Digital Controlled Oscillator
A monolithically integrated, digitally controlled oscillator is presented. It has an output frequency range from 18.9 Hz to ≫ 20 MHz, the long term stability of a quartz oscillator and a short term clock edge uncertainty with a standard deviation of 0.4 ns. The digital frequency control is fully linear with a resolution of 18.9 Hz. The only required external component is a reference quartz. The circuit operates from a single 5 V power supply and is fabricated in a 1.5 ¿m, double metal, single poly, CMOS process. The chip area is 4.1 mm2.
DTMF Generator based on Interleaved Oversampling
A circuit is described which uses one oversampling frequency synthesizer in an interleaved mode to generate dual-tone multi-frequency (DTMF) telephone dialling tones. The synthesizer is based on direct digital synthesis using phase accumulation. The Digital to analogue conversion is carried out using a first order sigma-delta (¿¿). This ¿¿ converter is also used in interleaved mode. The smoothing filter consists of a simple second order RC filter.
Frequency Synthesizers-A Survey of Techniques
A general survey is given of the different synthesizer techniques with emphasis on the application in communication equipment. After enumeration of the fundamental concepts of addition and multiplication, the different systems are examined and classified. This leads to the conclusion that for high requirements of spectral purity of the output signal, electronic tuning, solid-state design, and microminiaturization, the loop systems are very attractive. Some applications of synthesizers in HF communications are treated.