RF Transmitters - Printable Version +- Free Academic Seminars And Projects Reports (https://easyreport.in) +-- Forum: Seminars Topics And Discussions (https://easyreport.in/forumdisplay.php?fid=30) +--- Forum: Engineering Seminars Topics (https://easyreport.in/forumdisplay.php?fid=7) +---- Forum: Electronics Seminar Topics (https://easyreport.in/forumdisplay.php?fid=11) +---- Thread: RF Transmitters (/showthread.php?tid=47803) |
RF Transmitters - sangram79 - 10-04-2017 RF Transmitters Architectures for Integration and Multi-Standard Operation Outline Motivation Transmitter Architectures Current Trends in Integration State-of-the-Art Examples (3) Direct Conversion 2-Stage Future Challenges References Motivation Increase in demand for low-cost, small-form-factor, low-power transceivers Proliferation of various wireless standards pushes for multi-standard operation CMOS is well suited for high levels of mixed signal radio integration [2] End goal: a low cost single chip radio transceiver covering multiple RF standards Transmitter Architectures Mixer-Based Direct Conversion (Homodyne) 2-Stage Conversion (Heterodyne) Both architectures can operate with constant and non-constant envelope modulation Well-suited for multi-standard operation PLL-Based Show promise with respect to elimination of discrete components Fundamentally limited to constant-envelope modulation schemes not suitable for multi-standard operation Transmitter Architectures Direct Conversion Attractive due to simplicity of the signal path suitable for high levels of integration Output carrier frequency = local oscillator (LO) frequency Important drawback: LO disturbance by PA output Transmitter Architectures Direct Conversion LO Pulling Noisy output of PA corrupts VCO spectrum - injection pulling or injection locking VCO frequency shifts toward frequency of external stimulus If injected noise frequency close to oscillator natural frequency, then LO output eventually locks onto noise frequency as noise level increases Transmitter Architectures Direct Conversion LO Frequency Offset Technique LO pulling can be alleviated by moving the PA output spectrum sufficiently far from the LO frequency LO offset can be achieved by mixing 2 VCO outputs 1 and 2 and filtering the result; leading to a carrier frequency of 1+ 2, far from either 1 or 2 BPF1 must have high selectivity to suppress spurs of the form m 1+m 2 to avoid degradation in quadrature generation and spurs in the up-converted signal Transmitter Architectures 2-Stage Up-Conversion Another approach to solving the LO pulling problem Up-convert in 2 stages so PA output spectrum is far from VCO frequency Quadrature modulation at IF ( 1), up-convert to 1+ 2 by mixing and filtering BPF1 suppresses the IF harmonics, while BPF2 removes the unwanted sideband 1- 2 Advantages: no LO pulling; better I/Q matching (less crosstalk between the 2 bit streams) Current Trends in Integrated Transceivers Both direct and 2-stage architectures are used (with modifications for better integration and multi-standard operation) Direct architecture achieves a low-cost solution with a high level of integration [3],[4],[6],[8] 2-stage results in better performance (ie. reduced LO pulling) at the expense of increased complexity and hence higher cost of implementation [5],[7],[9],[10],[11] Transmitter and receiver designed concurrently to enable hardware and possibly power sharing For more information abut this article,please follow the link: http://eecg.toronto.edu/ kphang/papers/2003/TYao_RF_TX_circuits.ppt |