QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 889 900MHZ DIRECT CONVERSION QUADRATURE DEMODULATOR LT5516 DESCRIPTION Demonstration circuit 889 is a 900MHz Direct Con- direct conversion receiver can eliminate the need for version Quadrature Demodulator featuring the intermediate frequency (IF) signal processing, as LT5516. The LT 5516 is an 800MHz to 1.5GHz direct well as the corresponding requirements for image conversion quadrature demodulator optimized for filtering and IF filtering. Channel filtering can be per- high linearity receiver applications including PA lin- formed directly at the outputs of the I and Q chan- earization. It is suitable for communications receiv- nels. These outputs can interface directly to chan- ers where an RF signal is directly converted into I nel-select filters (LPFs) or to a baseband amplifier. and Q baseband signals with bandwidth up to Demonstration circuit 889 is designed for operations 260MHz. The LT5516 incorporates balanced I and Q in the frequency range between 800MHz and 1.5GHz. mixers, LO buffer amplifiers and a precision, high Design files for this circuit board are available. frequency quadrature generator. Call the LTC factory. In an RF receiver, the high linearity of the LT5516 , LTC and LT are registered trademarks of Linear Technology Corporation provides excellent spur-free dynamic range. This Table 1. Typical Performance Summary (T = 25C) A PARAMETER CONDITION (f = 900MHz, f =901MHz) VALUE RF LO Supply Voltage 4V to 5.25V Supply Current V = 5V, EN = High 117mA CC Maximum Shutdown Current V = 5V, EN = Low 20A CC Frequency Range 800MHz to 1.5GHz LO Input Power -13dBm to -2dBm Conversion Gain Voltage Gain, Load Impedance = 1kPP = -10dBm, P = -5dBm 4.3dB RF LO Noise Figure P = -5dBm, R1 = 8.2Ohm 11.4dB LO rd 2-Tone, -10dBm/Tone, ff == 220000kkHHzz,, PP = -5dBm, R1 = 3.3Ohm Input 3 Order Intercept 21.5dBm LO nd Input 2 Order Intercept 2-Tone, -10dBm/Tone, ff == 220000kkHHzz,, PP = -5dBm, R1 = 3.3Ohm 51dBm LO Input 1dB Compression P = -5dBm, R1 = 3.3Ohm 9dBm LO Baseband Bandwidth 260MHz I/Q Gain Mismatch P = -5dBm, P = -5dBm, output frequency = 1MHz 0.3dB RF LO I/Q Phase Mismatch P = -5dBm, P = -5dBm, output frequency = 1MHz 1 RF LO Output Impedance Differential 120 LO to RF leakage P = -5dBm -65dBm LO RF to LO Isolation P = -10dBm 57dB RF 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 889 900MHZ DIRECT CONVERSION QUADRATURE DEMODULATOR APPLICATION NOTE return resistor, R1. However, lowering supply current FREQUENCY RANGE will degrade linearity. Demonstration circuit 889 is optimized for the fre- quency range from 800MHz to 1.5GHz, particularly for OUTPUT FILTERING the 900MHz Cellular band. This frequency range is Proper filtering of unwanted high frequency mixing limited by the bandwidth of the RF and LO transform- products at the I- and Q- outputs is important to main- ers on the PCB. Outside this range, appropriate exter- tain superior linearity. The most convenient method is nal RF and LO matching transformers designed for the to terminate each output with a shunt capacitor to intended frequency are required to maintain best per- ground. The capacitor value should be optimized de- formance. pending upon the operating frequency. However, the capacitors may reduce baseband output bandwidth. CURRENT CONSUMPTION If lower power consumption is required, the LT5516s supply current can be reduced by increasing the DC QUICK START PROCEDURE Demonstration circuit 889 is easy to set up to evaluate 4. Set Signal Generator 1 to provide a 901MHz, the performance of the LT5516. Refer to Figure 1 for -5dBm, CW signal to the demo board LO input port. proper measurement equipment setup and follow the 5. Set the Signal Generators 2 and 3 to provide two - procedure below: 10dBm CW signals to the demo board RF input NOTE: portone at 899.9MHz, and the other at 900.1MHz. a. Use high performance signal generators with low 6. Set the Spectrum Analyzers start frequency to harmonic output for 2-tone measurements. Oth- 100kHz and stop frequency to 1400kHz. Perform nd rd erwise, low-pass filters at the signal generator input 2 order and 3 order distortion measurement. outputs should be used to suppress higher-order Sufficient spectrum analyzer input attenuation harmonics. should be used to avoid saturating the instrument. b. High quality combiners that provide 50-ohm ter- 7. IIP2 = P1 P2 + Pin, IIP3 = (P1 P3) / 2 + Pin. mination on all ports and have good port-to-port Where P1 is the lowest power level of the two fun- isolation should be used. Attenuators on the out- damental output tones at either 900kHz or 1100kHz, nd puts of the signal generators are recommended to P2 is the 2 order product at 200kHz, P3 is the larg- rd further improve source isolation and to reduce re- est 3 order product at either 700kHz or 1300kHz, flection into the sources. and Pin is the input power (in this case, -10dBm). All units are in dBm. 1. Connect all test equipment as shown in Figure 1. 8. Voltage conversion gain can also be measured. But 2. Set the DC power supplys current limit to 170mA, beware that the gain is reduced by combiner loss and adjust output voltage to 5V. plus 6.85dB, because the load impedance to each 3. Connect Vcc to the 5V DC supply, and then connect output pin is 50W in this setup. Please refer to the EN to 5V the demodulator is enabled (on). LT5516 data sheet for more detailed explanation 2