A Low-Jitter and Low-Power CMOS PLL for Clock Multiplication

this paper describes a phase-locked loop (PLL) designed for clock multiplication in a LVDS transmitter. The PLL consists of a novel low-jitter charge-pump, a fully differential ring-oscillator based VCO, a dynamic-logic PFD, a 2nd order passive loop filter and a digital frequency divider. The PLL exhibits simultaneously low jitter and low power consumption. It has been integrated into a 0.35 um CMOS process, occupying 0.09 mm2 of silicon area. For a 350 MHz output frequency, the circuit features a cycle-to-cycle jitter of 7.1 ps rms and 65 ps peak-to-peak. At that frequency, the PLL consumes 12 mW from a supply voltage of 3.3 V.

Hybrid continuous-discrete-time multi-bit delta-sigma A/D converters with auto-ranging algorithm

Sergio Pesenti

In wireless portable applications, a large part of the signal processing is performed in the digital domain. Digital circuits show many advantages. The power consumption and fabrication costs are low even for high levels of complexity. A well established and highly automated design flow allows one to benefit from the constant progress in CMOS technologies. Moreover, digital circuits offer robust and programmable signal processing means and need no external components. Hence, the trend in consumer electronics is to further reduce the part of analog signal processing in the receiver chain of wireless transceivers. Consequently, analog-to-digital converters with higher resolutions and bandwidths are constantly required. The ultimate goal is the direct digitization of radio frequency signals, where the conversion would be performed immediately after the front-end amplifier. ΔΣ-modulation-based converters have proved to be the most suitable to achieve the required performance. Switched-capacitor implementations have been widely used over the last two decades. However, recent publications and books have shown that continuous-time architectures can achieve the same performance with lower power consumption. Most designs found throughout the literature use a single- or few-bit internal quantizer with a high-order modulation. As a result, in order to achieve the resolutions and bandwidths required today, the sampling frequency must exceed 100MHz. This approach leads to non-negligible power consumption in the clock generation. Moreover, the presence of such fast squared signals is not suitable for a system-on-chip comprising radio frequency receivers. In this thesis we propose a low-power strategy relying on a large number of internal levels rather than on a high sampling frequency or modulation order. Besides, a hybrid continuous-discrete-time approach is used to take advantage of the accuracy of switched-capacitor circuits and the low power consumption of continuous-time implementation. The sensitivity to clock jitter brought about by the continuous-time stage is reduced by the use of a large number of levels. An auto-ranging algorithm is developed in this thesis to overcome the limitation of a large-size quantizer under low-voltage supply. Finally, the strategy is applied to a design example addressing typical specifications for a Bluetooth receiver with direct conversion.

EPFL2007

Low power frequency synthesizer for mobile communications systems

Imre Kovacs

A novel frequency synthesizer with a strong emphasis on low-power consumption (2mW) was developed for this thesis. A BAW-resonator was used for the design of the high-frequency oscillator. The BAW's high Q-Factor ensured a minimal power consumption, while providing outstanding phase noise performance. This type of frequency synthesizer can be implemented in practically every mobile wireless system standard, which is relying on batteries as the power supply, such as Bluetooth, Zigbee and others. For this work, a Bluetooth-compatible standard was taken in order to derive the system specifications. The frequency synthesizer then was designed and implemented in a 180nm CMOS process. The approach of the "Sliding-IF" architecture was chosen and modified in order to take full advantage on the BAW oscillator. Therefore a two-stage frequency translation of the signal was necessary, similar to the super-heterodyne transceiver topology. The channel selection and the frequency error correction is done at the second stage, since the BAW-based oscillator does practically not provide any frequency tuning. For this, a Delta-Sigma-Modulator based Fractional-N PLL was developed. A system supply voltage of 1.2V was chosen in order to keep power consumption as low as possible. This supply voltage can also be easily supplied by AA or AAA-batteries and a low-voltage regulator. The most important technique to reduce overall power consumption was to reduce the high-frequency requirements to the system blocks. This was done by modifying the "Sliding-IF" architecture and by the use of the BAW resonator. The minimization of the power consumption required careful choice and design of each of the system blocks. For this, several approaches were analyzed, especially the topology of each block and its optimization were important. A special emphasis on the analysis, design and discussion was also made on the noise, and especially the phase noise. A ring oscillator, a LC-VCO and a BAW-oscillator were implemented and measured in order to validate the theory and the simulation results. The complete frequency synthesizer with an Automatic Amplitude Control, Frequency Dividers, Mixer, Charge-Pump, Phase-Frequency Detector and a Delta-Sigma-Modulator was designed and implemented. This thesis was elaborated in the frame of the MiNAMI and MiMOSA projects of the European research programme (FP6).

EPFL2009

Reducing Energy Dissipation in ULP Systems: PLL-Free FBAR-Based Fast Startup Transmitters

Christian Enz, David Ruffieux, Raghavasimhan Thirunarayanan

The energy dissipated by conventional phase-locked-loop-based transmitters (TXs) during the long startup phase is a major bottleneck that reduces the energy autonomy of duty-cycled ultra-low-power systems. In order to tackle this problem, this paper presents a loop-free TX based on a film-bulk acoustic wave resonator (FBAR) that has a 5-s startup time and requires just 3-s for channel switching. The presented TX takes advantage of the high-frequency stability of the FBAR digitally controlled oscillator (DCO) to operate in open loop mode. In order to avoid the problem of the same frequency stability that also hinders addressing multiple channels, the DCO output is mixed with a divided down version (which gives the IF) of itself. By adjusting the division ratio suitably, frequency of the system can then be tuned. To further relax the tuning requirements on the FBAR, the divider for producing the IF is implemented as a phase-switching divider with a step size of 0.2. Integrated in a 65-nm technology node, the TX can address all the bands within the 2.36-2.5-GHz frequency range viz. Medical body area network, industrial, scientific, and medical, and low-power active medical implant bands. Moreover, this TX is able to reach up to 16-Mb/s peak data rate while consuming 9.2 mA at 1.2 V.