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 Demonstration circuit 1120A features broad- range RF power detector featuring the LT 5538. band input impedance matching optimized for evaluating the LT5538 at frequencies between The LT5538 is a 40MHz to 3.8GHz monolithic 40MHz and 2.7GHz. It can be easily reconfig- logarithmic RF power detector capable of ured for higher operating frequencies up to measuring RF signals from 75dBm to 10dBm. 3.8GHz or optimized to specific frequencies for The RF signal in a decibel scale is precisely narrow band applications. Refer to the Applica- converted into DC voltage on a linear scale. tion Note section and the LT5538 data sheet for The wide input dynamic range is achieved us- details. ing cascaded RF detectors and RF limiters. Their outputs are summed to generate an accu- rate linear DC voltage proportional to the input Design files for this circuit board are availa- RF signal in dBm. The output is buffered with a ble. Call the LTC factory. low impedance driver. The LT5538 delivers su- , LT, LTC, and LTM are registered trademarks of Linear Technology perior temperature stabile output (within 1dB Corp. All other trademarks are the property of their respective owners. over full temperature rage) from 40MHz to 3.8GHz. Table 1. Typical Demo Circuit Performance Summary (Vcc = 5V, EN = 5V, TA = 25C, source impedance = 50 , unless otherwise noted. Test circuit shown in Figure 2.) PARAMETER CONDITION VALUE Standard Demonstration Circuit 1120A, >10dB Return Loss RF Input Frequency Range 40MHz to 2.7GHz (Can be re-matched up to 3.8GHz, refer to the Application Note 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%, f = 880MHz 100ns RF Fall Time 1.6V to 0.5V, 10% to 90%, f = 880MHz 180ns RF 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 (V = 5V, EN = 5V, T = 25C, source imped- CC A ance = 50, unless otherwise noted. Test circuit shown in Figure 2.) PARAMETER CONDITION VALUE fRF = 40MHz RF Input Power Range -75dBm to 10dBm Linear Dynamic Range 1dB Linearity Error 76dB Output Slope 19.9mV/dB Logarithmic Intercept -87.5dBm Sensitivity -72dBm fRF = 450MHz RF Input Power Range -75dBm to 10dBm Linear Dynamic Range 1dB Linearity Error 75dB Output Slope 19.6mV/dB Logarithmic Intercept -87.3dBm Sensitivity -71.5dBm fRF = 880MHz RF Input Power Range -75dBm to 10dBm Linear Dynamic Range 1dB Linearity Error 75dB Output Slope 19.0mV/dB Logarithmic Intercept -88.8dBm Sensitivity -71.5dBm fRF = 2140MHz RF Input Power Range -72dBm to 10dBm Linear Dynamic Range 1dB Linearity Error 70dB Output Slope 17.7mV/dB Logarithmic Intercept -89.0dBm Sensitivity -69.0dBm f = 2700MHz RF RF Input Power Range -72dBm to 10dBm Linear Dynamic Range 1dB Linearity Error 65dB Output Slope 17.6mV/dB Logarithmic Intercept -87.5dBm Sensitivity -69.5dBm f = 3600MHz RF RF Input Power Range -65dBm to 10dBm Linear Dynamic Range 1dB Linearity Error 57dB Output Slope 18mV/dB Logarithmic Intercept -81.4dBm Sensitivity -63dBm 2