RF Input Impedance Matching Data for the LTC5564 Schottky Detector – Design Note 1030 John Chung, Bruce Hemp Introduction File Links The LTC 5564 is an UltraFast™ RF power detector for applications in the 600MHz to 15GHz frequency range. It combines a temperature compensated Schottky diode peak detector, a gain selectable operational amplifier and a fast comparator in a 16-lead 3mm × 3mm package. FILE NAME CONTENTS LTC5564_-10dBm.S1P Input Reflection Coefficient, S11, PIN = –10dBm, Touchstone Format. 101 Freq. Points, 0.5GHz to 16.5GHz. LTC5564_0dBm.S1P Input Reflection Coefficient, S11, PIN = 0dBm, Touchstone Format. 101 Freq. Points, 0.5GHz to 16.5GHz. ® Performance of the RF detector, specifically detector response and bandwidth, depends on proper impedance matching into the detector RF input. The impedance measurements presented here can be used in conjunction with a CAD simulation tool to simplify the task of RF input impedance matching. GND RF INPUT SMA CONNECTOR The phase reference plane for the measurement is 1.1mm away from the edge of the QFN package. This distance was chosen to give a comfortable margin against typical DFM rules regarding the distance between components. For higher frequencies, the accuracy of the S11 measurement becomes diminished by various factors specific to each individual PCB design, such as ground via inductance, the quality of the microstrip transitions, etc. Nonetheless, the S1P data helps in producing the first cut design, saving development time. 05/13/1030 GND GND RF Input Impedance Measurement Input impedance was measured on a LTC5564 demo board DC1646A, modified for minimal RF trace length as shown in Figure 1. For the purpose of this measurement, the detector input DC block was omitted since the test equipment supports DC voltage at its input. In a real world application, a DC block function must be included as part of the matching network design. The measured LTC5564 input impedance is shown in Figure 2 and Table 1. Cu CONNECTING TRACE: 18 MIL WIDTH, TAPERED AT IC PAD N4000-13 SUBSTRATE: THICKNESS IS 17 MILS BETWEEN LAYER 1 AND GROUND LAYER 2 1.1mm REFERENCE PLANE DN1030 F01 Figure 1. Test Setup Showing Location of the Reference Plane Note that the input impedance to the Schottky detector is a slight function of RF drive level, as seen in Figure 2. There is no measurable input impedance variation over the specified supply voltage range of 3V to 5.5V. Refer to the DC1646A demo board manual for several LTC5564 RF input matching circuit examples. Conclusion The LTC5564 RF input impedance was measured and converted to a 1-port S-parameter file, which can be read by most industry-standard RF CAD programs, expediting the matching process. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and UltraFast is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. 0dBm –10dBm PHASE REFERENCE PLANE: 1.1mm FROM THE EDGE OF THE QFN PACKAGE Figure 2. Measured S11 for the LTC5564 Table 1. LTC5564 Input Impedance, PIN = –10dBm INPUT IMPEDANCE (SERIES EQUIV.) VOLT. REFL. COEFF. (ZO = 50Ω) INPUT IMPEDANCE (SERIES EQUIV.) VOLT. REFL. COEFF. (ZO = 50Ω) RS jXS MAG ANG FREQUENCY (GHz) RS jXS MAG ANG 0.5 126.2 –59.8 0.521 –19.4 9.3 50.7 91.2 0.671 47.4 1.3 65.9 –58.6 0.468 –48.0 10.1 63.7 109.7 0.700 38.9 2.1 40.7 –40.3 0.416 –79.0 10.9 92.0 132.1 0.715 29.4 2.9 31.0 –22.5 0.350 –114.7 11.7 120.8 143.3 0.717 23.7 3.7 28.5 –11.2 0.305 –144.2 12.5 170.8 143.6 0.712 16.9 4.5 24.1 –0.1 0.350 –179.7 13.3 211.7 78.6 0.658 9.2 5.3 20.9 12.8 0.442 146.0 14.1 197.7 3.7 0.596 0.6 6.1 21.9 27.1 0.508 115.3 14.9 115.7 –22.0 0.415 –11.0 6.9 26.6 40.9 0.542 91.7 15.7 95.8 46.1 0.425 27.6 7.7 30.3 57.7 0.617 73.1 16.5 168.9 83.8 0.621 14.2 8.5 38.4 76.7 0.663 57.7 FREQUENCY (GHz) Note: For a less granular version of this data, use the S1P data file (101 frequency points) Data Sheet Download www.linear.com/LTC5564 Linear Technology Corporation For applications help, call (408) 432-1900 dn1030f 0513 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2013