LT5581
1
5581fa
TYPICAL APPLICATION
DESCRIPTION
6GHz RMS Power Detector
with 40dB Dynamic Range
The LT
®
5581 is a 10MHz to 6GHz, low power monolithic
precision RMS power detector. The RMS detector uses
a proprietary technique to accurately measure the RF
power from –34dBm to +6dBm (at 2.14GHz) of modulated
signals with a crest factor as high as 12dB. It outputs a DC
voltage in linear scale proportional to an RF input signal
power in dBm. The LT5581 is suitable for precision power
measurement and control for a wide variety of RF standards,
including GSM/EDGE, CDMA, CDMA2000, W-CDMA,
TD-SCDMA, UMTS, LTE and WiMAX, etc. The fi nal DC
output is connected in series with an on-chip 300Ω resistor,
which enables further fi ltering of the output modulation
ripple with just a single off-chip capacitor.
10MHz to 6GHz Infrastructure Power
Amplifi er Level Control
FEATURES
APPLICATIONS
n Frequency Range: 10MHz to 6GHz
n Accurate Power Measurement of High Crest Factor
(Up to 12dB) Waveforms
n 40dB Log Linear Dynamic Range
n Exceptional Accuracy Over Temperature
n Fast Response Time: 1μs Rise, 8μs Fall
n Low Power: 1.4mA at 3.3V
n Log-Linear DC Output vs Input RF Power in dBm
n Small 3mm × 2mm 8-Pin DFN Package
n Single-Ended RF Input
n GSM/EDGE, CMDA, CDMA2000, W-CDMA, LTE,
WiMAX RF Power Control
n Pico-Cells, Femto-Cells RF Power Control
n Wireless Repeaters
n CATV/DVB Transmitters
n MIMO Wireless Access Points
n Portable RMS Power Measurement Instrumentation
Linearity Error vs RF Input Power,
2140MHz Modulated Waveforms
9
8
7
6
5
1
2
3
4
VCC
EN
VOUT
GND
CSQ
RFIN
GNDGND
GND
DIGITAL
POWER
CONTROL
POWER
AMP
DIRECTIONAL
COUPLER
0.01µF
1000pF
0.1µF
VCC
2.7VDC TO 5.25VDC
RFIN RFOUT
CMATCH
LMATCH
68
50
CFILT
0.01µF
5581 TA01a
LT5581
ADC
2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
LINEARITY ERROR (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 TA01b
TA = 25°C
CW
WCDMA, UL
WCDMA DL 1C
WCDMA DL 4C
LTE DL 1C
LTE DL 4C
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 7342431.
LT5581
2
5581fa
The l denotes the specifi cations which apply over the full operating temperature
range, otherwise specifi cations are at TA = 25°C, VCC = 3.3V, EN = 3.3V, unless otherwise noted (Note 2). Test circuit is shown in Figure 1.
PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS
Supply Voltage .........................................................5.5V
Maximum Input Signal Power—Average .............15dBm
Maximum Input Signal Power—Peak (Note 7) ....25dBm
DC Voltage at RFIN ....................................... –0.3V to 2V
VOUT Voltage ....................................–0.3V to VCC + 0.3V
Maximum Junction Temperature, TJMAX ............... 150°C
Operating Temperature Range.................. –40°C to 85°C
Storage Temperature Range ................... –65°C to 150°C
CAUTION: This part is sensitive to electrostatic discharge. It
is very important that proper ESD precautions be observed
when handling the LT5581.
(Note 1)
TOP VIEW
9
DDB PACKAGE
8-LEAD
(
3mm s 2mm
)
PLASTIC DFN
5
6
7
8
4
3
2
1VCC
EN
VOUT
GND
CSQ
RFIN
GND
GND
TJMAX = 150°C, θJA = 76°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LT5581IDDB#PBF LT5581IDDB#TRPBF LDKM 8-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi
cations, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
AC Input
Input Frequency Range (Note 4) 10-6000 MHz
Input Impedance 205||1.6 ||pF
fRF = 450MHz
RF Input Power Range Externally Matched to 50 Source –34 to 6 dBm
Linear Dynamic Range, CW (Note 3) ±1dB Linearity Error 40 dB
Linear Dynamic Range, CDMA (Note 3) ±1dB Linearity Error; CDMA 4-Carrier 40 dB
Output Slope 31 mV/dB
Logarithmic Intercept (Note 5) –42 dBm
Output Variation vs Temperature Normalized to Output at 25˚C, –40°C < TA < 85°C;
PIN = –34 to +6dBm
±1 dB
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –27 to –10dBm
±0.5 dB
Deviation from CW Response;
PIN = –34dBm to 0dBm
TETRA π/4 DQPSK
CDMA 4-Carrier 64-Channel Fwd 1.23Mcps
±0.1
±0.5
dB
dB
LT5581
3
5581fa
The l denotes the specifi cations which apply over the full operating temperature
range, otherwise specifi cations are at TA = 25°C, VCC = 3.3V, EN = 3.3V, unless otherwise noted (Note 2). Test circuit is shown in Figure 1.
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
2nd Order Harmonic Distortion At RF Input; CW Input; PIN = 0dBm –57 dBc
3rd Order Harmonic Distortion At RF Input; CW Input; PIN = 0dBm –52 dBc
fRF = 880MHz
RF Input Power Range Externally Matched to 50 Source –34 to 6 dBm
Linear Dynamic Range, CW (Note 3) ±1dB Linearity Error 40 dB
Linear Dynamic Range, EDGE (Note 3) ±1dB Linearity Error; EDGE 3π/8-Shifted 8PSK 40 dB
Output Slope 31 mV/dB
Logarithmic Intercept (Note 5) –42 dBm
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –34 to +6dBm
±1 dB
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –27 to –10dBm
±0.5 dB
Deviation from CW Response, Pin = –34 to +6dBm EDGE 3π/8 Shifted 8PSK ±0.1 dB
fRF = 2140MHz
RF Input Power Range Externally Matched to 50 Source –34 to 6 dBm
Linear Dynamic Range, CW (Note 3) ±1dB Linearity Error 43 dB
Linear Dynamic Range, WCDMA (Note 3) ±1dB Linearity Error; 4-Carrier WCDMA 37 dB
Output Slope 31 mV/dB
Logarithmic Intercept (Note 5) –42 dBm
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –34 to 6dBm
±1 dB
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –27 to –10dBm
±0.5 dB
Maximum Deviation from CW Response
PIN = –34 to –4dBm
WCDMA 1-Carrier Uplink
WCDMA 64-Channel 4-Carrier Downlink
±0.1
±0.5
dB
dB
fRF = 2600MHz
RF Input Power Range Externally Matched to 50 Source –34 to 6 dBm
Linear Dynamic Range, CW (Note 3) ±1dB Linearity Error 40 dB
Output Slope 31 mV/dB
Logarithmic Intercept (Note 5) –42 dBm
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –34 to +6dBm
±1 dB
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –27 to –10dBm
±0.5 dB
Maximum Deviation from CW Response
PIN = –34 to 2dBm
WiMAX OFDMA Preamble
WiMAX OFDM Burst
±0.1
±0.5
dB
dB
fRF = 3500MHz
RF Input Power Range Externally Matched to 50 Source –30 to 6 dBm
Linear Dynamic Range, CW (Note 3) ±1dB Linearity Error 36 dB
Output Slope 31 mV/dB
Logarithmic Intercept (Note 5) –41 dBm
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –30 to +6dBm
±1 dB
LT5581
4
5581fa
The l denotes the specifi cations which apply over the full operating temperature
range, otherwise specifi cations are at TA = 25°C, VCC = 3.3V, EN = 3.3V, unless otherwise noted (Note 2). Test circuit is shown in Figure 1.
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –27 to –10dBm
±0.5 dB
Deviation from CW Response
PIN = –34 to –4dBm
WiMAX OFDMA Preamble
WiMAX OFDM Burst
±0.1
±0.5
dB
dB
fRF = 5800MHz
RF Input Power Range Externally Matched to 50 Source –25 to 6 dBm
Linear Dynamic Range, CW (Note 3) ±1dB Linearity Error 31 dB
Output Slope 31 mV/dB
Logarithmic Intercept (Note 5) –33 dBm
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –25 to +6dBm
±1 dB
Output Variation vs Temperature Normalized to Output at 25°C, –40°C < TA < 85°C;
PIN = –20 to +6dBm
±0.5 dB
Deviation from CW Response WiMAX OFDM Burst; PIN = –25 to 6dBm ±0.2 dB
Output
Output DC Voltage No Signal Applied to RF Input 180 mV
Output Impedance Internal Series Resistor Allows for Off-Chip Filter Cap 300
Output Current Sourcing/Sinking 5/5 mA
Rise Time 0.2V to 1.6V, 10% to 90%, fRF = 2140MHz 1 µs
Fall Time 1.6V to 0.2V, 10% to 90%, fRF = 2140MHz 8 µs
Power Supply Rejection Ratio (Note 6) For Over Operating Input Power Range 49 dB
Integrated Output Voltage Noise 1kHz to 6.5kHz Integration BW, PIN = 0dBm CW 150 µVRMS
Enable (EN) Low = Off, High = On
EN Input High Voltage (On) l2V
EN Input Low Voltage (Off) l0.3 V
Enable Pin Input Current EN = 3.3V 20 µA
Turn-On Time; CW RF input VOUT Within 10% of Final Value; PIN = 0dBm 1 µs
Settling Time; RF Pulse VOUT Within 10% of Final Value; PIN = 0dBm 1 µs
Power Supply
Supply Voltage l2.7 3.3 5.25 V
Supply Current No RF Input Signal 1.4 mA
Shutdown Current EN = 0.3V, VCC = 3.3V 0.2 6 µA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LT5581 is guaranteed functional over the operating
temperature range from –40°C to 85°C.
Note 3: The linearity error is calculated by the difference between the
incremental slope of the output and the average output slope from
–20dBm to 0dBm. The dynamic range is defi ned as the range over which
the linearity error is within ±1dB.
Note 4: An external capacitor at the CSQ pin should be used for input
frequencies below 250MHz. Lower frequency operation results in
excessive RF ripple in the output voltage.
Note 5: Logarithmic intercept is an extrapolated input power level from the
best fi tted log-linear straight line, where the output voltage is 0V.
Note 6: PSRR is determined as the dB value of the change in VOUT voltage
over the change in VCC supply voltage.
Note 7: Not production tested. Guaranteed by design and correlation to
production tested parameters.
LT5581
5
5581fa
Performance characteristics taken at VCC = 3.3V,
EN = 3.3V and TA = 25°C, unless otherwise noted. (Test circuit shown in Figure 1)
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage and Linearity Error
at 450MHz
Linearity Error Temperature
Variation from 25°C at 450MHz
Linearity Error vs RF Input Power,
450MHz Modulated Waveforms
Output Voltage and Linearity Error
at 880MHz
Linearity Error Temperature
Variation from 25°C at 880MHz
Linearity Error vs RF Input Power,
880MHz Modulated Waveforms
Output Voltage vs Frequency Output Voltage vs Frequency Linearity Error vs Frequency
RF INPUT POWER (dBm)
–40
VOUT (V)
0.8
1.8
2.0
–30 –20 –10
0.4
1.4
0.6
1.6
0.2
0
1.2
1.0
–35 –25 010
–15 –5 5
5581 G01
10MHz
450MHz
880MHz
2.14GHz
2.6GHz
3.5GHz
5.8GHz
TA = 25°C
RF INPUT POWER (dBm)
–40
VOUT (V)
0.8
1.8
2.0
–30 –20 –10
0.4
1.4
0.6
1.6
0.2
0
1.2
1.0
–35 –25 010
–15 –5 5
5581 G02
880MHz
2.14GHz
2.6GHz
3.5GHz
TA = 25°C
RF INPUT POWER (dBm)
–40
LINEARITY ERROR (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G03
10MHz
450MHz
880MHz
2.14GHz
2.6GHz
3.5GHz
5.8GHz
TA = 25°C
2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
–40
VOUT (V)
0.8
1.8
2.0
–30 –20 –10
0.4
1.4
0.6
1.6
0.2
0
1.2
1.0
–0.5
2.0
2.5
–1.5
1.0
–1.0
1.5
–2.0
–2.5
0.5
0
–35 –25 010
–15 –5 5
5581 G04
25°C
85°C
–40°C
LINEARITY ERROR (dB)
1
2
0
–1
–2
–3
3
RF INPUT POWER (dBm)
–40
VARIATION (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G05
–40°C
85°C
2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
LINEARITY ERROR(dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G06
TA = 25°C
CW
TETRA
CDMA 4C
RF INPUT POWER (dBm)
–40
VOUT (V)
LINEARITY ERROR (dB)
0.8
1.8
2.0
–30 –20 –10
0.4
1.4
0.6
1.6
0.2
0
1.2
1.0
–0.5
2.0
2.5
–1.5
1.0
–1.0
1.5
–2.0
–2.5
0.5
0
–35 –25 010
–15 –5 5
5581 G07
25°C
85°C
–40°C 2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
–40
VARIATION (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G08
–40°C
85°C
2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
LINEARITY ERROR(dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G09
TA = 25°C
CW
EDGE
LT5581
6
5581fa
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage and Linearity Error
at 2600MHz
Linearity Error Temperature
Variation from 25°C at 2600MHz
Linearity Error vs RF Input Power,
2.6GHz Modulated Waveforms
Output Voltage and Linearity Error
at 3500MHz
Linearity Error Temperature
Variation from 25°C at 3500MHz
Linearity Error vs RF Input Power,
3.5GHz Modulated Waveforms
Output Voltage and Linearity Error
at 2140MHz
Linearity Error Temperature
Variation from 25°C at 2140MHz
Linearity Error vs RF Input Power,
2140MHz Modulated Waveforms
RF INPUT POWER (dBm)
–40
VOUT (V)
LINEARITY ERROR (dB)
0.8
1.8
2.0
–30 –20 –10
0.4
1.4
0.6
1.6
0.2
0
1.2
1.0
–0.5
2.0
2.5
–1.5
1.0
–1.0
1.5
–2.0
–2.5
0.5
0
–35 –25 010
–15 –5 5
5581 G10
25°C
85°C
–40°C 2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
–40
VARIATION (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G11
–40°C
85°C
2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
LINEARITY ERROR (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G12
TA = 25°C
CW
WCDMA, UL
WCDMA DL 1C
WCDMA DL 4C
LTE DL 1C
LTE DL 4C
RF INPUT POWER (dBm)
–40
VOUT (V)
LINEARITY ERROR (dB)
0.8
1.8
2.0
–30 –20 –10
0.4
1.4
0.6
1.6
0.2
0
1.2
1.0
–0.5
2.0
2.5
–1.5
1.0
–1.0
1.5
–2.0
–2.5
0.5
0
–35 –25 0
–15 –5 510
5581 G13
25°C
85°C
–40°C 2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
–40
VARIATION (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G14
–40°C
85°C
2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
LINEARITY ERROR (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G15
TA = 25°C
CW
WiMax OFDM PREAMBLE
WiMax OFDM BURST
WiMax OFDMA PREAMBLE
RF INPUT POWER (dBm)
–40
VOUT (V)
LINEARITY ERROR (dB)
0.8
1.8
2.0
0–30 –20 –10 10
0.4
1.4
0.6
1.6
0.2
1.2
1.0
–0.5
2.0
2.5
–1.5
1.0
–1.0
1.5
–2.0
–2.5
0.5
0
–35 –25 0
–15 –5 5
5581 G16
25°C
85°C
–40°C 2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
–40
VARIATION (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G17
–40°C
85°C
2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
LINEARITY ERROR (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G18
TA = 25°C
CW
WiMax OFDMA PREAMBLE
WiMax OFDM BURST
LT5581
7
5581fa
TYPICAL PERFORMANCE CHARACTERISTICS
Slope vs Frequency Slope Distribution vs Temperature Supply Current vs Supply Voltage
Logarithmic Intercept
vs Frequency
Logarithmic Intercept Distribution
vs Temperature
Output Voltage and Linearity Error
at 5800MHz
Linearity Error Temperature
Variation from 25°C at 5800MHz
Linearity Error vs RF Input Power,
5.8GHz Modulated Waveforms
RF INPUT POWER (dBm)
–40
VOUT (V)
LINEARITY ERROR (dB)
0.8
1.8
2.0
0–30 –20 –10 10
0.4
1.4
0.6
1.6
0.2
1.2
1.0
–0.5
2.0
2.5
–1.5
1.0
–1.0
1.5
–2.0
–2.5
0.5
0
–35 –25 0
–15 –5 5
5581 G19
25°C
85°C
–40°C 2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
–40
VARIATION (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G20
–40°C
85°C
2
1
0
–2
–1
–3
3
RF INPUT POWER (dBm)
LINEARITY ERROR (dB)
–30 –20 –10
–35 –25 010
–15 –5 5
5581 G21
TA = 25°C
CW
WiMax OFDM BURST
FREQUENCY (GHz)
0
26
SLOPE (mV/dB)
30
12 435
34
28
32
6
5581 G22
TA = 25°C
SUPPLY VOLTAGE (V)
2.6
SUPPLY CURRENT (mA)
1.6
1.8
1.4
1.2
3.4 4.2
33.8 4.6 5 5.4
1.0
0.8
2.0
5581 G24
–40°C
85°C
25°C
FREQUENCY (GHz)
0
–50
LOGARITHMIC INTERCEPT (dBm)
–40
12 435
–30
–45
–35
6
5581 G25
TA = 25°C
SLOPE (mV/dB)
28
DISTRIBUTION (%)
30
40
50
20
10
029 30 31 32 33 34
5581 G23
TA = 85°C
TA = 25°C
TA = –40°C
LOGARITHMIC INTERCEPT (dBm)
–48
DISTRIBUTION (%)
30
40
50
20
10
0–47 –46 –45 –44 –43 –41–42
5581 G26
TA = 85°C
TA = 25°C
TA = –40°C
LT5581
8
5581fa
TYPICAL PERFORMANCE CHARACTERISTICS
Output Transient Response
Output Transient Response with
CW RF and EN Pulse
Output Voltage and Linearity Error
vs VCC at 2140MHz
Return Loss vs Frequency
Reference in Figure 1 Test Circuit
Output Transient Response with
RF and EN Pulse
RF INPUT POWER (dBm)
–40
VOUT (V)
LINEARITY ERROR (dB)
0.8
1.8
2.0
–30 –20 –10
0.4
1.4
0.6
1.6
0.2
0
1.2
1.0
–0.5
2.0
2.5
–1.5
1.0
–1.0
1.5
–2.0
–2.5
0.5
0
–35 –25 010
–15 –5 5
5581 G28
3.3V
5V
TA = 25°C
FREQUENCY (GHz)
0
–30
RETURN LOSS (dB)
–25
–20
–15
–10
0
1234
5581 G29
56
–5
L1, C1 = 2.2nH, 1.5pF
L1, C1 = 1nH, 1.5pF
L1, C1 = 0nH, 1pF
L1, C1 = 0nH, 0.5pF
L1, C1 = 0nH, 0pF
TA = 25°C
TIME (ms)
0
OUTPUT VOLTAGE (V)
RF PULSE ENABLE (V)
1.5
2.0
2.5
0.7
1.0
0.5
0.2 0.4
0.1 0.9
0.3 0.5 0.8
0.6 1
0
–0.5
3.0
–5
0
5
–10
–15
–20
–25
10
5581 G30
RF & EN PULSE ON
RF&EN
PULSE
OFF
RF&EN
PULSE
OFF
PIN = 10dBm
PIN = 0dBm
PIN = –10dBm
PIN = –20dBm
PIN = –30dBm
TA = 25°C, VCC = 5V
TIME (µs)
0
OUTPUT VOLTAGE (V)
RF PULSE ENABLE (V)
1.5
2.0
2.5
70
1.0
0.5
20 40
10 90
30 50 80
60 100
0
3.0
–5
0
5
–10
–15
–20
10
5581 G31
RF PULSE ON
RF
PULSE
OFF
RF
PULSE
OFF
PIN = 10dBm
PIN = 0dBm
PIN = –10dBm
PIN = –20dBm
PIN = –30dBm
TA = 25°C, VCC = 5V
TIME (ms)
0
OUTPUT VOLTAGE (V)
ENABLE (V)
1.5
2.0
2.5
0.7
1.0
0.5
0.2 0.4
0.1 0.9
0.3 0.5 0.8
0.6 1
0
–0.5
3.0
–2
0
2
–4
–6
–8
–10
4
5581 G32
EN PULSE ON
EN
PULSE
OFF
EN
PULSE
OFF
PIN = 10dBm
PIN = 0dBm
PIN = –10dBm
PIN = –20dBm
PIN = –30dBm
TA = 25°C
Supply Current vs RF Input Power
RF INPUT POWER (dBm)
–25
0
SUPPLY CURRENT (mA)
4
8
12
–20 –15 –10 –5 5010
16
2
6
10
14
15
5581 G27
TA = 25°C
LT5581
9
5581fa
PIN FUNCTIONS
VCC (Pin 1): Power Supply, 2.7V to 5.25V. VCC
should be bypassed with a 0.1µF ceramic capacitor.
EN (Pin 2): Chip Enable. A logic low or no-connect on the
enable pin shuts down the part. A logic high enables the
part. An internal 500k pull-down resistor ensures the part is
off when the enable driver is in a three-state condition.
VOUT (Pin 3): Detector Output.
GND (Pins 4, 5, 6): Ground.
RFIN (Pin 7): RF Input. Should be DC-blocked with coupling
capacitor; 1000pF recommended. This pin has an internal
200 termination.
CSQ (Pin 8): Optional Low Frequency Range Extension
Capacitor. This pin is for frequencies below 250MHz. Use
0.01µF from pin to ground for 10MHz operation.
Exposed Pad (Pin 9): Ground. The Exposed Pad must
be soldered to the PCB. For high frequency oper-
ation, the backside ground connection should have a low
inductance connection to the PCB ground, using many
through-hole vias. See the layout information in the
Applications Information section.
BLOCK DIAGRAM
LT5581
7
EXPOSED
PAD
OUTPUT
BUFFER
9
VOUT
RFIN
5581 BD
EN VCC
3
2
CSQ
8 1 4 5 6
150kHz LPF 300
GND
RMS
DETECTOR
BIAS
LT5581
10
5581fa
TEST CIRCUIT
Figure 1. Evaluation Circuit Schematic
REF DES VALUE SIZE PART NUMBER
C6 100pF 0603 AVX 06033A101KAT2A
C7 0.1µF 0603 AVX 06033C104KAT2A
C3 0.01µF 0603 AVX 06033C103KAT2A
C2 1000pF 0603 AVX 06033C102KAT2A
R2 68 0603
FREQUENCY
RANGE
RFIN MATCH
L1 C1
1GHz to 2.2GHz 2.2nH 1.5pF
2GHz to 2.6GHz 1.2nH 1.5pF
2.6GHz to 3.4GHz 0 1pF
3.8GHz to 5.5GHz 0 0.5pF
4.6GHz to 6GHz 0 0
9
8
7
6
5
1
2
3
4
VCC
EN
EN
NC NC
NC
VOUT
GND
CSQ
RFIN
GNDGND
GND
L1
2.2nH
C3
0.01µF
PINS 4, 5, 6: OPTIONAL GROUND
C2
1000pF
VCC
R2
68
R3
0
C4
OPT
5581 F01
LT5581
C5
OPT
RF
GND
DC
GND
EE = 4.4
0.018"
0.018"
0.062"
VOUT
RFIN
C7
0.1µF
C6
100pF
C1
1.5pF
LT5581
11
5581fa
APPLICATIONS INFORMATION
OPERATION
To achieve an accurate average power measurement of
the high crest factor modulated RF signals, the LT5581
combines a proprietary high speed power measurement
subsystem with an internal 150kHz low pass averag-
ing fi lter and an output voltage buffer in a completely
integrated solution with minimal off-chip components.
The resulting output voltage is directly proportional to
the average RF input power in dBm. Figure 1 shows the
evaluation circuit schematic, and Figures 2 and 3 show
the associated board artwork. For best high frequency
performance, it is important to place many ground vias
directly under the package.
RF Input Matching
The input resistance is about 205. Input capacitance
is 1.6pF. The impedance vs frequency of the RF input is
detailed in Table 1.
Figure 2. Top Side of Evaluation Board Figure 3. Bottom Side of Evaluation Board
Table 1. RF Input Impedance
FREQUENCY
(MHz)
INPUT
IMPEDANCE
(Ω)
S11
MAG ANGLE (°)
10 203.6-j5.5 0.606 –0.8
50 199.5-j22.4 0.603 –3.4
100 191.7-j40.3 0.601 –6.4
200 171.1-j68.5 0.601 –12.3
400 121.8-j95.4 0.608 –24
500 100.2-j97.5 0.613 –29.8
800 56.8-j86.5 0.631 –46.5
900 48-j81.2 0.638 –51.8
1000 41.1-j76 0.645 –56.8
1500 22.2-j55 0.679 –79.5
2000 14.6-j41.4 0.710 –97.9
2100 13.6-j39.2 0.716 –101.2
2500 10.8-j32.1 0.737 –112.9
3000 8.6-j25 0.759 –125.7
3500 7.3-j19.4 0.774 –136.9
4000 6.6-j14.5 0.783 –147.1
5000 8.8-j9.6 0.709 –157.6
6000 6.4-j0 0.774 –179.9
5581 F035581 F02
LT5581
12
5581fa
A shunt 68 resistor can be used to provide a broadband
impedance match at low frequencies up to 1.3GHz, and
from 4.5GHz to 6GHz. As shown in Figure 4, a nominal
broadband input match can be achieved up to 2.2GHz by
using an LC matching circuit consisting of a series 2.2nH
inductor (L1) and a shunt 1.5pF capacitor (C1). This
match will maintain a return loss of about 10dB across
the band. For matching at higher frequencies, values for
L1 and C1 are listed in the table of Figure 1. The input
refl ection coeffi cient referenced to the RF input pin (with
no external components) is shown on the Smith Chart
in Figure 5. Alternatively, it is possible to match using
an impedance transformation network by omitting R1
and transforming the 205 load to 50. The resulting
match, over a narrow band of frequencies, will improve
sensitivity up to about 6dB maximum; the dynamic range
remains the same. For example, by omitting R1 and set-
ting L1 = 1.8nH and C1 = 3pF, a 2:1 VSWR match can
be obtained from 1.95GHz to 2.36GHz, with a sensitivity
improvement of 5dB.
The RFIN input DC blocking capacitor (C2) and the CSQ
bias decoupling capacitor (C3), can be adjusted for low
frequency operation. For input frequencies down to 10MHz,
0.01µF is needed at CSQ. For frequencies above 250MHz,
the on-chip 20pF decoupling capacitor is suffi cient, and
CSQ may be eliminated as desired. The DC-blocking ca-
pacitor can be as large as 2200pF for 10MHz operation, or
100pF for 2GHz operation. A DC-blocking capacitor larger
than 2200pF results in an undesirable RF pulse response
on the falling edge. Therefore, for general applications,
the recommended value for C2, is conservatively set at
1000pF.
Output Interface
The output buffer of the LT5581 is shown in Figure 6. It
includes a push-pull stage with a series 300 resistor.
The output stage is capable of sourcing and sinking 5mA
of current. The output pin can be shorted to GND or VCC
without damage, but going beyond VCC + 0.5V or GND
– 0.5V may result in damage, as the internal ESD protection
diodes will start to conduct excessive current.
The residual ripple, due to RF modulation, can be reduced
by adding external components RSS and CLOAD (R3 and
C4 on the Evaluation Circuit Schematic in Figure 1) to the
APPLICATIONS INFORMATION
Figure 4. Simplifi ed Circuit Schematic of the RF Input Interface Figure 5. Input Refl ection Coeffi cient
CSQ
VCC
5581 F04
205
LT5581
8
L1
C3
0.01µF
C2
1000pF
R1
68
RFIN
(MATCHED)
C1
20pF
RFIN
7
LT5581
13
5581fa
APPLICATIONS INFORMATION
output pin, to form an RC lowpass fi lter. The internal 300
resistor in series with the output pin enables fi ltering of
the output signal with just the addition of CLOAD. Figure
7 shows the effect of the external fi lter capacitor on the
residual ripple level for a 4-carrier WCDMA signal at
2.14GHz with –10dBm. Adding a 10nF capacitor to the
output decreases the peak-to-peak output ripple from
135mVP-P to 50mVP-P. The fi lter –3dB corner frequency
can be calculated with the following equation:
fCR
CLOAD SS
=+
1
2 300π()
Figure 8 shows the transient response for a 2.6GHz
WiMAX signal, with preamble and burst ripple reduced
by a factor of 3, using a 0.047µF external fi lter capacitor.
The average power in the preamble section is –10dBm,
while the burst section has a 3dB lower average power.
With the capacitor, the ripple in the preamble section is
about 0.5dB peak-to-peak. The modulation used was
OFDM (WiMAX 802.16-2004) MMDS band, 1.5MHz BW,
with 256 size FFT and 1 burst at QPSK 3/4.
Figure 9 shows how the peak-to-peak ripple decreases with
increasing external fi lter capacitance value. Also shown is
how the RF pulse response will have longer rise and fall
times with the addition of this lowpass fi lter cap.
Figure 6. Simplifi ed Circuit Schematic of the Output Interface
Figure 8. Residual Ripple for 2.6GHz WiMAX OFDM 802.16-2004
Figure 7. Residual Ripple, Output Transient Response
for RF Pulse with WCDMA 4-Carrier Modulation
Figure 9. Residual Ripple, Output Transient Times for RF Pulse
with WCDMA 4-Carrier Modulation vs External Filter Capacitor C4
300 RSS
VOUT
INPUT
VCC
40µA
VOUT
(FILTERED)
CLOAD
5581 F06
LT5581
3
TIME (µs)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
0.8
1.0
1.2
0.6
0.4
070
20 40
10 90
30 50 80
60 100
0.2
0
1.4
1.10
1.15
1.20
1.05
1.00
0.95
0.90
1.25
5581 F07
TA = 25°C
NO CAP
0.01µF
TIME (ms)
OUTPUT VOLTAGE (V)
0.8
1.0
1.2
0.6
0.4
0 1.4
0.4 0.8
0.2 1.8
0.6 1 1.6
1.2 2
0.2
0
1.4
5581 F08
TA = 25°C NO CAP
0.047µF
EXTERNAL CAPACITOR (µF)
0.001
OUTPUT RIPPLE PEAK-TO-PEAK (dB)
RISE TIME AND FALL TIME (µs)
3
5
7
2
1
0.01 0.1 1
0
9
4
6
8
100
10
1
1000
5581 F09
TA = 25°C
RIPPLE
RISE
FALL
LT5581
14
5581fa
Figure 10. RF Pulse Response Rise Time
and Fall Time vs RF Input Power
Figure 10 shows that rise time and fall time are strong
functions of RF input power. Data is taken without the
output fi lter capacitor.
For a given RF modulation type—WCDMA, for example—
the internal 150kHz fi lter provides nominal fi ltering of the
residual ripple level. Additional external fi ltering occurs in
the log domain, which introduces a systematic log error
in relation to the signal’s crest factor, as shown in the
following equation in dB.1
Error|dB = 10 • log10(r + (1 – r)10–CF/10) – CF • (r-1)
Where CF is the crest factor and r is the duty cycle of the
measurement (or number of measurements made at the
peak envelope, divided by the total number of periodic
measurements in the measurement period). It is important
to note that the CF refers to the 150kHz low pass fi ltered
envelope of the signal. The error will depend on the statistics
and bandwidth of the modulation signal in relation to the
internal 150kHz fi lter. For example, in the case of WCDMA,
simulations prove that it is possible to set the external fi lter
capacitor corner frequency at 15kHz and only introduce
an error less than 0.1dB.
Figure 11 depicts the output AM modulation ripple as a
function of modulation difference frequency for a 2-tone
input signal at 2140MHz with –10dBm input power. The
resulting deviation in the output voltage of the detector
shows the effect of the internal 150kHz fi lter.
APPLICATIONS INFORMATION
Figure 11. Output DC Voltage Deviation and Residual
Ripple vs 2-Tone Separation Frequency
Figure 12. Output Voltage Noise Density Figure 13. Integrated Output Voltage Noise
1 Steve Murray, “Beware of Spectrum Analyzer Power Averaging Techniques,” Microwaves
& RF, Dec. 2006.
INPUT POWER (dBm)
–30
RISE TIME AND FALL TIME (µs)
6
7
8
5
4
–20 –10
–25 –15 –5 0 5
1
0
3
9
2
5581 F10
FALL TIME
RISE TIME
TA = 25°C
2-TONE FREQUENCY SEPARATION (MHz)
0.001
OUTPUT AC RIPPLE (dB)
DEVIATION OF OUTPUT VOLTAGE (dB)
15
20
25
10
5
0.01 0.1 110
0
30
–1.5
–1.0
–0.5
–2.0
–2.5
–3.0
0
5581 F11
TA = 25°C
FREQUENCY (kHz)
0.1
NOISE VOLTAGE (µVRMS/ Hz)
2.0
4.0
10
1.0
3.5
1.5
0.5
0
3.0
2.5
1100 1000
5581 F12
0dBm
–10dBm
–20dBm
–30dBm
NO RF INPUT
TA = 25°C
FREQUENCY (kHz)
0.1
INTEGRATED NOISE (mVRMS)
0.8
1.8
2.0
10
0.4
1.4
0.6
1.6
0.2
0
1.2
1.0
1100 1000
5581 F13
0dBm
–10dBm
–20dBm
–30dBm
NO RF INPUT
TA = 25°C
LT5581
15
5581fa
The output voltage noise density and integrated noise are
shown in Figures 12 and 13, respectively, for various input
power levels. Noise is a strong function of input level. There
is roughly a 10dB reduction in the output noise level for
an input level of 0dBm versus no input.
Enable Pin
A simplifi ed schematic of the EN pin is shown in Figure
14. To enable the LT5581, it is necessary to put greater
than 1V on this pin. To disable or turn off the chip, this
voltage should be below 0.3V. At an enable voltage of
3.3V, the pin draws roughly 20µA. If the EN pin is not
connected, the chip is disabled through an internal 500k
pull-down resistor.
APPLICATIONS INFORMATION
Figure 14. Enable Pin Simplifi ed Schematic
EN
VCC
5581 F14
300k 300k
LT5581
500k
2
It is important that the voltage applied to the EN pin never
exceeds VCC by more than 0.5V, otherwise, the supply
current may be sourced through the upper ESD protection
diode connected at the EN pin.
LT5581
16
5581fa
PACKAGE DESCRIPTION
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
2.00 ±0.10
(2 SIDES)
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
0.40 ± 0.10
BOTTOM VIEW—EXPOSED PAD
0.56 ± 0.05
(2 SIDES)
0.75 ±0.05
R = 0.115
TYP
R = 0.05
TYP
2.15 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
14
85
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0 – 0.05
(DDB8) DFN 0905 REV B
0.25 ± 0.05
2.20 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.61 ±0.05
(2 SIDES)
1.15 ±0.05
0.70 ±0.05
2.55 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
0.50 BSC
LT5581
17
5581fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 4/10 Updated Note 2 in Electrical Characteristics Section 4
LT5581
18
5581fa
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
LT 0410 REV A • PRINTED IN USA
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