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Published in John D. Cressler, Circuits and Applications Using Silicon Heterostructure Devices, 2018
Lawrence E. Larson, Donald Y.C. Lie
However, although it is actively researched, the direct conversion receiver has not gained completely widespread acceptance to date, especially in high-performance wireless receivers, due to its intrinsic sensitivity to dc offset problems, even-order harmonics of the input signal that interfere with the desired signal, and local-oscillator leakage problems back to the antenna. These issues are all actively pursued by a variety of worldwide research groups, and it is anticipated that they will gradually become solved with further design maturity. The LO feedthrough problem has been addressed through the use of subharmonic mixer approaches—a technique borrowed from millimeter-wave radio astronomy—where the mixer is driven at half the desired frequency [8]. This reduces the problem of LO feedthrough and frequency “pulling” of the local oscillator at the expense of a higher local oscillator drive power.
Design of 0.13 µm low power CMOS subharmonic mixer for DCR applications
Published in International Journal of Electronics Letters, 2021
S Manjula, D Selvathi, M Suganthy, P Anandan
Gilbert mixer is very popular to produce good conversion gain (Gilbert, 1997; Sullivan et al., 1997) at high supply voltage. The Gilbert mixer converts the RF incoming voltage into current and multiplication is performed with the LO signal in the current domain. The Gilbert-type mixer will not eliminate the DC offset problem in DCR. To eliminate DC offset and leakage problem, LO frequency signal is far from the received RF signal. To achieve this, subharmonic mixer is proposed in which frequency of LO is 1/2 of RF frequency. Various subharmonic passive mixers were designed (Bao et al., 2006; Kodkani & Larson, 2008; Mazzanti et al., 2011; Teo & Yeoh, 2008). The passive subharmonic mixer required high gain LNA for minimising noise contribution at baseband due to the conversion loss but the high gain LNA is very difficult to design at the RF stage. In passive subharmonic mixers, conversion loss is a prime design factor.