Analog-to-digital conversion via duty-cycle modulation

Abstract

An exchange of the amplitude axis for the time axis offers a possibility of overcoming resolution problems in analog-to-digital conversion in low-voltage CMOS circuits and/or of circumventing special resistor options in silicided processes. This exchange can be effected via some form of duty-cycle modulation. For its implementation a circuit configuration is described, consisting of an asynchronous sigma-delta modulator, followed by a phasesynchronized tapped ring oscillator which produces a poly-phase signal for sampling the asynchronous signal at a relatively low frequency. A detailed analysis is presented which accurately predicts the properties of the conversion scheme with respect to aliasing, quantization noise and nonlinear distortion. The results are illustrated with simulations of a design example.

Analytical Expressions for the Distortion of Asynchronous Sigma–Delta Modulators

“…In particular, the modulation frequency is not necessarily constant. On the other hand, [8] and [9] do focus on the same class of ASDMs as our manuscript. However, [8] concerns a simulation based aproach instead of an analytical one.…”

“…Asynchronous Sigma Delta Modulators (ASDMs) are a known family of self-oscillating Pulse Width Modulators (PWMs), that can be implemented using a schmitt-trigger and a continuous time loop filter [7]- [9]. The purpose of this paper is to find analytical expressions that can predict the distortion of such modulators and their carrier frequency (the frequency at which they oscillate).…”

Analyzing the Effect of Clock Jitter on Self-Oscillating Sigma Delta Modulators

“…(2), and as has been shown in [17], the oscillation signal is modulated by the ASDM's input signal. Furthermore, in an actual realization, the oscillation signal may also contain phase noise caused by several noise sources in the system.…”

“…2 actually represents an asynchronous sigma delta modulator (ASDM, [15]- [18]). The ASDM's output signal has been analyzed in literature and its oscillation frequency, f c , has been calculated ( [17]), for slowly varying input signals. It takes the following form:…”

Modeling and Simulation of a New Duty-Cycle Modulation Scheme for Signal Transmission Systems

“…As reported in [1], although the general DCM principle is not new, over years many types of implementation techniques with specific characteristics have been built for application in a variety of application areas. In the pulse width modulation (PWM) technique where T m (x) = T m is kept constant, a basic PWM circuit requires a triangle wave oscillator and a comparator [2], and a whole minimal implementation requires three integrated operational amplifiers and four passive components.…”