Abstract
This paper describes a direct-conversion E-band transmitter (TX) in 65-nm CMOS. To demonstrate the feasibility of E-band 1024-quadrature amplitude modulation (QAM), a 67 to 86 GHz direct-conversion CMOS transmitter with broadband image rejection is presented. The transmitter contains an I (in-phase) and Q (quadrature-phase) modulator and a five-stage power amplifier. To achieve a 40 dBc image-rejection ratio (IRR) of the I/Q modulator for E-band, a broadband half-quadrature generator (HQG), which contains a composite right/left-handed (CRLH) based divider, quadrature couplers, and baluns is proposed. For the purpose of minimizing the phase imbalance, phase balance lines are utilized in HQG to achieve a 1-degree phase accuracy under different tuning lines. Subsequently, the reflection can be mitigated by optimizing the impedance matching between the HQG and the mixer core. Meanwhile, because millimeter-wave (MMW) circuits are susceptible to process variations, a process-variation-tolerant design is introduced to mitigate IRR variation, especially under 40 dBc. The transmitter demonstrates a measured flat conversion gain (CG) of 23±2 dB from 56 to 86 GHz. The proposed TX achieves an IRR better than 40 dBc from 67 to 86 GHz (bandwidth of 19 GHz) with a peak IRR of 56.2 dBc at 70 GHz. Furthermore, the proposed TX has exhibited a 6 bit/s/Hz spectral efficiency with 1024-QAM under the orthogonal frequency-division multiplexing (OFDM) modulation format. The 1.129 mm 2 ~E-band TX achieves a measured output power of 6.5 dBm with a total dc power consumption of 164 mW from a 1.2 V supply voltage.
Highlights
The demands for greater bandwidths used in 5G mobile and wireless backhaul drives the research to develop the low-cost millimeter-wave (MMW) CMOS transceiver
In the E-band which has lower oxygen absorption than at 60 GHz, there is a total bandwidth of 17 GHz that can be used as 5G wireless backhaul links
It is observed that the error vector magnitude (EVM) of all modulations with the same symbol rates is less than 3%
Summary
The demands for greater bandwidths used in 5G mobile and wireless backhaul drives the research to develop the low-cost millimeter-wave (MMW) CMOS transceiver. It requires different calibration settings at different frequency points, which is difficult to be used in a single multi-gigahertz channel Another 18 Gbits/s 64-QAM design in the D-band is mentioned in [7] with a spectral efficiency of 3.6 bit/s/Hz in a 5 GHz channel. In [8], the calibration method applied for 64-QAM is to use automatic gain control (AGC) for gain compensation while the phase compensation is manually tuned This method can achieve a SSR larger than 40 dBc at 51-64 GHz, but the phase error becomes 3.0◦. For a 1024-QAM design, we need more design tolerances to accommodate all process variations, especially to achieve an image-rejection ratio (IRR) better than 40 dBc. As seen from the previously mentioned calibration methods, having a high IRR at a wide bandwidth as well as having a small phase error is important, so having a process-variation-tolerant design is needed.
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