QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1120A 40MHZ TO 3.8GHZ RF POWER DETECTOR WITH 75dB DYNAMIC RANGE LT5538 DESCRIPTION Demonstration circuit 1120A is a wide dynamic range RF power detector featuring the LT®5538. The LT5538 is a 40MHz to 3.8GHz monolithic logarithmic RF power detector capable of measuring RF signals from –75dBm to 10dBm. The RF signal in a decibel scale is precisely converted into DC voltage on a linear scale. The wide input dynamic range is achieved using cascaded RF detectors and RF limiters. Their outputs are summed to generate an accurate linear DC voltage proportional to the input RF signal in dBm. The output is buffered with a low impedance driver. The LT5538 delivers superior temperature stabile output (within ±1dB over full temperature rage) from 40MHz to 3.8GHz. Demonstration circuit 1120A features broadband input impedance matching optimized for evaluating the LT5538 at frequencies between 40MHz and 2.7GHz. It can be easily reconfigured for higher operating frequencies up to 3.8GHz or optimized to specific frequencies for narrow band applications. Refer to the “Application Note” section and the LT5538 data sheet for details. Design files for this circuit board are available. Call the LTC factory. , LT, LTC, and LTM are registered trademarks of Linear Technology Corp. All other trademarks are the property of their respective owners. Table 1. Typical Demo Circuit Performance Summary (Vcc = 5V, EN = 5V, TA = 25°C, source impedance = 50 , unless otherwise noted. Test circuit shown in Figure 2.) PARAMETER RF Input Frequency Range CONDITION Standard Demonstration Circuit 1120A, >10dB Return Loss (Can be re-matched up to 3.8GHz, refer to the “Application Note” VALUE 40MHz to 2.7GHz Supply Voltage 3V to 5.25V Supply Current 29mA Shutdown Current EN = Low 1uA EN = High (On) > 1V EN = Low (Off) < 0.3V Turn On Time 300ns Turn Off Time 1us Output DC voltage No RF Input Signal Present 350mV Output Impedance 150 Output Source Current 10mA Output Sink Current 200uA Rise Time 0.5V to 1.6V, 10% to 90%, fRF = 880MHz 100ns Fall Time 1.6V to 0.5V, 10% to 90%, fRF = 880MHz 180ns 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1120A 40MHZ TO 3.8GHZ RF POWER DETECTOR WITH 75dB DYNAMIC RANGE Table 2. Typical Demo Circuit Performance Summary, continued (VCC = 5V, EN = 5V, TA = 25°C, source impedance = 50, unless otherwise noted. Test circuit shown in Figure 2.) PARAMETER CONDITION VALUE ±1dB Linearity Error 76dB fRF = 40MHz RF Input Power Range Linear Dynamic Range -75dBm to 10dBm Output Slope 19.9mV/dB Logarithmic Intercept -87.5dBm Sensitivity -72dBm fRF = 450MHz RF Input Power Range Linear Dynamic Range -75dBm to 10dBm ±1dB Linearity Error 75dB Output Slope 19.6mV/dB Logarithmic Intercept -87.3dBm Sensitivity -71.5dBm fRF = 880MHz RF Input Power Range Linear Dynamic Range -75dBm to 10dBm ±1dB Linearity Error 75dB Output Slope 19.0mV/dB Logarithmic Intercept -88.8dBm Sensitivity -71.5dBm fRF = 2140MHz RF Input Power Range Linear Dynamic Range -72dBm to 10dBm ±1dB Linearity Error 70dB Output Slope 17.7mV/dB Logarithmic Intercept -89.0dBm Sensitivity -69.0dBm fRF = 2700MHz RF Input Power Range Linear Dynamic Range -72dBm to 10dBm ±1dB Linearity Error 65dB Output Slope 17.6mV/dB Logarithmic Intercept -87.5dBm Sensitivity -69.5dBm fRF = 3600MHz RF Input Power Range Linear Dynamic Range -65dBm to 10dBm ±1dB Linearity Error 57dB Output Slope 18mV/dB Logarithmic Intercept -81.4dBm Sensitivity -63dBm 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1120A 40MHZ TO 3.8GHZ RF POWER DETECTOR WITH 75dB DYNAMIC RANGE NOTE: 1. Depending on the operating frequency, C8 ABSOLUTE MAXIMUM RATINGS Power Supply Voltage ................................5.5V Enable Voltage ...................... -0.3V, VCC + 0.3V RF Input Power ...................................... 15dBm Operating Ambient Temperature-40°C to +85°C Storage Temperature Range .. -65°C to +125°C Maximum Junction Temperature ............. 150°C RF INPUT INTERFACE The standard demonstration circuit 1120A is configured for broadband RF input to ease evaluations at various frequencies. However, it can be easily reconfigured for narrowband operations, which offers slightly improved sensitivity and some frequency selectivity. Examples of some common RF input frequency matching are presented in Table 3. Please refer to circuit schematic in Figure 4. Their return loss plots are shown in Figure 1 and Figure 2. can be either a capacitor or an inductor. Similarly, L1 can also be a capacitor, an inductor, or a zero-ohm jumper. 2. The LT5538 IC’s IN- pin (Pin 3) is coupled to ground via an internal 20pF capacitor. At low input frequencies, a large value external ac-decoupling capacitor (C5) should be used. At high frequencies, the internal capacitor is sufficient, and C5 can be left open. 0 2 -5 -10 INPUT RETURN LOSS (dB) APPLICATION NOTE 1 -15 -20 -25 -30 -35 Table 3. RF Input Matching Component Values C8 (*1) L1 (*1) 402700 1pF 401300 - 600 27nH -40 C4 C5 (*2) 10dB RL Range (MHz) Trac e No. 1.5n H 1nF 1nF 0.3-2700 1 0 1nF 1nF 0.3-1300 2 27pF 100p F 100p F 300-1300 100p F 600-1450 4 3 900 12nH 12pF 1900 2.7n H 3.3p F 22pF - 17002100 5 2140 2.2n H 2.7p F 22pF - 19002300 6 2600 1.5n H 1.5p F 22pF - 25002800 7 0.7p F 3.3p F 22pF 33003900 8 - 500 1000 1500 2000 2500 FREQUENCY (MHz) 3000 3500 4000 Figure 1. RF Input Return Loss for Wideband Matching 0 -5 -10 100p F 3600 0 INPUT RETURN LOSS (dB) RF Input (MHz) -15 7 -20 -25 6 -30 -35 3 -40 0 500 4 1000 5 1500 2000 2500 FREQUENCY (MHz) 8 3000 3500 4000 Figure 2. RF Input Return Loss for Narrowband Matching 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1120A 40MHZ TO 3.8GHZ RF POWER DETECTOR WITH 75dB DYNAMIC RANGE QUICK START PROCEDURE Demonstration circuit 1120A is easy to set up to evaluate the performance of the LT5538. Refer to Figure 3 for proper measurement equipment setup and follow the procedure below: 5. Connect RF signal generator output to demo NOTE: Care should be taken to never exceed VCC pin to EN pin. Now the detector is enabled (on) and is ready for measurement. absolute maximum input ratings. Never apply DC power to EN pin before VCC pin. 1. Connect DC power supply negative (-) output to demo board GND pin. 6. Using a jumper cable, connect demo board 7. Apply an RF input signal and measure output DC voltage. 8. The linearity dynamic range is defined as the 2. Connect DC power supply positive (+) output (3V to 5.25V) to demo board VCC pin. 3. Connect voltmeter negative (-) lead to demo board GND pin. 4. Connect voltmeter positive (+) lead to the demo board OUT pin. board RFin port (SMA connector J1) via coaxial cable. range over which the linearity error is within ±1dB. The linearity error is calculated by the difference between the incremental slope of the output and the average output slope from -50dBm to -20dBm. 9. Sensitivity is defined as the minimum input power required for the linearity error to be within 3dB of the ideal log-linear transfer curve. Figure 3. Proper Measurement Equipment Setup Figure 4. Demonstration Circuit Schematic 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1120A 40MHZ TO 3.8GHZ RF POWER DETECTOR WITH 75dB DYNAMIC RANGE 5