A low-voltage folded switching mixer
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In the double-quadrature low-IF front-end with adaptive image rejection, performance of the down-conversion mixer has a great influence on the overall front-end performance. Actually, the down-conversion mixer can be considered as the most important building block in the double-quadrature down-converter. Therefore, it has to satisfy very challenging requirements. First, the down-conversion mixer has to be low power because the double-quadrature low-IF front-end employs four of them. Second, it has to provide a high voltage gain in order to compensate for the attenuation introduced by the RCPF, which is implemented as two stage RC polyphase filter. Third, taking into account the trends in the CMOS technology, the down-conversion mixer has to be robust in terms of technology scaling. For digital circuits, CMOS technology scaling yields an improvement in power consumption, operating speed and number of transistors per unit area. While CMOS technology scaling is quite beneficial for digital circuits, this is not the case for RF analog circuits. The most severe consequence of technology scaling that affects the RF analog design is a reduction of the voltage supply. Insufficient voltage headroom causes that not all circuit topologies can satisfy the required specifications. Hence, research into low-voltage circuit topologies is important. This chapter discusses a low-voltage, lowpower AC-coupled folded switching mixer with current-reuse. This mixer can operate at a supply voltage of 1 V and still offer good performance.
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