PS to perform direct digital-to- RF signal synthesis. An RF DAC synthesizes output signals of at least 500 MHz signal bandwidth at carrier frequencies of 2.0 GHz or higher. Compared to conventional RF trans- mitter architectures such as zero-intermediate-frequency (ZIF), complex-IF and real-IF, the RF DAC architecture solution occupies less area with fewer components. It operates at lower power and delivers excellent dynamic performance. In terms of RF performance, the RF DAC has significant benefits over other architectures. The digital up-conversion with digital filtering implemented in direct digital synthesis elimi- nates gain-phase errors and achieves perfect carrier suppression with no LO leakage. The result is excellent EVM performance when transmitting high-order modulations like New Radio Access RF and Transceiver Design Considerations Up-converter Up-converter Lowpass Bandpass filter filter RF out RF out Lowpass Bandpass filter filter Clock Zero-IF transmitter PLL/VCO Clock Complex-IF transmitter PLL/VCO Bandpass RF out RF out filter PLL/VCO Clock PLL/VCO Real-IF transmitter Direct RF transmitter Figure 5.23 Illustration of RF transmitter architecture options [16]. 64QAM. The quadrature NCO makes the RF DAC an agile transmitter capable of tuning across the entire spectrum of LTE/NR sub-6 GHz bands (and mmWave bands using an external mixer and filter). Since the RF DAC is broadband and frequency agile with high dynamic range, a single device can synthesize multi-carrier, multi-band, and multi-standard signals including GSM, WDMA, LTE and NR. As a result, a fully digital software-defined radio can be realized using common hardware across multiple BS hardware platforms [16]. Another advantage of direct-conversion RF DAC technology is enabling lower cost digital predistortion (DPD) observation receiver. Macro-cell base stations typically use DPD techni- ques for RF PA linearization. This requires a PA observation receiver channel to monitor the PA output. The observation receiver detects PA distortion produ