Signal Processing Techniques Enabling Wideband A/D Converters

With an ever-widening signal spectrum and incorporation of multiple standards that share the available spectrum at the same time, research towards building wideband analog-to-digital converters (ADCs) has gained significant momentum. Furthermore, with an aim to improve spectral efficiency, increasingly complex modulation schemes are being invoked having high peak-to-average ratios, the latter translating to high dynamic ranges for the received signals. Consequently, the ADCs deployed in these receivers need to be of quite high precision as well. With these two primary goals for ADCs (high bandwidth, high resolution) in mind, this thesis presents a few different techniques for achieving them. In the first part of this thesis, we shall explore the art of dithering to linearize an A/D converter system. In particular, a digital-signal conditioning technique (using subtractive dither) is developed as a stepping-stone for a high resolution system. The effects of filtering the dither signal to shape its spectral content outside the signal band while maintaining its benefits are studied in detail. Design strategies for finite impulse response (FIR) filters that accomplish spectral shaping as well as allay quantizer non-linearity are derived theoretically. In the second part of this thesis, the proposed dithering technique is used for linearizing an ADC system that is intrinsically non-linear, namely a VCO-based ADC. Ring voltage-controlled oscillator (VCO)-based ADCs have surfaced as elegant alternatives to the traditional...