Radio Frequency Integrated Circuit Design - Webs

Mixers
Figure 7.37 Single-balanced and double-balanced CMOS mixers.
Compared to bipolar, for the MOS mixer, the LO voltage is typically
required to be larger to ensure there is complete switching of the quad network.
In order to minimize the amount of extra LO voltage, the switching transistors
usually have a large W /L in order to switch with minimal overdrive. (Here
overdrive refers to V GS − VT ). For the RF port, one can design with a larger
overdrive in order to linearize the input. However, this will reduce the transconductance
and hence will reduce the gain and increase the noise figure.
Another opportunity with CMOS is to replace an NMOS differential pair
with a PMOS differential pair in the RF input and the quad network, which
allows them to be stacked and the current to be reused as shown in Figure 7.38
[4]. In such a case, the output is potentially a high-gain node, so some form
of common mode feedback is required for this circuit.
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