LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 LMV225/LMV226/LMV228 RF Power Detector for CDMA and WCDMA Check for Samples: LMV225, LMV226, LMV228 FEATURES DESCRIPTION • • • • The LMV225/LMV226/LMV228 are 30 dB RF power detectors 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 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 integrated 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. 1 2 • • 30 dB Linear in dB Power Detection Range Output Voltage Range 0.2 to 2V Logic Low Shutdown Multi-Band Operation from 450 MHz to 2000 MHz Accurate Temperature Compensation Packages: – DSBGA Thin 1.0 mm x 1.0 mm x 0.6 mm – DSBGA Ultra Thin 1.0 mm x 1.0 mm x 0.35 mm – WSON 2.2 mm x 2.5 mm x 0.8 mm – (LMV225 and LMV228) APPLICATIONS • • • • CDMA RF Power Control WCDMA RF Power Control CDMA2000 RF Power Control PA Modules The LMV225 has an RF power detection range from –30 dBm to 0 dBm and is ideally suited for direct use in combination with resistive taps. The LMV226/LMV228 have a detection 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 requirements. The LMV225/LMV226/LMV228 power detectors are offered in the thin 1.0 mm x 1.0 mm x 0.6 mm DSBGA package and the ultra thin 1.0 mm x 1.0 mm x 0.35 mm DSBGA package. The LMV225 and the LMV228 are also offered in the 2.2 mm x 2.5 mm x 0.8 mm WSON package. Typical Application RF ANTENNA ANTENNA RF PA R1 PA VDD 1.8 k: C 100 pF 50: VDD LMV225 C 100 pF RFIN/EN OUT R2 ENABLE RFIN/EN 10 k: GND OUT ENABLE R2 10 k: Figure 1. LMV225 LMV226/ LMV228 GND Figure 2. LMV226/LMV228 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2003–2013, Texas Instruments Incorporated LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. ABSOLUTE MAXIMUM RATINGS (1) (2) Supply Voltage VDD - GND ESD Tolerance 6.0V Max (3) Human Body Model 2000V Machine Model 200V −65°C to 150°C Storage Temperature Range Junction Temperature (4) 150°C Max Mounting Temperature, Infrared or convection (20 sec) Tin/Lead 235°C Lead-Free 260°C (1) (2) (3) (4) 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 specified. For specifications and the test conditions, see the Electrical Characteristics. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. Human body model: 1.5 kΩ in series with 100 pF. Machine model, 0Ω in series with 100 pF. 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) - TA)/θJA. All numbers apply for packages soldered directly into a PC board OPERATING RATINGS (1) Supply Voltage 2.7V to 5.5V −40°C to +85°C Temperature Range RF Frequency Range (1) 2 450 MHz to 2 GHz 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 specified. For specifications and the test conditions, see the Electrical Characteristics. Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 2.7 DC AND AC ELECTRICAL CHARACTERISTICS Unless otherwise specified, all limits are specified to VDD = 2.7V; TJ = 25°C. Boldface limits apply at temperature extremes. Symbol IDD Parameter Condition Supply Current Active Mode: RFIN/EN = VDD (DC), No RF Input Power Present Min Typ Max LMV225 4.8 7 8 LMV226 4.9 6.2 8 LMV228 4.9 6.2 8 0.44 4.5 μA 0.8 V Shutdown: RFIN/EN = GND (DC), No RF Input Power Present VLOW EN Logic Low Input Level VHIGH EN Logic High Input Level ton Turn-on-Time tr IEN PIN (2) Rise Time (3) No RF Input Power Present, Output Loaded with 10 pF (4) LMV225 2.1 LMV226 1.2 LMV228 1.7 Step from no Power to 0 dBm Applied, Output Loaded with 10 pF LMV225 4.5 Step from no Power to 15 dBm Applied, Output Loaded with 10 pF LMV226 1.8 LMV228 4.8 LMV225 LMV226 LMV228 (1) (2) (3) (4) (5) μs μs 1 (5) mA V Current into RFIN/EN Pin Input Power Range Units 1.8 (2) (1) μA −30 0 dBm −43 −13 dBV −15 15 dBm −28 2 dBV −15 15 dBm −28 2 dBV 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 = TA. No specification of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ > TA. All limits are specified by design or statistical analysis Turn-on time is measured by connecting a 10 kΩ resistor to the RFIN/EN pin. Be aware that in the actual application on the front page, the RC-time constant of resistor R2 and capacitor C adds an additional delay. Typical values represent the most likely parametric norm. Power in dBV = dBm + 13 when the impedance is 50Ω. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 3 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com 2.7 DC AND AC ELECTRICAL CHARACTERISTICS (continued) Unless otherwise specified, all limits are specified to VDD = 2.7V; TJ = 25°C. Boldface limits apply at temperature extremes. (1) Symbol Parameter Logarithmic Slope Condition (6) 900 MHz 1800 MHz 1900 MHz 2000 MHz Logarithmic Intercept (6) 900 MHz 1800 MHz 1900 MHz 2000 MHz VOUT Output Voltage No RF Input Power Present Min LMV225 44.0 LMV226 44.5 LMV228 DSBGA 44.0 LMV228 WSON 48.5 LMV225 39.4 LMV226 41.6 LMV228 DSBGA 41.9 LMV228 WSON 47.4 LMV225 38.5 LMV226 41.2 LMV228 DSBGA 41.6 LMV228 WSON 46.6 LMV225 38.5 LMV226 41.0 LMV228 DSBGA 41.2 45.4 −45.5 LMV226 −24.5 LMV228 DSBGA −27.2 LMV228 WSON −23.7 LMV225 −46.6 LMV226 −25.1 LMV228 DSBGA −28.2 LMV228 WSON −23.8 LMV225 −46.3 LMV226 −24.9 LMV228 DSBGA −28.0 LMV228 WSON −23.7 LMV225 −46.7 LMV226 −24.7 LMV228 DSBGA −28.0 LMV228 WSON -23.6 LMV225 214 350 LMV226 223 350 228 350 LMV228 LMV226 Only 4.5 ROUT Output Impedance LMV225/LMV228 only, no RF Input Power Present Units mV/dB LMV225 Output Current Sourcing/Sinking 4 Max LMV228 WSON IOUT (6) Typ dBm 5.3 19.8 mV mA 29 34 kΩ Device is set in active mode with a 10 kΩ resistor from VDD to RFIN/EN. RF signal is applied using a 50Ω RF signal generator AC coupled to the RFIN/EN pin using a 100 pF coupling capacitor. Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 2.7 DC AND AC ELECTRICAL CHARACTERISTICS (continued) Unless otherwise specified, all limits are specified to VDD = 2.7V; TJ = 25°C. Boldface limits apply at temperature extremes. (1) Symbol en Parameter Condition Min RF Input = 1800 MHz, −10 dBm for LMV225 and 5 dBm for LMV226/LMV228, Measured at 10 kHz Output Referred Noise Variation Due to Temperature Typ nV/√Hz LMV225 +0.64 −1.07 900 MHz, RFIN = 15 dBm Referred to 25°C LMV226 +0.05 −0.02 LMV228 DSBGA +0.22 −0.36 LMV228 WSON +0.87 −0.87 1800 MHz, RFIN = 0 dBm Referred to 25°C LMV225 +0.09 −0.86 1800 MHz, RFIN = 15 dBm Referred to 25°C LMV226 +0.07 −0.10 LMV228 DSBGA +0.29 −0.57 LMV228 WSON +1.04 −1.23 1900 MHz, RFIN = 0 dBm Referred to 25°C LMV225 +0 −0.69 1900 MHz, RFIN = 15 dBm Referred to 25°C LMV226 +0 −0.10 LMV228 DSBGA +0.23 −0.64 LMV228 WSON +1.05 −1.45 2000 MHz, RFIN = 0 dBm Referred to 25°C LMV225 +0 −0.86 2000 MHz, RFIN = 15 dBm Referred to 25°C LMV226 +0 −0.29 LMV228 DSBGA +0.27 −0.65 LMV228 WSON +1.04 −2.02 Product Folder Links: LMV225 LMV226 LMV228 Units 700 900 MHz, RFIN = 0 dBm Referred to 25°C Copyright © 2003–2013, Texas Instruments Incorporated Max Submit Documentation Feedback dB 5 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com 5.0 DC AND AC ELECTRICAL CHARACTERISTICS Unless otherwise specified, all limits are specified to VDD = 5.0V; TJ = 25°C. Boldface limits apply at temperature extremes. Symbol IDD Parameter Supply Current Condition Active Mode: RFIN/EN = VDD (DC), no RF Input Power Present. Min Typ Max LMV225 5.3 7.5 9 LMV226 5.3 6.8 9 LMV228 5.4 6.8 9 0.32 4.5 μA 0.8 V Shutdown: RFIN/EN = GND (DC), no RF Input Power Present. VLOW EN Logic Low Input Level VHIGH EN Logic High Input Level ton Turn-on-Time tr IEN PIN (2) 1.8 (2) Rise Time (3) No RF Input Power Present, Output Loaded with 10 pF (4) Input Power Range LMV225 2.1 LMV226 1.0 LMV228 1.7 Step from no Power to 0 dBm Applied, Output Loaded with 10 pF LMV225 4.5 Step from no Power to 15 dBm Applied, Output Loaded with 10 pF LMV226 1.4 LMV228 4.8 LMV226 LMV228 (1) (2) (3) (4) (5) 6 mA μs μs 1 LMV225 Units V Current Into RFIN/EN Pin (5) (1) μA −30 0 dBm −43 −13 dBV −15 15 dBm −28 2 dBV −15 15 dBm −28 2 dBV 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 = TA. No specification of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ > TA. All limits are specified by design or statistical analysis Turn-on time is measured by connecting a 10 kΩ resistor to the RFIN/EN pin. Be aware that in the actual application on the front page, the RC-time constant of resistor R2 and capacitor C adds an additional delay. Typical values represent the most likely parametric norm. Power in dBV = dBm + 13 when the impedance is 50Ω. Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 5.0 DC AND AC ELECTRICAL CHARACTERISTICS (continued) Unless otherwise specified, all limits are specified to VDD = 5.0V; TJ = 25°C. Boldface limits apply at temperature extremes. (1) Symbol Parameter Logarithmic Slope Condition (6) 900 MHz 1800 MHz 1900 MHz 2000 MHz Logarithmic Intercept (6) 900 MHz 1800 MHz 1900 MHz 2000 MHz VOUT Output Voltage No RF Input Power Present Min LMV225 44.6 LMV226 44.6 LMV228 DSBGA 44.2 LMV228 WSON 48.4 LMV225 40.6 LMV226 42.2 LMV228 DSBGA 42.4 LMV228 WSON 48.3 LMV225 39.6 LMV226 41.8 LMV228 DSBGA 42.2 LMV228 WSON 47.8 LMV225 39.7 LMV226 41.6 LMV228 DSBGA 41.8 LMV228 WSON 47.2 LMV225 −47.0 LMV226 −25.0 LMV228 DSBGA −27.7 LMV228 WSON −23.9 LMV225 −48.5 LMV226 −25.7 LMV228 DSBGA −28.9 LMV228 WSON −23.6 LMV225 −48.2 LMV226 −25.6 LMV228 DSBGA −28.7 LMV228 WSON −23.1 LMV225 −48.9 LMV226 −25.5 LMV228 DSBGA −28.7 LMV228 WSON −23.0 Output Current Sourcing/Sinking LMV226 Only ROUT Output Impedance No RF Input Power Present (6) Max dBm 222 400 LMV226 231 400 244 400 4.5 Units mV/dB LMV225 LMV228 IOUT Typ 5.3 23.7 mV mA 29 31 kΩ Device is set in active mode with a 10 kΩ resistor from VDD to RFIN/EN. RF signal is applied using a 50Ω RF signal generator AC coupled to the RFIN/EN pin using a 100 pF coupling capacitor. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 7 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com 5.0 DC AND AC ELECTRICAL CHARACTERISTICS (continued) Unless otherwise specified, all limits are specified to VDD = 5.0V; TJ = 25°C. Boldface limits apply at temperature extremes. (1) Symbol en 8 Parameter Condition Min Typ Output Referred Noise RF Input = 1800 MHz, −10 dBm for LMV225 and 5 dBm for LMV226/LMV228, Measured at 10 kHz Variation Due to Temperature 900 MHz, RFIN = 0 dBm Referred to 25°C LMV225 +0.89 −1.16 900 MHz, RFIN = 15 dBm Referred to 25°C LMV226 +0.25 −0.16 LMV228 DSBGA +0.46 −0.62 LMV228 WSON +1.39 −1.19 1800 MHz, RFIN = 0 dBm Referred to 25°C LMV225 +0.3 −0.82 1800 MHz, RFIN = 15 dBm Referred to 25°C LMV226 +0.21 −0.09 LMV228 DSBGA +0.55 −0.78 LMV228 WSON +1.39 −1.43 1900 MHz, RFIN = 0 dBm Referred to 25°C LMV225 +0.34 −0.63 1900 MHz, RFIN = 15 dBm Referred to 25°C LMV226 +0.21 −0.19 LMV228 DSBGA +0.55 −0.93 LMV228 WSON +1.54 −1.64 2000 MHz, RFIN = 0 dBm Referred to 25°C LMV225 +0.22 −0.75 2000 MHz RFIN = 15 dBm Referred to 25°C LMV226 +0.25 −0.34 LMV228 DSBGA +0.61− 0.91 LMV228 WSON +0.89 −0.99 Submit Documentation Feedback 700 Max Units nV/√Hz dB Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 CONNECTION DIAGRAM GND RFIN/EN A1 A2 6 OUT 1 VDD NC 2 1.0mm GND B1 B2 5 NC RFIN/EN 3 4 VDD OUT 1.0mm 500Pm 300Pm 125Pm BUMP PITCH BUMP DIAMETER SOLDER DOT DIAMETER/ PASSIVATION OPENING Figure 3. 4-Bump DSBGA – Top View See Package Number YZR0004 or YPD0004 Figure 4. 6-pin WSON – Top View See Package Number NGF0006A PIN DESCRIPTIONS Pin Power Supply Output Name Description DSBGA WSON6 A2 4 VDD Positive Supply Voltage B1 1 GND Power Ground A1 3 RFIN/EN 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 RFIN/EN pin is internally terminated with 50Ω in series with 45 pF. B2 6 Out Ground referenced detector output voltage (linear in dBm) Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 9 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com Block Diagrams VDD LOGIC ENABLE DETECTOR OUT I/I RFIN/EN 10 dB 10 dB 10 dB GND Figure 5. LMV225 VDD LOGIC ENABLE + - I/I OUT RFIN/EN 10 dB 10 dB 10 dB GND Figure 6. LMV226 10 Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 VDD LOGIC ENABLE I/I OUT RFIN/EN 10 dB 10 dB 10 dB GND Figure 7. LMV228 Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 11 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS LMV225 Unless otherwise specified, VDD = 2.7V, TJ = 25°C. Supply Current vs. Supply Voltage (LMV225) Output Voltage vs. RF Input Power (LMV225) 2.50 8 2.25 900MHz 2.00 85°C 7 1800MHz 1.75 2000MHz 6.5 6 VOUT (V) SUPPLY CURRENT (mA) 7.5 25°C 5.5 1.50 1900MHz 1.25 1.00 0.75 5 0.50 -40°C 4.5 0.25 4 2.5 3 3.5 4 4.5 0.00 -50 5 -40 0 10 20 Output Voltage and Log Conformance vs. RF Input Power @ 900 MHz (LMV225) Output Voltage and Log Conformance vs. RF Input Power @ 1800 MHz (LMV225) 2.50 2.50 2.25 3 2.00 2 1.75 1.75 -40°C 1.50 1 1.25 0 -40°C -1 85°C 4 3 25°C 2 1.50 1 -40°C 1.25 0 -40°C 1.00 -1 0.75 -2 0.75 -2 0.50 -3 0.50 -3 0.25 -4 0.25 -4 0.00 -50 -5 0.00 -50 -5 -40 -30 -20 -10 0 10 20 -40 RF INPUT POWER (dBm) -30 Figure 10. 25°C 2.00 25°C 1.50 -40°C 4 2.25 3 2.00 2 1.75 1 1.25 1.00 2.50 0 -1 -40°C VOUT (V) 85°C 1.75 0 10 20 Output Voltage and Log Conformance vs. RF Input Power @ 2000 MHz (LMV225) 5 ERROR (dB) 2.50 85°C -10 Figure 11. Output Voltage and Log Conformance vs. RF Input Power @ 1900 MHz (LMV225) 2.25 -20 RF INPUT POWER (dBm) 5 25°C 85°C 4 85°C 3 25°C 2 1.50 -40°C 1 1.25 0 1.00 -1 -40°C 0.75 -2 0.75 -2 0.50 -3 0.50 -3 0.25 -4 0.25 -4 0.00 -50 -5 0.00 -50 -5 -40 -30 -20 -10 0 10 20 -40 RF INPUT POWER (dBm) -20 -10 0 10 20 RF INPUT POWER (dBm) Figure 12. Submit Documentation Feedback -30 ERROR (dB) 1.00 VOUT (V) 25°C 5 85°C 25°C ERROR (dB) 5 4 25°C ERROR (dB) 85°C 2.00 VOUT (V) -10 Figure 9. 85°C 12 -20 Figure 8. 2.25 VOUT (V) -30 RF INPUT POWER (dBm) SUPPLY VOLTAGE (V) Figure 13. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 TYPICAL PERFORMANCE CHARACTERISTICS LMV225 (continued) Unless otherwise specified, VDD = 2.7V, TJ = 25°C. Logarithmic Slope vs. Frequency (LMV225) Logarithmic Intercept vs. Frequency (LMV225) 47 -43 46 -40°C -44 44 INTERCEPT (dBm) SLOPE (mV/dB) 45 25°C 43 42 41 85°C 40 -40°C -45 25°C -46 -47 39 38 85°C 37 400 800 1200 1600 -48 400 2000 800 1200 1600 2000 FREQUENCY (MHz) FREQUENCY (MHz) Figure 14. Figure 15. 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) 1.5 1.5 85°C 1.0 85°C 0.5 ERROR (dB) ERROR (dB) 1.0 0.0 -0.5 0.5 0.0 -0.5 -40°C -1.0 -1.0 -1.5 -1.5 -40°C -50 -40 -30 -20 -10 0 10 -50 20 -40 -30 -20 -10 0 10 20 RF INPUT POWER (dBm) RF INPUT POWER (dBm) Figure 16. Figure 17. 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) 1.5 1.5 85°C 1.0 1.0 0.5 0.5 ERROR (dB) ERROR (dB) 85°C 0.0 -0.5 -1.0 0.0 -0.5 -1.0 -40°C -40°C -1.5 -1.5 -50 -40 -30 -20 -10 0 10 20 -50 RF INPUT POWER (dBm) Figure 18. -40 -30 -20 -10 0 10 20 RF INPUT POWER (dBm) Figure 19. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 13 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS LMV225 (continued) Unless otherwise specified, VDD = 2.7V, TJ = 25°C. PSRR vs.Frequency (LMV225 in DSBGA) 70 PSRR vs. Frequency (LMV225 in WSON) 5V 60 PSRR (dB) 50 40 2.7V 30 20 10 0 100 1k 10k 100k 1M FREQUENCY (Hz) Figure 20. Figure 21. RF Input Impedance vs. Frequency @ Resistance and Reactance (LMV225 in DSBGA) RF Input Impedance vs. Frequency @ Resistance and Reactance (LMV225 in WSON) 150 100 IMPEDANCE (:) R 50 0 X -50 -100 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 FREQUENCY (GHz) Figure 22. Figure 23. TYPICAL PERFORMANCE CHARACTERISTICS LMV226 Unless otherwise specified, VDD = 2.7V, TJ= 25°C. Output Voltage vs. RF Input Power (LMV226) 7.0 2.50 6.5 2.25 6.0 2.00 900 MHz 1800 MHz 85°C 1.75 5.5 VOUT (V) SUPPLY CURRENT (mA) Supply Current vs. Supply Voltage (LMV226) 5.0 25°C 4.5 4.0 1.50 1.00 2000 MHz 0.75 -40°C 3.5 0.50 3.0 0.25 2.5 2.5 3 3.5 4 4.5 5 0.00 -50 SUPPLY VOLTAGE (V) Submit Documentation Feedback -40 -30 -20 -10 0 10 20 RF INPUT POWER (dBm) Figure 24. 14 1900 MHz 1.25 Figure 25. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 TYPICAL PERFORMANCE CHARACTERISTICS LMV226 (continued) Unless otherwise specified, VDD = 2.7V, TJ= 25°C. Output Voltage and Log Conformance vs. RF Input Power @ 900 MHz (LMV226) Output Voltage and Log Conformance vs. RF Input Power @ 1800 MHz (LMV226) 2.50 5 2.50 2.25 4 2.25 3 2.00 2 1.75 85°C 2.00 5 4 85°C 85°C 25°C 0 1.25 -40°C 1.00 -1 0.75 2 -40°C 25°C 1 1.50 0 1.25 -40°C 1.00 -1 -2 0.75 -2 0.50 -3 0.50 -3 0.25 -4 0.25 -4 -5 0.00 -50 0.00 -50 -40 -30 -20 -10 10 0 20 ERROR (dB) VOUT (V) 1 VOUT (V) -40°C 25°C ERROR (dB) 85°C 1.50 3 25°C 1.75 -5 -40 RF INPUT POWER (dBm) -30 -20 -10 0 10 20 RF INPUT POWER (dBm) Figure 26. Figure 27. Output Voltage and Log Conformance vs. RF Input Power @ 1900 MHz (LMV226) Output Voltage and Log Conformance vs. RF Input Power @ 2000 MHz (LMV226) 2.50 5 2.50 2.25 4 2.25 3 2.00 2 1.75 85°C 85°C 25°C VOUT (V) 3 1 0 1.25 -40°C 2 -40°C 25°C 1.50 1 0 1.25 -40°C 1.00 -1 -2 0.75 -2 0.50 -3 0.50 -3 0.25 -4 0.25 -4 -5 0.00 -50 1.00 -1 0.75 0.00 -50 -40 -30 -20 -10 0 10 20 ERROR (dB) -40°C VOUT (V) 25°C 1.50 4 85°C 85°C 25°C 1.75 ERROR (dB) 2.00 5 -5 -40 -30 -20 -10 0 10 20 RF INPUT POWER (dBm) RF INPUT POWER (dBm) Figure 28. Figure 29. Logarithmic Slope vs. Frequency (LMV226) Logarithmic Intercept vs. Frequency (LMV226) -23.0 46 25°C 45 -23.5 44 -24.0 INTERCEPT (dBm) SLOPE (mV/dB) -40°C 43 85°C 42 41 -40°C 25°C -24.5 -25.0 -25.5 85°C -26.0 40 39 400 800 1200 1600 2000 -26.5 400 800 1200 1600 FREQUENCY (MHz) FREQUENCY (MHz) Figure 30. Figure 31. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 2000 Submit Documentation Feedback 15 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS LMV226 (continued) Unless otherwise specified, VDD = 2.7V, TJ= 25°C. 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) 1.5 1.5 1.0 1.0 85°C ERROR (dB) ERROR (dB) 85°C 0.5 0.5 0.0 -0.5 -40°C 0.0 -0.5 -40°C -1.0 -1.5 -50 -1.0 -30 -40 -20 -10 0 10 -1.5 -50 20 -40 -30 -20 -10 0 10 20 RF INPUT POWER (dBm) RF INPUT POWER (dBm) Figure 32. Figure 33. 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) 1.5 1.5 1.0 85°C 1.0 85°C 0.5 ERROR (dB) ERROR (dB) 0.5 0.0 -0.5 0.0 -0.5 -40°C -1.0 -1.5 -50 -40°C -1.0 -40 -30 -20 -10 0 10 -1.5 -50 20 -40 RF INPUT POWER (dBm) 70 -30 -20 -10 0 10 20 RF INPUT POWER (dBm) Figure 34. Figure 35. PSRR vs. Frequency (LMV226) RF Input Impedance vs. Frequency @ Resistance and Reactance (LMV226) 150 5V 60 100 R IMPEDANCE (:) PSRR (dB) 50 40 2.7V 30 20 50 0 X -50 10 0 100 1k 10k 100k 1M -100 0.4 Figure 36. 16 Submit Documentation Feedback 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 FREQUENCY (GHz) FREQUENCY (Hz) Figure 37. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 TYPICAL PERFORMANCE CHARACTERISTICS LMV228 IN DSBGA Unless otherwise specified, VDD = 2.7V, TJ= 25°C. Supply Current vs. Supply Voltage (LMV228 in DSBGA) Output Voltage vs. RF Input Power (LMV228 in DSBGA) 7.0 2.50 6.5 2.25 1800 MHz 85°C 1.75 5.5 1900 MHz VOUT (V) SUPPLY CURRENT (mA) 900 MHz 2.00 6.0 5.0 25°C 4.5 1.50 1.25 2000 MHz 1.00 4.0 0.75 3.5 -40°C 0.50 3.0 0.25 2.5 2.5 3 3.5 4 4.5 0.00 -50 5 -40 -30 SUPPLY VOLTAGE (V) -20 -10 0 10 20 RF INPUT POWER (dBm) Figure 38. Figure 39. Output Voltage and Log Conformance vs. RF Input Power @ 900 MHz (LMV228 in DSBGA) Output Voltage and Log Conformance vs. RF Input Power @ 1800 MHz (LMV228 in DSBGA) 2.50 85°C 2.25 25°C 2.00 5 2.50 4 2.25 3 2.00 2 1.75 5 85°C 4 25°C 3 0 1.25 -40°C 1.00 -1 0.75 2 -40°C 25°C 1.50 1.25 1 0 -40°C 1.00 -1 -2 0.75 -2 0.50 -3 0.50 -3 0.25 -4 0.25 -4 -5 0.00 -50 0.00 -50 -40 -30 -20 -10 0 10 20 ERROR (dB) VOUT (V) 1 25°C VOUT (V) -40°C 85°C 1.50 ERROR (dB) 85°C 1.75 -5 -40 -30 -20 -10 0 10 20 RF INPUT POWER (dBm) RF INPUT POWER (dBm) Figure 40. Figure 41. Output Voltage and Log Conformance vs. RF Input Power @ 1900 MHz (LMV228 in DSBGA) Output Voltage and Log Conformance vs. RF Input Power @ 2000 MHz (LMV228 in DSBGA) 2.50 85°C 2.25 25°C 2.00 5 2.50 4 2.25 3 2.00 2 1.75 5 85°C 0 -40°C 1.00 -1 0.75 2 -40°C 1.50 1 25°C 0 1.25 -40°C 1.00 -1 -2 0.75 -2 0.50 -3 0.50 -3 0.25 -4 0.25 -4 -5 0.00 -50 0.00 -50 -40 -30 -20 -10 0 10 20 ERROR (dB) 1 VOUT (V) VOUT (V) -40°C 25°C 1.25 3 85°C ERROR (dB) 85°C 1.75 1.50 4 25°C -5 -40 RF INPUT POWER (dBm) Figure 42. -30 -20 -10 0 10 20 RF INPUT POWER (dBm) Figure 43. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 17 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS LMV228 IN DSBGA (continued) Unless otherwise specified, VDD = 2.7V, TJ= 25°C. Logarithmic Slope vs. Frequency (LMV228 in DSBGA) Logarithmic Intercept vs. Frequency (LMV228 in DSBGA) 44.5 -25.5 -40°C 25°C 44.0 -26.0 -40°C INTERCEPT (dBm) SLOPE (mV/dB) 43.5 43.0 85°C 42.5 42.0 41.5 -26.5 25°C -27.0 -27.5 -28.0 85°C -28.5 41.0 40.5 400 800 1200 1600 -29.0 400 2000 800 1200 1600 2000 FREQUENCY (MHz) FREQUENCY (MHz) Figure 44. Figure 45. Output Variation vs. RF Input Power Normalized to 25°C @ 900 MHz (LMV228 in DSBGA) Output Variation vs. RF Input Power Normalized to 25°C @ 1800 MHz (LMV228 in DSBGA) 1.5 1.5 1.0 1.0 85°C 85°C 0.5 ERROR (dB) ERROR (dB) 0.5 0.0 -0.5 -40°C 0.0 -0.5 -40°C -1.0 -1.0 -1.5 -50 -40 -30 -20 -10 0 10 -1.5 -50 20 -30 -20 -10 0 10 20 RF INPUT POWER (dBm) Figure 46. Figure 47. Output Variation vs. RF Input Power Normalized to 25°C @ 1900 MHz (LMV228 in DSBGA) Output Variation vs. RF Input Power Normalized to 25°C @ 2000 MHz (LMV228 in DSBGA) 1.5 1.5 1.0 1.0 85°C 0.0 -0.5 -40°C -1.0 -1.5 -50 85°C 0.5 ERROR (dB) ERROR (dB) 0.5 18 -40 RF INPUT POWER (dBm) -40 -30 -20 -10 0 0.0 -0.5 -1.0 10 20 -1.5 -50 -40°C -40 -30 -20 -10 0 RF INPUT POWER (dBm) RF INPUT POWER (dBm) Figure 48. Figure 49. Submit Documentation Feedback 10 20 Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 TYPICAL PERFORMANCE CHARACTERISTICS LMV228 IN DSBGA (continued) Unless otherwise specified, VDD = 2.7V, TJ= 25°C. PSRR vs. Frequency (LMV228 in DSBGA) 70 RF Input Impedance vs. Frequency @ Resistance and Reactance (LMV228 in DSBGA) 150 5V 60 100 R IMPEDANCE (:) PSRR (dB) 50 40 2.7V 30 20 50 0 X -50 10 -100 0.4 0 100 1k 10k 100k 1M 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 FREQUENCY (GHz) FREQUENCY (Hz) Figure 50. Figure 51. TYPICAL PERFORMANCE CHARACTERISTICS LMV228 IN WSON Unless otherwise specified, VDD = 2.7V, TJ= 25°C. Supply Current vs. Supply Voltage (LMV228 in WSON) Output Voltage vs. RF Input Power (LMV228 in WSON) 7.0 SUPPLY CURRENT (mA) 6.5 6.0 85°C 5.5 5.0 25°C 4.5 4.0 3.5 -40°C 3.0 2.5 2.5 3 3.5 4 4.5 5 SUPPLY VOLTAGE (V) Figure 52. Figure 53. Output Voltage and Log Conformance vs. RF Input Power @ 900 MHz (LMV228 inWSON) Output Voltage and Log Conformance vs. RF Input Power @ 1800 MHz (LMV228 in WSON) 1.80 3 1.60 1.40 2 1.40 1.20 1 1.00 0 VOUT (V) 1.60 85°C 25°C 0.80 -1 -40°C 0.60 -40°C 25°C 0.20 0.00 -50 -40 -30 4 85°C 3 2 1.20 1 25°C 1.00 -2 0.60 -3 0.40 -4 0.20 0 -40°C 0.80 -1 -2 85°C 85°C 0.40 5 ERROR (dB) 2.00 4 VOUT (V) 5 1.80 ERROR (dB) 2.00 -20 -10 0 10 -5 20 0.00 -50 -3 -40°C -4 25°C -40 -30 -20 -10 0 10 RF INPUT POWER (dBm) RF INPUT POWER (dBm) Figure 54. Figure 55. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 -5 20 Submit Documentation Feedback 19 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS LMV228 IN WSON (continued) Unless otherwise specified, VDD = 2.7V, TJ= 25°C. 2.00 5 4 1.80 4 3 1.60 1.40 2 1.40 2 1.20 1 1.20 1 85°C VOUT (V) 25°C 1.00 0 -40°C 0.80 -1 0.60 -40°C 0.20 0.00 -50 25°C -40 -30 1.00 0.60 -3 0.40 -4 0.20 0 25°C 0.80 -2 3 85°C -1 -40°C -2 85°C 85°C 0.40 VOUT (V) 5 1.80 ERROR (dB) 2.00 1.60 20 Output Voltage and Log Conformance vs. RF Input Power @ 2000 MHz (LMV228 in WSON) ERROR (dB) Output Voltage and Log Conformance vs. RF Input Power @ 1900 MHz (LMV228 in WSON) -20 -10 0 10 -5 20 0.00 -50 -3 -40°C -4 25°C -40 -30 -20 -10 0 10 -5 20 RF INPUT POWER (dBm) RF INPUT POWER (dBm) Figure 56. Figure 57. Logarithmic Slope vs. Frequency (LMV228 in WSON) Logarithmic Intercept vs. Frequency (LMV228 in WSON) Figure 58. Figure 59. Output Variation vs. RF Input Power Normalized to 25°C @ 900 MHz (LMV228 in WSON) Output Variation vs. RF Input Power Normalized to 25°C @ 1800 MHz (LMV228 in WSON) Figure 60. Figure 61. Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 TYPICAL PERFORMANCE CHARACTERISTICS LMV228 IN WSON (continued) Unless otherwise specified, VDD = 2.7V, TJ= 25°C. Output Variation vs. RF Input Power Normalized to 25°C @ 1900 MHz (LMV228 in WSON) Output Variation vs. RF Input Power Normalized to 25°C @ 2000 MHz (LMV228 in WSON) Figure 62. Figure 63. PSRR vs. Frequency (LMV228 in WSON) RF Input Impedance vs. Frequency @ Resistance and Reactance (LMV228 in WSON) Figure 64. Figure 65. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 21 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com APPLICATION NOTES CONFIGURING A TYPICAL APPLICATION The LMV225/LMV226/LMV228 are power detectors intended 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 combination 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. DEVICE CHARACTERISTICS Input Range (dBm) Output Buffer LMV225 −30 / 0 No High Resistive Tap Application 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 coupler 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 R1 and the 50Ω input resistance (RIN) of the device realize this attenuation (Figure 66). To minimize insertion loss, resistor R1 needs to be sufficiently large. The following example demonstrates how to determine the proper value for R1. RF ANTENNA PA R1 1.8 k: C 100 pF VDD RFIN/EN LMV225 RIN ENABLE R2 10 k: OUT CIN GND Figure 66. Typical LMV225 Application with High Resistive Tap 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. R1 should realize a minimum attenuation of 31 - 0 = 31 dB. The attenuation realized by R1 and the effective input resistance RIN of the detector equals: AdB = 20·LOG 1 + R1 = 31dB RIN (1) Solving this expression for R1, using that RIN = 50Ω, yields: AdB 31 R1 = 10 20 -1 · RIN = 10 20 -1 · 50 = 1724: (2) In Figure 66, R1 is set to 1800Ω resulting in an attenuation of 31.4 dB. 22 Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 DIRECTIONAL COUPLER APPLICATION The LMV226/LMV228 also has a 50Ω input resistance. However, 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 connected via the directional coupler to the PA without the need of additional external attenuator (Figure 67). Different PA ranges can be configured using couplers with other coupling factors. ANTENNA RF PA 50: VDD C 100 pF RFIN/EN LMV226/ LMV228 OUT ENABLE R2 10 k: GND Figure 67. Typical LMV226/LMV228 Application with Directional Coupler SHUTDOWN FUNCTIONALITY The LMV225/LMV226/LMV228 RFIN/EN pins have 2 functions combined: • Enable/Shutdown • Power input The capacitor C and the resistor R2 (Figure 66 and Figure 67) separate the DC shutdown functionality from the AC power measurement. The device is active when Enable = HI, otherwise 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: 1 f= C · CIN 2 S (R1 + RIN) C + CIN where • RIN = 50Ω, CIN = 45 pF typical (3) With R1 = 1800Ω and C = 100 pF, this results in a corner frequency of 2.8 MHz. This corner frequency is an indicative 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 CIN to assure a proper performance of the high resistive tap. Capacitor C shouldn’t be chosen excessively large since the RC-time, it introduces in combination with resistor R2, adds to the turn-on time of the device. The LMV226/LMV228 do not use a resistor R1 like the LMV225. Though a resistor is seen on the coupler side (RCOUPLER). Therefore a similar equation holds for the LMV226/LMV228 LF corner frequency, where R1 is replaced with the coupler output impedance (RCOUPLER). With RCOUPLER = 50Ω and 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 68 shows the typical output voltage versus PA output power of the LMV225 setup as depicted in Figure 66. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 23 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com LMV225 OUTPUT VOLTAGE (V) 2.25 2.00 LMV225 RF INPUT POWER 1.75 31.4 dB 1.50 1.25 1.00 0.75 0.50 PA OUTPUT POWER 0.25 0.00 -50 -40 -30 -20 -10 0 10 20 30 40 POWER (dBm) Figure 68. Typical power detector response, VOUT vs. PA output Power OUTPUT RIPPLE DUE TO AM MODULATION A CDMA modulated carrier wave generally contains some amplitude modulation that might disturb the RF power measurement 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. Expressions 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 68 can be described as: VIN(t) = VIN [1 + μ(t)] cos (2 · π · f · t) where • • VIN is the amplitude of the carrier frequency Amplitude modulation μ(t) can be between -1 and 1 (4) VIN (1 + P VIN VIN (1 - P 0 Figure 69. AM Modulated RF Signal 24 Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 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 69). This signal has a maximum amplitude VIN • (1+μ) and a minimum amplitude VIN • (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 formula: 2 2 VIN (1 + P)2 VRIPPLE = VY VIN (1 - P)2 +30 -VY 10 LOG 2RIN +30 10 LOG 2RIN PINMIN IN dBm PINMAX IN dBm where • • VY is the slope of the detection curve (Figure 70) μ is the modulation index (5) Equation 5 can be reduced to: VRIPPLE = VY · 20 LOG 1+P 1-P (6) Consequently, the ripple is independent of the average input power of the RF input signal and only depends on the logarithmic slope VY 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 VOUT of the LMV225/LMV228 is linear in dB, or proportional to the input power PIN 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 VOUT will vary linearly over about 5 to 6 dB in the curve (Figure 70). VOUT (V) 200mV SLOPE = VY 5dB PZ PIN (dBm) Figure 70. VOUT vs. RF Input Power PIN The output voltage variation ΔVOUT 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: ΔVO = VY · ΔPIN (7) In which VYis 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, VY = 40 mV/dB. With ΔPIN = 5 dB for CDMA, ΔVOUT = 200 mVPP. This is valid for all VOUT. Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 25 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com 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. COUT = 1.5 nF at the output of the LMV225/LMV228 to ground, this ripple is further attenuated. The cut-off frequency follows from: fC = 1 2 S COUT RO (8) With the output resistance of the LMV225/LMV228 RO = 19.8 kΩ typical and COUT = 1.5 nF, the cut-off frequency equals fC = 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. Since the LMV226 has a low output impedance buffer, a capacitor to reduce the ripple will not be effective. Output Ripple Measurement Figure 71 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 mVPP. Connecting a capacitor of 1.5 nF at the output to ground, results in a ripple of 12 mVPP. 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 paragraph. 1000 OUTPUT RIPPLE (mVPP) NO ADDITIONAL CAPACITOR 100 10 COUT = 1.5nF 1 -50 -40 -30 -20 -10 0 10 RF INPUT POWER (dBm) Figure 71. Output Ripple vs. RF Input Power PRINCIPLE OF OPERATION The logarithmic response of the LMV225/LMV226/LMV228 is implemented by a logarithmic amplifier as shown in Figure 72. The logarithmic amplifier consists of a number of cascaded linear gain cells. With these gain cells, a piecewise approximation of the logarithmic function is constructed. + + + + Y A/0 X0 A/0 X1 A/0 X2 A/0 X3 X4 Figure 72. Logarithmic Amplifier 26 Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 Every gain cell has a response according to Figure 73. At a certain threshold (EK), 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. y x0 xA A/0 x y x EK Figure 73. Gain Cell All gain cell outputs are AM-demodulated with a peak detector and summed together. This results in a logarithmic function. The logarithmic range is about: 20 · n · log (A) where • • n = number of gain cells A = gain per gaincell (9) Figure 74 shows a logarithmic function on a linear scale and the piecewise approximation of the logarithmic function. Y Y = LOG (X) 3 EK/A EK/A EK/A 1 X (LIN) EK 2 Figure 74. Log-Function on Lin Scale Figure 75 shows a logarithmic function on a logarithmic scale and the piecewise approximation of the logarithmic function. Y Y=X Y = AX 2 Y=A X 3 Y=A X EK/A3 EK/A2 EK/A1 EK X (Log) Figure 75. Log-Function on Log Scale Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 27 LMV225, LMV226, LMV228 SNWS013L – AUGUST 2003 – REVISED MARCH 2013 www.ti.com The maximum error for this approximation occurs at the geometric mean of a gain section, which is e.g. for the third segment: EK A 2 · EK A 1 = EK A A (10) The size of the error increases with distance between the thresholds. LAYOUT CONSIDERATIONS For a proper functioning part a good board layout is necessary. Special care should be taken for the series resistance R1 (Figure 66) that determines the attenuation. For high resistor values the parasitic capacitance of the resistor may significantly impact the realized attenuation. The effective attenuation will be lower than intended. To reduce the parasitic capacitance across resistor R1, this resistor can be composed of several components in series instead of using a single component. 28 Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 LMV225, LMV226, LMV228 www.ti.com SNWS013L – AUGUST 2003 – REVISED MARCH 2013 REVISION HISTORY Changes from Revision K (March 2013) to Revision L • Page Changed layout of National Data Sheet to TI format .......................................................................................................... 28 Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LMV225 LMV226 LMV228 Submit Documentation Feedback 29 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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