A 900-MHz Direct Delta-Sigma Receiver in 65-nm CMOS

Direct delta-sigma receiver architecture is introduced for wireless communication systems, such as LTE or WiMax. Architecture is based on direct downconversion, delta-sigma feedback that is up-converted to RF, and N-path filtering technique. Hence, the core receiver functions including channel selection filtering are embedded to a RF ADC with excellent linearity performance. This is achieved by transforming narrow-band filtering partially to RF injecting feedback into the input of the second amplifier stage, hence relieving requirements of the most critical subsequent stages. A 900-MHz direct delta-sigma receiver prototype occupies an active area of 1.2 mm
²
in 65-nm CMOS. The receiver for low-band cellular operations achieves NF of 2.3 and 6.2 dB in conventional and delta-sigma modes, respectively, and out-of-band IIP3 up to +4 dBm when the delta-sigma loop is active. The chip consumes 80 mW from a 1.2-V supply.