Broadband High-Speed Ka-Band CMOS Direct-Conversion Up-Converters Using Neutralization Technique for 4096-QAM Modulation

This article presents design and analysis of broadband high-speed Ka-band direct-conversion double-sideband (DSB) and in-phase and quadrature (I/Q) up-converters using neutralization technique in a 90-nm CMOS process. The proposed up-converters incorporate neutralized amplifiers and reflection-type modulators to enhance the output power while maintaining modulation fidelity. The operation principle of the reflection-type modulator is analyzed using Volterra series to characterize the nonlinear behavior through Volterra kernels. The design methodology of the proposed DSB and I/Q up-converters is presented in detail, accompanied by theoretical analysis and simulation results. The discussion focuses on device sizing with appropriate biasing, the nonlinear behavior of the proposed circuits, and layout implementation considerations. From 22 to 34 GHz, the proposed DSB and I/Q up-converters demonstrate maximum output powers of 19 and 14 dBm under binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) modulation schemes, respectively. In addition, the I/Q up-converter supports 1024-quadrature amplitude modulation (1024-QAM) and 4096-QAM schemes, achieving measured rms error vector magnitudes (EVMs) of less than −35 and −40 dBc, respectively, with a maximum channel power of 4 dBm.