Design of IF-RF-Based Heterodyne Transmitter Using Current Steering DAC with 5.4 GHz Spur-Free Bandwidth

Abstract

The paper presents an intermediate frequency (IF) radio frequency (RF)-based heterodyne transmitter using current steering DAC. In the proposed design, a single digital AND gate is used as IF mixer and modulator of input data. This IF signal is further mixed with local oscillator signal in the current steering DAC to obtain RF output signal. The AND gate-based IF modulator converts input signal to square wave. This square wave does not contain even harmonics and consists of odd harmonics, which reduces harmonic mixing products. In addition, double differential architecture has been used in current steering DAC to cancel even harmonics. With cancellation of even harmonics in IF and RF signals, the output spectrum consists of only odd multiple of RF output frequency, resulting in spur-free bandwidth of 5.4 GHz for the RF output frequency of 2.4 GHz. The proposed transmitter employs 64-quadrature amplitude modulation which gives an output power of 446 m dBm without a power amplifier. Monte-Carlo simulations have been performed to verify the reliability of the circuit against process and mismatch variations, and it has been found that the circuit parameters are less sensitive to process variations.