Advantage and disadvantgaes of Direct Conversion Receiver


Direct conversion receiver
advantages of the DCR are:
• No image frequency problem at down-conversion.
• Base band processing can be implemented in a main
stream technology such as CMOS.
• Programmable base band filter and ADC with digital post-filtering can all be realized in the same technology.
disadvantages are:
• LO self-mixing: the local oscillator has limited isolation to the RF path. A part of the LO signal leaks into the RF path, is down-converted to base-band by the mixer and results in an unwanted DC-offset.
• Large amplitude modulated signals are converted to the base band section via second order distortion of the IQmixers leading to time varying DC offset. In order to prevent this kind of DC-offset, a large second order intercept point (IP2) of the IQ-mixers is necessary
Re: Advantage and disadvantgaes of Direct Conversion Receiver
Some other disadvantages are
The signal processing at base-band is subject to
considerable flicker noise from the preceding mixer
stage in CMOS implementations.
• Because no intermediate stage amplification and filtering takes place the requirements for the base band filter linearity and noise are more demanding as for the heterodyne receiver.
• I/Q amplitude and phase mismatches can be a critical
issue for the DCR-topology