Digitally controlled oscillator for all-digital frequency locked loops

摘要

A digitally controlled oscillator is presented as a suitable solution for all-digital frequency lock loops. The system consists of a bias circuit, current-voltage converters and a current controlled oscillator, which is implemented using log-domain circuits. In this way, the oscillation frequency can be tuned using the bias currents. The bias circuit consists of a binary decoder and a current division network. The role of the decoder is to control the output current values of the division network via a 10-bit digital control word. Thus, it was possible to obtain 1024 distinct bias current values which yielded 1024 frequency values. The current-voltage converter transforms the output current into a voltage necessary for the next stage. All circuits were implemented using Virtuoso Analog Design Environment from Cadence using a 180nm CMOS technology. The MOS transistors for the log-domain blocks are working in sub-threshold region. Spectre simulations were performed to demonstrate de functionality of the proposed circuit.