QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 966 HIGH LINEARITY DIRECT QUADRATURE MODULATOR LT5568 DESCRIPTION Demonstration circuit 966 is an I/Q modulator mixer signals to a 50W single-ended output. featuring the LT 5568. The LT 5568 is a The four balanced I and Q base-band input 700MHz to 1.05GHz direct I/Q modulator ports are intended for DC coupling from a designed for high performance wireless source with a common-mode voltage level of applications, including wireless infrastructure. It about 0.5V. The differential input impedance of may also be configured as an image reject the baseband inputs is approximately 100W, upconverting mixer, by applying 90 phase- making them ideally suited for current-drive shifted signals to the I and Q inputs. applications. A high-speed, internally matched LO amplifier The LO path consists of an LO buffer with drives two double-balanced mixer cores, single-ended input, and precision quadrature allowing the use of a low power, single-ended generators which produce the LO drive for the LO source. It allows direct modulation of an RF mixers. signal using differential baseband I and Q Demonstration circuit 966 is designed for an RF signals. It supports GSM, EDGE, CDMA, output frequency range from 700MHz to CDMA2000, W-CDMA, 64-QAM, OFDM and 1.05GHz. other modulation formats. Design files for this circuit board are avail- The I/Q baseband inputs consist of voltage-to- able. Call the LTC factory. current converters that in turn drive double- LT is a registered trademark of Linear Technology Corporation. balanced mixers. The outputs of these mixers are summed and applied to an on-chip RF transformer, which converts the differential 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 966 HIGH LINEARITY DIRECT QUADRATURE MODULATOR Table 1. Typical Performance Summary (T = 25C) A PARAMETER CONDITION (f = 2MHz, f =850MHz) VALUE BB LO Supply Voltage 4.5V to 5.25V Supply Current V = 5V, EN = High 113 mA CC Maximum Shutdown Current V = 5V, EN = Low 230 A CC RF Frequency Range 700 to 1050 MHz Baseband Frequency Range DC to 380 MHz LO Input Return Loss Z = 50W, P = 0dBm 13 dB 0 LO RF Output Return Loss Z = 50W 30 dB 0 LO Input Power -10 to +5 dBm LO Frequency Range 700 to 1050 MHz Conversion Gain P = -10dBm, P = 0dBm, defined as P /P -6.8 dB RF LO RF BB rd Output 3 Order Intercept 2-Tone, P = -10dBm/Tone, Df = 100KHz, P = 0dBm +22.9 dBm RF LO nd Output 2 Order Intercept 2-Tone, P = -10dBm/Tone, Df = 100KHz, P = 0dBm +63 dBm RF LO Output 1dB Compression P = 0dBm +8.3 dBm LO LO leakage P = 0dBm -43 dBm LO Image Rejection P = 0dBm -46 dBc LO 2