Active mixer integrates baluns and enhances port isolation for base-station receivers
By Joshua Israelsohn -- EDN, May 12, 2005
Linear Technology’s LT5527 active downconverting RF mixer integrates RF and local-oscillator baluns that operate on single-ended inputs. The mixer operates at 400 MHz to 3.7 GHz and provides on-chip 50V termination over a wide frequency range with few external matching components (Picture). The chip includes a low-noise. high-speed differential local-oscillator buffer that requires a typical local-oscillator input drive of –3 dBm. The low drive levels help reduce typical LO-to-RF leakage to –36 dBm from 400 MHz to 2.1 GHz and –44 dBm from 2.1 to 3.2 GHz.
The downconverter’s core is a double-balanced mixer. At 1.9 GHz, the LT5527 provides a 23.5-dBm input-third-order intercept, 12.5-dB noise figure and 2.3-dB conversion gain. The chip covers cellular, WCDMA-, TD-SCDMA-, UMTS-, GSM900-, GSM1800, and GSM1900-infrastructure requirements. The 5527 can also serve in wireless data applications, such as MMDS (multichannel microwave distribution system), low-band WiMax, and 900-MHz, 2.4-GHz, and 3.5-GHz WLAN.
The $5.80 (1000) LT5527 is available in a 4×4-mm QFN-16, runs on unipolar 5V supplies, and typically draws 78 mA. In shutdown mode, the chip’s quiescent current drops to 100 μA.
Linear Technology Corp, www.linear.com.
