Showing papers on "Crystal oven published in 1997"

Method and system for calibrating a crystal oscillator

Abstract: A method and system are provided for calibrating a batch of devices each containing a circuit which is responsive to a control signal for producing a desired output which varies in accordance with a first predetermined function of a specific ambient condition, the control signal having a magnitude which varies as a second predetermined function of the specific ambient condition, the second function being based on data stored as a look-up table in a memory of the device and which must be individually calibrated for each device. In a preferred embodiment, the device is a digital temperature controlled crystal oscillator which produces a desired output frequency and includes a voltage controlled oscillator (VCO) responsive to a control signal having a magnitude which varies as a predetermined function of ambient temperature in order to compensate for temperature variations in the oscillator output frequency. For such an application, the invention requires the connection of an accurate frequency source to each oscillator in the batch so as to enable the output frequency of the oscillator to be equalized thereto or to a multiple thereof. In calibration mode, the digital equivalent of the resulting analog control voltage is stored; whilst in compensation mode it is extracted from the memory, converted to an equivalent analog voltage and applied to the VCO. The invention is also applicable to compensate for aging of crystal oscillators in the field without requiring reconfiguring the complete look-up table.

Crystal oscillator programmable with frequency-defining parameters

Abstract: A programmable crystal oscillator is provided having a memory for storing frequency-defining parameters. Typically, one of these parameters is used to program an adjustable capacitive load circuit coupled to a crystal to thereby adjust the crystal source frequency. Additional parameters are used to program the output frequency of a phase locked loop circuit coupled to receive the adjusted source frequency. A further parameter can also be used to divide the output frequency of the phase locked loop circuit to supply a specified output frequency. The oscillators can be manufactured as generic programmable crystal oscillators without regard for output frequency and then quickly programmed to produce customer-specified output frequencies with a high degree of accuracy.

A 2.1-MHz crystal oscillator time base with a current consumption under 500 nA

Abstract: A micropower crystal oscillator module for watch applications is presented. The integrated circuit is encapsulated with a 2.1-MHz crystal in a miniature vacuum package to reduce parasitic effects. The circuit comprises frequency tuning with a resolution of /spl plusmn/3 s/year ~/spl plusmn/0.1 parts per million (ppm)\ and auxiliary circuits. A single output delivers a signal of 16 384 Hz with a frequency stability of /spl plusmn/2 ppm over the temperature range (-10 to 70/spl deg/C). The oscillator core has two complementary active MOSFET's and amplitude stabilization in order to get both low power consumption and high stability. New coupling and biasing circuits between the oscillator and the dynamic frequency dividers allow to achieve a current consumption under 0.5 /spl mu/A for a supply voltage between 1.8 and 3.5 V.

Design considerations for high-frequency crystal oscillators digitally trimmable to sub-ppm accuracy

Abstract: The current consumption of crystal oscillators is usually determined by the steady-state amplitude requirement, rather than the minimum transconductance for oscillation to exist, In a bipolar implementation transconductance is proportional to current, so that current consumption scales with frequency and load capacitance in the same way as transconductance. In a complementary metal-oxide-semiconductor (CMOS) implementation, current scales as the square of transconductance. It is therefore important to distinguish current from transconductance in power estimation for high frequency oscillators. Analytical expressions relating current to steady-state amplitude are used in this paper to estimate the minimum power required for a crystal oscillator at a given frequency. A 78 MHz crystal oscillator is described, which forms part of a regulated system in a pager where the oscillation frequency is controlled digitally to sub-ppm accuracy. The oscillator can be pulled from /spl plusmn/65 ppm to the required frequency with 0.2 ppm accuracy, with a maximum current consumption of 197 /spl mu/A. The circuit has been fabricated in a 1-/spl mu/m CMOS technology. The measured phase noise is -113 dBc/Hz at 300 Hz offset.

A low-profile high-performance crystal oscillator for timekeeping applications

Abstract: A crystal oscillator is described that uses various unusual techniques to achieve double-oven class temperature stability with a single oven. Stability of better than 1 part in 10/sup 11/ over a temperature range of -40/spl deg/ to +85/spl deg/ C has been demonstrated. The use of the single stage oven allows for a form factor with a relatively low height (19 mm. or 3/4 inch) for an oscillator of this performance class. The low profile facilitates card-based designs. In timekeeping applications such as wireless and telecom synchronization, the temperature coefficient of frequency (tempco) is more important than ever. The temperature extremes involved in wireless base stations increase the error due to temperature while the use of GPS timing receivers to discipline quartz oscillators greatly reduces the error due to aging, leaving tempco as the major component. Numerous design innovations are described such as a hermetic oven mass assembly and a non-ovenized digital temperature controller. This controller permits automated optimization of the oven set point and thermal gain. An overview of a novel zero-gradient oven technique used to achieve the double-oven performance is given, with more details in a related paper. Frequency pulling due to the oscillator circuit components is greatly reduced by a novel balanced-bridge controlled oscillator circuit that is described briefly here and in more detail in another related paper.

A dual mode oscillator based on narrow-band crystal oscillators with resonator filters

Abstract: A dual mode crystal oscillator using two narrow-band transistor Colpitts circuits has been developed. This oscillator excites arbitrary two-modes in a common resonator even if the modes are close to each other. The practical circuit structure and analysis of the proposed oscillator, and the experimental results are described.

Oven for heating a crystal for a laser frequency conversion

Abstract: An oven for heating a crystal for nonlinear frequency conversion of a laser beam. A grasping device resiliently grasps together the first and second sides of the crystal while allowing for generally unrestricted thermal expansion of the crystal. A heater element and a temperature sensor are each supported by the grasping device and are each in thermal contact with the crystal. A temperature controller is connected to the heater element and the temperature sensor.

Method and apparatus for producing a temperature stable frequency using two oscillators

Abstract: A method and apparatus for producing a temperature stable frequency at reduced cost. Advantage is taken of an existing, relatively temperature insensitive, low frequency and low cost watch crystal and an existing, high frequency, low cost, but relatively temperature sensitive system clock. A calibration module coupled to the watch crystal and clock calibrates the watch crystal to a reference frequency at a reference temperature and calibrates the clock to the watch crystal at an operating temperature, to relate the clock frequency to the reference frequency at any operating temperature and thereby provide a high precision, relatively temperature insensitive time or frequency base at low cost.

Temperature compensation circuit for a crystal oscillator and method of providing same

Abstract: A temperature compensation (TC) circuit (10) for a crystal oscillator module (12) used in a communication device (200). An existing microcontroller (210) of the communication device (200) is used to provide TC digital data (30) for a crystal oscillator (18). In this way, the crystal oscillator module (12) does not require an on-board memory which substantially cuts costs. TC digital data (30) is converted to a TC signal (22) in a digital-to-analog converter which controls the crystal oscillator frequency. To compensate for radio voltage regulator variations over temperature, the crystal oscillator module (12) includes an on-board voltage regulator (34) which supplies a characterized regulated voltage (36) to the digital-to-analog converter such that the TC signal (22) from the digital-to-analog converter is inherently corrected for voltage variations in the voltage regulator (34). This improves stability of output frequency (20) from 5 ppm to about 2 ppm.

A phase noise model to improve the frequency stability of ultra stable oscillator

Abstract: The goal of this study is to set up an improved model of the frequency stability behavior of the oscillating loop. A computer aided analysis is performed in which the transfer functions of the loop can be entirely described. This allows to predict phase noise performance of a given design. As a result the model provides ultimate limits of an oscillator concerning f/sup 0/, f/sup -1/, f/sup -3/ and f/sup -4/ phase noise versus the quartz resonator parameters for a given electronics noise. The model can also be used the opposite way to determine electronics noise for desired performances of an oscillator. Basic definitions are first recalled. The paper includes a description of the improved model that we developed starting from the Leeson's model. This improved model is in good agreement with experimental results obtained from 10 MHz crystal oscillators with SC cut quartz resonator.

FM canceler loop to reduce shock and vibration effects in crystal oscillators

Abstract: A canceler loop is used to provide negative feedback to a crystal oscillator to reduce the effects of shock and vibration on the spectral purity of the crystal oscillator. The canceler loop demodulates the output of the crystal oscillator and supplied a stabilizing voltage representative of the demodulated output to cancel frequency modulation induced by shock and vibration. The stabilizing voltage is used to cancel the noise sidebands of the frequency spectrum of the crystal oscillator output without tuning the center frequency.

Crystal oscillator for measuring crystal impedance of a crystal unit

Abstract: A crystal oscillator for measuring crystal impedance (CI) easily and accurately of various crystal units having an oscillating frequency in a wide band and various CI-values in a broad rage. A DC input voltage is measured, representing CI of a crystal unit, in a crystal oscillator, wherein an integrating circuit is provided in an output section providing a frequency oscillated from the crystal unit as an output, and one or more AGC amplifiers having an amplification rate proportional to a DC input voltage is provided between the crystal unit and the integrating circuit.

The Resonating Properties of a Crystal Unit of Fundamental Frequency 150 MHz.

Abstract: 150 MHz rectangular AT-cut quartz crystal units were prepared by means of photolithography. For the elimination of the effect on a frequency response by the mechanically damaged layer, chemical etching on both sides was employed. Gold evaporated films were used as the electrodes for frequency stability during long-term driving. As a result, crystal units which had excellent frequency stability during long-term driving and low crystal impedance were obtained. Furthermore, a Colpitts crystal oscillator was constructed, and some experimental data are presented.

A new type of balanced-bridge controlled oscillator

Abstract: A novel bridge-stabilized crystal oscillator circuit having exceptional temperature stability is described. The contribution to the oscillator temperature coefficient from the circuit components (exclusive of the crystal) is reduced to about 10/sup -11///spl deg/C, which is several orders of magnitude better than conventional oscillator circuits. This avoids a situation where the overall tempco is limited by circuit component drift rather than crystal stability, which can easily occur with conventional circuits when the crystal is ovenized at a turnover point. Previous attempts to use a bridge in an oscillator were made by Meacham, who used an imperfectly balanced bridge, and Sulzer, who used a balanced pseudo-bridge. The reasons why these are unsatisfactory are discussed. Although the bridge greatly reduces reactive frequency pulling, it does not directly address the additional issue of pulling due to variations in crystal drive current amplitude. However, it is an enabling technology for a novel ALC circuit with greatly improved stability. The new bridge controlled oscillator is also much less sensitive to other environmental effects such as humidity, power supply voltage, load impedance, and stray capacitance.

Influence of the various factors on the passive hydrogen maser frequency instability

Abstract: The influence of the thermal noise on the passive hydrogen maser frequency instability is analysed. New dependencies of the frequency instability on the excitation signal parameters are obtained in comparison with the results which were presented in the known publications. The excitation signal phase modulation index and the atom line saturation factor are specified which provide the minimum of the maser frequency instability. The influence of the modulation frequency on the passive hydrogen maser frequency instability is analysed. The influence of fast phase fluctuations of the quartz oscillator on the hydrogen maser frequency instability is discussed. It is shown that unlike the other passive frequency standards not frequency, but phase fluctuations of the quartz oscillator near the even harmonics of the modulation frequency affect the maser frequency instability. This influence is two orders less than for other passive standards. Frequency shifts due to a spurious amplitude modulation of the excitation signal at the frequency modulation /spl Omega/, a spurious phase modulation at the frequency 2 /spl Omega/, an inaccuracy of the receiver tuning to the signal frequency are calculated.

A study on estimation of frequency aging for rectangular AT-cut resonators

Abstract: This paper suggests estimate method of frequency-aging characteristic for the purpose of improving stabilization of frequency-aging characteristic of crystal resonator. This is the method in which change of quantity is calculated using estimated formula for every factor of frequency change from data of frequency-aging characteristic and by analyzing the temperature dependence. As such, this method enables frequency-aging characteristics in resonators to be estimated and evaluated with greater speed and accuracy.

Base station oscillator tuned with received clock signal

Abstract: To generate a carrier frequency, a base station needs an oscillator with a long-term stability better than 5·10 -8 . In the case of crystal oscillators it is therefore necessary to regularly adjust the frequency so as to compensate for frequency drift due to aging. The oscillator (OSC) of a base station (BTS) is automatically tuned with the pulse repetition frequency of the clock (CLK) of a digital communication signal (STM). To prevent variations in the pulse repetition frequency of the clock (CLK) from affecting the stability of the carrier frequency (CAR), the oscillator (OSC) is only tuned during times that a quality indicator contained in the digital communication signal (STM) guarantees a high frequency accuracy of 10 -11 .

Mutual-mode drive level dependence in dual-mode resonators

Abstract: Dual-mode oscillators are widely used in high-stability frequency references. The presence of the second excited mode allows one to get information about the temperature of crystal resonator or its aging. However, dual-mode excitation results in the appearance of additional components of basic mode frequency instability. One of them is mutual drive level dependence, i.e. the first mode frequency versus the second mode excitation level. This phenomenon has not been practically investigated up to now. The given work deals with the detailed analysis of mutual drive level dependence for dual-mode resonators with wide-spread SC and DT cuts. This work presents the results of experimental investigation on the basis of which the causes and components of mutual drive level dependence are analyzed. The consequences of this dependence (namely worsening of oscillator frequency stability) are analyzed as well. The work is based on the experimental data and has practical orientation.

Temperature compensation circuit for a crystal oscillator

Abstract: A temperature compensation circuit (10) for a crystal oscillator module (12) used in a communication device (200). An existing microcontroller (210) of the communication device (200) is used to provide temperature compensating digital data (30) for a crystal oscillator (18). In this way, the crystal oscillator module (12) does not require an on-board memory which substantially cuts costs. The temperature compensation digital data (30) is converted to a temperature compensation signal (22) in a digital-to-analog converter which controls the crystal oscillator frequency. However, typical digital-to-analog converters are driven by voltage regulators which vary over temperature. To solve this problem, the crystal oscillator module (12) includes an on-board voltage regulator (34) which supplies a characterized regulated voltage (36) to the digital-to-analog converter such that the temperature compensation signal (22) from the digital-to-analog converter is inherently corrected for voltage variations in the voltage regulator (34). This improves stability of the output frequency (20) from about 5ppm to about 2ppm.