.7
LMV226 −24.7
LMV228 uSMD −28.0
LMV228 LLP -23.6
V
OUT
Output Voltage No RF Input Power
Present
LMV225 214 350
mVLMV226 223 350
LMV228 228 350
I
OUT
Output Current
Sourcing/Sinking
LMV226 Only 4.5 5.3 mA
R
OUT
Output Impedance LMV225/LMV228 only, no RF Input Power
Present
19.8 29
34
kΩ
e
n
Output Referred Noise RF Input = 1800 MHz, −10 dBm for
LMV225 and 5 dBm for LMV226/LMV228,
Measured at 10 kHz
700
nV/
LMV225/LMV226/LMV228
www.national.com3
2.7 DC and AC Electrical Characteristics (Continued)
Unless otherwise specified, all limits are guaranteed to V
DD
= 2.7V; T
J
= 25˚C. Boldface limits apply at temperature extremes.
(Note 4)
Symbol Parameter Condition Min Typ Max Units
Variation Due to Temperature 900 MHz, RF
IN
= 0 dBm
Referred to 25˚C
LMV225 +0.64
−1.07
dB
900 MHz, RF
IN
=15dBm
Referred to 25˚C
LMV226 +0.05
−0.02
LMV228 uSMD +0.22
−0.36
LMV228 LLP +0.87
−0.87
1800 MHz, RF
IN
= 0 dBm
Referred to 25˚C
LMV225 +0.09
−0.86
1800 MHz, RF
IN
=15dBm
Referred to 25˚C
LMV226 +0.07
−0.10
LMV228 uSMD +0.29
−0.57
LMV228 LLP +1.04
−1.23
1900 MHz, RF
IN
= 0 dBm
Referred to 25˚C
LMV225 +0
−0.69
1900 MHz, RF
IN
=15dBm
Referred to 25˚C
LMV226 +0
−0.10
LMV228 uSMD +0.23
−0.64
LMV228 LLP +1.05
−1.45
2000 MHz, RF
IN
= 0 dBm
Referred to 25˚C
LMV225 +0
−0.86
2000 MHz, RF
IN
=15dBm
Referred to 25˚C
LMV226 +0
−0.29
LMV228 uSMD +0.27
−0.65
LMV228 LLP +1.04
−2.02
5.0 DC and AC Electrical Characteristics
Unless otherwise specified, all limits are guaranteed to V
DD
= 5.0V; T
J
= 25˚C. Boldface limits apply at temperature extremes.
(Note 4)
Symbol Parameter Condition Min Typ Max Units
I
DD
Supply Current Active Mode: RF
IN
/E
N
=
V
DD
(DC), no RF Input
Power Present.
LMV225 5.3 7.5
9
mA
LMV226 5.3 6.8
9
LMV228 5.4 6.8
9
Shutdown: RF
IN
/E
N
= GND (DC), no RF
Input Power Present.
0.32 4.5 µA
V
LOW
E
N
Logic Low Input Level
(Note 6)
0.8 V
V
HIGH
E
N
Logic High Input Level
(Note 6)
1.8 V
LMV225/LMV226/LMV228
www.national.com 4
5.0 DC and AC Electrical Characteristics (Continued)
Unless otherwise specified, all limits are guaranteed to V
DD
= 5.0V; T
J
= 25˚C. Boldface limits apply at temperature extremes.
(Note 4)
Symbol Parameter Condition Min Typ Max Units
t
on
Turn-on-Time (Note 9) No RF Input Power
Present, Output Loaded
with 10 pF
LMV225 2.1
µsLMV226 1.0
LMV228 1.7
t
r
Rise Time (Note 7) Step from no Power to
0 dBm Applied, Output
Loaded with 10 pF
LMV225 4.5
µs
Step from no Power to
15 dBm Applied, Output
Loaded with 10 pF
LMV226 1.4
LMV228 4.8
I
EN
Current Into RF
IN
/E
N
Pin 1µA
P
IN
Input Power Range (Note 5) LMV225 −30
0
dBm
−43
−13
dBV
LMV226 −15
15
dBm
−28
2
dBV
LMV228 −15
15
dBm
−28
2
dBV
Logarithmic Slope (Note 8) 900 MHz LMV225 44.6
mV/dB
LMV226 44.6
LMV228 uSMD 44.2
LMV228 LLP 48.4
1800 MHz LMV225 40.6
LMV226 42.2
LMV228 uSMD 42.4
LMV228 LLP 48.3
1900 MHz LMV225 39.6
LMV226 41.8
LMV228 uSMD 42.2
LMV228 LLP 47.8
2000 MHz LMV225 39.7
LMV226 41.6
LMV228 uSMD 41.8
LMV228 LLP 47.2
LMV225/LMV226/LMV228
www.national.com5
5.0 DC and AC Electrical Characteristics (Continued)
Unless otherwise specified, all limits are guaranteed to V
DD
= 5.0V; T
J
= 25˚C. Boldface limits apply at temperature extremes.
(Note 4)
Symbol Parameter Condition Min Typ Max Units
Logarithmic Intercept (Note 8) 900 MHz LMV225 −47.0
dBm
LMV226 −25.0
LMV228 uSMD −27.7
LMV228 LLP −23.9
1800 MHz LMV225 −48.5
LMV226 −25.7
LMV228 uSMD −28.9
LMV228 LLP −23.6
1900 MHz LMV225 −48.2
LMV226 −25.6
LMV228 uSMD −28.7
LMV228 LLP −23.1
2000 MHz LMV225 −48.9
LMV226 −25.5
LMV228 uSMD −28.7
LMV228 LLP −23.0
V
OUT
Output Voltage No RF Input Power
Present
LMV225 222 400
mVLMV226 231 400
LMV228 244 400
I
OUT
Output Current
Sourcing/Sinking
LMV226 Only 4.5 5.3 mA
R
OUT
Output Impedance No RF Input Power Present 23.7 29
31
kΩ
e
n
Output Referred Noise RF Input = 1800 MHz, −10 dBm for
LMV225 and 5 dBm for LMV226/LMV228,
Measured at 10 kHz
700 nV/
LMV225/LMV226/LMV228
www.national.com 6
5.0 DC and AC Electrical Characteristics (Continued)
Unless otherwise specified, all limits are guaranteed to V
DD
= 5.0V; T
J
= 25˚C. Boldface limits apply at temperature extremes.
(Note 4)
Symbol Parameter Condition Min Typ Max Units
Variation Due to Temperature 900 MHz, RF
IN
= 0 dBm
Referred to 25˚C
LMV225 +0.89
−1.16
dB
900 MHz, RF
IN
=15dBm
Referred to 25˚C
LMV226 +0.25
−0.16
LMV228 uSMD +0.46
−0.62
LMV228 LLP +1.39
−1.19
1800 MHz, RF
IN
= 0 dBm
Referred to 25˚C
LMV225 +0.3
−0.82
1800 MHz, RF
IN
=15dBm
Referred to 25˚C
LMV226 +0.21
−0.09
LMV228 uSMD +0.55
−0.78
LMV228 LLP +1.39
−1.43
1900 MHz, RF
IN
= 0 dBm
Referred to 25˚C
LMV225 +0.34
−0.63
1900 MHz, RF
IN
=15dBm
Referred to 25˚C
LMV226 +0.21
−0.19
LMV228 uSMD +0.55
−0.93
LMV228 LLP +1.54
−1.64
2000 MHz, RF
IN
= 0 dBm
Referred to 25˚C
LMV225 +0.22
−0.75
2000 MHz RF
IN
=15dBm
Referred to 25˚C
LMV226 +0.25
−0.34
LMV228 uSMD +0.61−
0.91
LMV228 LLP +0.89
−0.99
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.
Note 2: Human body model: 1.5 kΩin series with 100 pF. Machine model, 0Ωin series with 100 pF.
Note 3: The maximum power dissipation is a function of TJ(MAX) ,θJA and TA. The maximum allowable power dissipation at any ambient temperature is PD=
(TJ(MAX) -T
A)/θJA. All numbers apply for packages soldered directly into a PC board
Note 4: Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating of
the device such that TJ=T
A. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ>TA.
Note 5: Power in dBV = dBm + 13 when the impedance is 50Ω.
Note 6: All limits are guaranteed by design or statistical analysis
Note 7: Typical values represent the most likely parametric norm.
Note 8: Device is set in active mode with a 10 kΩresistor from VDD to RFIN/EN. RF signal is applied using a 50ΩRF signal generator AC coupled to the RFIN/EN
pin using a 100 pF coupling capacitor.
Note 9: Turn-on time is measured by connecting a 10 kΩresistor to the RFIN/ENpin. Be aware that in the actual application on the front page, the RC-time constant
of resistor R2and capacitor C adds an additional delay.
LMV225/LMV226/LMV228
www.national.com7
Connection Diagrams
4-Bump micro SMD 6-pin LLP
20076002
Top View
20076063
Top View
Pin Descriptions
Pin Name Description
micro SMD LLP6
Power Supply A2 4 V
DD
Positive Supply Voltage
B1 1 GND Power Ground
A1 3 RF
IN
/E
N
DC voltage determines enable state of the device (HIGH = device
active). AC voltage is the RF input signal to the detector (beyond 450
MHz). The RF
IN
/E
N
pin is internally terminated with 50Ωin series with
45 pF.
Output B2 6 Out Ground referenced detector output voltage (linear in dBm)
Ordering Information
Package Part Number Package
Marking
Transport Media NSC Drawing
4-Bump micro SMD
LMV225TL I250 Units Tape and Reel TLA04AAA
0.6 mm thick
LMV225TLX 3k Units Tape and Reel
LMV225UR I 250 Units Tape and Reel URA04AAA
0.35 mm thick
LMV225URX I 3k Units Tape and Reel
6-pin LLP LMV225SD A90 1k Units Tape and Reel SDB06A
LMV225SDX 4.5k Units Tape and Reel
4-Bump micro SMD
LMV226TL I250 Units Tape and Reel TLA04AAA
0.6 mm thick
LMV226TLX 3k Units Tape and Reel
LMV226UR I250 Units Tape and Reel URA04AAA
0.35 mm thick
LMV226URX 3k Units Tape and Reel
4-Bump micro SMD
LMV228TL I250 Units Tape and Reel TLA04AAA
0.6 mm thick
LMV228TLX 3k Units Tape and Reel
LMV228UR I250 Units Tape and Reel URA04AAA
0.35 mm thick
LMV228URX 3k Units Tape and Reel
6-pin LLP LMV228SD A89 1k Units Tape and Reel SDB06A
LMV228SDX 4.5k Units Tape and Reel
Note: TL and TLX products are offered both with leaded and lead free bumps.
UR and URX products are offered with lead free bumps.
LMV225/LMV226/LMV228
www.national.com 8
Block Diagrams
20076064
LMV225
20076049
LMV226
20076047
LMV228
LMV225/LMV226/LMV228
www.national.com9
Typical Performance Characteristics LMV225
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C.
Supply Current vs. Supply Voltage (LMV225) Output Voltage vs. RF Input Power (LMV225)
20076004 20076005
Output Voltage and Log Conformance vs.
RF Input Power @900 MHz (LMV225)
Output Voltage and Log Conformance vs.
RF Input Power @1800 MHz (LMV225)
20076006 20076007
Output Voltage and Log Conformance vs.
RF Input Power @1900 MHz (LMV225)
Output Voltage and Log Conformance vs.
RF Input Power @2000 MHz (LMV225)
20076008 20076009
LMV225/LMV226/LMV228
www.national.com 10
Typical Performance Characteristics LMV225
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C. (Continued)
Logarithmic Slope vs. Frequency (LMV225) Logarithmic Intercept vs. Frequency (LMV225)
20076010 20076011
Output Variation vs. RF Input Power
Normalized to 25˚C @900 MHz (LMV225)
Output Variation vs. RF Input Power
Normalized to 25˚C @1800 MHz (LMV225)
20076012 20076013
Output Variation vs. RF Input Power
Normalized to 25˚C @1900 MHz (LMV225)
Output Variation vs. RF Input Power
Normalized to 25˚C @2000 MHz (LMV225)
20076014 20076015
LMV225/LMV226/LMV228
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Typical Performance Characteristics LMV225
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C. (Continued)
PSRR vs. Frequency
(LMV225 in microSMD)
PSRR vs. Frequency
(LMV225 in LLP)
20076023 20076065
RF Input Impedance vs. Frequency @Resistance and
Reactance (LMV225 in micro SMD)
RF Input Impedance vs. Frequency @Resistance and
Reactance (LMV225 in LLP)
20076024 20076066
LMV225/LMV226/LMV228
www.national.com 12
Typical Performance Characteristics LMV226
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C.
Supply Current vs. Supply Voltage (LMV226) Output Voltage vs. RF Input Power (LMV226)
20076051 20076052
Output Voltage and Log Conformance vs.
RF Input Power @900 MHz (LMV226)
Output Voltage and Log Conformance vs.
RF Input Power @1800 MHz (LMV226)
20076053 20076054
Output Voltage and Log Conformance vs.
RF Input Power @1900 MHz (LMV226)
Output Voltage and Log Conformance vs.
RF Input Power @2000 MHz (LMV226)
20076055 20076056
LMV225/LMV226/LMV228
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Typical Performance Characteristics LMV226
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C. (Continued)
Logarithmic Slope vs. Frequency (LMV226) Logarithmic Intercept vs. Frequency (LMV226)
20076057 20076058
Output Variation vs. RF Input Power
Normalized to 25˚C @900 MHz (LMV226)
Output Variation vs. RF Input Power
Normalized to 25˚C @1800 MHz (LMV226)
20076059 20076060
Output Variation vs. RF Input Power
Normalized to 25˚C @1900 MHz (LMV226)
Output Variation vs. RF Input Power
Normalized to 25˚C @2000 MHz (LMV226)
20076061 20076062
LMV225/LMV226/LMV228
www.national.com 14
Typical Performance Characteristics LMV226
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C. (Continued)
PSRR vs. Frequency
(LMV226)
RF Input Impedance vs. Frequency @Resistance and
Reactance (LMV226)
20076023 20076024
LMV225/LMV226/LMV228
www.national.com15
Typical Performance Characteristics LMV228 in microSMD
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C.
Supply Current vs. Supply Voltage
(LMV228 in microSMD)
Output Voltage vs. RF Input Power
(LMV228 in microSMD)
20076034 20076035
Output Voltage and Log Conformance vs.
RF Input Power @900 MHz (LMV228 in microSMD)
Output Voltage and Log Conformance vs.
RF Input Power @1800 MHz (LMV228 in microSMD)
20076036 20076037
Output Voltage and Log Conformance vs.
RF Input Power @1900 MHz (LMV228 in microSMD)
Output Voltage and Log Conformance vs.
RF Input Power @2000 MHz (LMV228 in microSMD)
20076038 20076039
LMV225/LMV226/LMV228
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Typical Performance Characteristics LMV228 in microSMD
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C. (Continued)
Logarithmic Slope vs. Frequency (LMV228 in microSMD)
Logarithmic Intercept vs. Frequency (LMV228 in
microSMD)
20076040 20076041
Output Variation vs. RF Input Power Normalized to 25˚C
@900 MHz (LMV228 in microSMD)
Output Variation vs. RF Input Power Normalized to 25˚C
@1800 MHz (LMV228 in microSMD)
20076042 20076043
Output Variation vs. RF Input Power Normalized to 25˚C
@1900 MHz (LMV228 in microSMD)
Output Variation vs. RF Input Power Normalized to 25˚C
@2000 MHz (LMV228 in microSMD)
20076044 20076045
LMV225/LMV226/LMV228
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Typical Performance Characteristics LMV228 in microSMD
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C. (Continued)
PSRR vs. Frequency
(LMV228 in microSMD)
RF Input Impedance vs. Frequency @Resistance and
Reactance (LMV228 in microSMD)
20076023 20076024
LMV225/LMV226/LMV228
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Typical Performance Characteristics LMV228 in LLP
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C.
Supply Current vs. Supply Voltage (LMV228 in LLP) Output Voltage vs. RF Input Power (LMV228 in LLP)
20076034 20076070
Output Voltage and Log Conformance vs.
RF Input Power @900 MHz (LMV228 inLLP)
Output Voltage and Log Conformance vs.
RF Input Power @1800 MHz (LMV228 in LLP)
20076071 20076072
Output Voltage and Log Conformance vs.
RF Input Power @1900 MHz (LMV228 in LLP)
Output Voltage and Log Conformance vs.
RF Input Power @2000 MHz (LMV228 in LLP)
20076073 20076074
LMV225/LMV226/LMV228
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Typical Performance Characteristics LMV228 in LLP
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C. (Continued)
Logarithmic Slope vs. Frequency (LMV228 in LLP) Logarithmic Intercept vs. Frequency (LMV228 in LLP)
20076079 20076080
Output Variation vs. RF Input Power Normalized to 25˚C
@900 MHz (LMV228 in LLP)
Output Variation vs. RF Input Power Normalized to 25˚C
@1800 MHz (LMV228 in LLP)
20076076 20076077
Output Variation vs. RF Input Power Normalized to 25˚C
@1900 MHz (LMV228 in LLP)
Output Variation vs. RF Input Power Normalized to 25˚C
@2000 MHz (LMV228 in LLP)
20076078 20076075
LMV225/LMV226/LMV228
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Typical Performance Characteristics LMV228 in LLP
Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C. (Continued)
PSRR vs. Frequency
(LMV228 in LLP)
RF Input Impedance vs. Frequency @Resistance and
Reactance (LMV228 in LLP)
20076065 20076066
LMV225/LMV226/LMV228
www.national.com21
Application Notes
CONFIGURING A TYPICAL APPLICATION
The LMV225/LMV226/LMV228 are power detectors in-
tended for CDMA and WCDMA applications. Power applied
at its input translates to a DC voltage on the output through
a linear-in-dB response. The LMV225 detector is especially
suited for power measurements via a high-resistive tap,
while the LMV226/LMV228 are designed to be used in com-
bination with a directional coupler. The LMV226 has an
additional output voltage buffer and therefore a low output
impedance. The key features of the devices are shown in
table 1.
TABLE 1. DEVICE CHARACTERISTICS
Input Range
(dBm)
Output
Buffer
Application
LMV225 −30 / 0 No High Resistive Tap
LMV226 −15 / 15 Yes Directional Coupler
LMV228 −15 / 15 No Directional Coupler
In order to match the output power range of the power
amplifier (PA) with the range of the LMV225’s input, the high
resistive tap needs to be configured correctly. In case of the
LMV226/LMV228 the coupling factor of the directional cou-
pler needs to be chosen correctly.
HIGH RESISTIVE TAP APPLICATION
The constant input impedance of the device enables the
realization of a frequency independent input attenuation to
adjust the LMV225’s range to the range of the PA. Resistor
R
1
and the 50Ωinput resistance (R
IN
) of the device realize
this attenuation (Figure 1). To minimize insertion loss, resis-
tor R
1
needs to be sufficiently large. The following example
demonstrates how to determine the proper value for R
1
.
Suppose the useful output power of the PA ranges up to +31
dBm. As the LMV225 can handle input power levels up to 0
dBm. R
1
should realize a minimum attenuation of 31-0=31
dB. The attenuation realized by R
1
and the effective input
resistance R
IN
of the detector equals:
(1)
Solving this expression for R
1
, using that R
IN
=50Ω, yields:
(2)
In Figure 1,R
1
is set to 1800Ωresulting in an attenuation of
31.4 dB
DIRECTIONAL COUPLER APPLICATION
The LMV226/LMV228 also has a 50Ωinput resistance. How-
ever, its input range differs compared to the LMV225, i.e.
−15 dBm to +15 dBm. If a typical attenuation of a directional
coupler is 20 dB, the LMV226/LMV228 can be directly con-
nected via the directional coupler to the PA without the need
of additional external attenuator (Figure 2). Different PA
ranges can be configured using couplers with other coupling
factors.
SHUTDOWN FUNCTIONALITY
The LMV225/LMV226/LMV228 RF
IN
/E
N
pins have 2 func-
tions combined:
•Enable/Shutdown
•Power input
The capacitor C and the resistor R
2
(Figure 1 and Figure 2)
separate the DC shutdown functionality from the AC power
measurement. The device is active when Enable = HI, oth-
erwise it is in a low power consumption shutdown mode.
During shutdown the output will be LOW.
Capacitor C should be chosen sufficiently large to ensure a
corner frequency far below the lowest input frequency to be
measured. In case of the LMV225 the corner frequency can
be calculated using:
(3)
Where R
IN
=50Ω,C
IN
= 45 pF typical.
With R
1
= 1800Ωand C = 100 pF, this results in a corner
frequency of 2.8 MHz. This corner frequency is an indicative
20076033
FIGURE 1. Typical LMV225 Application with High
Resistive Tap
20076046
FIGURE 2. Typical LMV226/LMV228 Application with
Directional Coupler
LMV225/LMV226/LMV228
www.national.com 22
Application Notes (Continued)
number. The goal is to have a magnitude transfer, which is
sufficiently flat in the used frequency range; capacitor C
should be chosen significantly larger than capacitor C
IN
to
assure a proper performance of the high resistive tap. Ca-
pacitor C shouldn’t be chosen excessively large since the
RC-time, it introduces in combination with resistor R
2
, adds
to the turn-on time of the device.
The LMV226/LMV228 do not use a resistor R
1
like the
LMV225. Though a resistor is seen on the coupler side
(R
COUPLER
). Therefore a similar equation holds for the
LMV226/LMV228 LF corner frequency, where R
1
is replaced
with the coupler output impedance (R
COUPLER
).
With R
COUPLER
=50Ωand C = 100 pF, the resulting corner
frequency is 50 MHz.
The output voltage is proportional to the logarithm of the
input power, often called “linear-in-dB”. Figure 3 shows the
typical output voltage versus PA output power of the LMV225
setup as depicted in Figure 1.
OUTPUT RIPPLE DUE TO AM MODULATION
A CDMA modulated carrier wave generally contains some
amplitude modulation that might disturb the RF power mea-
surement used for controlling the PA. This section explains
the relation between amplitude modulation in the RF signal
and the ripple on the output of the LMV225/LMV228. Expres-
sions are provided to estimate this ripple on the output. The
ripple can be further reduced by lowpass filtering at the
output. This is realized by connecting an capacitor from the
output of the LMV225/LMV228 to ground.
Estimating Output Ripple
The CDMA modulated RF input signal of Figure 3 can be
described as:
V
IN
(t)=V
IN
[1 + µ(t)] cos (2 · π·f·t) (4)
In which V
IN
is the amplitude of the carrier frequency and the
amplitude modulation µ(t) can be between -1 and 1.
The ripple observed at the output of the detector equals the
detectors response to the power variation at the input due to
AM modulation (Figure 4). This signal has a maximum am-
plitude V
IN
•(1+µ) and a minimum amplitude V
IN
•(1-µ),
where 1+µ can be maximum 2 and 1-µ can be minimum 0.
The amplitude of the ripple can be described with the for-
mula:
(5)
where V
Y
is the slope of the detection curve (Figure 5) and µ
is the modulation index. Equation (5) can be reduced to:
(6)
Consequently, the ripple is independent of the average input
power of the RF input signal and only depends on the
logarithmic slope V
Y
and the ratio of the maximum and the
minimum input signal amplitude.
For CDMA, the ratio of the maximum and the minimum input
signal amplitude modulation is typically in the order of 5 to 6
dB, which is equivalent to a modulation index µ of 0.28 to
0.33.
A further understanding of the equation above can be
achieved via the knowledge that the output voltage V
OUT
of
the LMV225/LMV228 is linear in dB, or proportional to the
input power P
IN
in dBm. As discussed earlier, CDMA has a
modulation in the order of 5 to 6 dB. Since the transfer is
linear in dB, the output voltage V
OUT
will vary linearly over
about 5 to 6 dB in the curve (Figure 5).
20076016
FIGURE 3. Typical power detector response, V
OUT
vs.
PA output Power
20076017
FIGURE 4. AM Modulated RF Signal
LMV225/LMV226/LMV228
www.national.com23
Application Notes (Continued)
The output voltage variation ∆V
OUT
is thus identical for RF
input signals that fall within the linear range (in dB) of the
detector. In other words, the output variation is independent
of the absolute RF input signal:
∆V
O
=V
Y
·∆P
IN
(7)
In which V
Y
is the slope of the curve. The log-conformance
error is usually much smaller than the ripple due to AM
modulation. In case of the LMV225/LMV228, V
Y
=40mV/
dB. With ∆P
IN
= 5 dB for CDMA, ∆V
OUT
= 200 mV
PP
. This is
valid for all V
OUT
.
Output Ripple with Additional Filtering
The calculated result above is for an unfiltered configuration.
When a low pass filter is used by shunting a capacitor of e.g.
C
OUT
= 1.5 nF at the output of the LMV225/LMV228 to
ground, this ripple is further attenuated. The cut-off fre-
quency follows from:
(8)
With the output resistance of the LMV225/LMV228 R
O
=
19.8 kΩtypical and C
OUT
= 1.5 nF, the cut-off frequency
equals f
C
= 5.36 kHz. A 100 kHz AM signal then gets attenu-
ated by 5.36/100 or 25.4 dB. The remaining ripple will be
less than 20 mV. With a slope of 40 mV/dB this translates
into an error of less than ±0.5 dB. Since the LMV226 has a
low output impedance buffer, a capacitor to reduce the ripple
will not be effective.
Output Ripple Measurement
Figure 6 shows the ripple reduction that can be achieved by
adding additional capacitance at the output of the LMV225/
LMV228. The RF signal of 900 MHz is AM modulated with a
100 kHz sinewave and a modulation index of 0.3. The RF
input power is swept while the modulation index remains
unchanged. Without the output capacitor the ripple is about
200 mV
PP
. Connecting a capacitor of 1.5 nF at the output to
ground, results in a ripple of 12 mV
PP
. The attenuation with
a 1.5 nF capacitor is then 20 •log (200/12) = 24.4 dB. This
is very close to the calculated number of the previous para-
graph.
PRINCIPLE OF OPERATION
The logarithmic response of the LMV225/LMV226/LMV228
is implemented by a logarithmic amplifier as shown in Figure
7. The logarithmic amplifier consists of a number of cas-
caded linear gain cells. With these gain cells, a piecewise
approximation of the logarithmic function is constructed.
Every gain cell has a response according to Figure 8.Ata
certain threshold (E
K
), the gain cell starts to saturate, which
means that the gain drops to zero. The output of gain cell 1
is connected to the input of gain cell 2 and so on.
20076018
FIGURE 5. V
OUT
vs. RF Input Power P
IN
20076025
FIGURE 6. Output Ripple vs. RF Input Power
20076019
FIGURE 7. Logarithmic Amplifier
LMV225/LMV226/LMV228
www.national.com 24
Application Notes (Continued)
All gain cell outputs are AM-demodulated with a peak detec-
tor and summed together. This results in a logarithmic func-
tion. The logarithmic range is about:
20·n·log(A)
where,
n = number of gain cells
A = gain per gaincell
Figure 9 shows a logarithmic function on a linear scale and
the piecewise approximation of the logarithmic function.
Figure 10 shows a logarithmic function on a logarithmic
scale and the piecewise approximation of the logarithmic
function.
The maximum error for this approximation occurs at the
geometric mean of a gain section, which is e.g. for the third
segment:
(9)
The size of the error increases with distance between the
thresholds.
LAYOUT CONSIDERATIONS
For a proper functioning part a good board layout is neces-
sary. Special care should be taken for the series resistance
R
1
(Figure 1) that determines the attenuation. For high re-
sistor values the parasitic capacitance of the resistor may
significantly impact the realized attenuation. The effective
attenuation will be lower than intended. To reduce the para-
sitic capacitance across resistor R
1
, this resistor can be
composed of several components in series instead of using
a single component.
20076020
FIGURE 8. Gain Cell
20076021
FIGURE 9. Log-Function on Lin Scale
20076022
FIGURE 10. Log-Function on Log Scale
LMV225/LMV226/LMV228
www.national.com25
Physical Dimensions inches (millimeters) unless otherwise noted
NOTES: UNLESS OTHERWISE SPECIFIED
1. EPOXY COATING
2. FOR SOLDER BUMP COMPOSITION, SEE “SOLDER INFORMATION” IN THE PACKAGE SECTION OF THE NATIONAL SEMICONDUCTOR WEB PAGE
(www.national.com).
3. RECOMMEND NON-SOLDER MASK DEFINED LANDING PAD.
4. PIN A1 IS ESTABLISHED BY LOWER LEFT CORNER WITH RESPECT TO TEXT ORIENTATION.
5. XXX IN DRAWING NUMBER REPRESENTS PACKAGE SIZE VARIATION WHERE X1 IS PACKAGE WIDTH, X2 IS PACKAGE LENGTH AND X3 IS
PACKAGE HEIGHT.
6. REFERENCE JEDEC REGISTRATION MO-211, VARIATION BA.
4-Bump micro SMD
NS Package Number TLA04AAA
X1 = 1.014 ±0.030 mm X2 = 1.014 ±0.030 mm X3 = 0.600 ±0.075 mm
LMV225/LMV226/LMV228
www.national.com 26
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
NOTES: UNLESS OTHERWISE SPECIFIED
1. FOR SOLDER BUMP COMPOSITION, SEE “SOLDER INFORMATION” IN THE PACKAGE SECTION OF THE NATIONAL SEMICONDUCTOR WEB PAGE
(www.national.com).
2. RECOMMEND NON-SOLDER MASK DEFINED LANDING PAD.
3. PIN A1 IS ESTABLISHED BY LOWER LEFT CORNER WITH RESPECT TO TEXT ORIENTATION.
4. XXX IN DRAWING NUMBER REPRESENTS PACKAGE SIZE VARIATION WHERE X1 IS PACKAGE WIDTH, X2 IS PACKAGE LENGTH AND X3 IS
PACKAGE HEIGHT.
5. NO JEDEC REGISTRATION AS OF MAY 2005.
4-Bump micro SMD
NS Package Number URA04AAA
X1 = 0.975 ±0.030 mm X2 = 0.975 ±0.030 mm X3 = 0.350 ±0.075 mm
LMV225/LMV226/LMV228
www.national.com27
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
6-Pin LLP
NS Package Number SDB06A
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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LMV225/LMV226/LMV228 RF Power Detector for CDMA and WCDMA
