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This paper reviews several techniques used to reduce the in-band phase noise contribution of [DELTA][SIGMA] fractional-N frequency synthesizers. The paper develops several practical techniques for specifying the noise and linearity of components used in a [DELTA][SIGMA] fractional-N synthesizer. As an example, it presents a synthesizer with an in-band phase noise floor of -97 dBc/Hz@10 KHz for an RF output frequency of 2.432 GHz and a reference frequency of 16 MHz. The synthesizer has a frequency resolution of 61 Hz and an on-chip crystal oscillator. The synthesizer was implemented in a 0.35-/[micro]m SiGe process and consumes 6 mA from a 3 V supply. The in-band phase-noise, spurs, and power consumption of this synthesizer are each low and comparable to the state-of-the-art. Index Terms--Bluetooth, Delta-Sigma, frequency modulation (FM), frequency-shift keying (FSK), Gausian frequency shift keying (GFSK), GMSK minimum shift keying (MSK), general packet radio service (GPRS), global system for mobile communications (GSM), multimode, radio, satellite, Sigma-Delta, wireless.

A technique of spread-spectrum transmission, interpolated frequency-hopping (IFH), is presented. IFH employs a carrier that moves smoothly and continuously in frequency, helping to alleviate problems, such as spectral splatter and transient mismatch, which are a concern in conventional phase-locked loop (PLL)-based frequency-hopping spread-spectrum systems. In IFH, the pseudorandom hopping code is passed through a digital interpolation filter prior to controlling the synthesizer instantaneous frequency output. While such filtering is commonly used in data pulse-shaping to improve the spectral characteristics of the modulated carrier, such filtering has not been reported for IFH codes, where the frequency deviations are changing and can span several MHz. The implications of matching the transient responses of two PLL-based frequency synthesizers using this method have also not been reported. Initial simulation and laboratory measurements indicate that, for certain cases, IFH shows a 1.9 dB improvement in received IF power, has a much sharper roll-off of inband phase noise when compared to conventional hopping, and provides a phase-coherent IF after despreading. An IFH transceiver system using [Delta]-[Sigma] frequency synthesis and a [Delta]-[Sigma] frequency discriminator is proposed. The system would be suitable for integrated mobile radio applications in slow-fading environments. Index Terms - Digital filters, frequency hopping, phase-locked loop, spread spectrum, VLSI.

The basic operation of a fractional-n frequency synthesizer has been published, but to date little has been presented on the digital [Delta][Sigma] modulators which are required to drive such synthesizers. This paper provides a tutorial overview, which relates digital [Delta][Sigma] modulation to other applications of [Delta][Sigma] modulation where the literature is more complete. The paper then presents a digital [Delta][Sigma] modulator architecture which is economical and efficient and which is practical to realize with commercially available components in comparison with other possible implementations which require extensive custom very large-scale integration (VLSI). A demonstration is made of a 28-b modulator using the architecture presented, which provides a 25-MHz tuning bandwidth and Index Terms - [Delta][Sigma] modulator, digital circuit, frequency synthesis, radio receivers.

Evaluates several techniques used to reduce the in-band phase noise contribution of ΔΣ (DS) fractional-N frequency synthesizers and develops several practical techniques for specifying the noise and linearity of components used in a DS fractional-N frequency synthesizers, as of November 2003. Highlights of such synthesizers used in this evaluation; Suitability of these synthesizers for resolving problems faced by radio system designers; Sources of in-band noise; Overview of the integrated circuit design used in this evaluation.