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.
Transients in Frequency Modulation
In a frequency-modulation system, a sudden jump in carrier frequency corresponding to a Heaviside unit signal will result in a transient depending on the receiving-filter bandwidth. If this bandwith exceeds twice the maximum frequency swing, the shape and duration of the transient is shown to be about the same as in an amplitude-modulation system with the same bandwidth; for narrower filters the transient lasts longer. These results are applied to several practical cases. The transient is favorably affected by using an amplitude limiter and by arranging the filter pass band so as to enclose the maximum frequency swing symmetrically.