Digital Control in Microwave Receiver Front-End Components

Abstract

In this thesis digital control techniques for two receiver front-end components i.e. the downconverter mixer and the modulator are presented. With decrease in size of CMOS-based geometries, decrease in performance and yield of analog components has become an issue. Using the digital components on a System-on-Chip to account for the shortcoming in analog circuitry and thereby developing 'self-calibrating' systems has become a reliable way to address this issue. In the telecommunications industry, this is directly correlated to lower post-fabrication testing times, quicker product development and lower overhead costs.

The first design presented is a 0.13 um CMOS mixer with variable gain capability. A Digital Assist system was put in place to extend the 3-dB bandwidth of the system using a microcontroller. An interpolation routine was used to predict the bias voltages based on variations in frequency and desired input power. The digital-to-analog converter on the microcontroller was used to set the required bias voltages. The mixer's bandwidth was extended from 12GHz to 15GHz using digital assist. The gain of the mixer with the digital assist in place could be varied from 1.2-9.8dB.

The second design presented is a 5.4GHz multi-scheme modulator fabricated in 0.13 um CMOS technology. The modulator is capable of carrying out quadrature amplitude modulation as well as phase-shift keying modulation. The modulator makes use of a novel OTA design to generate a set of orthogonal basis vectors which allows for facile mapping of the modulated data on the I-Q plane. The modulator carries out modulation in 4-PSK, 8-PSK, 4-QAM and 16-QAM modes with a maximum error vector magnitude of only 8.51%. A digital assist model to attain ubiquitous operation inside a system is also presented for this modulator.