MEMS-based oscillators are an emerging class of highly miniaturized, batch manufacturable timing devices that can rival the electrical performance of well-established quartz-based oscillators. In this review, a description is given of the key properties of a MEMS resonator that determine the overall performance of a MEMS oscillator. Piezoelectric, capacitive and active resonator transduction methods are compared and their impact on oscillator noise and power dissipation is explained. An overview is given of the performance of MEMS resonators and MEMS-based oscillators that have been demonstrated to date. Mechanisms that affect the frequency stability of the resonator, such as temperature-induced frequency drift, are explained and an overview is given of methods that have been demonstrated to improve the frequency stability. The aforementioned performance indicators of MEMS-based oscillators are benchmarked against established quartz and CMOS technologies.

https://iopscience.iop.org/article/10.1088/0960-1317/22/1/013001/pdf

A review of MEMS oscillators for frequency reference and timing applications

A dedicated wake-up receiver may be used in wireless sensor nodes to control duty cycle and reduce network latency. However, its power dissipation must be extremely low to minimize the power consumption of the overall link. This paper describes the design of a 2 GHz receiver using a novel ldquouncertain-IFrdquo architecture, which combines MEMS-based high-Q filtering and a free-running CMOS ring oscillator as the RF LO. The receiver prototype, implemented in 90 nm CMOS technology, achieves a sensitivity of -72 dBm at 100 kbps (10-3 bit error rate) while consuming just 52 muW from the 0.5 V supply.

A 52 $\mu$ W Wake-Up Receiver With $-$ 72 dBm Sensitivity Using an Uncertain-IF Architecture

This paper presents the design of a low-voltage ultralow-power relaxation oscillator without external components. The application field for this oscillator is the clock generation of low-power wake-up functions for battery-operated systems. A detailed analysis of the oscillator, including the temperature performance, is derived and verified with experimental results. The oscillator operates at a typical frequency of 3.3 kHz and consumes 11 nW from a 1-V supply at room temperature, and a temperature drift of less than 500 ppm/°C is achieved over the temperature range of -20°C to 80°C. An efficient design implementation has resulted in a cell area of 0.1 mm2 in a standard 0.35- μm digital CMOS technology.

Analysis and Design of an Ultralow-Power CMOS Relaxation Oscillator

The design of a 1.8 GHz 3-stage current-starved ring oscillator with a process- and temperature- compensated current source is presented. Without post-fabrication calibration or off-chip components, the proposed low variation circuit is able to achieve a 65.1% reduction in the normalized standard deviation of its center frequency at room temperature and 85 ppm/ ° C temperature stability with no penalty in the oscillation frequency, the phase noise or the start-up time. Analysis on the impact of transistor scaling indicates that the same circuit topology can be applied to improve variability as feature size scales beyond the current deep submicron technology. Measurements taken on 167 test chips from two different lots fabricated in a standard 90 nm CMOS process show a 3x improvement in frequency variation compared to the baseline case of a conventional current-starved ring oscillator. The power and area for the proposed circuitry is 87 μW and 0.013 mm2 compared to 54 μ W and 0.01 mm 2 in the baseline case.

A Low-Power, Process-and- Temperature- Compensated Ring Oscillator With Addition-Based Current Source

The design of a 100 kHz frequency reference based on the electron mobility in a MOS transistor is presented. The proposed low-voltage low-power circuit requires no off-chip components, making it suitable for application in wireless sensor networks (WSN). After a single-point calibration, the spread of its output frequency is less than 1.1% (3sigma) over the temperature range from -22degC to 85degC . Fabricated in a baseline 65 nm CMOS technology, the frequency reference circuit occupies 0.11 mm2 and draws 34 muA from a 1.2 V supply at room temperature.

A Low-Voltage Mobility-Based Frequency Reference for Crystal-Less ULP Radios

This work demonstrates a self-referenced CMOS LCO, or CMOS harmonic oscillator (CHO), that exhibits 90ppm total frequency error over process, bias and temperature, thus making it suitable for replacing XOs in many applications. Additionally, the clock generator can be configured to produce a number of different output frequencies, has 1/4 of the frequency error of the oscillator in [3] and includes a direct modulation technique enabling SSCG.

/pdf/a-0-5-to-480mhz-self-referenced-cmos-clock-generator-with-3tn3es7t47.pdf

A 0.5-to-480MHz Self-Referenced CMOS Clock Generator with 90ppm Total Frequency Error and Spread-Spectrum Capability

Recent trends in the development of integrated silicon frequency sources are discussed. Within that context, a 25-MHz self-referenced solid-state frequency source is presented and demonstrated where measured performance makes it suitable for replacement of crystal oscillators (XOs) in data interface applications. The frequency source is referenced to a frequency-trimmed and temperature-compensated 800-MHz free-running LC oscillator (LCO) that is implemented in a standard logic CMOS process and with no specialized analog process options. Mechanisms giving rise to frequency drift in integrated LCOs are discussed and supported by analytical expressions. Design objectives and a compensation technique are presented where several implementation challenges are uncovered. Fabricated in a 0.25-mum 1P5M CMOS process, and with no external components, the prototype frequency source dissipates 59.4 mW while maintaining plusmn152 ppm frequency inaccuracy over process, plusmn 10% variation in the power supply voltage, and from - 10degC to 80degC. Variation against other environmental factors is also presented. Nominal period jitter and power-on start-up latency are 2.75 psrms and 268 mus, respectively. These performance metrics are compared with an XO at the same frequency.

/pdf/a-25-mhz-self-referenced-solid-state-frequency-source-57n0bk954l.pdf

A 25-MHz Self-Referenced Solid-State Frequency Source Suitable for XO-Replacement

A monolithic and unpackaged silicon die is presented as a frequency source suitable for quartz crystal resonator (XTAL) and oscillator (XO) replacement. The frequency source is referenced to a free-running, frequency-trimmed and temperature-compensated 3GHz RF LC oscillator. A programmable divider array enables the device to provide frequencies ranging from 6 to 133MHz. A post-processed Faraday shield contains fringing electromagnetic fields and enables the device to be delivered in unpackaged form such that it can be assembled into any package or via any assembly technique. The device dissipates approximately 2mA from a 1.8–3.3V power supply and drifts no more than ±300ppm over all operating conditions including a panel of industry-standard reliability tests.

/pdf/a-silicon-die-as-a-frequency-source-53a9acs8bi.pdf

A silicon die as a frequency source

A 25 MHz all-CMOS clock generator is demonstrated where measured performance makes it suitable for direct replacement of the reference crystal oscillator (XO) for serial wire interfaces. Fabricated in a 0.25 mum 1P5M logic CMOS process, and with no external components, the developed clock generator dissipates 59.4 mW while exhibiting plusmn152 ppm frequency error over process, plusmn10% variation in the power supply voltage and from -5-75degC. Nominal period jitter and power-on start-up latency are 3.93 psrms and 268 mus respectively.

/pdf/a-25mhz-all-cmos-reference-clock-generator-for-xo-4uc98612hx.pdf

J. Kuhn

Papers

A 0.5-to-480MHz Self-Referenced CMOS Clock Generator with 90ppm Total Frequency Error and Spread-Spectrum Capability

A 25-MHz Self-Referenced Solid-State Frequency Source Suitable for XO-Replacement

A silicon die as a frequency source

A 25MHz all-CMOS reference clock generator for XO-replacement in serial wire interfaces