Lina Bai

An MCXO test system and its function in MCXO performances

Describes an MCXO test system used mainly for MCXOs based on AT cut crystals. This system is composed of a temperature chamber, several switch groups, a PC, a high-resolution frequency meter, a frequency standard, a control system including a simulator and a controller. It can be used to produce the MCXOs with AT cut crystals and in the different temperature range /spl plusmn/1/spl sim/3/spl times/10/sup -7/ frequency-temperature stability can be obtained. In the test procedure for MCXOs, the system supplies MCXO standard temperature conditions, measures the frequency-temperature characteristics of the uncompensated MCXOs, obtains control signal (voltage, pulse width or digital code signal)-temperature sensed, signal data for the compensated MCXOs. According to the test data, the compensation table or equations for the completed MCXOs can be obtained. In the test system, high precision and fast speed frequency measurement combined with suitable computer control can be used instead of a complicated frequency synthesizer and is useful for MCXO production with different frequencies.

The technical development of crystals and oscillators in China and their market situation

In recent years, the quantity and requirement for manufacturing crystals and oscillators in China has increased quickly. The paper introduces the manufacture, research and the characteristics of techniques developed regarding crystals and oscillators in the last 10 years in China. Along with the demands of industry, science and markets, the number of companies making and developing crystals and oscillators has increased from several to more than 300 in the last 20 years in China. Manufacturing technology and equipment also are improved a lot. Most of the precision crystals made in China are of glass packages. Now more and more companies plan to build production lines to make cold weld crystals and other precision crystals in China, and at least two companies have built a line. The main design techniques in China are based on experiments. However, in recent years, special design software has been used for oscillator design, and some advanced instruments and equipment are used. The market situation for crystals and oscillators is also introduced.

On precise phase difference measurement approach using border stability of detection resolution.

For the precise phase difference measurement, this paper develops an improved dual phase coincidence detection method. The measurement resolution of the digital phase coincidence detection circuits is always limited, for example, only at the nanosecond level. This paper reveals a new way to improve the phase difference measurement precision by using the border stability of the circuit detection fuzzy areas. When a common oscillator signal is used to detect the phase coincidence with the two comparison signals, there will be two detection fuzzy areas for the reason of finite detection resolution surrounding the strict phase coincidence. Border stability of fuzzy areas and the fluctuation difference of the two fuzzy areas can be even finer than the picoseconds level. It is shown that the system resolution obtained only depends on the stability of the circuit measurement resolution which is much better than the measurement device resolution itself.

The measurement of transient stability with high resolution

Transient stability measurement of frequency source plays an important part in the real-time short-term stability and the characterization of distal phase noise, so its accurate measurement is of great significance. Measurement of transient noise and short-term stability of signals with the conventional digital counting methods is very difficult and the measurement accuracy is low. So we introduce a unique phase coincidence detection technology which is an important detection method and our group has worked on it for decade to measure the frequency source transient stability. When the phase difference of two signals is less than a certain value, phase coincidence detection circuit will output a narrow pulse which represents the phase coincidence, we call it the phase coincidence detection resolution threshold. When the phase difference of two signals is adjusted to the verge of coincidence detection resolution, we can judge the transient frequency stability of signals accurately from the continuity and discontinuity of the coincidence information. According to the results of multiple phase coincidence detection circuits which combine as a coincidence detection array, the phase variation in detail can be obtained. The measurement resolution depends on the stability of the coincidence detection circuit. This paper describes the principle, the experiment process and the results of transient stability measurement methods.

The technique development of OCXO in China

Recent years the technique level of OCXOs are enhanced and the production and application quantities also increase obviously in China. Because of the request for higher specifications, lower cost, and more quantity to OCXOs, many technologies have to be developed to suit to the market. This paper introduces the main technique development of OCXOs in China including the results in production and research developed by factories, institutes and universities. Recent years the production of OCXOs becomes industrialized from conventional laboratory production. Some measurement techniques, production and aging equipment, test systems are developed. In the middle class OCXOs, to lower the cost vacuum packaged resistance weld crystals are used instead of cold weld crystals and glass packaged crystals, and 10/sup -9//day aging can be obtained in big quantity production. The most precision crystals are AT cut. The glass packaged precision SC cut crystals have been made since more than twenty years ago, and now some companies are paying attention to build new production line to make cold weld SC cut crystals. For lower cost, smaller size, higher precision, wider temperature range, and mass production, some circuit design techniques were developed. One chip integrated OCXO circuits are used in middle class OCXOs. It includes oscillation, buffer amplifier, and the main temperature control circuit together. By using it OCXO with SC cut crystal 1/spl times/10/sup -10//day aging and /spl plusmn/3/spl times/10/sup -9/ frequency temperature performance can be obtained, and OCXO with AT cut crystal 3/spl times/10/sup -9//day aging and /spl plusmn/1/spl times/10/sup -8/ frequency-temperature performance can be obtained. As a level representation, ultra-stable OCXO was also developed. Although BVA precision crystals cannot be made in China, through a long-period research the special quartz crystal frequency standard has been accomplished. It can show 5/spl times/10/sup -12//day aging, 3/spl times/10/sup -13//s stability and -148dB/Hz phase noise at 100 Hz offset.

Comparison between AMCXO and MCXO and necessity to develop AMCXO

Introduces a new temperature compensated crystal oscillator - AMCXO, a MCXO based on an analogue approach - and compares the performance differences between MCXO and AMCXO and analyses the necessity to develop AMCXO. Combined with their test systems AMCXO and MCXO are both based on computer to generate the control signals to the compensated crystal oscillators according to temperature variation. However, in the practical temperature compensated crystal oscillators the execution devices are much different to each other. MCXO uses a set of digital units including a microprocessor to complete the compensation. In it equations or tables are used to express the relationship between the control signal and temperature. AMCXO uses an analogue memory, which has the same functions as the digital units of MCXO. In AMCXO a curve or figure based on the equations or table is used to express the same relationship. Now AMCXO is mainly based on AT cut crystals. Therefore, in this paper we only compared it with the MCXO based on AT cut crystals.

Direct precision frequency measurement and correction technology with double ADC

A new method of direct precision frequency measurement is proposed in this paper, which uses the clock cursor effect between the sampling clock signal and input signal and ADC (analog to digital converter) quantization error suppression technique in the background of digital measurement with double ADC. On this basis, a precision frequency corrector is designed. Compared with the traditional frequency synthesizer, this device takes the non-standard frequency signal of the crystal oscillator as the reference to realize the standard frequency signal output through the frequency correction function. Meanwhile, the output signal is obviously narrower in range, from 0.0001 Hz to 0.1 Hz. The frequency corrector can also realize the second stability of less than 3 × 10-12 and a small frequency correction of 10-11 orders of magnitude.

Precise measurement of complicated frequency signals

Based on the border effect and relevant theories, it is found that measurement precision depends on resolution stability which is much higher than resolution itself. With the help of this new theory and the more sensitive discrimination of the border of a fuzzy area, it is possible to greatly improve the measurement precision. Since there are a lot of complicated frequency signals in quantum frequency standards, telecommunication, fundamental subjects and other fields, precise measurement is significantly important. In a great deal of measurement of complicated frequency signals, discrete fuzzy areas are common. In this paper, we put forward a feasible and high-precision frequency measurement scheme to make it easier to capture border information, which shows great advantages of border effect.

The border effect in frequency signal processing and the phase measurement with arbitrary frequency relationship

Based on the achievement of phase coincidence detection, the processing and elimination of quantization error is possible in digital frequency measurement. Because of the limited resolution of phase detection, a fuzzy area is to be formed. The higher precision can be obtained using the border stability of fuzzy areas. The decisive factor of the actual precision is the resolution stability of the border of fuzzy area, called the border effect. Therefore, utilizing the circuit with ns resolution one can obtain ps level or higher precision. On the basis of improving measuring resolution significantly and the phase variation regularity of periodic signals, through the frequency measurement with phase continuous, the measured frequency signal is compared with its theoretical nominal frequency by multiple periods and with measuring gate time one by one. Eventually, the measurement of phase variation of any measured signal in a wide frequency range can be realized. Compared with other measurement techniques and instruments it is a great advancement. Because of the phase information is obtained for the different even very complicated frequency signals, higher frequency measurement precision can be realized without any frequency transformation. It is possible to realize higher measurement and control precision.

Border effect-based precise measurement of any frequency signal*

Limited detection resolution leads to fuzzy areas during the measurement, and the discrimination of the border of a fuzzy area helps to use the resolution stability. In this way, measurement precision is greatly improved, hence this phenomenon is named the border effect. The resolution fuzzy area and its application should be studied to realize high-resolution measurement. During the measurement of any frequency signal, the fuzzy areas of phase-coincidence detection are always discrete and irregular. In this paper the difficulty in capturing the border information of discrete fuzzy areas is overcome and extra-high resolution measurement is implemented. Measurement precision of any frequency-signal can easily reach better than 1 × 10−11/s in a wide range of frequencies, showing the great importance of the border effect. An in-depth study of this issue has great significance for frequency standard comparison, signal processing, telecommunication, and fundamental subjects.