Design of Wideband Direct-Conversion Receiver for 5G Wireless Applications

This thesis presents the design of a wideband direct-conversion receiver in 28nm CMOS technology as part of the heterogeneous transceiver for 5G wireless applications. The receiver down-converts the RF signal from the 7 GHz IF frequency to baseband. One of the key challenges for the receiver is the wide baseband bandwidth in the order of GHz, which makes the design of the receiver's baseband section particularly demanding. Furthermore, as the number of bands and antennas (MIMO) increases, the number of external RF filters must be reduced, which imposes strict linearity requirements since the receiver must handle powerful out-of-band blockers. The presented receiver covers RF channel bandwidths ranging from 50 MHz to 2 GHz that belong to 5G-FR2 bands. The voltage gain of the receiver is 45 dB and can be programmed down to 0 dB. It has a baseband bandwidth of 25 MHz to 1 GHz and more than 33 dB OOB selectivity at a frequency 4 times the band edge, consistent with 5G specifications. For maximum gain, the receiver has a noise figure of 5.6 dB and a slope of less than 0.7 dB/dB in the noise increase as the gain decreases. For any gain configuration, the receiver displays a measured in-band OIP3 of greater than +23dBm. The power consumption is 68 mW at maximum receiver gain and 56 mW at minimum receiver gain. The receiver has been fully integrated and measurement results are fully complying with the design specifications. The receiver front-end is composed of two cascaded LNTAs based on a common-gate transformer-based architecture. It achieves wideband matching from 5 GHz to 9 GHz, a high RF gain of 80 mS, and gain variability of 31 dB. The LNTA drives a double-balanced passive mixer. Two baseband paths are used to cover the very wide bandwidth range required. The first consists of a Rauch filter followed by a first order TIA and is used to cover baseband channel bandwidth from 25 MHz to 200 MHz. The second consists of an open loop second order filter followed by a wideband filtering TIA and covers channel baseband bandwidth from 400 MHz to 1 GHz. The primary contribution of the author in the baseband section is the design of the open loop filter which provide second order low pass filtering in the current domain. The filter, based on a regulated cascode architecture, achieves a bandwidth up to 1 GHz and a gain variability of 14 dB, which is compliant with the receiver specifications. A frequency dependent negative capacitance is connected at the filter input to improves the filter Q and provides an out-of-band selectivity equivalent to a 3rd-order Butterworth filter. In addition, different negative capacitance circuits have been studied including a novel frequency dependent negative capacitance circuit which provides negative in-band capacitance and positive out-of-band capacitance. Such a solution further improves the Q and selectivity of the filter. The filter was tested as a stand-alone block providing an in-band IIP3 of +16dBm, which is two times higher compared to state-of-the-art wideband open loop filters with comparable noise and power dissipation.