QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1131A HIGH SIGNAL LEVEL DOWNCONVERTING MIXER LT5557 DESCRIPTION Demonstration circuit 1131A is optimized for evalua- allows convenient interfacing to differential IF filters tion of the LT5557 active downconverting mixer with and amplifiers, or is easily matched to drive a single- transformer-based IF output matching. Its RF input ended 50WWWW load, with or without an external trans- and LO input ports are internally matched to 50WW, WW former. from 1.6 to 2.3GHz, and from 1 to 5GHz, respectively. The LT5557s high level of integration minimizes the The IF output is 50WWWW matched to 240MHz using an L-C total solution cost, board space and system-level varia- bandpass network followed by an 8:1 transformer. tion. The LT5557 active mixer is optimized for high linearity, Design files for this circuit board are available. Call wide dynamic range downconverter applications. The the LTC factory. IC includes a high-speed differential LO buffer amplifier , LT, LTC, and LM are registered trademarks of Linear Technology Corporation. driving a double-balanced mixer. Broadband, inte- grated transformers on the RF and LO inputs provide single-ended 50WWWW interfaces. The differential IF output Table 1. Typical Demonstration Circuit Performance Summary (V = 3.3V, EN = High, T = 25C, f = 1950MHz, P = -6dBm, f = CC A RF RF LO 1710MHz, P = -3dBm, IF output measured at 240MHz, unless otherwise noted. Test circuit shown in Figure 2.) LO PARAMETER CONDITION VALUE Supply Voltage 2.9 to 3.9V Total Supply Current EN = High (> 2.7V) 81.6mA Maximum Shutdown Current EN = Low (< 0.3V) 100A RF Input Frequency Range Return Loss > 12dB 1600 to 2300MHz LO Input Frequency Range Return Loss > 10dB 1000 to 4200MHz IF Output Frequency Range Return Loss > 10dB 220 to 260MHz LO Input Power -8 to 2dBm Conversion Gain 2.9dB rd Input 3 Order Intercept 2 RF tones, -6dBm/tone, Df = 1MHz 24.7dBm Single-Sideband Noise Figure 11.7dB LO to RF Leakage < -45dBm LO to IF Leakage < -42dBm RF to LO isolation > 42dB RF to IF isolation > 41dB 2RF-2LO Output Spurious Product F = 1830MHz, P = -6dBm, f = 240MHz -53dBc RF RF IF (f = f f /2) RF LO IF 3RF-3LO Output Spurious Product F = 1790MHz, P = -6dBm, f = 240MHz -70dBc RF RF IF (f = f f /3) RF LO IF Input 1dB Compression 8.8dBm 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1131A HIGH SIGNAL LEVEL DOWNCONVERTING MIXER APPLICATION NOTE ABSOLUTE MAXIMUM INPUT RATING TEST EQUIPMENT AND SETUP + - Supply Voltage (V , V , IF , IF ) ................. 4V Refer to Figure 1 for proper measurement equipment CC1 CC2 Enable Voltage ........................0.3V to V + 0.3V setup. CC LO Input Power........................................ +10dBm Use high performance signal generators with low har- LO Input DC Voltage ..................... -1V to V + 1V CC monic output for 2-tone measurements. Otherwise, RF Input Power ........................................ +12dBm low-pass filters at the signal generator outputs should RF Input DC Voltage..................................... 0.1V be used to suppress higher-order harmonics. High quality combiners that provide broadband 50WWWW CAUTION: This part is sensitive to electrostatic dis- termination on all ports and have good port-to-port charge (ESD). Observe proper ESD precautions when isolation should be used. Attenuators on the outputs handling the LT5557. of the signal generators are recommended to further improve source isolation, to prevent the sources from modulating each other and generating intermodulation FREQUENCY RANGE products. Demonstration circuit 1131A is optimized for evaluat- ing the LT5557 IC for downconverting a RF signal in Spectrum analyzers can produce significant internal the frequency range of 1.6GHz to 2.3GHz to a 240MHz distortion products if they are overdriven. Generally, IF frequency with either low-side or high- side LO in- spectrum analyzers are designed to operate at their jection. best with about 30dBm to -40dBm at their input. Suf- ficient spectrum analyzer input attenuation should be The LT5557s RF input is internally matched to 50WW WW used to avoid saturating the instrument. from 1.6GHz to 2.3GHz with better than 12dB return loss. Its LO input port is internally matched to 50WWWW Before performing measurements on the DUT, the sys- from 1GHz to 5GHz with better than 10dB return loss. tem performance should be evaluated to ensure that: The frequency range of both ports is easily extended 1) a clean input signal is obtained, and 2) the spectrum with simple external matching. Please refer to the analyzer internal distortion is minimized. LT5557 datasheet Applications Information section. Demonstration circuit 1131A utilizes a transformer for impedance transformation and differential to single- ended conversion on the IF output port. The IF output is 50WW matched for 240MHz, but can be modified for WW other IF frequencies. Equations for calculating com- ponent values, as well as values for several common IF frequencies are given in the LT5557 datasheet Applica- tions Information section. QUICK START PROCEDURE Demonstration circuit 1131A is easy to set up to evalu- Note 1: Care should be taken to never exceed absolute ate the performance of the LT5557. Refer to Figure 1 maximum input ratings. for proper measurement equipment setup and follow Note 2: DC power should never be applied to the EN the procedure below: pin before it is applied to the V pin. CC 2