## 3 Current Status of the Circuit Component in the MMW Regime
### Mixer
#### 3.3.1 Mixer in CMOS Technology  
Figure 8 illustrates the conversion gain _versus_ fractional bandwidth of the published MMW CMOS mixers. In [125], for a broadband performance, a compact asymmetrical broadside-coupled balun is proposed. Also, a moderate conversion gain and low power consumption can be achieved by using the forward body biased technique. In this case, the threshold voltage and the supply voltage can be reduced for a transistor, which operates in weak inversion region. In [131], the wide-band performance of the mixer is achieved by utilizing the miniature symmetric offset stack Marchand single and dual baluns; meanwhile, the measured conversion loss is 12 dB. In [132], the distributed topology incorporates with a cascode complementary switching pair are utilized for broadband and high conversion gain performances. In [133], the broadband performance is attributed to the \(g_{\mathrm{m}}\) of the switching core itself. The input impedance of the switching core is 1/\(g_{\mathrm{m}}\) and is not heavily dependent on the operation frequency. Thus, a broadband performance is achieved. In [134], a Darlington cell and a wideband Lange coupler, which is composed of the microstrip-line, constitute the mixer. The proposed mixer has a measured CG of 6 dB with a power consumption of 4.2 mW. Note that the maximum CG is 6.5 dB at 36 GHz. Except for the recent published works, some representative MMW mixers are illustrated later. **A 5 to 45 GHz wideband distributed mixer** is designed and implemented with a standard 180 nm CMOS process [132]. Also, the port-to-port isolation is improved by taking the advantage of a cascaded complementary switching pair as illustrated in Figure 9. The distributed mixer is composed of the four-stage distributed topology to carry out a wide bandwidth and minimize its conversion loss. The distributed mixer has a 40 GHz operation bandwidth that is from 5 to 45 GHz with the conversion loss of 11 to 13.2 dB. All port-to-port isolations are better than 30 dB at a LO power level of 8 dBm with a 1.4 mW dc power consumptions. Note that the chip size is 0.92 mm \(\times\) 0.72 mm as shown in Figure 10.  
**Compact balanced mixers** that consist of three miniature asymmetric broadside Marchand baluns are designed, implemented and reported in order to demonstrate the utility of the CMOS technology [135]. There are two baluns, which are analyzed in [135], both have compact chip size of 0.06 mm\({}^{2}\). Besides, the compact asymmetric broadside balun with low-loss broadband characteristics are suitable for the mixer designs. These baluns take advantage of the two asymmetric multilayer meander coupled lines; as a result, the size can be minimized. Moreover, from 10 to 60 GHz, the balun has an insertion loss better than 4.1 dB around 35 GHz with an amplitude imbalance less than 1 dB and a phase imbalance less than 5\({}^{\circ}\). Furthermore, there are three circuits in [135] for the demonstration of the design concept with the proposed miniature technique. The first circuit is a mixer, which is designed to operate in Ku-band. It incorporates with a miniaturized balun. The size of the miniaturized balun can be reduced about 80% compared with the conventional balun. This Ku band mixer has a conversion loss better than 6.8 dB with a chip size of 0.24 mm\({}^{2}\). The second circuit is a 15-60 GHz broadband single-balanced mixer, which has a conversion loss better than 15 dB with a chip area of 0.24 mm\({}^{2}\) as well. Finally, a three-conductor miniaturized dual balun is designed and adapted in the third mixer. This star mixer (the third mixer) incorporates with two miniature dual baluns to achieve a conversion loss of better than 15 dB from 27 to 54 GHz with a chip area of 0.34 mm\({}^{2}\). From the above design examples, the key concept of the miniaturization is verified for MMW mixer design. Figure 8: Common-gate (CG) _versus_ fractional bandwidth of the recent published MMW CMOS mixers. Data taken from [125,131,132,133,134].