A PWM Based Fully Integrated Digital Transmitter/PA for WLAN and LTE Applications

In this paper, we present a 23 dBm PWM based fully digital transmitter designed in standard 45 nm CMOS process. The digital transmitter utilizes sigma-delta modulation and pulse-width modulation to convert high resolution baseband I and Q signals into 3-level switching signals, thereby allowing efficient Class-D PA stages to be used. In addition, cascaded sigma-delta stages and switched-capacitor combining are incorporated into the architecture to significantly reduce the out-of-band quantization noise while maintaining excellent efficiency. The proposed transmitter is fully digital from baseband to RF and can be used to replace the entire analog/RF signal chain in a traditional transmitter. It achieves peak output power of 23 dBm with 47% power-added efficiency (PAE). For an 20 MHz OFDM signal with 8.2 dB peak-to-average power ratio (PAR), the PAE is 23%. The linearity of the digital transmitter meets WiFi spectral mask without any digital predistortion.