LMV232TLEVAL

User's Guide SNWA009A – March 2008 – Revised April 2013 AN-1806 LMV232 Evaluation Board 1 General Description This board, the LMV232TLEVAL, can be used to evaluate the Texas Instruments LMV232 dual-channel mean square power detector. The LMV232 mean square power detector is particularly suited for accurate power measurement of RF modulated signals that exhibit large peak to average ratios, that is, large variations of the signal envelope. Such noise-like signals are encountered in applications such as CDMA and wideband CDMA cellphones. 2 Basic Operation The LMV232 power detector provides an accurate power measurement for arbitrary input signals, low and high peak-to-average ratios and crest factors. This is because its operation is not based on peak detection, but on direct determination of the mean square value. The single supply, ranging from 2.5V to 3.3V, can be applied through connectors P5 and P6 of the evaluation board. The device has two digital interfaces. The signal connected to P3 (SD) puts the device in an active mode or a shutdown mode. When SD = HIGH, the device is in shutdown, if SD = LOW the device is active. The signal connected to P4 (BS) selects the active RF input signal. When BS = HIGH, RFIN1 is active (P1). When BS = LOW, RFIN2 is active (P2). The output voltage is measured through connector P8. Connector P7 can be used to monitor the voltage on the FB pin of the LMV232 when a 0Ω resistor is placed in R2. Further details can be found in the Application Notes section of LMV232 Dual-Channel Integrated Mean Square Power Detector for CDMA & WCDMA (SNWS017). The LMV232 conversion gain and bandwidth can be configured by a resistor and a capacitor. Resistor R1 sets the conversion gain from RFIN to the output voltage. A higher resistor value will result in a higher conversion gain. The maximum dynamic range is achieved when the resistor value is as high as possible, i.e. the output signal just doesn’t clip and the voltage stays within the baseband ADC input range. The filter bandwidth is adjusted by capacitor C4. The capacitor value should be chosen such that the response time of the device is fast enough and modulation on the RF input signal is not visible at the output (ripple suppression). The -3 dB filter bandwidth of the output filter is determined by the time constant R1*C4. Generally a capacitor value of 1.5 nF is a good choice. All trademarks are the property of their respective owners. SNWA009A – March 2008 – Revised April 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated AN-1806 LMV232 Evaluation Board 1 Schematics 3 www.ti.com Schematics The schematic of the evaluation board is shown in Figure 1. VDD R2 N/C U1 P1 B3 RFIN1 RFIN1 RFIN2 P2 RFIN2 A1 A2 A3 C3 SD VDD C2 R1 6.2 k: C4 1.5 nF OUT P8 OUT B1 BS GND P3 J1 SD R3 100 k: C5 10 nF P5 VDD VDD P4 FB FB LMV232 C1 P7 P6 + C3 100 µF GND J2 U1 ± pin B3 C2 10 nF U1 ± pin B1 BS R4 100 k: C1 10 nF 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 C1, C2, C5 0603 Capacitor 10 nF C3 Case_C Capacitor 100 µF C4 0603 Capacitor 1.5 nF J1, J2 Header 1 × 3 For Jumper P1, P2 Connector SMA P3, P4, P7, P8 Connector BNC P5, P6 Connector Banana R1 0603 Resistor 6.2 kΩ R2 0603 Resistor Not Connected R3, R4 0603 Resistor 100 kΩ U1 DSBGA LMV232 AN-1806 LMV232 Evaluation Board SNWA009A – 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 SNWA009A – March 2008 – Revised April 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated AN-1806 LMV232 Evaluation Board 3 Measurement Procedure 6 www.ti.com Measurement Procedure The performance of the LMV232 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. The LMV232 is set in active mode by connecting SD (P3) to GND, while RFIN1 is selected by connecting BS (P4) to 2.7V. Both RFIN2 (P2) and FB (P7) can be left unconnected. The resulting DC output voltage is measured with a multimeter connected to OUT (P8). VDD Power Supply VDD BS P4 RFIN1 RF Signal Generator RFIN2 P5 Evaluation Board LMV232 P1 OUT P8 Digital Volt Meter FB P7 P2 P3 SD P6 GND Figure 3. Measurement Setup 7 Measurement Results Figure 4 and Figure 5 show the measurement results for the LMV232. The power is swept at 900 MHz for different temperatures (Figure 4). The resulting error with respect to an ideal fitted curve is shown in Figure 5. Figure 4. VOUT - VPEDESTAL vs. RF Input Power at 900 MHz 4 AN-1806 LMV232 Evaluation Board Figure 5. Input Referred Error vs. RF Input Power at 900 MHz SNWA009A – 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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