Literature Survey

1.2.1 Broadband and High Efficiency Power Amplifier

To satisfy the ever-growing demand of 5G communication for high data rates, the millimeter-wave (mm-Wave) transceiver is expected to achieve a wide spectrum bandwidth. Moreover, power amplifiers with high efficiency are a beneficial on the thermal handling and the power consumption of the system. To meet these requirements, implementation of power amplifiers with high peak efficiency and wide output power bandwidth has become a critical research topic. Besides, study on the linearity of power amplifier is also a challenging research topic. To increase the data rates, OFDM modulation is one of the possible solutions which has more critical requirement on the linearity. Table 1.1 shows the comparison of the recent publications of mm-Wave CMOS PAs. There are many techniques adopted to enhance the peak efficiency or the bandwidth in mm-Wave PA design. Transformer matching which considered as the high-order matching circuit is one of the most common method for broadband design [3],[22],[23]. Reference [3] reports a broadband PA work fabricated in 65 nm CMOS technology which provides saturated output power of 15.3 dBm and discusses the design of transformer matching with uncoupled resonant frequency, Q factor, and peak impedance. However, the bandwidth with the peak PAE above 30 % only covers from 24 – 32 GHz which shows degradation from the 3-dB S21 bandwidth from 22 – 42 GHz.

Recently, the harmonic-tuned PAs are one of the solution to enhance the peak efficiency [4],[5],[18],[21]. Moreover, the modulation performances of the published PAs are listed in Table 1.2. There are several linearization techniques, which is realized by adding PMOS, varactors, or second harmonic termination [12],[18],[22]. Since these techniques are designed on the chip with the PA, no external implementation is required.

In reference [18], it demonstrates that the IM3 distortion which caused by the common mode feedback of the neutralization capacitors can be improved with the second harmonic matching. Furthermore, the AM-AM and AM-PM distortion can be improved with the two-step second harmonic termination. Although several mm-Wave PAs based on class-F or inverse class-F (class-F^-1) have outstanding performance, the high efficiency is achieved over a limited bandwidth. Moreover, in references [4] and [21], these PAs require several inductors and capacitors to achieve the proposed harmonic matching which generates additional insertion loss. Therefore, it is challenging to achieve high peak efficiency and broadband simultaneously based on reported broadband PA designs in recent years.

Table 1.1 Comparison of recently published mm-Wave PA.

Ref. Process Topology Freq.

Table 1.2 Modulation performance summary of published mm-Wave CMOS PA.

# Normalized by average power (EVMrms), * Normalized by peak power (EVMmax)

1.2.2 High Linearity Up-Conversion Mixer

To achieve high speed wireless data transmission, the millimeter-wave (mm-Wave) transceiver achieves this requirement by both wide spectrum bandwidth and using high-order QAM modulation signal which needs a harsh requirement on the linearity of the system. In a wireless communication system, linearity is one of the most important specifications of the mixer. Active mixer can provide higher conversion gain with lower LO power but demonstrate poor linearity compared with passive mixer. Furthermore, the IM3 distortion plays an important role in the SNR when transmitter is operated in the high power region. To enhance the linearity of the mixer, several linearization techniques are applied, and Table 1.3 summarizes the published up-conversion mixers and transmitters. The previous work [41] demonstrates an up-conversion mixer which provides an output 1-dB compression point (OP1dB) of -6.2 dBm and third-order intercept point (OIP3) of 13.6 dBm. Nonetheless, the linearization technique is carried out at 10 GHz. At mm-Wave frequency bands, it is difficult to use the same method to improve the linearity. There are many techniques used to enforce the linearity of mixer

in the MMW frequency [6],[28]-[32],[39]. Multiple gate transistors (MGTR) [28]-[30]

and distributed derivative superposition (distributed DS) [31],[32] are the techniques to cancel third-order intermodulation (IM3) current which are originally developed for the LNA. The ideas utilize several parallel transistors with various sizes and bias condition to cancel the third-harmonic signals. Reference [32] presents a 38-54 GHz up-conversion mixer which provides a conversion gain of -2.5 dB and third-order intercept point (OIP3) of 4 dBm. Splitting cascode topology is the other approach that has a dramatic cancellation of IM3 distortion [39]. The proposed topology consists of two paths with different bias condition in the transconductance stage. This work shows the outstanding OIP3 of 32 dBm with dc power of 154.4 mW and possesses two sweet-spots of IM3 according to the two-tone measurement results. However, all of the approaches mentioned above require specific bias conditions for the main and auxiliary transistors to cancel third-harmonic signals. Furthermore, the improvement of IM3

distortion is impressive in the low power region among those works. Therefore, to compare with the published mixers and transmitter, linearity improvement is desired for high data rates 5G communication. Moreover, the IM3 cancellation in the wide IF power region is still a hot topic.

Table 1.3 Performance summary of the published up-conversion mixers and transmitter. amplifier, and a 28-GHz high linearity up-conversion mixer. The contributions of these works will be introduced as following.

1.3.1 30-40 GHz Broadband and Efficiency CMOS PA

A 30-40 GHz high efficiency and broadband power amplifier with continuous mode harmonic-tuned output network using 65-nm CMOS process is proposed. The advantage of continuous harmonic-tuned output matching is that the efficiency can be enhanced in the wide bandwidth through rectifying the current and voltage waveform.