A low spurious 400M–6GHz SiGe-MMIC Direct Conversion Transceiver using 2ƒLO LO switching configuration for cognitive radio

A low spurious SiGe-MMIC direct conversion transceiver using 2f_LO LO switching configuration for cognitive radio is described. In the proposed configuration, LO signals for Tx and Rx blocks are generated by frequency divider behind switching circuits. By applying this configuration to the transceiver, the offset frequency of maximum Tx spurious in FDD mode is doubled compared to the conventional configuration. Also, theoretical analysis shows that the proposed configuration can lower LO signal spurious level by 12 dB. Through these effects, receiver sensitivity degradation by Tx signal can be avoided and required characteristics of Tx BPF is relaxed. The direct conversion transceiver MMIC using 2f_LO LO switching configuration is fabricated in 0.18 mum SiGe-BiCMOS process. Measured results show a high modulation accuracy over 400 M-6 GHz, and low Tx spurious characteristics.