LMV227
Production RF Tested, RF Power Detector for CDMA and
WCDMA
General Description
The LMV227 is a 30 dB RF power detector 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 compensated output volt-
age that relates linearly to the RF input power in dBm. The
circuit operates with a single supply from 2.7V to 5V. The
LMV227 has an integrated filter for low-ripple average power
detection of CDMA signals with 30 dB dynamic range. Addi-
tional filtering can be applied using a single external capaci-
tor.
The LMV227 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 device is active for Enable =
HI, otherwise it goes into a low power consumption shut-
down 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 requirements. The output
signal bandwidth can optionally be lowered externally as
well.
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
Applications
nCDMA RF power control
nWCDMA RF power control
nCDMA2000 RF power control
nPA modules
Typical Application
20118101
July 2006
LMV227 Production RF Tested, RF Power Detector for CDMA and WCDMA
© 2006 National Semiconductor Corporation DS201181 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) 235˚C
Operating Ratings (Note 1)
Supply Voltage 2.7V to 5.5V
Temperature Range −40˚C to +85˚C
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.
4.9 7
8
mA
Shutdown: RF
IN
/E
N
= GND (DC), No
RF Input Power Present.
0.6 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 No RF Input Power Present 2.1 µs
t
r
Rise Time (Note 7) Step from No Power to 0 dBm Applied 4.5 µs
I
EN
Current into RF
IN
/E
N
Pin 1µA
P
IN
Input Power Range (Note 5) 0
-30
dBm
-43
-13
dBV
Logarithmic Slope (Note 8) 900 MHz 43.3
mV/dB
1800 MHz 43.9
1855 MHz 36 43.5 51
1900 MHz 44.0
2000 MHz 43.2
Logarithmic Intercept (Note 8) 900 MHz −46.7
dBm
1800 MHz −44.1
1855 MHz −56 −44.3 −33
1900 MHz −42.8
2000 MHz −43.7
V
OUT
Output Voltage No RF Input Power Present 208 350 mV
R
OUT
Output Impedance No RF Input Power Present 20.3 29
34
kΩ
e
n
Output Referred Noise RF Input = 1800 MHz, −10 dBm,
Measured at 10 kHz
700 nV/
Variation over Temperature 900 MHz, RF
IN
= 0 dBm Referred to
25˚C
+0.64
−1.07
dB
1800 MHz, RF
IN
= 0 dBm Referred to
25˚C
+0.09
−0.86
1900 MHz, RF
IN
= 0 dBm Referred to
25˚C
+0
−0.69
2000 MHz, RF
IN
= 0 dBm Referred to
25˚C
+0
−0.86
LMV227
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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.
5.3 7
9
mA
Shutdown: RF
IN
/E
N
= GND (DC), No
RF Input Power Present.
0.49 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 No RF Input Power Present 2.1 µs
t
r
Rise Time (Note 7) Step from No Power to 0 dBm Applied 4.5 µs
I
EN
Current Into RF
IN
/E
N
Pin 1µA
P
IN, MIN
Input Power Range (Note 5) -30
0
dBm
-43
-13
dBV
Logarithmic Slope (Note 8) 900 MHz 43.6
mV/dB
1800 MHz 44.5
1900 MHz 44.5
2000 MHz 43.7
Logarithmic Intercept (Note 8) 900 MHz -48.1
dBm
1800 MHz -45.6
1900 MHz -44.2
2000 MHz -45.6
V
OUT
Output Voltage No RF Input Power Present 211 400 mV
R
OUT
Output Impedance No RF Input Power Present 23.4 29
31
kΩ
e
n
Output Referred Noise RF Input = 1800 MHz, −10 dBm,
Measured at 10 kHz
700 nV/
Variation over Temperature 900 MHz, RF
IN
= 0 dBm Referred to
25˚C
+0.89
−1.16
dB
1800 MHz, RF
IN
= 0 dBm Referred to
25˚C
+0.3
−0.82
1900 MHz, RF
IN
= 0 dBm Referred to
25˚C
+0.34
−0.63
2000 MHz RF
IN
= 0 dBm Referred to
25˚C
+0.22
−0.75
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.
LMV227
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Connection Diagram
6-pin LLP
20118102
Top View
Pin Descriptions
Pin Name Description
Power Supply 4 V
DD
Positive supply voltage
1 GND Power ground
3RF
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 6 OUT Ground referenced detector output voltage (linear in dBm)
Ordering Information
Package Part Number Package
Marking
Transport Media NSC Drawing
6-pin LLP LMV227SD A88 2k Units Tape and Reel SDB06A
LMV227SDX 9k Units Tape and Reel
Note: This product is offered both with leaded and lead free bumps.
Block Diagram
20118103
LMV227
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Typical Performance Characteristics Unless otherwise specified, V
DD
= 2.7V, T
J
= 25˚C.
Supply Current vs. Supply Voltage Output Voltage vs. RF Input Power
20118104 20118105
Output Voltage and Log Conformance vs. RF Input
Power @900 MHz
Output Voltage and Log Conformance vs. RF Input
Power @1800 MHz
20118106 20118107
Output Voltage and Log Conformance vs. RF Input
Power @1900 MHz
Output Voltage and Log Conformance vs. RF Input
Power @2000 MHz
20118108 20118109
LMV227
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Typical Performance Characteristics Unless otherwise specified, V
DD
= 2.7V, T
J
=
25˚C. (Continued)
Logarithmic Slope vs. Frequency Logarithmic Intercept vs. Frequency
20118110 20118111
Output Variation vs. RF Input Power Normalized to 25˚C
@900 MHz
Output Variation vs. RF Input Power Normalized to 25˚C
@1800 MHz
20118112 20118113
Output Variation vs. RF Input Power Normalized to 25˚C
@1900 MHz
Output Variation vs. RF Input Power Normalized to 25˚C
@2000 MHz
20118114 20118115
LMV227
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Typical Performance Characteristics Unless otherwise specified, V
DD
= 2.7V, T
J
=
25˚C. (Continued)
PSRR vs. Frequency
RF Input Impedance vs. Frequency @Resistance and
Reactance
20118135 20118136
LMV227
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Application Notes
CONFIGURING A TYPICAL APPLICATION
The LMV227 is a power detector intended for CDMA and
WCDMA applications. Power measured on its input trans-
lates to a DC voltage on the output through a linear-in-dB
response. The detector is especially suited for power mea-
surements via a high-resistive tap, which eliminates the
need for a directional coupler. In order to match the dynamic
output range of the power amplifier (PA) with the dynamic
range of the LMV227’s input, the high resistive tap needs to
be configured correctly.
Input Attenuation
The constant input impedance of the device enables the
realization of a frequency independent input attenuation to
adjust the LMV227’s dynamic range to the dynamic range of
the PA. Resistor R
1
and the 50Ωinput resistance of the
device realize this attenuation (Figure 1). To minimize inser-
tion loss, resistor 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 and the LMV227 can handle input power levels up to 0
dBm. Hence, 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
DC and AC Behavior of the RF
IN
/E
N
Pin
The LMV227 RF
IN
/E
N
pin has 2 functions combined:
•Shutdown functionality
•Power detection
The capacitor C and the resistor R
2
of Figure 1 separate the
DC shutdown functionality from the AC power measurement.
The device is active when Enable = HI, otherwise it goes into
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. The corner frequency can be calculated using:
(3)
Where R
IN
=50Ω,C
IN
= 45 pF typical.
With R
1
= 1800Ωand C is 100 pF, this results in a corner
frequency of 2.8 MHz
The output voltage is linear with the logarithm of the input
power, often called "linear-in-dB". Figure 2 shows the typical
output voltage versus PA output power of the LMV227 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 LMV227. Expressions are
provided to estimate this ripple on the output. The ripple can
be further reduced by connecting an additional capacitor to
the output of the LMV227 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 the amplitude modulation µ(t) can be between −1
and 1.
20118133
FIGURE 1. Typical Application
20118116
FIGURE 2. Typical Power Detector Response, V
OUT
vs.
PA Output Power
LMV227
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Application Notes (Continued)
The ripple observed on the output of the detector equals the
detectors response to variation on the input due to AM
modulation (Figure 3). This signal has a maximum amplitude
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 ripple can
be described with the formula:
(5)
where V
Y
is the slope of the detection curve (Figure 4) 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 LMV227 is linear in dB, or proportional to the input power
P
IN
in dBm. As discussed earlier, CDMA contains amplitude
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 4).
Besides the ripple due to AM modulation, the log- conform-
ance error contributes to a variation in V
OUT
. For details see
the typical performance characteristics curves. The output
voltage variation ∆V
OUT
thus is always the same for RF input
signals which fall within the linear range (in dB) of the
detector plus the log-conformance error:
∆V
O
=V
Y
·∆P
IN
+ Log Conformance Error (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 LMV227, V
Y
= 40 mV/dB. With
∆P
IN
= 5 dB for CDMA, the ∆V
O
= 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 LMV227 to ground, this
ripple is further attenuated. The cut-off frequency follows
from:
(8)
With the output resistance of the LMV227 R
O
= 19.8 kΩ
typical and C
OUT
= 1.5 nF, the cut-off frequency equals f
C
=
5.36 kHz. A 100 kHz AM signal then gets attenuated 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.
Output Ripple Measurement
Figure 5 shows the ripple reduction that can be achieved by
adding additional capacitance on the output of the LMV227.
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 addition capacitance 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 number calculated in the previous paragraph.
20118117
FIGURE 3. AM Modulated RF Signal 20118118
FIGURE 4. V
OUT
vs. RF Input Power P
IN
LMV227
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Application Notes (Continued)
PRINCIPLE OF OPERATION
The logarithmic response of the LMV227 is implemented by
a de-modulating logarithmic amplifier as shown in Figure 6.
The logarithmic amplifier consists of a number of cascaded
linear gain cells. With these gain cells, a piecewise approxi-
mation of the logarithmic function is constructed.
Every gain cell has a response according to Figure 7.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.
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 8 shows a logarithmic function on a linear scale and
the piecewise approximation of the logarithmic function.
Figure 9 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:
The size of the error increases with distance between the
thresholds.
20118125
FIGURE 5. Output Ripple vs. RF Input Power
20118119
FIGURE 6. Logarithmic Amplifier
20118120
FIGURE 7. Gain Cell
20118121
FIGURE 8. Log-Function on Lin Scale
20118122
FIGURE 9. Log-Function on Log Scale
LMV227
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Application Notes (Continued)
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. This series
resistance should have a sufficiently high bandwidth. The
bandwidth will drop when the parasitic capacitance of the
resistance is to high, which will cause a significant attenua-
tion drop at the GSM frequencies and can cause non-linear
behavior. To reduce the parasitic capacitance across resistor
R
1
, it can be composed of several resistor in series in stead
of a single component.
LMV227
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Physical Dimensions inches (millimeters) unless otherwise noted
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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LMV227 Production RF Tested, RF Power Detector for CDMA and WCDMA
