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LT5581 6GHz RMS Power Detector with 40dB Dynamic Range FEATURES
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DESCRIPTION
The LT(R)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, TDSCDMA, UMTS, LTE and WiMAX, etc. The final DC output is connected in series with an on-chip 300 resistor, which enables further filtering of the output modulation ripple with just a single off-chip capacitor.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 7342431.
Frequency Range: 10MHz to 6GHz Accurate Power Measurement of High Crest Factor (Up to 12dB) Waveforms 40dB Log Linear Dynamic Range Exceptional Accuracy Over Temperature Fast Response Time: 1s Rise, 8s Fall Low Power: 1.4mA at 3.3V Log-Linear DC Output vs Input RF Power in dBm Small 3mm x 2mm 8-Pin DFN Package Single-Ended RF Input
APPLICATIONS
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GSM/EDGE, CMDA, CDMA2000, W-CDMA, LTE, WiMAX RF Power Control Pico-Cells, Femto-Cells RF Power Control Wireless Repeaters CATV/DVB Transmitters MIMO Wireless Access Points Portable RMS Power Measurement Instrumentation
TYPICAL APPLICATION
10MHz to 6GHz Infrastructure Power Amplifier Level Control
RFIN POWER AMP VCC 2.7VDC TO 5.25VDC 0.1F DIGITAL POWER CONTROL 1 2 ADC CFILT 0.01F 3 4 VCC EN VOUT GND GND 9
5581 TA01a
Linearity Error vs RF Input Power, 2140MHz Modulated Waveforms
DIRECTIONAL COUPLER RFOUT 2 LINEARITY ERROR (dB) CMATCH 1 0 -1 -2 CW WCDMA, UL WCDMA DL 1C WCDMA DL 4C LTE DL 1C LTE DL 4C 3 TA = 25C
LT5581
0.01F 8 CSQ 1000pF 7 RFIN GND GND 6 5
LMATCH
50
68
-3 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
5
10
5581 TA01b
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1
LT5581 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW VCC 1 EN 2 VOUT 3 GND 4 9 8 7 6 5 CSQ RFIN GND GND
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 ............... 150C Operating Temperature Range.................. -40C to 85C Storage Temperature Range................... -65C to 150C CAUTION: This part is sensitive to electrostatic discharge. It is very important that proper ESD precautions be observed when handling the LT5581.
DDB PACKAGE 8-LEAD (3mm 2mm) PLASTIC DFN TJMAX = 150C, JA = 76C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LT5581IDDB#PBF TAPE AND REEL LT5581IDDB#TRPBF PART MARKING LDKM PACKAGE DESCRIPTION 8-Lead (3mm x 2mm) Plastic DFN TEMPERATURE RANGE -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 3.3V, EN = 3.3V, unless otherwise noted (Note 2). Test circuit is shown in Figure 1.
PARAMETER AC Input Input Frequency Range (Note 4) Input Impedance fRF = 450MHz RF Input Power Range Linear Dynamic Range, CW (Note 3) Linear Dynamic Range, CDMA (Note 3) Output Slope Logarithmic Intercept (Note 5) Output Variation vs Temperature Output Variation vs Temperature Deviation from CW Response; PIN = -34dBm to 0dBm Normalized to Output at 25C, -40C < TA < 85C; PIN = -34 to +6dBm Normalized to Output at 25C, -40C < TA < 85C; PIN = -27 to -10dBm TETRA /4 DQPSK CDMA 4-Carrier 64-Channel Fwd 1.23Mcps Externally Matched to 50 Source 1dB Linearity Error 1dB Linearity Error; CDMA 4-Carrier -34 to 6 40 40 31 -42 1 0.5 0.1 0.5 dBm dB dB mV/dB dBm dB dB dB dB
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ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
TYP 10-6000 205||1.6
MAX
UNITS MHz ||pF
2
LT5581 ELECTRICAL CHARACTERISTICS
PARAMETER 2nd Order Harmonic Distortion 3rd Order Harmonic Distortion fRF = 880MHz RF Input Power Range Linear Dynamic Range, CW (Note 3) Linear Dynamic Range, EDGE (Note 3) Output Slope Logarithmic Intercept (Note 5) Output Variation vs Temperature Output Variation vs Temperature Deviation from CW Response, Pin = -34 to +6dBm fRF = 2140MHz RF Input Power Range Linear Dynamic Range, CW (Note 3) Linear Dynamic Range, WCDMA (Note 3) Output Slope Logarithmic Intercept (Note 5) Output Variation vs Temperature Output Variation vs Temperature Maximum Deviation from CW Response PIN = -34 to -4dBm fRF = 2600MHz RF Input Power Range Linear Dynamic Range, CW (Note 3) Output Slope Logarithmic Intercept (Note 5) Output Variation vs Temperature Output Variation vs Temperature Maximum Deviation from CW Response PIN = -34 to 2dBm fRF = 3500MHz RF Input Power Range Linear Dynamic Range, CW (Note 3) Output Slope Logarithmic Intercept (Note 5) Output Variation vs Temperature Normalized to Output at 25C, -40C < TA < 85C; PIN = -30 to +6dBm Externally Matched to 50 Source 1dB Linearity Error -30 to 6 36 31 -41 1 dBm dB mV/dB dBm dB
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The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 3.3V, EN = 3.3V, unless otherwise noted (Note 2). Test circuit is shown in Figure 1.
CONDITIONS At RF Input; CW Input; PIN = 0dBm At RF Input; CW Input; PIN = 0dBm Externally Matched to 50 Source 1dB Linearity Error 1dB Linearity Error; EDGE 3/8-Shifted 8PSK MIN TYP -57 -52 -34 to 6 40 40 31 -42 Normalized to Output at 25C, -40C < TA < 85C; PIN = -34 to +6dBm Normalized to Output at 25C, -40C < TA < 85C; PIN = -27 to -10dBm EDGE 3/8 Shifted 8PSK Externally Matched to 50 Source 1dB Linearity Error 1dB Linearity Error; 4-Carrier WCDMA 1 0.5 0.1 -34 to 6 43 37 31 -42 Normalized to Output at 25C, -40C < TA < 85C; PIN = -34 to 6dBm Normalized to Output at 25C, -40C < TA < 85C; PIN = -27 to -10dBm WCDMA 1-Carrier Uplink WCDMA 64-Channel 4-Carrier Downlink Externally Matched to 50 Source 1dB Linearity Error 1 0.5 0.1 0.5 -34 to 6 40 31 -42 Normalized to Output at 25C, -40C < TA < 85C; PIN = -34 to +6dBm Normalized to Output at 25C, -40C < TA < 85C; PIN = -27 to -10dBm WiMAX OFDMA Preamble WiMAX OFDM Burst 1 0.5 0.1 0.5 MAX UNITS dBc dBc dBm dB dB mV/dB dBm dB dB dB dBm dB dB mV/dB dBm dB dB dB dB dBm dB mV/dB dBm dB dB dB dB
3
LT5581 ELECTRICAL CHARACTERISTICS
PARAMETER Output Variation vs Temperature Deviation from CW Response PIN = -34 to -4dBm fRF = 5800MHz RF Input Power Range Linear Dynamic Range, CW (Note 3) Output Slope Logarithmic Intercept (Note 5) Output Variation vs Temperature Output Variation vs Temperature Deviation from CW Response Output Output DC Voltage Output Impedance Output Current Sourcing/Sinking Rise Time Fall Time Power Supply Rejection Ratio (Note 6) Integrated Output Voltage Noise Enable (EN) Low = Off, High = On EN Input High Voltage (On) EN Input Low Voltage (Off) Enable Pin Input Current Turn-On Time; CW RF input Settling Time; RF Pulse Power Supply Supply Voltage Supply Current Shutdown Current No RF Input Signal EN = 0.3V, VCC = 3.3V
l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 3.3V, EN = 3.3V, unless otherwise noted (Note 2). Test circuit is shown in Figure 1.
CONDITIONS Normalized to Output at 25C, -40C < TA < 85C; PIN = -27 to -10dBm WiMAX OFDMA Preamble WiMAX OFDM Burst Externally Matched to 50 Source 1dB Linearity Error MIN TYP 0.5 0.1 0.5 -25 to 6 31 31 -33 Normalized to Output at 25C, -40C < TA < 85C; PIN = -25 to +6dBm Normalized to Output at 25C, -40C < TA < 85C; PIN = -20 to +6dBm WiMAX OFDM Burst; PIN = -25 to 6dBm No Signal Applied to RF Input Internal Series Resistor Allows for Off-Chip Filter Cap 0.2V to 1.6V, 10% to 90%, fRF = 2140MHz 1.6V to 0.2V, 10% to 90%, fRF = 2140MHz For Over Operating Input Power Range 1kHz to 6.5kHz Integration BW, PIN = 0dBm CW 2 0.3 20 1 1 2.7 3.3 1.4 0.2 6 5.25 1 0.5 0.2 180 300 5/5 1 8 49 150 MAX UNITS dB dB dB dBm dB mV/dB dBm dB dB dB mV mA s s dB VRMS V V A s s V mA A
EN = 3.3V VOUT Within 10% of Final Value; PIN = 0dBm VOUT Within 10% of Final Value; PIN = 0dBm
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 to meet specified performance from -40C to 85C. 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 defined 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 fitted 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.
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LT5581 TYPICAL PERFORMANCE CHARACTERISTICS
EN = 3.3V and TA = 25C, unless otherwise noted. (Test circuit shown in Figure 1) Output Voltage vs Frequency
2.0 1.8 1.6 1.4 VOUT (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 10 TA = 25C 10MHz 450MHz 880MHz 2.14GHz 2.6GHz 3.5GHz 5.8GHz 2.0 1.8 1.6 1.4 VOUT (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 10
Performance characteristics taken at VCC = 3.3V,
Output Voltage vs Frequency
TA = 25C 880MHz 2.14GHz 2.6GHz 3.5GHz 3 2 LINEARITY ERROR (dB) 1 0 -1 -2
Linearity Error vs Frequency
TA = 25C
-3 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
10MHz 450MHz 880MHz 2.14GHz 2.6GHz 3.5GHz 5.8GHz
5
10
5581 G01
5581 G02
5581 G03
Output Voltage and Linearity Error at 450MHz
2.0 1.8 1.6 1.4 VOUT (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 25C 85C - 40C 2.5 2.0 1.5 LINEARITY ERROR (dB) VARIATION (dB) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 10 2 1 0 -1 -2 3
Linearity Error Temperature Variation from 25C at 450MHz
3 2 85C LINEARITY ERROR(dB) 1 0 -1 -2
Linearity Error vs RF Input Power, 450MHz Modulated Waveforms
TA = 25C CW TETRA CDMA 4C
-40C
-3 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
5
10
-3 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
5
10
5581 G04
5581 G05
5581 G06
Output Voltage and Linearity Error at 880MHz
2.0 1.8 1.6 1.4 VOUT (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 25C 85C - 40C 2.5 2.0 1.5 LINEARITY ERROR (dB) VARIATION (dB) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 10 2 1 0 -1 -2 3
Linearity Error Temperature Variation from 25C at 880MHz
3 2 85C LINEARITY ERROR(dB) 1 0 -1 -2
Linearity Error vs RF Input Power, 880MHz Modulated Waveforms
TA = 25C CW EDGE
-40C
-3 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
5
10
-3 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
5
10
5581 G07
5581 G08
5581 G09
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LT5581 TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage and Linearity Error at 2140MHz
2.0 1.8 1.6 1.4 VOUT (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 25C 85C - 40C 2.5 2.0 1.5 LINEARITY ERROR (dB) VARIATION (dB) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 10 -3 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 10 2 1 0 -40C -1 -2 85C LINEARITY ERROR (dB) 2 1 0 -1 -2 CW WCDMA, UL WCDMA DL 1C WCDMA DL 4C LTE DL 1C LTE DL 4C 3
Linearity Error Temperature Variation from 25C at 2140MHz
3
Linearity Error vs RF Input Power, 2140MHz Modulated Waveforms
TA = 25C
-3 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
5
10
5581 G10
5581 G11
5581 G12
Output Voltage and Linearity Error at 2600MHz
2.0 1.8 1.6 1.4 VOUT (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 25C 85C - 40C 2.5 2.0 1.5 LINEARITY ERROR (dB) VARIATION (dB) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 10 2 1 0 -1 -2 3
Linearity Error Temperature Variation from 25C at 2600MHz
3 2 85C LINEARITY ERROR (dB) 1 0 -1 -2
Linearity Error vs RF Input Power, 2.6GHz Modulated Waveforms
TA = 25C
-40C
-3 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
5
10
-3 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
CW WiMax OFDM PREAMBLE WiMax OFDM BURST WiMax OFDMA PREAMBLE
5
10
5581 G13
5581 G14
5581 G15
Output Voltage and Linearity Error at 3500MHz
2.0 1.8 1.6 1.4 VOUT (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 10 25C 85C - 40C 2.5 2.0 1.5 LINEARITY ERROR (dB) VARIATION (dB) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 2 1 0 -1 -2 3
Linearity Error Temperature Variation from 25C at 3500MHz
3 2 85C LINEARITY ERROR (dB) 1 0 -1 -2
Linearity Error vs RF Input Power, 3.5GHz Modulated Waveforms
TA = 25C
-40C
CW WiMax OFDMA PREAMBLE WiMax OFDM BURST 5 10
-3 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
5
10
-3 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm)
5581 G16
5581 G17
5581 G18
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LT5581 TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage and Linearity Error at 5800MHz
2.0 1.8 1.6 1.4 VOUT (V) 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 10 25C 85C - 40C 2.5 2.0 1.5 LINEARITY ERROR (dB) VARIATION (dB) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 -3 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5 10 2 1 0 -1 -2 LINEARITY ERROR (dB) 2 1 0 -1 -2 -3 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) CW WiMax OFDM BURST 3
Linearity Error Temperature Variation from 25C at 5800MHz
3
Linearity Error vs RF Input Power, 5.8GHz Modulated Waveforms
TA = 25C
85C -40C
5
10
5581 G19
5581 G20
5581 G21
Slope vs Frequency
34 TA = 25C 50
Slope Distribution vs Temperature
TA = -40C TA = 25C TA = 85C SUPPLY CURRENT (mA) 2.0 1.8
Supply Current vs Supply Voltage
40 32 DISTRIBUTION (%) SLOPE (mV/dB) 30
85C 1.6 25C 1.4 -40C 1.2 1.0 0.8 2.6
30
20
28
10
26 0 1 2 3 4 FREQUENCY (GHz) 5
5581 G22
0 6 28 29 30 31 32 SLOPE (mV/dB) 33 34
5581 G23
3
3.4
3.8
4.2
4.6
5
5.4
SUPPLY VOLTAGE (V)
5581 G24
Logarithmic Intercept vs Frequency
-30 LOGARITHMIC INTERCEPT (dBm) TA = 25C 50
Logarithmic Intercept Distribution vs Temperature
TA = -40C TA = 25C TA = 85C
40 -35 DISTRIBUTION (%) 30
-40
20
-45
10
-50 0 1 2 3 4 FREQUENCY (GHz) 5
5581 G25
0 6
-48
-47 -46 -45 -44 -43 -42 LOGARITHMIC INTERCEPT (dBm)
-41
5581 G26
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LT5581 TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs RF Input Power
16 14 SUPPLY CURRENT (mA) 12 VOUT (V) 10 8 6 4 2 0 -25 -20 -15 -10 -5 0 5 RF INPUT POWER (dBm) 10 15 TA = 25C 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -35 -30 -25 -20 -15 -10 -5 0 RF INPUT POWER (dBm) 5
Output Voltage and Linearity Error vs VCC at 2140MHz
TA = 25C 3.3V 5V 2.5 2.0 1.5 LINEARITY ERROR (dB) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 10
5581 G27
5581 G28
Return Loss vs Frequency Reference in Figure 1 Test Circuit
0 -5 OUTPUT VOLTAGE (V) RETURN LOSS (dB) -10 -15 -20 -25 -30 TA = 25C 3.0
Output Transient Response with RF and EN Pulse
TA = 25C, VCC = 5V RF & EN PULSE ON PIN = 10dBm PIN = 0dBm PIN = -10dBm PIN = -20dBm PIN = -30dBm RF & EN PULSE OFF 10 5 RF PULSE ENABLE (V) 0 -5 -10 -15 -20 -25 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 TIME (ms)
5581 G30
2.5 RF & EN PULSE OFF 2.0 1.5 1.0 0.5 0
-0.5 0 1 1
5 6 2 3 4 FREQUENCY (GHz) L1, C1 = 2.2nH, 1.5pF L1, C1 = 0nH, 0.5pF L1, C1 = 1nH, 1.5pF L1, C1 = 0nH, 0pF L1, C1 = 0nH, 1pF 5581 G29
Output Transient Response
3.0 TA = 25C, VCC = 5V RF PULSE ON RF 2.5 PULSE OFF 2.0 1.5 1.0 0.5 0 0 PIN = 10dBm PIN = 0dBm PIN = -10dBm PIN = -20dBm PIN = -30dBm -15 10 RF PULSE OFF 5 RF PULSE ENABLE (V) OUTPUT VOLTAGE (V) 0 -5 -10 3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5
Output Transient Response with CW RF and EN Pulse
TA = 25C EN PULSE OFF EN PULSE ON EN PULSE OFF 4 2 0 ENABLE (V) -2 -4 -6 -8 -10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 TIME (ms)
5581 G32
OUTPUT VOLTAGE (V)
PIN = 10dBm PIN = 0dBm PIN = -10dBm PIN = -20dBm PIN = -30dBm
-20 10 20 30 40 50 60 70 80 90 100 TIME (s)
5581 G31
1
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LT5581 PIN FUNCTIONS
V CC (Pin 1): Power Supply, 2.7V to 5.25V. V CC should be bypassed with a 0.1F 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 0.01F from pin to ground for 10MHz operation. Exposed Pad (Pin 9): Ground. The Exposed Pad must be soldered to the PCB. For high frequency operation, 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
9 LT5581 EXPOSED PAD
150kHz LPF 7 RFIN RMS DETECTOR
OUTPUT BUFFER 300 VOUT 3
BIAS CSQ 8 2 EN 1 VCC 4 5
GND
6
5581 BD
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LT5581 TEST CIRCUIT
C7 0.1F VCC C6 100pF C3 0.01F C5 OPT EN 1 VCC EN CSQ RFIN 8 C2 1000pF 7 L1 2.2nH R2 68 C1 1.5pF RFIN
2 VOUT C4 OPT R3 0
LT5581
3
VOUT GND GND 9
GND
6
NC
NC
4
GND
5
NC
PINS 4, 5, 6: OPTIONAL GROUND 0.018" 0.062" 0.018" DC GND EE = 4.4 RF GND
5581 F01
REF DES C6 C7 C3 C2 R2
VALUE 100pF 0.1F 0.01F 1000pF 68
SIZE 0603 0603 0603 0603 0603
PART NUMBER AVX 06033A101KAT2A AVX 06033C104KAT2A AVX 06033C103KAT2A AVX 06033C102KAT2A
FREQUENCY RANGE 1GHz to 2.2GHz 2GHz to 2.6GHz 2.6GHz to 3.4GHz 3.8GHz to 5.5GHz 4.6GHz to 6GHz
RFIN MATCH L1 2.2nH 1.2nH 0 0 0 C1 1.5pF 1.5pF 1pF 0.5pF 0
Figure 1. Evaluation Circuit Schematic
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LT5581 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 averaging filter 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.
Table 1. RF Input Impedance
FREQUENCY (MHz) 10 50 100 200 400 500 800 900 1000 1500 2000 2100 2500 3000 3500 4000 5000 6000 INPUT IMPEDANCE () 203.6-j5.5 199.5-j22.4 191.7-j40.3 171.1-j68.5 121.8-j95.4 100.2-j97.5 56.8-j86.5 48-j81.2 41.1-j76 22.2-j55 14.6-j41.4 13.6-j39.2 10.8-j32.1 8.6-j25 7.3-j19.4 6.6-j14.5 8.8-j9.6 6.4-j0 S11 MAG 0.606 0.603 0.601 0.601 0.608 0.613 0.631 0.638 0.645 0.679 0.710 0.716 0.737 0.759 0.774 0.783 0.709 0.774 ANGLE () -0.8 -3.4 -6.4 -12.3 -24 -29.8 -46.5 -51.8 -56.8 -79.5 -97.9 -101.2 -112.9 -125.7 -136.9 -147.1 -157.6 -179.9
5581 F02
5581 F03
Figure 2. Top Side of Evaluation Board
Figure 3. Bottom Side of Evaluation Board
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LT5581 APPLICATIONS INFORMATION
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 reflection coefficient 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 setting 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, 0.01F is needed at CSQ. For frequencies above 250MHz, the on-chip 20pF decoupling capacitor is sufficient, and CSQ may be eliminated as desired. The DC-blocking capacitor 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
VCC C3 0.01F 8 RFIN (MATCHED) C2 1000pF 7 C1 R1 68 RFIN CSQ 205
LT5581
20pF
L1
5581 F04
Figure 4. Simplified Circuit Schematic of the RF Input Interface
Figure 5. Input Reflection Coefficient
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12
LT5581 APPLICATIONS INFORMATION
the output pin, to form an RC lowpass filter. The internal 300 resistor in series with the output pin enables filtering of the output signal with just the addition of CLOAD. Figure 7 shows the effect of the external filter 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 filter -3dB corner frequency can be calculated with the following equation: 1 fC = 2 CLOAD(300 + R SS ) Figure 8 shows the transient response for a 2.6GHz WiMAX signal, with preamble and burst ripple reduced by a factor
1.4 LT5581 VCC 1.2 OUTPUT VOLTAGE (V) 1.0 0.8 0.6 0.4 0.2
5581 F06
of 3, using a 0.047F external filter 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 filter capacitance value. Also shown is how the RF pulse response will have longer rise and fall times with the addition of this lowpass filter cap.
TA = 25C NO CAP 0.01F
1.25 1.20 OUTPUT VOLTAGE (V) 1.15 1.10 1.05 1.00 0.95
40A
300 INPUT
VOUT 3
RSS VOUT (FILTERED) CLOAD
0 0
0.90 10 20 30 40 50 60 70 80 90 100 TIME (s) 5581 F07
Figure 6. Simplified Circuit Schematic of the Output Interface
Figure 7. Residual Ripple, Output Transient Response for RF Pulse with WCDMA 4-Carrier Modulation
9 1000 RISE TIME AND FALL TIME (s)
1.4 1.2 OUTPUT VOLTAGE (V) 1.0 0.8 0.6 0.4 0.2 0 0
TA = 25C
OUTPUT RIPPLE PEAK-TO-PEAK (dB)
NO CAP 0.047F
8 7 6 5 4 3 2 1 0 0.001
RIPPLE RISE FALL
TA = 25C
100
10
1 0.01 0.1 1
5581 F09
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 TIME (ms) 5581 F08
EXTERNAL CAPACITOR (F)
Figure 8. Residual Ripple for 2.6GHz WiMAX OFDM 802.16-2004
Figure 9. Residual Ripple, Output Transient Times for RF Pulse with WCDMA 4-Carrier Modulation vs External Filter Capacitor C4
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13
LT5581 APPLICATIONS INFORMATION
Figure 10 shows that rise time and fall time are strong functions of RF input power. Data is taken without the output filter capacitor. For a given RF modulation type--WCDMA, for example--the internal 150kHz filter provides nominal filtering of the residual ripple level. Additional external filtering 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 filtered envelope of the signal. The error will depend on the statistics and bandwidth of the modulation signal in relation to the internal 150kHz filter. For example, in the case of WCDMA, simulations prove that it is possible to set the external filter 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
1 Steve Murray, "Beware of Spectrum Analyzer Power Averaging Techniques," Microwaves
& RF, Dec. 2006.
9 8 RISE TIME AND FALL TIME (s)
TA = 25C FALL TIME
30 25 OUTPUT AC RIPPLE (dB) 20 15 10 5
TA = 25C
0 DEVIATION OF OUTPUT VOLTAGE (dB) -0.5 -1.0 -1.5 -2.0 -2.5 -3.0
7 6 5 4 3 2 1 0 -30 -25 -20 -15 -10 -5 0
5581 F10
RISE TIME
5
0 0.001
INPUT POWER (dBm)
10 1 2-TONE FREQUENCY SEPARATION (MHz)
5581 F11
0.01
0.1
Figure 10. RF Pulse Response Rise Time and Fall Time vs RF Input Power
Figure 11. Output DC Voltage Deviation and Residual Ripple vs 2-Tone Separation Frequency
4.0 3.5 NOISE VOLTAGE (VRMS / Hz) 3.0 2.5 2.0 1.5 1.0 0.5
2.0 TA = 25C INTEGRATED NOISE (mVRMS) 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 1000
5581 F12
TA = 25C 0dBm -10dBm -20dBm -30dBm NO RF INPUT
0 0.1
0dBm -10dBm -20dBm -30dBm NO RF INPUT 1 100 10 FREQUENCY (kHz)
0 0.1
1
100 10 FREQUENCY (kHz)
1000
5581 F13
Figure 12. Output Voltage Noise Density
Figure 13. Integrated Output Voltage Noise
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14
LT5581 APPLICATIONS INFORMATION
resulting deviation in the output voltage of the detector shows the effect of the internal 150kHz filter. 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 simplified 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 20A. If the EN pin is not connected, the chip is disabled through an internal 500k pull-down resistor. 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 VCC
2
EN 500k 300k 300k
5581 F14
Figure 14. Enable Pin Simplified Schematic
PACKAGE DESCRIPTION
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 0.05 (2 SIDES) 0.70 0.05 2.55 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.20 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 BAR TOP MARK (SEE NOTE 6)
3.00 0.10 (2 SIDES)
R = 0.05 TYP 2.00 0.10 (2 SIDES) 0.56 0.05 (2 SIDES) 0.75 0.05
R = 0.115 TYP 5
0.40 0.10 8
0.200 REF
4 0.25 0.05 2.15 0.05 (2 SIDES)
1 0.50 BSC
PIN 1 R = 0.20 OR 0.25 x 45 CHAMFER
(DDB8) DFN 0905 REV B
0 - 0.05
BOTTOM VIEW--EXPOSED PAD
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
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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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LT5581 RELATED PARTS
PART NUMBER DESCRIPTION RF Power Detectors LTC(R)5505 RF Power Detectors with >40dB Dynamic Range LTC5507 100kHz to 1000MHz RF Power Detector LTC5508 300MHz to 7GHz RF Power Detector LTC5509 300MHz to 3GHz RF Power Detector LTC5530 300MHz to 7GHz Precision RF Power Detector LTC5531 300MHz to 7GHz Precision RF Power Detector LTC5532 300MHz to 7GHz Precision RF Power Detector LT5534 50MHz to 3GHz Log RF Power Detector with 60dB Dynamic Range LTC5536 Precision 600MHz to 7GHz RF Power Detector with Fast Comparator Output LT5537 Wide Dynamic Range Log RF/IF Detector LT5538 75dB Dynamic Range 3.8GHz Log RF Power Detector LT5570 60dB Dynamic Range RMS Detector Infrastructure LT5514 Ultralow Distortion, IF Amplifier/ADC Driver with Digitally Controlled Gain LT5517 40MHz to 900MHz Quadrature Demodulator LT5518 1.5GHz to 2.4GHz High Linearity Direct Quadrature Modulator LT5519 LT5520 LT5521 LT5522 LT5525 LT5526 LT5527 LT5528 LT5557 LT5560 LT5568 LT5572 LT5575 0.7GHz to 1.4GHz High Linearity Upconverting Mixer 1.3GHz to 2.3GHz High Linearity Upconverting Mixer 10MHz to 3700MHz High Linearity Upconverting Mixer 600MHz to 2.7GHz High Signal Level Downconverting Mixer High Linearity, Low Power Downconverting Mixer High Linearity, Low Power Downconverting Mixer 400MHz to 3.7GHz High Signal Level Downconverting Mixer 1.5GHz to 2.4GHz High Linearity Direct Quadrature Modulator 400MHz to 3.8GHz, 3.3V High Signal Level Downconverting Mixer Ultralow Power Active Mixer 700MHz to 1050MHz High Linearity Direct Quadrature Modulator 1.5GHz to 2.5GHz High Linearity Direct Quadrature Modulator 800MHz to 2.7GHz High Linearity Direct Conversion I/Q Demodulator COMMENTS 300MHz to 3GHz, Temperature Compensated, 2.7V to 6V Supply 100kHz to 1GHz, Temperature Compensated, 2.7V to 6V Supply 44dB Dynamic Range, Temperature Compensated, SC70 Package 36dB Dynamic Range, Low Power Consumption, SC70 Package Precision VOUT Offset Control, Shutdown, Adjustable Gain Precision VOUT Offset Control, Shutdown, Adjustable Offset Precision VOUT Offset Control, Adjustable Gain and Offset 1dB Output Variation over Temperature, 38ns Response Time, Log Linear Response 25ns Response Time, Comparator Reference Input, Latch Enable Input, -26dBm to +12dBm Input Range Low Frequency to 1GHz, 83dB Log Linear Dynamic Range 0.8dB Accuracy Over Temperature 40MHz to 2.7GHz, 0.5dB Accuracy Over Temperature 850MHz Bandwidth, 47dBm OIP3 at 100MHz, 10.5dB to 33dB Gain Control Range 21dBm IIP3, Integrated LO Quadrature Generator 22.8dBm OIP3 at 2GHz, -158.2dBm/Hz Noise Floor, 50 Single-Ended RF and LO Ports, 4-Channel W-CDMA ACPR = -64dBc at 2.14GHz 17.1dBm IIP3 at 1GHz, Integrated RF Output Transformer with 50 Matching, Single-Ended LO and RF Ports Operation 15.9dBm IIP3 at 1.9GHz, Integrated RF Output Transformer with 50 Matching, Single-Ended LO and RF Ports Operation 24.2dBm IIP3 at 1.95GHz, NF = 12.5dB, 3.15V to 5.25V Supply, Single-Ended LO Port Operation 4.5V to 5.25V Supply, 25dBm IIP3 at 900MHz, NF = 12.5dB, 50 Single-Ended RF and LO Ports Single-Ended 50 RF and LO Ports, 17.6dBm IIP3 at 1900MHz, ICC = 28mA 3V to 5.3V Supply, 16.5dBm IIP3, 100kHz to 2GHz RF NF = 11dB, ICC = 28mA, , -65dBm LO-RF Leakage IIP3 = 23.5dBm and NF = 12.5dBm at 1900MHz, 4.5V to 5.25V Supply, ICC = 78mA, Conversion Gain = 2dB 21.8dBm OIP3 at 2GHz, -159.3dBm/Hz Noise Floor, 50, 0.5VDC Baseband Interface, 4-Channel W-CDMA ACPR = -66dBc at 2.14GHz IIP3 = 23.7dBm at 2600MHz, 23.5dBm at 3600MHz, ICC = 82mA at 3.3V 10mA Supply Current, 10dBm IIP3, 10dB NF Usable as Up- or Down-Converter. , 22.9dBm OIP3 at 850MHz, -160.3dBm/Hz Noise Floor, 50, 0.5VDC Baseband Interface, 3-Ch CDMA2000 ACPR = -71.4dBc at 850MHz 21.6dBm OIP3 at 2GHz, -158.6dBm/Hz Noise Floor, High-Ohmic 0.5VDC Baseband Interface, 4-Ch W-CDMA ACPR = -67.7dBc at 2.14GHz 50, Single-Ended RF and LO Inputs. 28dBm IIP3 at 900MHz, 13.2dBm P1dB, 0.04dB I/Q Gain Mismatch, 0.4 I/Q Phase Mismatch
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0708 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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