A 1.55GHz to 2.45GHz Center Frequency Continuous-Time Bandpass Delta-Sigma Modulator for Frequency Agile Transmitters

摘要

This paper presents a 4th order continuous-time bandpass delta-sigma modulator (CT-BPDSM) with a programmable center frequency ranging from 1.55GHz to 2.45GHz. The modulator is suited to be applied in multi-standard class-S power amplifiers. The circuit features a multi-feedback architecture with return-to-zero (RZ) and half-return-to-zero (HRZ) pulses. The loop filters consist of LC-resonators with emitter degenerated input transconductors and Q-enhancement circuits. A configuration register allows to program the resonator input transconductors, the Q-enhancement circuits and the resonator capacitances with 5 bit resolution. Fine tuning of the resonator center frequency is achieved with varactors. The circuit is implemented in a 200GHz-f{sub}T SiGe-bipolar technology. The measured SNR at 2.2GHz center frequency is 45.5dB in a bandwidth of 20MHz. At 1.55GHz the SNR decreases to 40.7dB. The measured uplink UMTS-FDD ACLR (adjacent channel leakage power ratio) of the modulator output is 48.4dB in the first adjacent channel.