QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1048A 1.5GHZ TO 2.7GHZ DIRECT CONVERSION I/Q RECEIVER LT5575 DESCRIPTION Demonstration circuit 1048A is a 1.5GHz to 2.7GHz Di- the RF and LO inputs. Only a few external capacitors rect Conversion I/Q Receiver featuring the LT5575. are needed for its application in an RF receiver system. The LT 5575 is an 800MHz to 2.7GHz direct conversion Demonstration circuit 1048A is designed for evaluating quadrature demodulator optimized for high linearity the LT5575 in the frequency range between 1.5GHz and receiver applications. It is suitable for communications 2.7GHz. It can be optimized for input frequencies below 1.5GHz by installing external shunt capacitors at RF in- receivers where an RF signal is directly converted into I put and LO input ports. Refer to the LT5575 data sheet and Q baseband signals with bandwidth up to 490MHz. for details. The LT5575 incorporates balanced I and Q mixers, LO buffer amplifiers and a precision, high frequency quad- Design files for this circuit board are available. Call rature phase shifter. The integrated on-chip broadband the LTC factory. transformers provide 50WWWW single-ended interfaces at , LTC and LT are registered trademarks of Linear Technology Corp. Table 1. Typical Performance Summary (T = 25C, V = 5V, EN = High, f = 1900MHz (DDDDf = 200kHz for 2-tone IIP2 and IIP3 tests), A CC RF P = -10dBm (-10dBm/tone for 2-tone IIP2 and IIP3 tests), f = 1901MHz, P = 0dBm, unless otherwise noted.) RF LO LO PARAMETER CONDITIONS VALUE Supply Voltage 4.5V to 5.25V Supply Current 132mA Maximum Shutdown Current EN = Low 100A + - + - Output DC Offset Voltage I - I , Q - Q < 9mV OUT OUT OUT OUT No External Matching (High Band) 1.5GHz to 2.7GHz RF/LO Input Frequency Range With External Matching (Low Band, Mid Band) 0.8GHz to 1.5GHz Baseband Frequency Range DC to 490MHz Baseband I/Q Output Impedance Single-Ended 65W // 5pF RF/LO Input Return Loss Z = 50W, 1.5GHz to 2.7GHz, Internally Matched > 10dB 0 LO Input Power -13dBm to 5dBm Conversion Gain Voltage Gain, R = 1kW 4.2dB LOAD Noise Figure Double-Side Band 12.7dB rd Input 3 -Order Intercept 2 RF tones, -10dBm/Tone, Df = 200kHz 22.6dBm nd Input 2 -Order Intercept 2 RF tones, -10dBm/Tone, Df = 200kHz 60dBm Input 1dB Compression 11.2dBm I/Q Gain Mismatch 0.01dB I/Q Phase Mismatch 0.4 LO to RF leakage -64.6dBm RF to LO Isolation 57.1dB 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1048A 1.5GHZ TO 2.7GHZ DIRECT CONVERSION I/Q RECEIVER APPLICATION NOTE ABSOLUTE MAXIMUM INPUT RATING OUTPUT FILTERING Power Supply Voltage ..........................................5.5V Proper filtering of unwanted high frequency mixing Enable Voltage .............................. 0.3V to V + 0.3V products at the I and Q outputs is important to maintain CC RF Input Power................................................ 20dBm superior linearity. The most convenient method is to LO Input Power................................................ 10dBm terminate each output with a shunt capacitor to ground. RF Input DC Voltage ...........................................0.1V The capacitor value should be optimized depending LO Input DC Voltage ...........................................0.1V upon the operating frequency. However, the capacitors may reduce baseband output bandwidth. Filtering ca- pacitor values for different frequency bands are listed in FREQUENCY RANGE Table 2. Demonstration circuit 1048A is designed for evaluating the LT5575 in the frequency range between 1.5GHz and 2.7GHz. In this frequency range, both of the LT5575s TEST EQUIPMENT AND SETUP RF and LO ports are internally matched to 50WW. Below WW Refer to Figure 1 for proper measurement equipment 1.5GHz, a shunt capacitor to ground placed close to the setup. RF and LO pins of the IC can be used to provide imped- Use high performance signal generators with low ance matching to maintain best performance. Matching harmonic output for 2-tone measurements. Other- capacitor values for different frequency bands are listed wise, low-pass filters at the signal generator outputs in Table 2. should be used to suppress higher-order harmonics. Table 2. RF and LO match and Baseband Output Filtering High quality combiners that provide broadband 50WW WW termination on all ports and have good port-to-port RF Match LO Match Baseband Frequency Range isolation should be used. Attenuators on the outputs C10 C12 C1-C4 of the signal generators are recommended to further Low Band: improve source isolation, to prevent the sources 4.7pF 3.9pF 10pF 800 to 1000MHz from modulating each other and generating inter- modulation products. Mid Band: 2pF 2pF 2.2pF 1000MHz to 1500MHz Spectrum analyzers can produce significant internal distortion products if they are overdriven. Generally, High Band: None None None spectrum analyzers are designed to operate at their best 1500MHz to 2700MHz with about 30dBm to -40dBm at their input. Sufficient spectrum analyzer input attenuation should be used to avoid saturating the instrument. Before performing measurements on the DUT, the system performance should be evaluated to ensure that: 1) a clean input signal is obtained and 2) the spectrum analyzer internal distortion is minimized. 2