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 phase-synchronized 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

This work describes a method for analysis of voltage-to-current converters (V-I converters or transconductors) and a novel V- I converter circuit with significantly improved linearity. The new circuit utilizes a combination of cross-coupling and local resistive feedback for a significant, simultaneous suppression of the third- and fifth-order harmonic distortion components in the transconductor characteristics. An evaluation of the optimal circuit dimensioning is shown. Simple and robust design rules are derived for the chosen operation conditions. The transistor implementation is presented and a prototype V- I converter is realized in a digital 0.18-/spl mu/m CMOS technology. The measured spurious-free dynamic range is 75 dB in a frequency band of 10 MHz. The circuit occupies less than 0.02 mm/sup 2/ and dissipates 360 /spl mu/W.

The use of electro-optical feedback in an analogue optical transmitter makes it possible to reduce both noise and distortion. Automatic gain control by means of an electronically controlled optical attenuator maintains linearity of the baseband amplifier. The performance of this high-quality optical video link and of the optical attenuator is presented.