LMV228SDEVAL

User's Guide SNWA010B – March 2008 – Revised April 2013 AN-1817 LMV225/LMV228 WSON Evaluation Board 1 General Description This board can be used to evaluate the Texas Instruments LMV225/LMV228 RF detectors. These logarithmic power detectors are intended for use in CDMA and WCDMA applications. They have a 30 dB dynamic range and an RF frequency range from 450 MHz to 2 GHz. The LMV228 is designed to be used in combination with a directional coupler, while the LMV225 detector is especially suited for power measurements via a high-resistive tap as well as directional coupler. The LMV225/LMV228 have an integrated filter for low-ripple average power detection of CDMA signals. Additional filtering can be applied using a single external capacitor. 2 Basic Operation The LMV225/LMV228 provide an accurate temperature and supply compensated DC output voltage that relates linearly to the applied RF input power in dBm. The single supply, ranging from 2.7V to 5.5V, can be applied through connectors P4 and P5. The signal applied to connector P2 puts the detector in an active or a shutdown mode. The detector is active for Enable = HI, otherwise it is in a low power consumption shutdown mode. The RF signal is applied through connector P1, while the output voltage is measured through connector P3. 2.1 Input The LMV225 has an RF power detection range from −30 dBm to 0 dBm and is designed for direct use in combination with resistive taps. The LMV228 has a detection range from −15 dBm to 15 dBm and are intended for use in combination with a directional coupler. Both detectors have an input impedance of 50Ω. Details about the configuration can be found in LMV225/LMV226/LMV228 RF Power Detector for CDMA and WCDMA (SNWS013). 2.2 Output The output voltage range is typically 0.2V to 2V and can be scaled down to meet ADC input range requirements. Since the LMV225/LMV228 have a current controlled output, the voltage range can be adjusted by changing the output resistance. To change this a resistor needs to be placed in R5. The output impedance of the detector (typical 19.8 kΩ) together with the resistor R5 translates the current into a voltage. The value of resistor R5 determines the exact scaling. A value of 19.8 kΩ for example divides the output voltage range by half. Besides scaling the output voltage, the output ripple can be reduced by lowpass filtering. This can be realized with capacitor C3. Further details can be found in the applications notes information section in LMV225/LMV226/LMV228 RF Power Detector for CDMA and WCDMA (SNWS013). All trademarks are the property of their respective owners. SNWA010B – March 2008 – Revised April 2013 Submit Documentation Feedback AN-1817 LMV225/LMV228 WSON Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 1 Schematic 3 www.ti.com Schematic The schematic of the evaluation board is shown in Figure 1. VDD U1 4 R2 0: P1 C2 100 pF RFIN/EN 3 RFIN LMV225/ LMV228 R3 N/C P3 OUT OUT 6 R5 N/C 1 C3 N/C R4 10 k: GND P2 P4 ENABLE R1 N/C U1 ± pin A2 VDD C1 N/C P5 + C4 100 µF C5 10 nF GND U1 ± pin B1 Figure 1. Schematic of the Evaluation Board 4 Bill of Materials The Bill of Material (BOM) of the evaluation board is listed in Table 1. Table 1. Bill of Materials of the Evaluation Board 2 Designator Description Comment C2 0603 Capacitor 100 pF C4 Case_C Capacitor 100 µF C5 0603 Capacitor 10 nF C1, C3 0603 Capacitor Not Connected P1 Connector SMA P2 Connector BNC P3 Connector BNC P4 Connector Banana P5 Connector Banana R2 0603 Resistor 0Ω R4 0603 Resistor 10 kΩ R1, R3, R5 0603 Resistor Not Connected U1 WSON LMV225 or LMV228 AN-1817 LMV225/LMV228 WSON Evaluation Board SNWA010B – March 2008 – Revised April 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Layout www.ti.com 5 Layout The layout of the evaluation board is shown in Figure 2. All Layers Silk Screen Figure 2. Layout of the Evaluation Board SNWA010B – March 2008 – Revised April 2013 Submit Documentation Feedback AN-1817 LMV225/LMV228 WSON Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 3 Measurement Procedure 6 www.ti.com Measurement Procedure The performance of the LMV225/LMV228 can be measured with the setup given in Figure 3. In this measurement example a supply voltage of 2.7V is applied by the power supply. To put the LMV225/LMV228 in active mode, the Enable (P2) is connected to 2.7V as well. The resulting DC output voltage is measured with a multimeter connected to P3. A 900 MHz RF signal is applied by the RF generator to connector P1, where the RF power is swept from −50 dBm to +20 dBm. VDD Power Supply VDD ENABLE P2 P4 Evaluation Board LMV225/LMV228 RFIN P1 RF Signal Generator OUT P3 Digital Volt Meter P5 GND Figure 3. Measurement Setup 7 Measurement Results Figure 4 and Figure 5 show the measurement results for the LMV225/LMV228 respectively. For each plot the RF power is swept at 900 MHz for different temperatures. Also the error in dBs with respect to an ideal straight line is plotted (Log conformance). 5 2.00 5 4 1.80 4 3 1.60 2 1.40 2 1.20 1 25°C 2.00 25°C VOUT (V) 1.75 -40°C 1.50 1 1.25 1.00 0 -40°C -1 -2 0.75 VOUT (V) 2.25 85°C ERROR (dB) 85°C 1.00 0.20 0.00 -50 -5 0.00 0 10 20 4 AN-1817 LMV225/LMV228 WSON Evaluation Board -3 -40°C 25°C -50 -40 RF INPUT POWER (dBm) Figure 4. LMV225 Output Voltage and Log Conformance vs. RF Input Power at 900 MHz -1 -2 85°C 0.40 0.25 -10 -40°C 0.60 -4 -20 0 0.80 -3 -30 3 25°C 0.50 -40 85°C ERROR (dB) 2.50 -30 -20 -10 0 10 RF INPUT POWER (dBm) -4 -5 20 Figure 5. LMV228 Output Voltage and Log Conformance vs. RF Input Power at 900 MHz SNWA010B – March 2008 – Revised April 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated 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. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. 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